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WorksheetsNLC FINAL TRANSFORMER
Total questions: 56
Worksheet time: 28mins
Which of these statements about a wye-wye bank is true?
The “lighter” transformer is larger in KVA than the other two
The industry standard is to leave the x2 idle when connecting the coils in parallel
Each of the three transformer provides one hot leg to deliver three-phase power
When connecting wye-wye, you must float the wye point
Which piece of test equipment checks the transformer coil for insulation damage?
Turns ratio tester ( TTR)
Continuity test
Transformer last check
Megger
System - 12,000
Nameplate - HV 12,000/20,800Y ---LV 120/240
KVA - 15 and 25
Service - 120/240 - 3 phase
If connected properly, what will the voltage be between lighter x1 and power x1?
120 volts
416 volts
208 volts
240 volts
The phase current is 1.73 times higher than a coil current in a _____ connection bank
Wye
Delta
Y
Neutral
Which arrow is pointing at the pressure relief valve?
A
B
C
D
Which of these definitions best explains impedance?
The direction of current flow through the two coils
It is the process by which oil circulates, cooling the core/coil assembly
Expressed in percentage, it is the comparison of the number of turns between the windings
Total opposition to current flow, caused by the transformer itself
Which of these connections is the correct one?
A
B
C
D
The system voltage is 1.73 times higher than the coil voltage in a ___ system
Wye
Delta
Neutral
Phased
If connected correctly, using transformers of different______ will work electrically but can cause
confusion for lineworkers who may need to work on the transformer bank in the future.
Polarity
Circuit voltages
Kva ratings
Transformer voltage ratings
System - 12,000
Nameplate - HV 12,000/20,800Y ---LV 120/240
KVA - 15 and 25
Service - 120/240 - 3 phase
Where will the x2 on the "power" transformer connect?
Leave idle
System neutral ( N)
Conductor ( P)
Conductor ( H)
Which of these statements refers to a wye connection?
Each transformer’s x1 connects to another transformer’s x2
H1s connect to phases, and H2s connect together and may or may not be grounded
Each transformer’s h1 connects to another transformer’s H2
X1 connects to x3 “ all the way around
Which of the following statements about tap changers is true?
The tap changer is a no-load manual switch connected to the secondary coil
The tap changer is a load manual switch connected to the primary coil
Each tap raises or lowers the secondary voltage by 2.5% or 4.5%
If a tap is raised, the number of turns in the secondary coil is reduced
What are "H1A" and "H1B"?
The low- voltage bushings on a padmount transformer
The primary bushings on a padmount transformer
The primary bushings on a pole-bolted transformer
The secondary bushings on an overhead transformer
Study each of the above connections carefully and choose the correct one.
A
B
C
D
In a delta-wye bank, what would be a typical hot leg-to-neutral voltage?
120
208
416
480
In a wye-wye bank, which of the following would be a typical hot leg-to-hot leg voltage?
277
240
120
208
Which transformer nameplate rating will allow the connection to be made on a system voltage of 14,400/24,900?
24,900GRDY/ 14,400
14,400
14,400 GRDY / 8,320
12,470/ 14, 400Y
Which of the nameplate ratings matches the connection in the image?
7,200/ 12,470Y
7,200 GRDY/ 12,470
12,000
12,470GRDY/ 7,200
Choose the statement below that best reflects the points of termination.
The secondary bushings have more insulation than the primary bushings
The labeling of the secondary bushings changes based on polarity
The H2 bushings is always on the left when facing tha transformer
The H1 bushing is always on the right when facing the transformer
Which of these transformers is "additive"?
12,000- 15 kVA
2,400/ 4,160Y- 250 kVA
7,200/ 12,470Y- 250 kva
7,200/ 12, 470Y- 15 kVA
What does "non-PCB" refer to?
The epoxy-live material used to coat and insulate the winding
The lack of a harmful substance in the newer insulating fluids
The old askarel- impregnated paper between the layers of widings
The direction that the primary winding is wrapped around the care
Which of these have fuses that are located internally but operated externally?
Conventional tramsformer
Pole-mounted tramsformer
Padmount transformer
CSP transformer
Which of these transformers is "subtractive"?
When facing the transformer, X1 bushing in on the right
When facing the transformer, x1 bushing is on the left
The other end of the primary winding in the case ground
Whem facing the transformer, the h2 bushing is on the right
Which of these transformers is "subtractive"?
12,000- 10 KVA
7,200/12,470- 37.5 KVA
2,400/ 4,160- 15 kVA
2,400/ 4160- 150 kVA
A standard transformer cools itself by:
CCirculating fluld through an oil pump
Relying on the ambient air temperature
Circulating oil by convection
Releasing pressure through the relief valve
The primary windings:
Have larger conductors than the secondary
Use thin, laminated sheets of aluminum
Have smaller sized wire than the secondary
Are coated with silicon to improve efficiency
Changing the number of turns in the coils will:
Increase the efficiency of the transformer
Induce more direct current
Affect the amount of induced voltage
Maximize convection
Select the true statement about transformer identification.
A CSP is protected internally by a current-limiting fuse
A CSP is protected internally by a voltage-limiting fuse
Bay-O-Net fuses are used in padmount transformers to isolate between HIA
and H1B
A transformer can be fed only from the primary bushings
In relation to windings, what do A, B, C, and D refer to?
The points where the core/coil assembly mounts to the inside of the case
A and B are the primary winding ends; C and D are secondary winding ends
The ends of the high-voltage windings where they connect to the breaker
The ends of the secondary windings, where they attach to the low-voltage
terminals
Which statement below about KVA is true?
An average-size home will draw a peak load of less than 1 KVA
The KVA refers to the voltage rating of the input winding
When transformers are banked together, the bank's rating is the sum of the individual transformers
The kVA number refers to the amperage rating of the transformer
Select the term that refers to the comparison of turns between the windings.
Turns ratio
Induction
Step up or step down, depending on the source
Polarity
Which of these statements about transformers is true?.
The primary side is the load side or customers side
A transformer works only on direct-current systems, not alternating-current systems
The primary side connects to the source; the secondary side connects to the load
Transformers step the current down to a consumable level
What is the purpose of the core?
Concentrate the magnetic lines of flux, Improving efficiency
Provide the connection between the two windings
Malntain the form of the concentrically wound colls
Suspend and isolate the colls inside the transformer
Select the true statement about conventional transformers.
They use an external fused device to protect against fault current
They sometimes come with a red light to Indicate abnormal loading conditions
They have secondary breakers connected between the windings and the primary
bushings
They rely on internal cutouts for surge suppression
Which of these statements about padmount transformers is true?
They are normally fed from the load side
They are physically attached to a conductor using hangar bolts
They receive their feed from an underground conductor
They connect directly to an overhead conductor
A coll of wire will become energized if it is placed close to another coil of wire attached to a source of power. What is this phenomenon called?
Capacitance
Induction
Convection
Mutual reactance
Which of the following is determined by the direction that the secondary coll is wrapped in relation to the primary coil?
Whether or not the voltage is stepped up or stepped down
Turns ratio
Impendece
Polarity
What is the most popular material for the windings?
Amorphous steel
Silicon-oriented steel, or electrical steel
Aluminum
Copper
Which of these is a CSP?
A
B
C
D
What is the turns ratio of a 7,200/12,470 transformer, with an output of 120/240?
1:30
1:60
15:1
30:1
Which of these statements about a wye-delta bank is true?
If they come with only two secondary bushings, then the secondary must be connected delta
Use the phrase "Alley-Cat, Bad-Dog" when paralleling the windings
The "power"-leg-to-hot leg voltage is 240 in a 120/240, three-phase service
The "power" transformer is larger in kVA than the other two
If the transformer has only one number for a primary coil voltage rating, the transformer:
Should be used on wye systems only
Should be used for delta connections only
Can be used only for open banks
Should be used for phase-to-ground connections only
Which of these statements regarding non-standard connections is true?
You can get 120/208 from single-phase delta
To complete a three-phase connection, you must ground at the x2 only
It's possible to get two 120/208 three-phase services from one delta-delta bank
A delta or wye can be grounded one time at any coil terminal and still operate properly
In a delta-delta bank, what would be a typical hot leg-to-ground voltage?
120
208
277
480
Which kind of secondary service voltage requires the wye point on the primary to be floated?
240/416
277/480
120/208
240/480
Which one of these banks is connected correctly?
A
B
C
D
Which of these service voltages on a work order require "Alley-Cat, Bad-Dog"?
240
240/480
120/208
120/240
Which of these statements about a delta-wye is true?
You must tie the wye point on the primary
The H1s all tie together but do not connect to neutral
The x2 bushings from each transformer tie together and connect to neutral
Only one x2 in the entire bank is connected to neutral
In a wye-delta bank, which of the following would be a typical hot leg-to-hot leg voltage?
120
240
416
277
Which of these statements abeut utilities' preferences is true?
Three-phase transformers are preferred because they have multiple applications
It's easier and less expensive to replace one single-phase unit in a bank
Utilities find that it's easier to install three single-phase transformer units
Using a three-phase transformer unit is more economical
Which of these images shows the proper connection, based on the following work order?
Work Order:
System - 7,200/12,470
Nameplate - HV 7,200/12,470Y ---LV 120/240
KVA - 25 and 37.5
Service - 120/240 - 3 phase
A
B
C
D
Which transformer nameplate rating will allow the connection to be made on a system voltage of 4,160/7,200?
7,200/12,470Y
4,160GRDY/ 2,400
7,200GRDY/ 12,400
2,400GRDY/ 4,160
Can a transformer with two primary bushings be connected phase-to-ground?
Yes, two-bushing transformers with the smaller number listed first may be connected phase-to-ground
Yes, all transformers with two primary bushings are designed to accept phase-to-ground connections
No, only transformers with one voltage listed can be connected wye
No, any transformer with two primary bushings must be connected delta only
Which transformer nameplate rating will allow the connection to be made on a system voltage of 2,400/4,160?
7,200GRDY/4,160
1,387/2,400Y
4,160/7,200Y
2,400GRDY/1,387
Work Order:
System - 12,000
Nameplate - HV 12,000/20,800Y ---LV 120/240
KVA - 15 and 25
Service - 120/240 - 3 phase
If connected properly, what will the voltage be between power x1 and power x3?
208 volts
240 volts
120 volts
0 volts, because that it where the bank ties together
What is the most important part of the transformer
Name plate
Polarity
KVA
Coil
