P-1

Question 1

What is Mutual Induction?

Answer 1

The action by which a change in current in one conductor induces a voltage in a neighbouring conductor.

Question 2

Whenever the current through a conductor increases, the magnetic flux around the conductor ______

Answer 2

Increases

Question 3

Transformers have efficiencies in the range of _________

Answer 3

96-99%

Question 4

Ideally, the material used in the core of a power transformer should have the properties of _______, __________, and _______.

Answer 4

Low retentivity, high permeability, and high resistance

Question 5

Are instrument Transformers normally additive or subtractive polarity?

Answer 5

Subtractive

Question 6

On a transformer, how can the high-voltage bushings be distinguished from the low-voltage bushings?

Answer 6

The high voltage bushings are longer than the low voltage bushings

Question 7

Is it important to observe the relative polarity of winding leads when making multi winding transformer connections?

Answer 7

Yes if not there will be large short circuit currents between the transformers

Question 8

List three conditions that must be met before transformers may be paralleled?

Answer 8

1. Same Primary Secondary Ratings
2. Polarity must be observed when connecting
3. Must have the same percent impedance

Question 9

What causes the terminal voltage of a transformer to change as the load changes?

Answer 9

The terminal voltage drops as the transformer is loaded, IZ increases as I increases

Question 10

If transformers of unequal percent impedances are paralleled, which one will carry more than its share of load?

Answer 10

The transformer with the lowest percent impedance will carry more than its share of the load

Question 11

When a voltmeter closure test is performed on the secondary of two transformers being paralleled, the meter should read ______ volts.

Answer 11

Zero Volts

Question 12

Name two copper losses in a transformer

Answer 12

High Voltage and Low voltage winding Isquare x R

Question 13

The IsXs voltage drop:

Answer 13

Leads the secondary load current by 90degrees

Question 14

Difference between no load and on load tap changer

Answer 14

No load to be used only when circuit is de-energized.

On load is used when energized without interfering the flow of power to the load

Question 15

Which of the two types tap changer never open the circuit?

Answer 15

Onload

Question 16

What is the purpose of the reactor in an on load tap changer?

Answer 16

Prevents short circuiting of the tap connecting during the switch

Question 17

Why does the reactor in the on-load tap changer offer negligible resistance to the primary circuit current once switching is complete?

Answer 17

The reactor is centre tapped, both flux each other out therefore no inductive reactance

Question 18

In a step down auto transformer, the secondary winding is apart of the primary winding? T or F

Answer 18

True

Question 19

Auto transformer, what is the relationship between the primary VA and the Secondary VA?

Answer 19

Equal

Question 20

Two most common types of instrument transformers?

Answer 20

Potential Transformers and Current Transformers

Question 21

How is the primary winding of a CT connected to the Primary circuit?

Answer 21

Series

Question 22

How is the Potential transformer connected?

Answer 22

Parallel

Question 23

Type of transformer often used for starting large motors?

Answer 23

Auto Transformer

Question 24

Pole mounted transformer in a residential area is called?

Answer 24

Distribution Transformer

Question 25

A 50kva transformers at a hydro-electric site is referred to as?

Answer 25

A power transformer

Question 26

A small transformer used to power residential inter-com systems is an example of?

Answer 26

A Signal Transformer

Question 27

Does core loss change significantly as load is added to the transformer?

Answer 27

No

Question 28

Do copper loss change significantly as load is added to the transformer?

Answer 28

Yes

Question 29

Could a leading power factor load cause a rise in line bus voltage on the secondary of a transformer?

Answer 29

Yes