Which method can be used to measure the power in a three-phase balanced and unbalanced load system?
Right Answer is:
Two wattmeter method
A wattmeter is an instrument with a potential coil and a current coil so arranged that its deflection is proportional to VI cosθ
V is the voltage (RMS value) applied across the potential coil
I is the current (RMS valued passing through the current coil
θ is the angle between V and I.
- In a three-phase system, total power is the sum of powers in three phases.
- The power is measured by the wattmeter.
- It consists of two coils. (i) current coil, and (ii) voltage coil.
- The current coil is connected in series with the load and it senses current.
- Voltage coil is connected across supply terminals and it senses voltages.
Two Wattmeter Method
- This method is used for balanced as well as unbalanced load.
- The current coils of the two wattmeters are inserted in any two lines and the voltage coil of each wattmeter is joined to a third line.
- The load may be a star or delta connected. The sum of the two wattmeter readings gives three-phase power.
W = W1 + W2 = Three-phase