Electrical Indicating Instruments - Multiple Choice Questions and Answers

Electrical Indicating Instruments - Multiple Choice Questions and Answers Points : Electrical Indicating Instruments - Multiple Choice Questions and Answers, Objective type question electrical technology, Mcqs 1. Moving coil instruments are…..
(a) Permanent magnet type
(b) Dynamometer type
(c) Repulsion type
(d) Both (a) & (b)

2. Permanent magnet type instruments are suitable for…
(a) a.c. measurement
(b) d.c. measurement
(c) Neither (a) nor (b)
(d) Both (b) & (c)

Applications of Moving Iron Instruments

Applications of Moving Iron Instruments Points : Applications of Moving Iron Instruments Due to the following advantages and uses of moving iron instruments, these are applicable for both a.c. & d.c. circuits. These instruments are robust due to simple construction of moving parts and the fact that there is no current lead to these parts. The stationary parts of these Instruments are also simple. Due to simple construction these instruments are of low cost. Following are the applications of moving-iron instruments.

1. Heavy current moving-iron Ammeters.

Parts of Repulsion type Instrument

Parts of Repulsion type Instrument Points : Parts of Repulsion type Instrument This has the following parts:
1. Moving fixed iron
2. Fixed coil
3. Control spring
4. Air damping device
5. Coil or solenoid
6. Spindle

Construction of Moving Iron Repulsion Type Instruments

Construction of Moving Iron Repulsion Type Instruments Points : Construction of Moving Iron Repulsion Type Instruments In repulsion type instrument there are two irons. A curved iron of soft iron is fixed to the inside of the bobbin former and another curved iron is mounted on a spindle, which passes axially through the solenoid. These two irons lie in the magnetic field produced by a solenoid. When there is no current in the solenoid, the two irons (moving & fixed) are almost touching each other and pointer rests on zero position. The solenoid is wound with insulated copper wire on a cylindrical non-magnetic timer.

Working Principle of Moving Iron Repulsion Type Instruments

Working Principle of Moving Iron Repulsion Type Instruments Points : Working Principle of Moving Iron Repulsion Type Instruments The repulsion type instrument works on the principle of repulsion. If two pieces or vanes of soft iron are mounted close together inside a coil and current is passed through the coil, the iron vanes are magnetized, with north poles at one end and the south poles at the other.

Parts of Attraction Type Instrument

Parts of Attraction Type Instrument Points : Parts of Attraction Type Instrument Following are the parts of the said instrument:
1. Moving iron
2. Current carrying coil or solenoid
3. Spindle
4. Pointer
5. Scale
6. Air damping chamber
7. Control & balance weights
8. Control spring

Construction of Attraction Type Moving Iron Instruments

Construction of Attraction Type Moving Iron Instruments Points : Construction of Attraction Type Moving Iron Instruments The simplest form of attraction type moving iron instrument uses a solenoid and a moving oval shaped soft iron pivoted eccentrically.

To this iron a pointer is attached so that it may deflect along with the moving iron over a graduated scale. The iron is made of sheet metal specially shaped to give a scale as nearly uniform as possible. The moving iron is drawn in to the field of solenoid when current flows through it. The movement of iron is always from weaker magnetic field outside the coil into the stronger magnetic field inside the coil regardless the direction of flow of currant in the coil.

When the current to be measured (or a definite fraction of the current to be measured or proportional to the voltage to be measured) is passed through the solenoid, a magnetic field is set up inside the solenoid, which magnetises the iron. Thus the iron is attracted in to the coil, causing the spindle and the pointer to rotate.

Working Principle of Attraction Type Moving Iron Instruments

Working Principle of Attraction Type Moving Iron Instruments Points : Working Principle of Attraction Type Moving Iron Instruments The attraction type instrument works on the principle of attraction. If a small piece of soft iron is pivoted or mounted near a coil and current is passed through the coil, the iron piece or vane is attracted and tends to be pulled in to the stronger magnetic field inside the coil.

Moving Iron Instruments

Moving Iron Instruments Points : Moving Iron Instruments, Definition Moving iron instruments are widely used in laboratories and switch boards at commercial frequencies because these are cheaper in cost, robust in construction. These can be manufactured with required accuracy. The moving iron instrument has the advantages of simplicity and ruggedness.

Errors in Dynamometer type Instruments

Errors in Dynamometer type Instruments Points : Errors in Dynamometer type Instruments, Low torque / weight ratio, Frequency, Eddy currents, External magnetic fields, Temperature change The main sources of errors in a dynamometer type instruments are due to:
i) Low torque / weight ratio
ii) Frequency
iii) Eddy currents
iv) External magnetic fields
v) Temperature change

Advantages and Disadvantages of Electrodynamometer Instruments

Advantages and Disadvantages of Electrodynamometer Instruments Points : Advantages and Disadvantages of Electrodynamometer Instruments Advantages

1. As the instrument coils are air cared, so these instruments are free from hysteresis and eddy current errors.
2. These instruments can be used on both a.c. and d.c. and since they have a precision grade accuracy, they are very useful as transfer instruments.

Applications of Dynamometers

Applications of Dynamometers Points : Applications of Dynamometers The major applications of Dynamometer type instruments are:
a) As an Ammeter
(b) As a Voltmeter
(c) As a Wattmeter
(d) As a Varmeter

Construction of Electrodynamic or Dynamometer Type Instruments

Construction of Electrodynamic or Dynamometer Type Instruments Points : Construction of Electrodynamic or Dynamometer Type Instruments The points of construction of dynamometer type instrument are described. i) Fixed Coils The field is produced by a fixed coil. The coil is divided into two sections to give a more uniform field near the centre and to allow passage of the instrument shaft. The instrument illustrated in the fig may by a milliampere, or may become a voltmeter by addition of a series resistance. The fixed coils are wound with fine wire for such applications.

Field coils (fixed) are usually wound with heavy wire carrying the main current in ammeters and wattmeters. The wire is stranded where necessary to reduce eddy current losses in conductors. The coils are usually varnished and baked to form a solid assembly. These are then clamped in places against he coil supports. This makes the construction rigid so that there is no shifting or change in dimension which might effect the calibration. The mounting supports are preferably made out of ceramic, as metal pats would weaken the field of the fixed coil due to eddy currents.

Working Principle of Electrodynamic or Dynamometer Type Instruments

Working Principle of Electrodynamic or Dynamometer Type Instruments Points : Working Principle of Electrodynamic or Dynamometer Type Instruments, Definition We have the idea of the working principle of the permanent magnet moving coil (PMMC) instrument. Considering how it would behave on a.c. It would have a torque in one direction during one half of the cycle and an equal effect in the opposite direction during the other half of the cycle. If the frequency were very low, the pointer would swing back and forth around the zero point.

Electrodynamic or Dynamometer Type Instruments

Electrodynamic or Dynamometer Type Instruments Points : Electrodynamic or Dynamometer Type Instruments, Definition An electrodynamic or dynamometer type instrument is a type of moving-coil instrument in which the operating field is not only produced by a permanent magnet but by another fixed coil.

Permanent Magnet Moving Coil Instrument (PMMC) as a D.C. Voltmeter

Permanent Magnet Moving Coil Instrument (PMMC) as a D.C. Voltmeter Points : Permanent Magnet Moving Coil Instrument (PMMC) as a D.C. Voltmeter AD. Arsonval basic meter movement is converted in to a voltmeter by connecting a series resistance with it. This series resistance is called a “multiplier”. This combination of meter and multiplier is put across the circuit, whose voltage is to be measured.

The multiplier limits the current through the meter so that it does not exceed the value for full scale deflection and thus prevents the movement from being damaged.

Permanent Magnet Moving Coil Instrument (PMMC) as D.C. Ammeter

Permanent Magnet Moving Coil Instrument (PMMC) as D.C. Ammeter Points : Permanent Magnet Moving Coil Instrument (PMMC) as D.C. Ammeter The basic movement of a d.c. ammeter is a PMMC D. Arsonval galvanometer. The coil winding of a basic movement is small and light. It can sense very small currents since the construction of an accurate instrument with a moving coil to carry current greater than 100 mA is impracticable due to the bulk and weight of the coil that would be required.

Construction of Permanent-Magnet Moving Coil (PMMC) Instrument

Construction of Permanent-Magnet Moving Coil (PMMC) Instrument Points : Construction of Permanent-Magnet Moving Coil (PMMC) Instrument The general construction of this instrument is shown. The main components are as follows: 1. Moving System Moving Coil The moving coil is wound with many turns of enameled or silk covered copper wire. The coil is mounted on a rectangular aluminium former which is pivoted on jewelled bearings. The coil moves freely in the field of a permanent magnet. Most voltmeter coils are wound on metal frames to provide the required electro- magnetic damping. Most ammeter coil, however, are wound on non-magnetic formers, because coil turns are effectively shorted by the ammeter shunt. The coil itself, therefore, provides electromagnetic damping.

Permanent-Magnet Moving Coil (PMMC) Instrument

Permanent-Magnet Moving Coil (PMMC) Instrument Points : Permanent-Magnet Moving Coil (PMMC) Instrument, Definition The permanent magnet moving coil instrument is the most accurate type for d.c. measurement is the most accurate type for d.c. measurements. This is the main type of instrument used as ammeters and voltmeters.

The operation of a permanent magnet moving coil type instrument is based upon the principle that when a current carrying conductor is placed in a magnetic field, it is actuated upon by a force which tends to move it to one side and Out of the field. This is similar to the principle of D Arsonval galvanometer. The difference being that a direct reading instrument is provided with a pointer and a scale.

The circuit arrangement shows a series-types ohmmeter. It consists of a PMMC instrument connected in parallel with a shunting resistor R₂. This parallel circuit is in series with resistor R1 and a battery of e.m.f. E. The series circuit is connected to the terminals A and B of the unknown resistance R_x.

From the fig. R₁= Current limiting resistor R₂ = Zero adjusting resistor R_m = Internal resistance of the meter E = e.m.f of internal Battery.

Fundamental of Electrical Measurements - Multiple Choice Questions and Answers

Fundamental of Electrical Measurements - Multiple Choice Questions and Answers Points : Fundamental of Electrical Measurements, Electrical, MCQS, Objective type question, Multiple choice questions and answer Select the correct answers of the following items:

1. Measurement may be done by....
a. Direct method
b. Indirect method
c. Both (a) & (b)
d. None of above

2. A Tangent Galvanometer is a type of...
a. Secondary instrument
b. Absolute instrument
c. Recording instrument
d. Digital instrument

Advantages of Recording Instrument over Indicating Instruments

Advantages of Recording Instrument over Indicating Instruments Points : Advantages of Recording Instrument over Indicating Instruments, What are the advantages of Recording instruments over indicating instruments? 1. There is no need of operator to record the changes in observations of electrical quantity to be measured.
2. These are reliable and robust in construction.
3. These are not affected by atmospheric conditions.

Uses of Recording Instruments

Uses of Recording Instruments Points : Uses of Recording Instruments, Application of Recording Instruments The recording type instruments are used in heavy industries, power houses, chemical plants, hospitals and laboratories, whereas the indicating instruments are used in houses, factories, workshop, generating stations, substations, laboratories, colleges and hospitals etc.

Difference between Indicating and Recording Instruments

Difference between Indicating and Recording Instruments Points : difference between indicating and recording instruments, compare the recording and indicating instrument, comparison the recording and indicating instrument, recording instrument vs indicating instrument

Difference between Indicating and Recording Instruments Indicating Instruments Recording Instruments 1. These instruments need an operator to observe the changes in electrical quantity being measured. As the changes are recorded on the graph paper, so no operator is needed. 2. The quantity is measured with the help of pointer & scale. Instead of pointer and scale the quantity is recorded on graph paper wit pen. 3. Moving system of these instruments is light. Due to extra pen friction their moving system is comparatively heavy. 4. Small bearings are used, due to less load on moving system. Their bearings are heavy due to greater load on moving system.

Galvanometer Type Recorders

Galvanometer Type Recorders Points : Galvanometer Type Recorders, Definition These recorders use a D. Arsonval galvanometer. The pointer is equipped with a recording pen mechanism (stylus). As the current flows through the coil, it deflects. The greater the amplitude of the incoming signal (which is proportional to the quantity being measured), the greater is the deflection. When the pointer comes to rest on account of controlling torque exerted by springs, the stylus also comes to rest. Thus, the value of the quantity is recorded.

Types of Strip Chart Recorders

Types of Strip Chart Recorders Points : Types of Strip Chart Recorders, Galvanometer type, Null Type (a) Galvanometer Type This type of strip chart recorder operates on the deflection principle. The deflection is produced by a galvanometer which produces a torque on account of a current passing through its coil. This current is proportional to the quantity being measured.

Parts of Strip Chart Recorder

Parts of Strip Chart Recorder Points : Parts of Strip Chart Recorder

1. A long roll of graph paper moving vertically.
2. A system of driving the paper at some selected speed. A speed selector switch is generally provided. Chart speeds of 1-100mm/second tire usually used.

Applications of Tangent Galvanometer

Applications of Tangent Galvanometer Points : Applications of Tangent Galvanometer There are following applications of said galvanometers:
i) Measurement of current.
ii) Measurement of earth magnetic horizontal component (1-1).

Precautions of Adjustments of the Tangent Galvanometer

Precautions of Adjustments of the Tangent Galvanometer Points : Precautions of Adjustments of the Tangent Galvanometer While adjusting the tangent galvanometer, the following pints should be taken in mind:
i) The support of copmus needle should he free from torsion.
ii) Copmus needle should always the in the centre of the scale.

Precautions in using a Tangent Galvanometer

Precautions in using a Tangent Galvanometer Points : Precautions in using a Tangent Galvanometer (a) To avoid eccentric error, readings of both ends of the pointer should the taken and mean of them should he used in calculation.
(b) Reading should be taken by reversing the current. This will eliminate error due to the coil not being the magnetic meridian.

Construction of Tangent Galvanometer

Construction of Tangent Galvanometer Points : Construction of Tangent Galvanometer Tangent Galvanometer is an absolute instrument used for calibration of secondary instruments. It is also called moving magnet galvanometer.

Construction of Pointers Electrical Indicating Instruments

Construction of Pointers Electrical Indicating Instruments Points : Construction of Pointers Electrical Indicating Instruments, Types of Pointers, Pointer Materials, Properties of Pointer Materials, Lightspot Indication, Use and Repair of Pointers A needle which deflects on a graduated scale to measure the quantity, directly by its deflection is called a pointer. The pointer of an instrument shows the position of moving system of that instrument.

Every indicating Instrument has a pointer. The shape and size of pointer used depend upon the type of instrument. In all cases, however, the weight and inertia of the pointer must be reduced as far as possible, both to reduce the load on the bearings of the moving system and to avoid the high degree of damping which would be necessary if the moving system had considerable inertia.

Construction of Permanent Magnet Electrical Indicating Instruments

Construction of Permanent Magnet Electrical Indicating Instruments Points : Construction of Permanent Magnet Electrical Indicating Instruments In most cases when permanent magnets are used in instruments it is essential that their strength shall not vary with time.

Such magnets may be of very hard steel, containing a small percentage of tungsten or of cobalt and chromium together. The coercive force of cobalt — chromium steel is high, and thus magnets made of this steel are not subject to self-demagnetisation to the same extent as tungsten-steel magnets.

Construction of Moving System Electrical Indicating Instruments

Construction of Moving System Electrical Indicating Instruments Points : Construction of Moving System Electrical Indicating Instruments Moving System The requirements of a moving system are that:
(i) The moving parts should be light.
(ii) The frictional forces should be minimum.

These requirements should be fulfilled in order that power required by the instrument for its operation is small. The power expenditure is proportional to the weight of the moving parts and the frictional forces opposing the movement. The moving system can be made light by using aluminium as far as possible. The frictional forces are reduced by using a spindle mounted between jewel bearings and by carefully balancing the system. Supporting the Moving Element The force or torque developed by the moving element of an electrical instrument is necessarily small in order that the power consumption of the instrument be kept low so that the introduction of the instrument into a circuit may cause the minimum change in the existing circuit conditions. Because of low power levels, the consideration of various methods of supporting the moving element becomes of vital importance. With the operating forces being small, the frictional forces must be kept to a minimum in order that the instrument reads correctly and is not erratic in action and is reliable.

Methods of Production of Damping Torque

Methods of Production of Damping Torque Points : Methods of Production of Damping Torque, Air friction damping, Fluid friction damping, Eddy current damping, Electromagnetic damping The methods of production of damping torque are:
(a) Air friction damping
(b) Fluid friction damping
(c) Eddy current damping
(d) Electromagnetic damping

Production of Damping Force

Production of Damping Force Points : Production of Damping Force The damping torque should be of such a magnitude that the pointer quickly comes to its final steady position, without overshooting.

If the instrument is “Under damped” the moving system will oscillate about the final steady position with a decreasing amplitude and will take some time before it comes to rest.

When the moving system moves rapidly but smoothly to its final steady position, the instrument is said to be “critically damped” or “dead beat”. If the damping torque is more than what is required for critical damping, the instrument is said to be “over damped”. In an over damped instrument, the moving system moves slowly to its final steady position in a lethargic fashion. The readings are very tedious to take.

Properties of Spring Material Used in Measuring Instruments

Properties of Spring Material Used in Measuring Instruments Points : Properties of Spring Material Used in Measuring Instruments The essential requirements for springs are:
i) They should be non-magnetic.
ii) They should be proof from mechanical fatigue.

Types of spring Used in Measuring Instrument

Types of spring Used in Measuring Instrument Points : Types of spring Used in Measuring Instrument, Mounting of spring There are two types of springs used:
(a) A hair-spring; usually of phosphor-bronze, which is attached to the moving system of the instrument.

(b) Flat spiral springs are used in almost all indicating instruments as the space required by these springs is less than for other types.

Tough Sheathed Cable System

Tough Sheathed Cable System Points : Tough Sheathed Cable System For most modem surface installations, P.V.C sheathed and insulated cables will be used, although T.R.S cable may be used in all situations except those where exposure to direct sun-light or damp is involved. In this type of wiring on the cable an external sheath is also provided which is very hard and easily beared the mechanical shocks. The materials which are mostly used for tough sheathing, such as, hard rubber, P.V.C material, plastic and lead. In this system, tough rubber sheathed cable, P.V.C sheathed cable, and plastic sheathed cable and lead alloy sheathed cables are extensively used. These, cables are installed on the wall direct or the conduit.

Bus Bar System for Rising Mains

Bus Bar System for Rising Mains Points : Bus Bar System for Rising Mains Totally-enclosed using-main bus bar systems consist of bar or lightly-insulated copper or aluminum bus bars in a metal trunking. The bus-bar may be of circular or rectangular cross section. This system is extensively used in multi-story buildings. It is usually consists of bus bars which have die, capacities of I 00A to 500A with two, three or four conductors. Tap-off boxes with fuse links or fuse switches can also provided for distribution to each floor, where distribution boards are fitted.

Overhead Bus-Bar System

Overhead Bus-Bar System Points : Overhead Bus-Bar System The Bus-Bar system can he used for 3-phase distribution of electricity in factories. This 3-phase supply is provided to electric machines. The bus-Bars are made of aluminum or copper material. These bus-bars are mounted on insulators and enclosed in standard lengths of steel trunking. The bus-bars are arranged in this way, by using bolts, thus forming a continuous bus-bar along the entire length of factory or workshop. At the intervals of every 1 meter, a lap-off point is provided on the bus-bars. At these points tap-off units are fitted. The tap-off unit is consists of three fuses which are mounted in a sheet case with a hinged door.

Uses of Catenary Wiring System

Uses of Catenary Wiring System Points : Uses of Catenary Wiring System This system is designed for large buildings, and the open areas where conduit system would be difficult to install.

Catenary Wiring System

Catenary Wiring System Points : Catenary Wiring System The catenary system of wiring is designed for large buildings. The open areas where screwed conduit system would be difficult to install, such places we also used catenary system. This is cheaper wiring system compared to other systems. V.R.I cable is used in catenary system. The cable consists of a number of P.V.C insulated cores mad up round a high-tensile galvanized steel wire, with suitable fillings of PVC to produce a circular shape. Usually standard cables are used in this system, such as 3/0036, 7/0,036, 7/0.064, which are consisted on two, three or four or more than four cores.

Uses of Ducting Wiring System

Uses of Ducting Wiring System Points : Uses of Ducting Wiring System Ducting system is extensively used in power house, grid station, oil refinery, airport, power labs, industries and commercial, buildings.

Installation Method of Ducting Wiring System

Installation Method of Ducting Wiring System Points : Installation Method of Ducting Wiring System The ducts are made in a building during construction work. Ducts are made in the floor in shape of circular or rectangular. After that concrete ducts are made in these digging paths.

Sometimes ducts are made into the walls. This is called skirting.

Ducting Wiring System

Ducting Wiring System Points : Ducting Wiring System Under floor path which ‘are used for cables lying is known duct in large buildings, stores and offices, where wiring scheme is very difficult, because the whole building is constructed with concrete and iron.

Uses of Trunking Wiring System

Uses of Trunking Wiring System Points : Uses of Trunking Wiring System Trunking system is used in industries, commercial places, workshops, telephone exchange, microwave system, laboratories, radio station, T.V station etc.

Advantages and Disadvantages of Trunking Wring System

Advantages and Disadvantages of Trunking Wring System Points : Advantages and Disadvantages of Trunking Wring System Advantages (i) Cheap and easy installation method.
(ii) The cables are enclosed in trunking, there is no risk of cable insulation to be damaged.
(iii) Cables are safe against dust and humidity.

Installation of Trunking

Installation of Trunking Points : Installation of Trunking, Materials of Trunking, Common Sizes of Trunking The installation layout must be planned before starting to work. If the installation is in a new or altered building, all internal structural and wall finishes should have been completed. The trunking should be cut using a fine tooth saw. Clean off any bums or swarf after making the cut. The main component of the trunking is generally fitted to the surface of the wall by using screws. It is advise- able to use Washers under the screw heads.

Non-Metallic Trunking

Non-Metallic Trunking Points : Non-Metallic Trunking, Wiring System Non-metallic thinking is used in domestic or commercial premises, particularly where rewiring of existing buildings, is required. The non-metallic trunking system is also surface mounted. Industrial non-metallic trunking is also available, in a range of sizes up-to 150 x 150 mm. Low voltages insulated or sheathed cables may be installed in plastic trunking.. The area where mechanical risk of injury is present, the trunking must be suitable protected.

Skirting Trunking

Skirting Trunking Points : Skirting Trunking Wiring System Skirting trunking is used extensively in commercial buildings, laboratories, hospitals etc. It consists of a shallow steel trunking, approximately 44mm deep with two or more compartments. One compartment is usually used for socket or lighting Wiring and one for bell or internal telephone wiring.

Trunking Wiring System

Trunking System Points : Trunking Wiring System Trunking for industrial and commercial installation is often used in place of the larger sizes of conduit. Trunking system is more flexible than conduit systems. Trunking is available in both metallic and non-metallic type. We can install the trunking easily in surface fitting. Surface metal turking come in various sizes and types of material. It may include heavy industrial listed surface metal trunking that can withstand physical damage and specially approved for industrial locations.

Industrial and Commercial Wiring System

Industrial and Commercial Wiring System Points : Industrial and Commercial Wiring System The installation methods, which are used for industrial and commercial purposes are known as power wiring system.

(1) Steel conduit system
(2) Trunking system

Cables and Fuse Sizes For Motor Circuit

Cables and Fuse Sizes For Motor Circuit Points : Cables and Fuse Sizes For Motor Circuit, Examples of calculation about cables and fuse sizes for motors Always, choose the correct size of cable for motor circuit. When we choose a cable for motor circuit, keep in mind that the current carrying capacity of motor and its terminal voltage drop. For example, if the voltage drop occurs in a motor circuit is 10% of terminal voltage4 it means the loss of power or torque (T x v²) is 20%. Always keep in mind these points, when we deal with 50H.P three phase motors and 20H1P single phase or D.C motors.

(1) Always use the 7/0.029 or large than cable size in motor circuits.

Faults in Power Wiring

Faults in Power Wiring Points : Faults in Power Wiring In this article, we discuss about the power wiring of a motor and any other device which are installed in power wiring etc. Now, let us study about power wiring, faults.

Faults in Power Wiring Symptom Cause Remedy (1) Motor will not start. (a) Voltage too low. (b) One fuses blown or open circuit. (a) Increase the voltages. (b) Replace fuse.

Motor foundation

Motor foundation Points : Motor foundation For the construction of motor foundation, first of all, we design a layout of foundation. The size of motor foundation is always kept according to size of motor. Usually, the size of foundation is equal to (2 x 2 x 3) feet. The concrete foundation is better compare to other types of foundations because the vibration effect is little in this type.

Dismantle and Assemble of Motors

Dismantle and Assemble of Motors Points : Dismantle and Assemble of Motors Dismantle Always remember these points, when you are starting to dismantling of a motor.

1. First of all, remove the pully of motor on the shaft, also remove the fan cover and then open the fan, which is screwed on the shaft of motor for cooling purpose.
2. The shaft or pully of the motor is always in front of your eyes and then you mark a line on the did covers and on the yoke. The advantage of this line is that, when you closing the motor you easily meet these mark points and close the motor cover.

Construction and Working of Three Point starter

Construction and Working of Three point starter Points : Construction and Working of Three point starter Construction The three point starter has a tapped resistor enclosed in a box. Contact buttons located on a panel mounted on the front of the box are connected to the tapped resistor. A movable arm with a spring reset can be moved over the contact buttons to cut out sections of the tapped resistor.

Three point starter

Three point starter Points : Three point starter, Definition Three point D.C starters are used for starting of D.C shunt motor. Two factors limit the current taken by a motor armature from a D.C source.
(1)The back e.m.f.

Automatic Star Delta Starter

Automatic Star Delta Starter Points : Automatic Star Delta Starter, Definition An automatic star-delta starter is shown. Automatic star delta starters usually embody an electronic timer with adjustable timing on the star connection and with a short but definite time delay at the change over.

Manually Star Delta Starter

Manually Star Delta Starter Points : Manually Star Delta Starter A manual star-delta starter is shown. When he switch is at (star/start) position the motor is run in star connection and when switch is at (delta/nm) position, motor run in delta position.

Star Delta Starter

Star Delta Starter Points : Star Delta Starter, Definition After D.O.L starting the next most common method is by the start-delta method. Motors started by a star -delta starter must have the leads of each phase winding brought out to the terminal connection box of the motor. In the start position the windings are connected in star (A connection of three windings made in such a manner that one end of each winding is connected together); in the running position they are reconnected in delta (A circuit formed by connecting three electrical devices in series to form a closed loop).

Direct on-line Starter

Direct on-line Starter Points : Direct on-line Starter, Definition Most three-phase, squirrel-cage induction motors with ratings up to 10 H.P are connected directly across the line. Across the line starting usually is accomplished using a magnetic starting switch controlled from a push-button. In fig an elementary control circuit with start and stop button and a sealing circuit are shown. First you understand this simple circuit.

Push Buttons

Push Buttons Points : Push Buttons, Definition A Master switches; manually operated plunger or button for an electrical actuating device; assembled into push-button stations. Push buttons stations are spring controlled switches and when pushed,, are used to complete motor or motor control circuit. In fig symbols used in schematic drawings to represent push button contacts are shown.

Thermal Relay

Thermal Relay Points : Definition of Thermal Relay Relay used in control circuits; operated by a change in one electrical circuit to control a device in the same circuit or another circuit. Overload means operation of equipment in excess of normal, full load, rating or of a conductor in excess of rated current which, when excess current passing through it, it would cause damage or dangerous over-heating. Overload protection is the result of a device that operates on excessive current, but not necessarily on a short circuit, to, cause the interruption of current flow to the device governed.

Magnetic Contactor

Magnetic Contactor Points :Definition of Magnetic Contactor An electro-magnetic device that repeatedly establishes or interrupts an electrical power circuit Contactors are required in automatic controls to transmit varying conditions in one circuit to influence of operation of other devices in the same or another electrical circuit.

A contactor is a simplified form of circuit breaker that is designed for frequent operation in the normal closing and opening of circuits under load. Contactor has a coil, which can be energized to close or open contacts in an electrical circuit.

Starter

Starter Points : Definition Starter, A device which is used to start and regulate the current to a motor during the staring period. It may be used to make or break the circuit and / or limit the starting current. It is equipped with over current protection devices, such as magnetic contactor with overload relays. There are two types of starter: manual and magnetic. A manual type starter consists of a start and stop buttons are built into the cover. When, we push the start or stop button, a mechanical linkage to the buttons closes or opens the main contacts.

Isolator

Isolator Points : What is Isolator, Definition The purpose of isolator is that it totally disconnects the motor, and its controller from the supply circuit. This becomes necessary; when working on the motor or the machinery that it drives, to guard against accidental starting, which would be most dangerous. It is always installed near the motor starter. It must plainly indicate whether it is in the open or closed position. It must open all the motor circuit wires simultaneously. The isolator must be manually operated.

Sub Circuit Protection

Sub Circuit Protection Points : What is Sub Circuit Protection, Definition When a motor is first connected to the line, the power consumed is very much higher then after the motor comes upto speed. The starting current of a motor may be 5 to 8 times the full load current. For example, an ordinary single phase IH.P, 230V motor consuming only 8A while running at full speed and full load, will require as much as 48 A, when motor is started. When the motor is first connected to the power line, it is not turning, so that locked-rotor condition does exists, until the motor starts to turn. The wire to the motor must then be big enough to carry easily its starting current momentarily, its running current continuously and its normal current plus a considerable overload current for short periods Therefore it is advised to use circuit breaker or fuses.

Motor Circuits

Motor circuits Points : What is Motor circuits, Definition Before studying about the motor starter circuits first we learn about some important - devices, which are used in motor starter circuits. Starter consists of a magnetic contactor, thermal relay, push buttons, light indicators and some time we use fuses or circuit breakers inside the starter, but this condition is rarely used. A motor is rated in horse power (H.P). This means that it will deliver the horse power, stamped on its name plate.

Precautions for Jointing

Precautions for Jointing Points : Safety Precautions for Jointing

1. The cable joints are made in this way that the joints are accessible for inspection, when fault is produce or routine inspection. For this purpose, we use inspection type joint boxes.
2. The joints are mechanically and electrically sound. If joints are loose, then transient produce, which are dangerous for electrical devices.

Precautions for Soldering

Precautions for Soldering Points : Safety Precautions for Soldering

1. It is recommended that, the surface of the jointing conductor or joint is cleaned properly.
2. Always use the flux after cleaning the joining surface because the fluxes removing the any adhere, which are present on the surface of the conductor.

Method of Soldering

Method of Soldering Points : Method of Soldering Before soldering first we prepared the joint. The insulation of the jointing conductor should be removed and next step is to clean the conductors carefully. The cleaning is usually done by scrapping with a knife, after that made the joint carefully. For solid jointing, is essential that the jointing portion is completely cleaned and no any particles are present on the jointing portion which may adhere.

Soldering

Soldering Points : Soldering, What is Soldering, Definition of Soldering First we made the joint mechanically and the next step is to solder it. The solder used for electrical joints in copper is a soft an 60% of tin and 40% of lead. It is best to practice that first solid wires and after that stranded. The melting point of is 200°c. For good soldering some requirements is essential e.g.

Cable Joints and it Types

Cable Joints and it Types Points : Cable Joints and it Types In this section, we learn about how we made the jots (straight, tee, Britannia, married joints etc) on single-core, single strand, single core multi strand and multi core cables. There are following qualities of a go.cd joint.

(i) It should remain the conductivity and mechanical strength of the conductor on which that joint is made.

(ii) It should be able to withstand ‘the circuit current in normal condition and fault current without failure.

Insulation Test

Insulation Test Points : Insulation Test, Wiring Test A thing installation after being completed must be tested for insulation resistance. Two tests should be made to ascertain. In first test the insulation resistance between the wiring and earth with all fuses and lamps in and all switches ON. In second test the insulation resistance between phases with all lamps out and all switches ON. The explanation of second test is described in short circuit test section, now here we only study the first test only.

Short Circuit Test

Short Circuit Test Points : Short Circuit Test The short circuit test should be made before the fans and lamps are installed; the test should he made with the fuses are inserted in distribution fuse board, all, switches ON, all lamps removed, all fans removed, all portable current carrying apparatus disconnected and the main switch closed.

Continuity Wiring Test for Earth Connection

Continuity Test for Earth Connection Points : Continuity Wiring Test for Earth Connection Another test that has to be taken on completion is to as certain the resistance from the farthest point of the conduit or cable sheathing to earth, which must not exceed (1Ω). Every earth continuity conductor must be checked to as certain that it is mechanically and eclectically continuous. The impedance of the earth-continuity conductor is sufficiently low to enable a satisfactory earth-fault current to pass to operate the protective devices.

Continuity Wiring Test

Continuity Wiring Test Points : Continuity Wiring Test Another lest that has to be taken on completion is to as certain the continuity of the circuit It is essential to reach the phase and neutral wires to each installed device in the wiring circuit. The procedure of this test is that all the lamps are out of circuit, disconnect the fans connection, all the switches are in OFF position and fuses are also out of circuit.

Polarity Wiring Test

Polarity Wiring Test Points : Polarity Wiring Test, Using Megger, Using continuity tester, Using test lamp A test has to be made to verification of polarity of all single pole switches, including switches on socket-outlets -and fuses are connected to phase wire and that there is no break in the conductors. For lighting circuit all the lamps, should be removed, the main switch is in ON position, all the fuses are connected in circuit and all the switches is in OFF position:

A.V.O Meter

A.V.O Meter Points : A.V.O Meter, Definition A.V.O Meter, Construction and Working of A.V.O Meter We can easily measure the A.C or D.C voltage, current and resistance by using a A.V.O meter. In this instrument all three electrical functions such as voltage, current and resistance are combined and therefore we can say it A.V.O meter. To using this meter we perform the polarity and continuity tests. For this purpose we use the ohmic scale.

Continuity Tester Testing Instruments

Continuity Tester Points :Definition Continuity Tester Testing Instruments, Construction and Working of Continuity Tester It is a simple testing instrument and constructed easily. In this instrument, we use a 3-volt or 6-volt battery, 3v or 6v lamp, a wooden box, lamp holder, connection leads and testing leads. We connect the lamp across battery. The lamp is fled into lamp holder and testing leads are connected to, outer, terminals of wooden box.

Test Lamp Testing Instruments

Test Lamp Points : Definition Test Lamp, Construction and Working of Test Lamp, Testing Instruments It is the simplest form of a testing instrument. It is consisted on a 15w, 220V 1am and two testing loads. We can also use 60w, for 100w lamp but 15W lamp is mere recommended. Test lamp consist of a 230V electric bulb of any wattage fitted in an insualted type pendent holder testing leads.

Megger Testing Instruments

Megger Points : Construction and Working of Megger Testing Instruments A megger is a universally used testing instrument for installation tests and it is combined on hand-driven D.C generator and n ohm-meter giving direct readings in ohms and mega ohms. The megger is the most popular type of insulation and continuity tester. The 500v model of both hand-driven and battery-type instruments are normally used for performing all tests on domestic wiring. In principal this instrument consists of a permanent magnet in the field of which is a voltage and a current coil fixed at an angle to one another with a pointer pivoted at the centre of rotation of the coils.

Preparing of Distribution Board

Preparing of Distribution Board Points : Preparing of Distribution Board Distribution boards are available in single phase or three phase construction. In fshows the different techniques to prepare the distribution board. If 3- Φ supply is available, first we control the 3-0 supply through 3- Φ main distribution board. In 3 - 0 main (D.B), the fuses and circuit breakers are installed. A main, 3 - pole switch is also available to out-off the supply.

Parts of Distribution Board

Parts of Distribution Board Points : Parts of Distribution Board There are eight parts of D.F.B. such as,
(a) Plastic or wooden board or metal clad panel board.
(b) Bus-bar.
(c) Porcelain insulator.
(d) Fuses.

Distribution Board

Distribution Board Points : Distribution Board “An assembly of parts, including one or more fuses or C.B’s arranged for the distribution of electrical energy to final sub-circuits or to other distribution boards.” it is a main consumer’s controlling point. The electricity company referred to every consumer to install a distribution board. The outgoing wires of the energy meter are in actual the incoming wires of the distributor board. The supply ends of all the circuits should must, be brought back to a specified point in the installation and these connected in parallel on a distribution board.’ in small installation, for example domestic or shop etc. require only one distribution board. The distribution boards are consists on fuses, circuit breakers and main switch.

Advantages and Disadvantages of Miniature Circuit Breakers

Advantages and Disadvantages of Miniature Circuit Breakers Points : Advantages and Disadvantages of Miniature Circuit Breakers Advantages

1. M.C.B’s is quick work against short circuit.
2. M.C.B’s is work quickly on overloading and under voltage.
3. The performance of M.C.B’s is good in case of earth leakage.

Advantages and Disadvantages of Fuse

Advantages and Disadvantages of Fuse Points : Advantages and Disadvantages of Fuse Advantages

1. Fuses are cheap.
2. Most fuses are self protecting and they extinguishing the arc.
3. The fuse element is changed very easily.

Types of Protective Devices for House Wiring

Types of Protective Devices for House Wiring Points : Types of Protective Devices for House wiring, Fuses, Circuit Breaker There are two types of protective devices such as:
(i) Fuses.
(ii) Circuit Breaker (i) Fuses. It. is a device consisting of a melt-able metal link inside a casing. This metal link is also referred to as the fuse’s element. Fuses are installed in such a away in circuit that they disconnect the circuit when faulty or overload current passing through it. This faulty current produced excessive heating and as a ‘result due to this heat the insulation of conductors is damaged. There f ore we can say that “Fuse is a device, which opened the circuit or fusing the element when the current in the circuit exceeds to its rated ‘certain value”.

Types of Fuses

Types of Fuses Points : Types of Fuses, Rewire able fuse, H.R.C fuse. cartridge fuse There are following types of fuses:
(a) Rewire able fuse
(b) H.R.C fuse
(c) Cartridge fuse

Types of Circuit Breakers

Types of Circuit Breakers Points : Types of Circuit Breakers, Miniature Circuit Breakers, Earth leakage Circuit Breakers Types of Circuit Breakers
(a) Miniature Circuit Breakers
(b) Earth leakage Circuit Breakers (a) Miniature Circuit Breakers Every electrical circuit and final circuit shall be protected against over current by suitable over current protective devices such as miniature Circuit Breakers.

The M.C.B’s is mounted in a D.F.H. The M,C.B’s work automatically when current passing through them exceeds the value for which they are set. M.C.B’s is designed in this way that it has a time delay type characteristics. The operating time of miniature circuit breaker is controlled by the magnitude of the over current which passing through it. Another characteristic of M.C.B’s is that it cannot operate at transient overload such as motor starting currents and switching surges. The breaker only operates if the overload is present for a long time which is dangerous for C.B’s.

Sketch of Nickel Iron Cell

Sketch of Nickel Iron Cell Points : Sketch of Nickel Iron Cell, Block Diagram of Iron Cell

Series and Parallel Connection of Batteries or Cell

Series and Parallel Connection of Batteries or Cell Points : Series and Parallel Connection of Batteries or Cell We have already studied in this chapter that the cell is a device which converts chemical energy into electrical energy. A cell consists of two electrodes immersed in an electrolyte. Due to chemical actions opposite charges are developed at the electrodes. The electrodes serve as +ve and —ye terminals of the cell.

Efficiency of Cell or Battery

Efficiency of Cell or Battery Points : Efficiency of Cell or Battery These are two types of efficiency: (i) Ampere-hour efficiency or (quantity efficiency),
(ii) Watt-hour efficiency or (energy efficiency).
Now, we will study in detail both efficiencies:

Efficiency of an Accumulator

Efficiency of an Accumulator Points : Efficiency of an Accumulator, E.M.F. of Accumulators Efficiency is defined as the ratio of output to input for any device. There are two efficiencies according to the units in which input and output are measured. If the measurements are made of the quantity of electricity, ie., ampere-hours, then the efficiency is called the quantity efficiency or ampere-hour efficiency; thus

Battery Containers and Covers

Battery Containers and Covers Points : Battery Containers and Covers The containers for holding the electrode plates and the electrolyte may be made of hard rubber, asphaltic compound, glass, plastic porcelain of lead-lined wood, depending upon the size of the cell and the nature of the service desired.

Affective Capacity of a Lead Acid Battery

Factor Affective Capacity of a Lead Acid Battery Points : Factor Affective Capacity of a Lead Acid Battery 1. Rate of discharge Higher the rate of discharge smaller is the capacity. 2. Permissible final voltage per cell Lower is the final voltage on discharge, higher is the capacity.

Capacity-Rating of a Lead Acid Accumulator

Capacity-Rating of a Lead Acid Accumulator Points : Capacity-Rating of a Lead Acid Accumulator The capacity of a battery can be expressed in ampere hours (Ah) or watt hours (Wh). The former is however, the more commonly used expression. e.g. A battery capable of 80 ampere hours. If the average voltage per element in the given case is 1.95 volts, the watt hour capacity of the given battery is product of the average voltage and the ampere-hour capacity, i.e., 80 x 1.95 of 156 watt hours per element. The capacity of the same cell will decrease if the discharge time is decreased or discharge current is increased. The other important factor is the final voltage per element.

Maintenance and Care of Lead Acid Batteries

Maintenance and Care of Lead Acid Batteries Points : Maintenance and Care of Lead Acid Batteries In order to keep the battery in good condition for Long period, the following instructions must be followed.

1. The cells must always be charged in right direction with direct current.
2. The cells should be charged at proper rate.
3. Over charge or discharge of the cells should be avoided.

Applications of Lead Acid Batteries

Applications of Lead Acid Batteries Points : Applications of Lead Acid Batteries

1. For petrol motor car starting and ignition.
2. As power source for industrial and mining battery locomotives, and for road vehicles like cars and trucks.
3. As a source of power supply in telephone exchange, laboratories and broadcasting stations.

Electrical Characteristics of Lead Acid Battery

Electrical Characteristics of Lead Acid Battery Points : Electrical Characteristics of Lead Acid Battery, As we know that batteries are group of cells connected together in series, parallel or series parallel to provide different voltage, current capacities and other features. The characteristics must always be considered. For example there may be number of batteries having desired voltage for an application, some of these may not have a low enough internal resistance to provide the needed voltage regulation at high current output, other may have insufficient total energy content in ampere hours etc.

Charging of Lead Acid Battery

Charging of Lead Acid Battery Points : Charging of Lead Acid Battery, Indications of Fully Charged Cell For charging a battery a d.c. supply of voltage little higher than the battery voltage is applied across the battery. The care should, be taken that positive terminal of battery should be connected to positive terminal of supply and negative plate to negative terminal of supply.

Chemical Action of Lead Acid Battery

Chemical Action of Lead Acid Battery Points : Chemical Action of Lead Acid Battery, The Changes During Discharging When battery is connected to the load, it supplies electric energy Thus during discharging chemical energy Is converted to electric energy. When the cell Is fully charged Its positive plate is of lead peroxide (Pb0₂), which Is dark brown In colour.

Construction of Lead Acid Battery

Construction of Lead Acid Battery Points : Construction of Lead Acid Battery Battery positive and negative plates are immersed in dilute sulphuric acid solution and kept apart by separators in each of its cells. Let us study in detail each part of the lead acid battery.

Lead Acid Battery

Lead Acid Battery Points : Definition, What is Lead Acid Battery Lead acid battery cells are used where large currents and energy storage is needed. Lead acid cells the most commonly used secondary cell and it is the power source for the electric system of the most cars, trucks and tractors.

Nickel-Cadmium Batteries

Nickel-Cadmium Batteries Points : Nickel-Cadmium Batteries Active material used for positive plate and the electrolyte used in nickel cadmium cells are the same as that used for nickel iron cell. For negative plate a mixture of cadmium and iron is used.

The number of positive plates used in nickel-cadmium cell is one more than the number of negative plates.

Characteristics of Nickel Iron Cell

Characteristics of Nickel Iron Cell Points : Characteristics of Nickel Iron Cell The characteristics of nickel iron cells are as given below:

1. Is light in weight.
2. When fully charged voltage per cell is 1.4 volt and is discharged till its voltage falls to 1.15 volt.

Construction of Nickel Iron Cell

Construction of Nickel Iron Cell Points : Construction of Nickel Iron Cell, Positive plate, Negative plate, Electrolyte, Container, Separator The various parts of the alkaline cell are as given below:
(i) Positive plate
(ii) Negative plate
(iii) Electrolyte
(iv) Container
(v) Separator

Classification of Cells

Classification of Cells Points : Classification of Cells, Primary cells, Secondary cells, Dry Cell, Leclanche Cell, Voltaic Cell, Daniel Cell, Zinc-chloride Cell, Magnesium Dry-Cell Batteries, Alakline-Mn02 Cell (Zn-MnO₂), Lithium-Sulfur Dioxide Cell The battery cells may be classified into two general classes:
(i) Primary cells
(ii) Secondary cells

Production of E.M.F. By Chemical Action

Production of E.M.F. By Chemical Action Points : Production of E.M.F. By Chemical Action A chemical cell is a device that uses the electric charges displaced by chemical action to produce an e.m.f. In this method two dissimilar metal plates (known as electrodes) are immersed in a solution called electrolyte. When these electrodes are externally connected by means of wires chemical action takes place inside the electrolyte. Thus a potential different is created between the two electrodes, which causes the flow of current in the external circuit through the connecting wires.

D.C. Batteries

D.C. Batteries Points : D.C. Batteries, What is D.C. Batteries As we know that to cause the flow of electric current, electromotive force is necessary. The e.m.f. can be set up by various way such as:

1. The relative motion of conductor w.r.t. magnetic field in case of generators and transformers,

Safety While Working on Motor

Safety While Working on Motor Points : Safety While Working on Motor The following factor must be consider while working on motor.

1. Do not start series motor without load or without belt.

Hopkinson Test

Hopkinson Test Points : Hopkinson Test The back to back test for dc machines was devised in its original form by Hopkinson and is similar to the Sumpner’s test for transformers. In practice the modification of the original Hopkinson test by Kapp is employed and it is usually called the Hopkinson test. Two dc shunt machines are mechanically coupled and losses are supplied electrically.

Swinburne’s Test

Swinburne’s Test Points : Swinburne’s Test This is an indirect method of determining the efficiency of a motor by measuring the losses. In this method the iron and friction losses are determined by measuring the input to the machine on no-load, the machine being run as a motor at normal voltage and speed.

Detailed Dynamometer Description

Detailed Dynamometer Description Points : Detailed Dynamometer Description Electrical dynamometer setup, showing engine, torque measurement arrangement and tachometer.
A dynamometer consists of an absorption (or absorber/driver) unit, and usually includes a means for measuring torque and rotational speed.

Dynamometer Test

Dynamometer Test Points : Dynamometer Test An absorbing dynamometer acts as a load that is driven by the prime mover that is under test. The dyno must be able to operate at any speed, and load the prime mover to any level of torque that the test requires. A dynamometer is usually equipped with some means of measuring the operating torque and speed.

Testing of Dc Machines

Testing of Dc Machines Points : Testing of Dc Machines, Direct Method, Indirect Method, Regenerative Method The most important performance tests to be conducted on dc machine are:
(i) The magnetization of open-circuit test.
(ii) The load characteristics.
(iii) The determination of efficiency curve.
(iv) The temperature rise test.

Starters for DC Shunt and Compound Wound Motors

Starters for DC Shunt and Compound Wound Motors Points : Starters for DC Shunt and Compound Wound Motors, Three-Point Starter, Operation, No-Volt Release, Over-Load Release Coil, Four-Point Starter, Precaution, Controller for Series Motors, Drum Controllers, Semi-automatic starters, Magnetic Blow-outs, Automatic Starters, Motor starters are generally manufactured in convenient sizes and styles for use as auxiliaries with dc shunt and compound motors. Their primary function is to limit the current in the armature circuit during the starting or accelerating period. They are always rated on the basis of output power and voltage of the motors with which they are to be employed. The simplest type of starter consists of an additional resistance (a rheostat) inserted in series with the armature alone (not with the motor as a whole), as illustrated in.

Speed Regulation of DC Motor

Speed Regulation of DC Motor Points : Speed Regulation of DC Motor The speed regulation of a dc motor is defined as the change in speed when the load on the motor is reduced from fill load to zero and is expressed in percentage of rated full load speed.

Speed Control of DC Series Motors

Speed Control of DC Series Motors Points : Speed Control of DC Series Motors, Armature Control Methods, Shunted Armature Control, Armature Terminal Voltage Control, Series Parallel Control Speed control of dc series motor may be accomplished through either armature control, field control or series-parallel control. (i) Armature Control Methods Speed adjustment of dc series motors by armature control may be had by any one of the following three methods.
(i) Armature resistance control.
(ii) Shunted armature control and.
(iii) Armature terminal voltage control.

Speed Control of DC Shunt Motors

Speed Control of DC Shunt Motors Points : Speed Control of DC Shunt Motors, Field Control Method, Armature Resistance Control, Armature Voltage Control, Ward-Leonard Method of Speed Control, Ward Leonard Higher System, The speed of a dc shunt motor can be controlled by field control, armature resistance control or armature voltage control. 1. Field Control Method In this method, speed variation is accomplished by means of a variable resistance inserted in series with the shunt field, as illustrated. A increase in controlling resistance reduces the field current with a consequent reduction In flux and an increase in speed. This method of speed control is very simple, convenient and most economical and is, therefore, extensively used in modern electric drives.

Speed Control of DC Motor

Speed Control of DC Motor Points : Speed Control of DC Motor Speed control means intentional change of the drive speed to a value required for performing the specific work process. This concept of speed control or adjustment should not be taken to include the natural change in speed which occurs due to change in the load on the drive shaft.

Direction of Rotation of DC Motor

Direction of Rotation of DC Motor Points : Direction of Rotation of DC Motor It is evident that if the armature current were reversed by reversing the armature leads, but leaving the field polarity the same, torque would be developed in a counters. clockwise direction. Likewise, if the field polarity were reversed leaving the armature current torque would be developed in a counter-clockwise direction. However, if both, the direction of the armature current and field polarity were revelries, torque would be developed in clock-wise direction as before.

Losses in D.C. Motors

Losses in D.C. Motors Points : Losses in D.C. Motors Like generators, motor losses can be divided roughly into two main classes:
(a) Constant losses (independent of load), which are mainly the mechanical losses as well as the iron and core losses; and
(b) Variable losses (dependent on load), and these mainly consist of the copper losses.

Application of D.C. Motors

Application of D.C. Motors Points : Application of D.C. Motors, D.C. Shunt Motor, Series motor, Compound motors 1. D.C. Shunt Motor For a given field current in a shunt motor, the speed drops from no load to full, load is about 6 to 8%. In view of this shunt motor is termed as constant as in Lathes, drilling machine, planers, shapers, metal cutting machine, blowers, fans, wood working machine paper mill etc.

Types of DC Motor

Types of DC Motor Points : Types of DC Motor, Permanent magnet , Separately excited , Series wound , Shunt wound, Compound wound dc motors Similar to dc generators, the dc motors can also be classified as
1. Permanent Magnet
2. Separately Excited
3. Series Wound
4. Shunt Wound
5. Compound Wound DC Motors.
6. Cumulative Compound Wound Motor
7. Differential Compound Wound Motor

Driving and Retarding Torques, Back EMF

Driving and Retarding Torques, Back EMF Points : Driving and Retarding Torques, Back EMF DC Motor The operation of the dc machine as generator. A prime mover drives the generator in anticlockwise direction. It generates an emf and if an external load is connected to the terminals, a current flows through the armature conductors in the directions shown by crosses and dots.

Back EMF of DC Motor

Back EMF of DC Motor Points : Back EMF of DC Motor According to motoring action, when current carrying conductor placed in a magnetic field so these conductors experience force whose direction will be given by Fleming’s left hand rule and motor (rotor) starts rotating.

Commutator Action in a DC Motor

Commutator Action in a DC Motor Points : Commutator Action in a DC Motor In the case of a dc motor, it is necessary that the current through the coils of the. armature winding be reversed as a particular coil leaves one pole (say, the north pole), crosses the neutral line and comes under the influence of next-pole which is of opposite polarity (i.e. the south pole). The operation of the commutator, that serves the above purpose, is given below:

Working Principle of DC Motor

Working Principle of DC Motor Points : Working Principle of DC Motor The principle upon which a dc motor works is very simple. If a current carrying conductor is placed in a magnetic field, mechanical force is experienced on the conductor, the direction of which is given by Fleming’s left hand rule (also called motor rule) and hence the conductor moves in the direction of force. The magnitude of the mechanical force experienced on the conductor is given by

Principle of D.C. Motor

Principle of D.C. Motor Points : Principle of DC Motor Motor principle is based on the principle that whenever current carrying conductor is placed in a magnetic field this conductor experiences a mechanical force whose direction will be given by Fleming’s left hand rule.

D.C. Motor

D.C. Motor Points : DC Motor, What is DC Motor, Definition of DC Motor An electric motor is a machine, which converts electrical energy into mechanical energy in the form of rotation.

Electricity Rules about Domestic Wiring

Electricity Rules about Domestic Wiring Points : Electricity Rules about Domestic Wiring

1. The 3/0.029 cable is used in final sub-circuits, if load capacity is 5A maximum.

Looping in System

Looping in System Points : Looping in System When we install a wiring and we want to avoid as for as possible to joints, then we use looping in connection scheme.

Jointing Method

Jointing Method Points : Jointing Method In this method of connection, the use of junction boxes may be adopted.

Flexible Conduit

Flexible Conduit Points : Flexible Conduit Flexible conduits are also available and these can be used, where there are awkward bends and where rigid conduit would be difficult to install.

Concealed Conduit Wiring Installation Method

Concealed Conduit Wiring Installation Method Points : Concealed Conduit Wiring Installation Method Steel and P.V.C plastic conduits are particularly suitable for concealed wiring system. The conduits are installed during building construction and can be safely buried in ceiling and walls. The conduits are buried in this way that the cables can be drawn in at any time after the completion of construction work.

Advantages and Disadvantages of Concealed Conduit Wiring

Advantages and Disadvantages of Concealed Conduit Wiring Points : Advantages and Disadvantages of Concealed Conduit Wiring Advantages

1. P.V.C conduit is non-corrosive, impervious of most chemicals, weather proof, and it will not support combustion.
2. There is no need of earthing in case of P.V.C plastic conduit system.

Concealed Conduit Wiring Materials and Tools

Concealed Conduit Wiring Materials and Tools Points : Concealed conduit wiring Materials and Tools Materials

1. Wood board / metal board / plastic board
2. Conduits (metal / P.V.C)
3. Insulation tape
4. Junctions box
5. Ceiling roses

Precautions of Concealed Conduit Wiring

Precautions of Concealed Conduit Wiring Points : Precautions of Concealed Conduit Wiring

1. If the ceiling is of reinforced concrete, it may be necessary to erect the conduit system on the shuttering and secure it. If not secure, then it may move out of position.

Uses of Concealed Conduit Wiring

Uses of Concealed Conduit Wiring Points : Uses of Concealed Conduit Wiring This wiring system is frequently used in homes, hospitals, hostels, commercial places, mosques, offices,

Uses of Conduit Wiring

Uses of Conduit Wiring Points : Uses of Conduit Wiring Conduit wiring system is used frequently in home, offices, textile mills, floor mills,

Conduit Wiring System

Conduit Wiring System Points : Conduit Wiring System Ordinary electrical conductors strung without protection soon proved faulty and dangerous.

Types of Conduit Wiring

Types of Conduit Wiring Points : Types of Conduit Wiring There are two types of conduit wiring,
(a) Surface conduit wiring
(b) Concealed conduit wiring

Surface Conduit Wiring Materials and Tools

Surface Conduit Wiring Materials and Tools Points : Surface Conduit Wiring Materials and Tools Materials

1. Conduits (metal / P.V.C).
2. P.V.C cable.
3. Insulation tape.
4. Ceiling roses.
5. Switch boards.

Conduit Wiring Installation Method

Conduit Wiring Installation Method Points : Conduit Wiring Installation Method The first consideration is to choose the most suitable routes for the conduits. The routes should, be chosen so as to keep the conduits are straight as possible. It is recommended that to use manufactured bends, inspection tees, elbows and junction boxes. Draw the lines on the suited routes by using coloured thread, made the holes into the walls at the distance of 1 meter and these holes arranged to equal distances.

Precautions of Conduit Wiring

Precautions of Conduit Wiring Points : Precautions of Conduit Wiring

1. The metal pipes or conduits are terminated in metal-clad board with a smooth bore brass bush or ring brass bush.
2. Before drawing the cables in conduit, make sure that there is no moisture is present in interior of the conduit.
3. If two or more than two conduits are run in parallel then multiple saddles must be used.

Advantages and Disadvantages of Conduit Wiring

Advantages and Disadvantages of Conduit Wiring Points : Advantages and Disadvantages of Conduit Wiring Advantages

1. P.V.C conduits offers a highly resistant against corrosion.
2. It is a durable and very popular system.
3. It is a water proof wiring system.
4. It will not support to combustion.

Casing Capping Wiring System

Casing Capping Wiring System Points : Casing Capping Wiring System It is the oldest wiring system and frequently used, few years ago. But, now today conduit wiring system is used. In other words conduit wiring system is preferred on the casing caping wiring system.

Casing Capping Wiring Installation Method

Casing Capping Wiring Installation Method Points : Casing Capping Wiring Installation Method First of all draw the lines on the walls with coloured thread. Made the holes on the wall at the distance of 1 meter and these holes are made on equal distances from each other.

Advantages and Disadvantages of Casing Capping Wiring

Advantages and Disadvantages of Casing Capping Wiring Points : Advantages and Disadvantages of Casing Capping Wiring Advantages

1. Due to caping, the cables are escaped from air, humidity, light and smoke etc.
2. There is no risk of electric shock because all the cables are covered.
3. It is cheaper compare to steel conduit and sheeted wiring system.

Precautions of Casing CappingWiring

Precautions of Casing Capping Wiring Points : Precautions of Casing Caping Wiring

1. Always use the porcelain tube or conduit when cables are passing through the walls.
2. All the joints are made, in junction boxes and also at switches and sockets.
3. Completely, varnished the casing and caping before installation.

Batten Wiring System

Batten Wiring System Points : Batten Wiring System In this wring system wooden batten is used.

Method of Batten Wiring Installation

Method of Batten Wiring Installation Points : Method of Batten Wiring Installation First of all, draw the straight lines with coloured thread on walls of the building. Always draw the lines to the height of 3m bove the ground surface.

Advantages and Disadvantages of Batten Wiring

Advantages and Disadvantages of Batten Wiring Points : Advantages and Disadvantages of Batten Wiring Advantages

1. The chance of leakage of current is very rare.
2. Batten wiring system has a long life.

Precautions of Batten Wiring

Precautions of Batten Wiring Points : Precautions of Batten Wiring

1. If cables are passing under water pipes or walls then metal pipes are used.
2. Use the correct size of clips, if large clips are used then the beauty of wiring is not maintained.

Materials and Tools of Batten Wiring

Materials and Tools of Batten Wiring Points : Materials and Tools of Batten Wiring Materials

1. Screws (1 .5, 2, 2.5 inch)
2. Batten (15, 20, 25, 40 mm)
3. Wooden round block
4. Ceiling rose
5. Switch board
6. Conduit pipe
7. Main switch

Cleat Wiring System

Cleat Wiring Points : Cleat Wiring Temporary electrical wiring on building and construction sites is necessary to enable lighting and power to be provided for the various points on the site.

Method of Cleat Wiring Installation

Method of Cleat Wiring Installation Points : Method of Cleat Wiring Installation First, draw the straight line on the wall with the help of colored thread and after that mark the points on the wall.

Advantages and Disadvantages of Cleat Wiring

Advantages and Disadvantages of Cleat Wiring Points : Advantages and Disadvantages of Cleat Wiring Advantages

1. The whole wiring is replaced in short period of the time and material of wiring is used on another place if we want.
2. The alternations and additions are possible in cleat wiring system and inspection of this wiring is very easy.

Precautions of Cleat Wiring

Precautions of Cleat Wiring Points : Precautions of Cleat Wiring

1. The cap, is not tightly screwed on the base because insulation of cables is damaged and not as loosely screw that as a result the cables are producing sag.
2. If cables are passing through under the water pipes, walls or roofs then cables are always passing through met conduits.

Materials and Tools of Cleat Wiring

Materials and Tools of Cleat Wiring Points : Materials and Tools of Cleat Wiring Materials

1. Metal pipe or porcelain tubes
2. P.V.C or V.I.R cable
3. Single way switches
4. Wooden round block
5. Insulation tape
6. Junction box

Types of Wiring System

Types of Wiring System Points : Types of Wiring System The wiring system which are commonly sued are as follows.
1. Cleat wiring
2. Batten wiring
3. Casing caping wiring
4. Conduit wiring (it has two types)

Choice of Wiring System

Choice of Wiring System Points : Choice of Wiring System, Type of Building, Voltages, Nature of Work in Building, Weather Condition, Durability, Safety, Safety, Flexibility, Switch Gears, Availability of Material, Beauty of Building Different factors must be kept in mind when you are selecting any wiring system. These factors are as follows, safety, capacity, nature of work in building, voltages, accessibility, flexibility, future requirements, easy maintenance, economical, wiring cost estimation, weather condition, building construction, heat, rain and switch gears. Some factors are briefly discussed here and you will be learning more deeply about these factors in your next classes.

Size of Cable for a Given Load

Size of Cable for a Given Load Points : Size of Cable for a Given Load To determine the correct size of a cable for a given load, we concern the tables of electric cables. In this, current carrying capacity of a able,’ Voltage drop in cable: temperature factors are given. Some points are given below, are very important to determine the correct size of a cable.

Current Carrying Capacity of a Cable

Current Carrying Capacity of a Cable Points : Current Carrying Capacity of a Cable The current carrying capacity of cable is limited by electrical and chemical deterioration of the insulation at high temperatures.

Voltage Grading of cable

Voltage Grading of cable Points : Voltage Grading of cable Generally wiring cables are manufactured in two voltages grading such as low and medium. The two grads are termed as 250/440V and 660/1100 voltage grade. For wiring purpose the cables are designed for maximum1100 V capacity. If there are two cables which have same conductor size insulation size is different. The insulation of medium voltage cable is thicker and the low voltage cable has thin insulation site. The minimum thickness of the insulation is determined by the supply voltage.

Types of cable W.R.T core

Types of cable W.R.T core Points : Types of cable W.R.T core “In electric cables, the insulated conductor is known as core.” If a cable is required containing more than one insulated core that is a multi core cable. A cable can have many numbers of cores but the most common are single, twin, three and four core cables.

Classification of Cables w.r.t Insulation

Classification of Cables w.r.t Insulation Points : Classification of Cables w.r.t Insulation The construction of cable is that to envelope the conductor a non-conducting material. The insulation is this material in which the electricity can’t flow. For cable insulation there are only insulation material are used such as. P.V.C, mica power, Fiber etc. The purpose of insulation is that to provide protection electric chock, leakage of current and fire etc.

Choice of Cable

Choice of Cable Points : Choice of Cable The essential components of a cable are a metallic conductor of low resistivity to carry the current and insulation around cable which provide dielectric medium for isolating conductors from one another and from their surroundings. It is recommended that always choose the correct size of cable that is big enough to prevent the development of dangerous temperatures and also big enough to avoid wasted power in the form of excessive voltage drop. This wasted power is used in heating the cable causing the temperature may be rise sufficiently to damage or even destroy the insulation of the cable and also efficiency of electrical devices is decreased. Cheaper cables are not good for electric wiring because the power loss and voltage drop in these cables are very high.
To choose the correct size of cable for electric wiring, some important points to be remember.

Tinning

Tinning Points : Tinning Copper and rubber, when brought into contact, react upon one another chemically. It was formerly thought that this action was due entirely to the sulfur in the rubber compound combining with the copper. Pure rubber, however, also reacts with the copper.

Voltage Build Up Process in D.C. Generator

Voltage Build Up Process in D.C. Generator Points : Voltage Build Up Process in D.C. Generator Let us consider a D.C. shunt generator: Consider an unloaded shunt generator, straight line Oa is the graphical plot ‘of Ohm’s law for field circuit and it represents field resistance which is constant throughout.

Safety while Working on Generator

Safety while Working on Generator Points : Safety while Working on Generator

1. In series generator the winding resistance is very low due to this reason find the properties of open circuit (o.c.c) of this generator (to get low supply voltage).

Parallel Operation of Compound Generator

Parallel Operation of Compound Generator Points : Parallel Operation of Compound Generator Since these machines possess winding in series with the armature and usually having a rising characteristics, it is again necessary to equalize their field currents.

Parallel Operation of Shunt Generators

Parallel Operation of Shunt Generators Points : Parallel Operation of Shunt Generators When two shunt generators are connected in parallel, they function together to supply power to a common load and they are completely stable whether or not their exact voltage versus current characteristics are identical. This is because of the drooping voltage-current characteristics of shunt generators. The circuit diagram for the operation of two shunt generators in parallel. Assume that generator A is in operation with switch SA closed and that the load it is delivering is about to be increased sufficiently to require the use of a machine of larger rating than A or the connection of a second generator to operate in parallel with A, The procedure for connection of two shunt generators in parallel is as follows:

Series Generators in Parallel

Series Generators in Parallel Points : Series Generators in Parallel Two identical series generators connected in parallel. Suppose E₁ and E₁ are initially equal, generators supply equal currents and have equal shunt resistances. Suppose E₁ increases slightly so that E₁ > E₂.

Load Sharing of DC Generator

Load Sharing of DC Generator Points : Load Sharing of DC Generator Because of their slightly drooping voltage characteristics, shunt generators are most suited for stable parallel operation. Their satisfactory operation is due to the fact that any tendency on the part of a generator take more or less than its proper share of load results in certain changes of voltage in the system which immediately oppose this tendency thereby restoring the original division of load. Hence, once paralleled, they are automatically held in parallel.

Procedure for Paralleling D.C. Generators

Procedure for Paralleling D.C. Generators Points : Procedure for Paralleling D.C. Generators (i) Close the disconnect switch of the incoming generator.
(ii) Start the prime-mover and adjust it to the rated speed of the machine.
(iii) Adjust the voltage of the incoming machine a few volts higher than the bus voltage.
(iv) Close the breaker of the incoming generator.

Conditions for Parallel Operation of Two Generators

Conditions for Parallel Operation of Two Generators Points : Conditions for Parallel Operation of Two Generators The conditions for parallel operation of two d.c. generators are:
1. Positive terminal of one machine should be connected to the positive terminal of other machines.
2. The voltages of two machines should be approximately equal before these machines are connected.

Parallel Operation of D.C. Generators

Parallel Operation of D.C. Generators Points : Parallel Operation of D.C. Generators Some times it is necessary to operate two or more generators in parallel to supply the power system. There are a number of good reasons for this parallel operation and these are:

Losses in D.C. Generators

Losses in D.C. Generators Points : Losses in D.C. Generators, The losses in d.c. machines may be divided into two groups:
(1) Variable losses, and
(2) Constant losses.

Methods of Improving Commutation

Methods of Improving Commutation Points : Methods of Improving Commutation Improvement of commutation means, the current from, the rotating armature winding to the external stationary circuit or vice versa should be made to pass through the commutator and brushes directly and not as a spark. The passage of current in any electric circuit, according to ohms law, is governed by emf and resistance. Hence methods of improving commutation can be classified as. Emf commutation and Resistance commutation

Brush Shifting

Brush Shifting Points : Brush Shifting DC Generator When the armature of a D.C. machine (without interpoles) carries current, the magnetic and mechanical neutrals do not coincide. Sparking will occur at the brushes unless they occupy positions that short circuit coil sides in the neutral zone. The brushes therefore, must be shifted to the magnetic neutral. The effect of the armature reaction depends upon the value of armature current.

Compensating Windings

Compensating Windings Points : Compensating Windings Compensating windings are used for the purpose of neutralizing the effect of armature reaction in the zones outside the conductors influence of the inter-poles and particularly to maintain a uniform flux distribution under the pole faces of the main poles.

Armature Reaction

Armature Reaction Points : Armature Reaction DC Generator Armature reaction is the term used to describe the effects of the armature mmf on the air-gap field. Armature mmf has definite effects on both the space distribution of the air-gap flux and the magnitude of the net flux per pole.

Levels of Compounding a Compound Generator

Levels of Compounding a Compound Generator Points : Levels of Compounding a Compound Generator The shunt generator gives a dropping external characteristic whereas the series generator yields a rising characteristic; therefore, if a machine is excited by both shunt and series field windings, the drop in terminal voltage of the generator can be compensated either in part or in full: also by making the series windings relatively a bit stronger, the terminal voltage may even be made to rise with load.