Electrical Measurements & Measuring Instruments Multiple Choice Questions on “Applications of Megger”.
1. Why is the scale of a megger calibrated in megaohms?
a) to indicate resistance
b) to minimise the current flow
c) to increase the voltage drop
d) to reduce the temperature
Clarification: Current flow through the circuit depends on the magnitude of the e.m.f source. In order to indicate the resistance value indicated by the pointer, the scale of a megger is calibrated.
2. Megger can be used for verifying the electrical insulation level of ____________
a) passive components such as resistance, capacitor and inductance
b) devices such as motor, cable, etc
c) solid state devices
d) liquid crystal devices
Clarification: Solid state devices consist of power electronic components and drives. One of the applications of a Megger circuit is in verifying the electrical insulation levels of devices such as motor, cable, generator, etc.
3. Continuity between any two points can be measured using _________
Clarification: A galvanometer is used for detecting the balance condition in a bridge circuit. An ammeter measures the current flow through the circuit while the voltmeter is used for determining the voltage across the bridge circuit. A megger circuit can be used to determine the continuity between any two points.
4. Electrical continuity between any two points exists if _________
a) there is current flow through them
b) there is a wire connecting the points
c) there is sufficient voltage drop
d) pointer shows deflection
Clarification: Voltage drop across the circuit is measured by using a voltmeter. When the pointer displays full deflection, then there is an electrical continuity between the two points.
5. Megger is also known as _________
Clarification: A galvanometer is used to detect the balance condition. A multimeter can be used for measurement of voltage, current, resistance and power. A megger is also known as a megohmmeter as it is used for the measurement of resistances in the order of Mῼ.
6. The application of a megger is _________
a) to measure resistance
b) to test for leakage
c) to limit the current
d) to increase the emf of the circuit
Clarification: Current flow through a circuit depends on the magnitude of the voltage source. Magnitude of the voltage source can be increased. A megger is mainly used for testing electrical leakages in wires.
7. What is the significance of a megger with respect to high resistance?
a) it is used to limit the current
b) it is used to provide stability
c) used for measuring high resistance with respect to ground
d) it is used for temperature protection
Clarification: Temperature protection can be provided to a bridge circuit by making use of heat sinks. Megger is used for determining very high resistances between the conducting part of a circuit and ground.
8. How is the megger calibrated?
a) in steps of 1 unit per division
b) based on the value of resistance to be measured
c) directly calibrated on the position of the pointer
d) reversely calibrated based on the pointer position
Clarification: The scale in a megger is calibrated such that normal position of a pointer indicates infinity while full scale corresponds to zero resistance.