# Electrical Measurements Questions and Answers – Lag Adjustment Devices

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers (MCQs) focuses on “Lag Adjustment Devices”.

1. The energy meter always measures the load energy correctly.
a) True
b) False

Explanation: When the difference in phase angles between the shunt magnetic flux and the applied voltage is 90 degrees (lagging), the reading of the load energy obtained from an energy meter is correct.

2. Obtaining correct reading from the energy meter requires ______________
a) low resistance and iron losses
b) high resistance and iron losses
c) high resistance and low iron losses
d) low resistance and high iron losses

Explanation: In order to obtain an exact reading for the energy consumed by a load using an energy meter, we require the pressure coil to have a low value of resistance and low iron losses.

3. Phase angle can be made 90 degrees using ____________
b) lag circuit
c) special design
d) transformer

Explanation: Phase angle in an energy meter can be made approximately 90 degrees by making use of a special design in the energy meter.

4. Shading coil consists of many thick turns.
a) True
b) False

Explanation: On the central limb of a shunt magnet we can make use of a shading coil. The shading coil consists of a few fairly thick turns. The figure below shows a shading coil on the central limb of the shunt magnet.

5. Copper shading bands are _________
a) placed as resistance
b) placed as wire
c) placed outside the central limb
d) placed around central limb

Explanation: The central limb of a shunt magnet consists of copper shading bands. They can be moved up or down by making use of the central limb. Figure below illustrates the use of copper shading bands.

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6. As copper shading bands move up ________
a) more flux is induced
b) less flux is induced
c) intermediate flux is induced
d) no flux is induced

Explanation: When the copper shading bands are moved up the central limb, more flux is induced. As a result the difference in angle between the phase and voltage increases. The angle can be made approximately equal to 90 degrees.

7. Shunt flux is made to lag the applied voltage using ________
d) transformer

Explanation: We make use of shading coil on the central limb of a shunt magnet and shading bands in order to make the shunt flux to lag the applied voltage by almost 90 degrees.

8. At overloads, magnetic shunt ________
a) aids the series flux
b) diverts series flux
c) maintains zero flux
d) disables the shunt flux

Explanation: As the magnetic shunt reaches saturation at overloads, magnetic shunt diverts the flux due to series magnet. As a result a large portion of the flux appears in the gap of the air disc. This compensates the self braking torque.

Sanfoundry Global Education & Learning Series – Electrical Measurements.