Page 847 - Basic Electrical Engineering

Figure 11.26 Error due to wattmeter connections: (a) when pressure coil is connected before the
current coil; (b) when the pressure coil is connected after the current coil

If the power factor of the load is leading, than the correction factor is
calculated as

Instead of applying a correction factor in the reading of the wattmeter, the
error due to the inductive effect of the pressure coil can be neutralized by

connecting a capacitor in series with the pressure coil so that the inductive
reactance is balanced by the capacitive reactance.

(b) Error due to method of connection of the current coil and pressure coil

There will be a certain amount of error due to the two types of connections of
the wattmeter current coil and pressure coil as shown in Fig. 11.26 (a) and

(b). For correct reading, the current coil should carry the load current and the
pressure coil be connected across the load. It may be noted that in Fig. 11.26

(b), the current coil carries a current, i which is slightly more than I (i = I L
C
c
L
+ i ). In Fig. 11.26 (a), the current coil carries a current i which is equal to I L
p
c
but the voltage across the pressure coil is slightly more than voltage across