Unit 2-2 Lesson 11
One reason why paralleling two small transformers for increased demand is not economical because ? . a. of the cost of the transformers b. of the distance of one of them from the load c. one of them will eventually become overloaded d. open wire secondary would have to be installed between them
A
When paralleling transformers, the voltmeter must read zero or not over ? . a. 10 V b. 20 V c. 30 V d. 40 V
A
A transformer's secondary must be ? when used as part of a 120/208 3-phase bank. a. grounded at X2 b. paralleled c. put in series d. shorted
B
Any transformers that are paralleled must be ? as paralleled. a. designed b. tagged c. tested d. treated
B
If a primary fuse blows on a paralleled transformer, the other transformer will ? . a. back-feed both transformers b. back-feed the one with the blown fuse c. burn out from the load d. operate normally
B
On a single-bushing transformer, the tank ground is ? . a. also the neutral connection b. also the neutral connection of the high voltage winding c. not needed because the secondary is grounded d. the only ground needed
B
One reason paralleling two small transformers for increased demand is not economical is because the ? , when added together, is/are greater than in one large transformer. a. circulating currents b. losses of each transformer c. radio noise d. weight
B
When paralleling two transformers, the impedance of the two transformers must be within ? and ? of each other. a. 89.5% / 94% b. 107.5% / 92.5% c. 110% / 100% d. 120% / 110%
B
If a single-bushing transformer has only one ground and the ground is broken, the tank may become energized at ? . a. 7,200 V b. one-half primary c. primary voltage d. secondary voltage
C
One can get 480 volts out of two 120/240-volt transformers by ? . a. neutral ground straps to remain connected, paralleling both the primary and secondary connections b. removing the neutral grounding straps, paralleling both the primary and secondary connections c. removing the neutral grounding straps, paralleling the primary and connecting the secondary in series d. removing the neutral grounding straps, connecting both the primary and secondary in series
C
A transformer rating of 120/240 shows that there is/are ? . a. one secondary coil tapped in half b. only one of the voltages available c. two coils tapped in the middle d. two secondary coils
D
In a long-term, paralleled transformer situation, if one transformer fuse opens, the customer continues to be served normally at 120/240. Select one: True False
False
Removing the grounding strap of a single-phase transformer results in one phase of 480 volts. Select one: True False
False
The voltage ratios are not important when connecting two transformers. Select one: True False
False
When installing a long-term paralleled transformer, the coils must be in series. Select one: True False
False
When paralleling transformers, the connection cannot be made if the voltmeter reads 8 volts between the conductors to be joined. Select one: True False
False
When the secondary coils of a 120/240 single-phase transformer are connected in parallel, the transformer will only deliver 240 volts phase to ground. Select one: True False
False
A conventional transformer can be used as a primary booster, but it must be marked as a hazard. Select one: True False
True
A two-bushing single-phase transformer can be connected to a wye or delta system. Select one: True False
True
Paralleling transformers is often done to avoid outages. Select one: True False
True
When paralleling transformers, both transformers must be connected to the same phases on the primary and on the secondary. Select one: True False
True
