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Quiz: Electrical Engineering 2 july 2020

Quiz: Electrical Engineering

Exam: UPSSSC JE

Topic: Miscellaneous

Each question carries 1 mark.

Negative marking: 1/4 mark

Time: 10 Minute

1. Potential transformers are used to measure _________
a) high voltages
b) low voltages
c) high currents
d) low currents

1. Potential transformer is similar in design to a
a) C.T.
b) Step up transformer
c) Power transformer
d) Step down transformer

1. The primary current in a C.T. is _________
a) independent of secondary circuit
b) dependent on the secondary circuit
c) depends on the transformation ratio
d) depends on the nominal ratio

1. The excitation current of a C.T.
a) varies over a fixed range of operation
b) varies over a wide range of normal operation
c) is fixed over a range of operation
d) is fixed always

1. Instrument transformers provide _________
a) electrical isolation from low rated winding
b) electrical isolation from high rated winding
c) electrical isolation from medium rated winding
d) no electrical isolation at all

1. A 5A ammeter can measure a current of up to 1000 A using a _________
a) 5/1000A C.T.
b) 1000A C.T.
c) 5A C.T.
d) 1000/5A C.T.

1. How can the meter circuit be isolated from power circuit?
a) by grounding
b) through electrical isolation
c) by physical separation
d) through mechanical isolation

1. In a DC machine, how coil-side emf varies towards the outer side of poles?
a) Decreases
b) Remains same
c) Increases
d) First increases the decreases

1. What is the effect of armature coils at points where brushes are located?
a) Induces positive emf
b) Induces negative emf
c) Induces zero emf
d) Depends on the speed of rotor

1. Coil span for 4-pole, 12-slot armature winding is_______
a) 24
b) 48
c) 8
d) 3

Solution

Sol. 1 Ans (a)

Potential transformers are also known as P.T. and are used in the measurement of high magnitude of voltages.

Sol. 2 Ans (c)

In terms of design, the potential transformer resembles a power transformer. Potential transformers have a very low loading capacity of the order of a few volt amperes.

Sol. 3 Ans (a)

A C.T. is used for the measurement of high magnitude of currents in a circuit, while a P.T. is used for the measurement of high magnitude of voltages in a circuit. Primary current in a C.T. is independent of the secondary circuit conditions.

Sol. 4 Ans (b)

In a potential transformer, the excitation current remains constant under normal operation. While in a current transformer, the excitation current varies over a wide range of operation.

Sol. 5 Ans (b)

In an instrument transformer, the low rated secondary windings provide electrical isolation from the high rated primary winding.

Sol. 6 Ans (d)

A 1000/5A current transformer can be used for measuring a current of up to 1000A by making use of an ammeter with 5A current reading.

Sol. 7 Ans (b)

Leads of the secondary winding transformer are brought to the switch board thus separating them from high voltage windings. In this way, the meter circuit is isolated from the high voltage power circuit.

Sol. 8 Ans (a)

Coil side current pattern is the same as the emf pattern. Only difference is that while the coil-side emf reduces towards the outer side of poles, the current remains the same in all the coil-sides except for alterations from pole to pole, while the coil side current reverses, the current exchanged with external circuit must be unidirectional.

Sol. 9 Ans (c)

Brushes are at magnetically neutral region hence, induced emf due to armature coils at brushes will be equal to zero. As in the magnetically neutral region change in flux will be equal to the zero, emf will not be induced (Faraday’s law).

Sol. 10 Ans (d)

Coil span is defined as a ratio of number of slots in the armature winding which are also equal to the number of commutator segments to the number of poles. Here, Slots in the armature winding= 12, Number of poles= 4.
YCS= 12/4= 3.

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