Extension of D.C & A.C Instruments - Multiple Choice Questions and Answers

Range Extension of D.C & A.C Instruments - Multiple Choice Questions and Answers Points : range extension of d.c & a.c instruments mcqs, objective type question, multiple choice questions and answer 1. For extending the range of d.c. meters, we use....
(a) Shunt
(b) Multiplier
(c) Both (a) & (b)
(d) C.T. & P.T.

2. The voltage drops across shunt and basic meter are...
(a) Different
(b) Same
(c) Maximum
(d) Minimum

Circuit Diagram of Loaded Current Transformer and Potential Transformer

Circuit Diagram of Loaded Current Transformer and Potential Transformer Points : Circuit Diagram of Loaded Current Transformer and Potential Transformer Shows C.T. and PT. connected with the load to measure load current, potential & the current coil of wattmeter is connected through C.T. and standard 5°A ammeter. The potential coil of wattmeter is connected with P.T. and standard 110 V voltmeter.

Characteristics of Potential Transformer

Characteristics of Potential Transformer Points : Characteristics of Potential Transformer (i) Effect of secondary current or VA If we increase the secondary burden, the secondary current is increased, and therefore, the primary current increase. Both primary and secondary voltage drops increase and thus for a given value of V, the value of V decreases and hence the actual ratio increases as the burden increases. The ratio error increase becoming more negative with increase in burden. This variation of ratio error is almost linear with change in burden.
With regard to phase angle, the voltage VP is more advanced in phase because of increased voltage drops with increase in secondary burden. The phasor V_s reversed is retarded in phase due to increase in secondary voltage drops. Thus with increase in burden, the phase angle between VP and V reversed increases, becoming more negative.

Characteristics of Current Transformer

Characteristics of Current Transformer Points : Characteristics of Current Transformer, Effect of P.F. of Secondary Burden on Errors, Effective of change of primary current, Effect of change in secondary burden, Effect of change of frequency, (1) Effect of P.F. of Secondary Burden on Errors a. Ratio Error It is observed that for all inductive burdens the secondary current. I_s lags behind the secondary induced voltage, E_s so that is +ve. Under these conditions the actual transformation ratio is always greater than the turns ratio. For burdens which are sufficiently capacitive, I loads E and so is -ve. under these conditions the actual transformation ratio decreases becoming less than the turns ratio for values of “6” approaching -900.

Theory of Potential Transformer

Theory of Potential Transformer Points : theory of potential transformer The general theory of potential transformer is similar to that for power transformers, except that, as the current in the burden is very small, the total primary current is not much greater than the “no-load” current. The voltage drops due to the resistance and leakage reactance of the windings are of great importance, as an accurate value ratio is required. The phasor diagram of PT.

Potential Transformer

Potential Transformer Points : Potential Transformer, Definition These transformers are extremely accurate ratio step-down transformers and are used in conjunction with standard low-range voltmeters (100-12-V) whose deflection when divided by transformation ratio gives the true voltage on the primary or high-voltage side.

Current Transformer Methods of Reduction of Errors

Current Transformer Methods of Reduction of Errors Points : Current Transformer Methods of Reduction of Errors The errors of C.T can be eliminated b the methods already explained. Also there are some design features which help us to minimize the errors. They are listed below:
(1) By designing the C.T. a low flux density.
(2) By using the core of high permeability material.

Theory of Current Transformer

Theory of Current Transformer Points : Theory of Current Transformer For satisfactory and accurate performance it is necessary that the ratio of transformer of the instrument transformer should he constant within close limits however, in practice, it is found that neither current transformation ratio I_i/I₂ (in case of current transformers) nor voltage transformation ratio V/V₂ (in case of potential transformers) remains constant.