# Electrical Measurements Questions and Answers – Phase Sequence Indicator

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers (MCQs) focuses on “Phase Sequence Indicator”.

1. Phase sequence indicator gives the maximum value of phase voltages.
a) True
b) False

Explanation: The phase sequence for a three phase supply indicates the order in which maximum values of phase voltages ER, EY, and EB occur. A three phase supply can be in either RYB or RBY configuration.

2. Synchronization of A.C. supply means __________
a) different phase sequence
b) same phase sequence
c) zero phase
d) using a transformer

Explanation: During synchronization, the phase sequences of any two given supplies are maintained equal. This is ensured by making use of a phase sequence indicator.

3. How many types of phase sequence indicators are there?
a) 1
b) 5
c) 2
d) 10

Explanation: Generally, two types of phase sequence indicators are used. The first one is the rotating type while the second type is the static type. Usually the rotating type of phase sequence indicator is used.

4. A rotating phase sequence indicator consists of ________
a) 1 coil
b) 2 coils
c) 5 coils
d) 3 coils

Explanation: A rotating type of phase sequence indicator basically consists of three coils. These are mounted at 120º to each other is space. The ends of the coils are connected to the terminals R, Y, and B respectively.

5. The three coils are ________
a) star connected
b) delta connected
c) not connected
d) shorted

Explanation: In a rotating type phase sequence indicator, the three coils are connected in the form of a star and excited by a three-phase supply.
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6. Excitation of the three coils produces ________
a) a static magnetic field
b) a rotating magnetic field
c) a static electric field
d) a rotating electric field

Explanation: Aluminum disc is mounted on the top of the three coils. A rotating magnetic field is produced when the three coils are excited by a supply of three phase. As a result e.m.f with eddy current effects are induced in the coils.

7. Eddy e.m.f produces a torque.
a) True
b) False

Explanation: A rotating magnetic field is produced when the three coils are excited by a supply of three phase. As a result, eddy e.m.f circulates in the disc. A torque is produced as a result of the interaction between the eddy currents and the rotating magnetic field.

8. Disc rotation is determined by ________
a) the supply voltage
b) an arrow
c) the turns ratio

Explanation: Direction of rotation of the disc is determined by making use of an arrow that is marked on the disc. The phase sequence of the supply voltage is same as that mentioned on the terminals of the meter provided disc rotates in the same direction as the arrow head.

Sanfoundry Global Education & Learning Series – Electrical Measurements.