Construction of Merz Price Demand Indictor

Construction of Merz Price Demand Indictor Points : Construction of Merz Price Demand Indictor This indicator is not in the form of a separate unit, but it is an attachment which can be used with any type of motor or clock-meter and it based on the fact that it the energy flowing in a circuit is measured, say, in watt- hours, for a series of time intervals of equal duration, then the individual blocks of energy measured are themselves equal to the average power consumed. This follows from the relation.

Average power in watts for the time period under consideration

= Energy measured in watt — hours/Time interval in hours

The same relation holds good while measuring Varh or Vah, during a definite interval of time, giving average Var or Va, respectively. Thus any mechanism which measure discreets blocks of Wh, Varh or Vah during a fixed time interval of short duration will be suitable for estimating their average values. It consists of a separate dial fitted inside the instrument, the pointer of which is driven by the spindle of the moving system of the meter through a train of gears and pin. Normally the pointer is driven forward for an half hour period or other period known as integrating time period and the energy consumed during this period is indicated on the dial by the pointer. At the end of time period, by means of a time switch and an operating mechanism the pointer is disconnected from the gearing, return to zero and reconnected to the gearing. A maximum demand pointer is advanced by the driving pointer, but is held by fraction when not being driven. This pointer will be advanced to a new position when one half- hours energy consumption exceeds than that in any preceding half hour, but will not be affected during the half hour periods when the energy consumption is lower than that corresponding to its existing position.

The circuit connections for a typical poly-phase maximum demand indicator and time switch, employing instrument transformers, when connected into 3-phase. 3-wire system.