Power Engineering 4th Class Chapter 82

If the secondary voltage is smaller than primary voltage in a transformer. This transformer is called? a) current transformer b) step down transformer c) potential transformer d) step up transformer e) resistance indicator

b

A transformer works on the principle of a) reverse polarity b) magnetic induction c) DC power flowing in one direction d) straight polarity e) automatic induction

b

When AC action causes a counter current in a coil of wire, it is termed: Choose one answer. a. Self inductance b. Capacitance c. Hysteresis d. Mutual inductance e. Electromagnetic induction

a

A transformer works on the principle of: Choose one answer. a. Hysteresis b. Electro-Magnetic induction c. Eddy currents d. Faraday's law e. Flux leakage

b

Which transformer is used to trap the harmonics on the primary windings? a) k-type transformer b) core type transformer c) potential transformer d) shell type transformer e) Autotransformer

a

Auto-transformers: Choose one answer. a. Can use less copper b. Use more copper c. Have large ratios of transformation d. Use separate windings for primary and secondary circuits e. Have an equal ratio of transformation

a

In a dc circuit, self-inductance is __ when voltage is at maximum, while in a ac circuit self inductance is __ a. Not a factor, continually a factor b. Sometimes a factor, not a factor c. Continually a factor, not a factor d. Not a factor, sometimes a factor

a

Single-phase transformers: Choose one answer. a. Use two common forms of construction known as the core type and the shell type. b. High voltage coil is nearest the iron core. c. Use two common forms of construction known as the internal type and the external type. d. Are very low in efficiency. e. Are used in all power supplies.

a

The capacity of a transformer can be increased by: 1. submerging the core and windings in a tank of oil 2. submerging the core and windings in a tank of water 3. forced air cooling the oil in a heat exchanger 4. wrapping the core with a thermal insulation 5. forced air cooling of the core a) 1, 3, 5 b) 2, 3, 4 c) 1, 4, 5 d) 2, 3, 4, 5 e) 2, 4, 5

a

The voltage induced in the secondary windings of the transformer, is _____ the turns ratio of the transformer. Choose one answer. a. Directly proportional to b. Reversed to c. Unrelated to d. Opposed by e. Inversely proportional to

a

Transformer cooling oil has a) a very high specific heat b) a poorer insulating characteristic than air c) a very high fire point d) no factors which necessitate better wire insulation e) a very low safety hazard

a

Transformers Choose one answer. a. Step up or down AC voltage b. Transforming AC voltage to DC voltage c. Rectify DC voltage to AC voltage d. Step up DC voltage e. Step down DC current

a

Primary and secondary windings are split into two equal parts, with one half of the primary and one half of the secondary wound on each of the two "legs" of the transformer. This transformer is called? a) current transformer b) core type transformer c) potential transformer d) shell type transformer e) resistance indicator

b

The size of the conductor is __ to the size of the current. a. Inversely proportional b. Proportional c. Equal d. None of the above

b

Transformers require: Choose one answer. a. More maintenance than other electric machinery b. Less maintenance than most other electric machinery c. No maintenance d. Inspection every three years e. Inspection every month

b

A transformer has a primary voltage of 500 volts and 20 turns on the primary winding. If the secondary winding has 5 turns, the voltage of the secondary is: Choose one answer. a. 2000 volts b. 2500 volts c. 125 volts d. 100 volts e. 4 volts

c

An instrument transformer used to measure voltage is called a: Choose one answer. a. Current transformer b. Step down transformer c. Potential transformer d. Step up transformer e. Auto-transformer

c

Because of environmental concerns, it is no longer permissible to add ____________ to transformer oil. Choose one answer. a. Chelates b. Anti-foaming substances c. Chlorinated hydrocarbons d. Freon e. Organic compounds

c

Copper losses in a transformer are reduced by a) using fan cooling b) using oil cooling c) using larger diameter wire d) reducing the primary voltage e) increasing the secondary voltage

c

Three major losses which occur in a transformer are iron losses, copper losses, and: Choose one answer. a. Cooling losses b. Heat losses c. Flux leakage d. Capacitive losses e. Inductive losses

c

Transformers are often cooled by: Choose one answer. a. immersing the core in a refrigerant bath b. turning the transformer off at regular intervals c. force cooling with fans d. immersing the core in cooling water e. using windings with less insulation

c

When magnetic flux produced by one coil induces an EMF in a second coil, it is called: Choose one answer. a. Self inductance b. Electromagnetic induction c. Mutual inductance d. Capacitive reactance e. Inductive reactance

c

A device used to change the voltage and current from one level to another, is known as a/an a) conductor b) resistor c) alternator d) transformer e) power booster

d

All of the primary and secondary is wound on the centre leg. This transformer is called? a) current transformer b) core type transformer c) potential transformer d) shell type transformer e) resistance indicator

d

An operating current transformer should never: Choose one answer. a. Be inspected until properly grounded b. Have its primary circuit opened c. Produce excessively high voltages d. Have its secondary circuit opened first e. Have its secondary connected to a meter

d

If the number of secondary turns is greater than the number of primary turns in a transformer. This transformer is called? a) current transformer b) step down transformer c) potential transformer d) step up transformer e) resistance indicator

d

Transformers should be inspected at least: Choose one answer. a. Quarterly b. Bi-annually c. Semi-annually d. Once or twice a year e. Every five years

d

When relative movement ceases, production of induced E ceases. This process is called a. Harmonic distortion b. Self inductance c. Mutual inductance d. Electro-magnetic induction

d

A phenomenon produced by electric switchgear that can result in excessively high voltages in transformers is known as: Choose one answer. a. Capacitive reactance b. Inductive reactance c. Phase lag d. Reactive voltage losses e. Harmonic distortion

e

Current transformers are: Choose one answer. a. Power step-up transformers b. Current step-up transformers c. K-type transformers d. High power factor transformers e. Voltage step-up transformers

e

Current transformers step down the current rather than the a) resistance b) flux strength c) conductance d) number of poles e) voltage

e

Double-wound transformers can be connected as? a) current transformer b) core type transformer c) potential transformer d) shell type transformer e) Autotransformer

e

If Ep/Es = Np/Ns, the Ns will equal: Choose one answer. a. Ep/NpEs b. EpEs/Np c. NpEsEp d. NpEp/Es e. NpEs/Ep

e

Iron loses in a transformer are caused by? a. Eddy currents b. Magnetic hysteresis c. Harmonic distortion d. All of the above e. A and B

e

Transformers are rated in terms of: 1. Volt amperes 2. Kilowatts 3. Kilovolt amperes 4. Ohms a) 1, 2 b) 2, 4 c) 2, 3 d) 3, 4 e) 1, 3

e

Transformers are rated in: Choose one answer. a. Polarity b. Service factor c. Watts d. Core temperature e. kVA

e