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Theory of Electrical Energy Measurement

Theory of Electrical Energy Measurement - Electric energy flow into two type of circuit i.e in DC circuit and AC circuit. This two different type of circuit consist of same electrical parameter i.e voltage and current.But this two parameters are slightly different to each other with respect to AC and DC circuit.Hence the measurement of electric power in this two different different circuit is different.But the theory behind the measurement of electric power is same for DC and AC circuit.Here we will discuss about the measurement of electric power in both AC and DC circuit. 

Theory of Electric Power Measurement

When a passive component or load is connected across the circuit it consumes electric power from the source.The power consumed by electric circuit is given by the product of the load current flowing through the circuit and and the terminal voltage of the circuit.This is the basic principle which is used for the measurement of electric power either in the DC or AC circuit. 

Electric Power Measurement In DC Circuit

Electric Power Consumed by load in DC Circuit is calculated by the product of dc load current drawn by the load and the voltage drop across the load.Hence the most effective method of electric power measurement voltmeter and ammeter method.The circuit diagram given below show the two possible connection of measurement of electric power in DC  circuit.



In figure (a) the voltmeter is connected across the supply side ,the measurement of electrical power from this method is sum of the electric power consumed by the load and electric power loss by ammeter. 
In figure (b) the voltmeter is connected only across the load side,so the measured power by this method is only power which is consumed by the load and a very small power loss by the voltmeter.From the figure (b) the loss power by the voltmeter is very low ,this method is suitable for the measurement of electrical power for DC circuit. 

Measurement of  Power In AC Circuit

Current flowing in AC circuit has alternating nature i.e it goes for positive for half period of time and again negative for next half period of time so due to this alternation of current the power flow in ac circuit being positive for half period of time and negative for another half period of time and for one complete period of time the average power is zero.But practically some amount of electric power flow through the circuit.
Due this reason calculation of electric power in electric circuit is different from calculation of electric power of DC circuit and difficult also.The power consumed by the AC circuit is the product of the supply voltage, the load current flowing through the circuit and the power factor of the circuit.

Power Consumed By AC Circuit = VICos𝜱

Where
V=Supply voltage
I = Supply Load Current
Cos𝜱= Power Factor of the circuit
𝜱=Angle between the supply voltage V and Supply load Current I

A basic circuit diagram of the electric measurement is given below.This circuit diagram consists of two different types of coil (a) Current Coil (b) Pressure Coil.Current coil measure the load current and pressure coil measure the voltage across the supply.The product of these two measured parameter is instantaneous power of the AC Circuit.The Pressure Coil of the circuit is connected in series with a high value resistor to limit current flow through it.


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