Question

Two wattmeters are connected to measure power in a 3-phase network. The two readings are 2000 watts and 1000 watts respectively. If another wattmeter to be connected such that its current coil is in one phase and the potential coil is across the other two phase terminals. Then the reading of wattmeter is _______VAR.

• A. $100$
• B. $1000$
• C. $1000\sqrt{3}$
• D. $3000$

Answer 1

The correct option is B $1000$

Reading of wattmeter - 1,
$W_1=2000watts$

Reading of wattmeter-2
$W_2=1000watts$

Reactive power of the network,

$Q=\sqrt{3}(W_1-W_2)=\sqrt{2}(2000-1000)$

$=1000\sqrt{3}VAR$

When the current coil is connected in one phase and the potential coil across the other two phases the wattmeter reads

$\frac{TotalVAR}{\sqrt{3}}=\frac{1000\sqrt{3}}{\sqrt{3}}=1000VAR$