Deck 5: Autotransformers

Question 1

The amount of power input and output for an autotransformer must be the same.

Answer 1

True

Question 2

The primary winding of a transformer is between points B and N, and has 120 volts applied to it. There are 120 turns of wire between points B and N. The selector switch is set to point D, and the load is now connected between points D and N. The secondary of this transformer contains 40 turns of wire. Assume that the load connected to the secondary has an impedance of 10 ohm. The amount of current flow in the secondary circuit is ____ amps.

A) 0.25
B) 3
C) 4
D) 9

Answer 2

C

Question 3

If the primary section of a transformer is connected across part of a winding, and the secondary is connected across the entire winding, the secondary section contains more windings than the primary. This type of transformer is a step-down transformer.

Answer 3

False

Question 4

An autotransformer has a 2:1 turns ratio. A voltage of 480 volts is connected across the entire winding. Since the transformer has a turns ratio of 2:1, a voltage of 240 volts will be supplied to the load. Ammeters connected in series with each winding indicate the current flow in the circuit. It is assumed that the load produces a current flow of 4 amperes on the secondary. A current flow of ____ amperes is supplied to the primary.

A) 2
B) 4
C) 6
D) 12

Question 5

Autotransformers rarely have multiple taps to provide different voltages.

Question 6

The autotransformer has one disadvantage: Since the load is connected to one side of the power line, there is ____ between the incoming power and the load.

A) line isolation
B) no line isolation
C) line continuation
D) no line continuation

Question 7

To calculate the current flow supplied to the primary, use the formula IP = ____.

A) IS / Ratio
B) IS x Ratio
C) 2(IS / Ratio)
D) Ratio / IS

Question 8

Autotransformers, like isolation transformers, can be used as step-up or step-down transformers.

Question 9

The volts-per-turn for any transformer is determined by the ____.

A) primary winding
B) secondary winding
C) number of turns
D) loads

Question 10

If the amount of voltage applied to the load is to be computed, the formula ____ can be used.

A) EP x ES = NP / NS
B) EP / ES = NP / NS
C) EP / ES = NP x NS
D) ES / Ep = NP / NS

Question 11

The amount of current flow in a secondary circuit can be computed using the formula I = Z / E.

Question 12

The primary winding of a transformer is between points B and N, and has 120 volts applied to it. There are 120 turns of wire between points B and N. The selector switch is set to point D, and the load is now connected between points D and N. The secondary of this transformer contains 40 turns of wire. The amount of voltage applied to the load is ____ V.

A) 30
B) 40
C) 90
D) none of the above

Question 13

If the number of primary turns is the sum of the turns between taps (such as 80 + 100 + 60 = 240 turns), and 120 volts are connected across the 240 turns, this transformer will have a volts-per-turn ratio of 2.0.

Question 14

An autotransformer uses the same winding as the primary transformer, but does not use the same winding as the secondary transformer.

Question 15

The autotransformer's one disadvantage can cause problems with certain types of equipment and must be a consideration when designing a power system.

Question 16

The primary current can be computed by using the formula ____.

A) EP / ES = IS / IP
B) EP x ES = IS / IP
C) EP / ES = IS x IP
D) ES / EP = IS / IP

Question 17

If a rotary switch were to be removed and replaced with a sliding tap that made contact directly with the transformer winding, the turns ratio could be adjusted continuously. This type of transformer is commonly referred to as a ____ depending on the manufacturer.

A) Variate
B) Rotarystat
C) Variac or Powerstat
D) Variate or Transtron

Question 18

The primary current can be computed by using the same formula that is used to compute primary current for an isolation-type transformer.

Question 19

Autotransformers have high efficiencies, most in the range of ____.

A) 80% to 83%
B) 84% to 86%
C) 90% to 93%
D) 95% to 98%

Question 20

An autotransformer is literally a self-transformer.