Question

Disc in an induction type energy meter rotates in the opposite direction when

• A. a large capacitor is connected on the load side
• B. a large inductor is connected on the load side
• C. current coil and voltage coil are wrongly connected
• D. either current coil or voltage coil is wrongly connected.

Answer 1

The correct option is D either current coil or voltage coil is wrongly connected.

In induction type energy meter.

Driving torque on disc,
${\tau }_d\propto {\varphi }_1{\varphi }_2$

where ${\varphi }_1$ is flux produced by current coil and ${\varphi }_2$ is flux produced by potential coil.

Now, if either PC or CC is wrong by connected, ${\varphi }_{1}or{\varphi }_2$ reverse so driving torque reverses. If both are wrongly connected then,

${\tau }_D\propto (-{\varphi }_1)(-{\varphi }_2)$

$\Rightarrow {\tau }_D$ direction remains same so disc rotates in same direction.