# Transformer Connections

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 Author: johnbowens ID: 122720 Filename: Transformer Connections Updated: 2011-12-29 15:57:15 Tags: transformer connections JATC IBEW electrical NEC Folders: Description: Transformer connections per the 2008 code cycle Electrical Field Reference Handbook and Transformers Workbook Show Answers:

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1. Three single voltage units are wired in Delta using what alphabetic arrangement? Transformer Principle and Applications, 2006: Transformer Connections, WB PP 22
A-B, B-C, C-A
2. A Wye connection alphabetic order in single voltage units is what? Transformer Principle and Applications, 2006: Transformer Connections, WB PP 22
• N-A, N-B, N-C
• Where A, B, & C are phases and N is nuetral or grounded conductor.
3. it is important to note that three-phase transformers with Delta-connected primaries when connected to a 30, 4-wire supply system do not utilize? (NC set transformer connections) source: http://www.federalpacific.com/university/transbasics/chapter3.html
The 4th wire or neutral.
4. A wye system is also known as what? Transformer Principle and Applications, 2006: Transformer Connections, WB PP 23
A wye system is also known as a star system.
5. A wye to delta connection may be made with what? Transformer Principle and Applications, 2006: Transformer Connections, WB PP 23
Three single phase transformers.
6. A single phase series connected winding provides what secondary voltage and has a line side voltage of what? Electrical Field Reference Handbook PP 413 (NC set Transformer connections)
• Series is High Voltage
7. Wye to delta connected transformers, with properly marked leads, always have an angular phase displacement of _________? Transformer Principle and Applications, 2006: Transformer Connections, WB PP 23
30 degrees.
8. A _______ connection may also be called a V connection because only two sides on the delta triangle are included. Transformer Principle and Applications, 2006: Transformer Connections, WB PP 23
Open Delta.
9. The voltage tolerance on most motors is plus minus what voltage? Transformer Principle and Applications, 2006: Transformer Connections, WB PP 23
10 percent.
10. Today, the majority of dwellings are wired with a how many wire service? Transformer Principle and Applications, 2006: Transformer Connections, WB PP 23
Three wire: 2 wire and a messenger.
11. A 3 phase connection method that has the wire from the ends of each coil connected end-to-end to form a closed loop is what? Transformer Principle and Applications, 2006: Transformer Connections, WB PP 23
Delta: A-B, B-C, C-A.
12. The Primary and secondary voltage on a single phase parallel-connected winding is what? Electrical Field Reference Handbook, Transformer Principle and Applications, 2006: Transformer Connections, WB PP 413
13. Transformer polarity refers to what? Transformer Principle and Applications, 2006: Transformer Connections, WB PP 24
The voltage-vector relationship of the transformer leads as brought outside the case.
14. Single phase transformer polarity is additive and subtractive when? Transformer Principle and Applications, 2006: Transformer Connections, PP 73

• h1 h2 h1 h2
• x1 x2 x2 x1
15. What must be done when the transformer secondary taps are not positively identified? Transformer Principle and Applications, 2006: Transformer Connections, PP 73
The transformer must be tested to determine the correct polarity. Tech Fact
16. In a Delta what is the winding voltage from phase A,B, & C? Electrical field reference manual, PP 414
17. What simplifies the task of connecting transformers in parallel? Transformer Principle and Applications, 2006: Transformer Connections, PP 74
The H1 lead is normally brought out on the right-hand side of the transformer case when facing the high voltage side.
18. Methods used to test for polarity and check transformer lead markings include what? Transformer Principle and Applications, 2006: Transformer Connections, PP 74
Transformer comparison, DC use, and AC use.
19. Testing for polarity on a transformer using the transformer comparison method is done how? Transformer Principle and Applications, 2006: Transformer Connections, PP 74
By using another transformer with the same known polarity, connecting high voltage leads in parallel (H1 of one and Hx of the other), and connecting the left hand low voltage leads (x1 and assumed x1). A reduced voltage is applied to the high voltage windings and a voltmeter applied to the low voltage free leads (x2 and assumed x2) a zero reading means relative polarity between the two is identical.

20. In a Delta system, the winding (phase) current is actually _________ percent of the line current; in other words, the line current is equal to phase current times ________. Transformer Principle and Applications, 2006: Transformer Connections, PP 77
• 57.7 percent
• 1.73
21. what is different from a transformer primary and a stator in a polyphase motor? Transformer Principle and Applications, 2006: Transformer Connections, PP 78
• Nothing.
• note: except that the secondary does not rotate in a transformer.
22. What type of transformer describes the following statement: "The three ends can be safely connected at the neutral point because no voltage difference exists between them." Transformer Principle and Applications, 2006: Transformer Connections, PP 78
A Wye transformer.
23. A Delta to Wye connected 3 phase system has how many volts on the primary and on the secondary phase to phase? Electrical Field Reference Manual, PP 415
• The primary has 2400V phase to phase across A & B only. Secondary has 277V with a nuetral across any phase and 480 without on B & C windings. Used where a 4 wire secondary distribution system is desired.
24. In 3 phase power, a total of _____line leads are required if the three circuits are kept separate from the generator to the apparatus using the current. This is impractical, so what is used? Transformer Principle and Applications, 2006: Transformer Connections, PP 76.
6, so common wires are used.
25. What provides a 120V/208V feeder for a panelboard? Transformer Principle and Applications, 2006: Transformer Connections, PP 81
A dual-wound delta primary connected onto the 480V phase-to-phase bus. No primary neutral, but the secondary neutral can be connected to a center tap to ground.
26. A third winding that is often used in power transformers to provide station power requirements or a tie with synchronous condensers is what? Transformer Principle and Applications, 2006: Transformer Connections, PP 82
A tertiary winding.
27. When is a Wye to Wye connection used? Transformer Principle and Applications, 2006: Transformer Connections, PP 82

A tertiary winding is used in a Wye to Wye connection for what purpose? Transformer Principle and Applications, 2006: Transformer Connections, PP 82
When tying together two high-voltage transmission systems of unequal voltage.

To suppress 3rd harmonics. (An odd numbered harmonic which adds to each other, although triplen harmonics, odd multiples of the third harmonic: 3, 9, 15th are only single phase load related) May cause transformer overheating, overloaded neutrals, telephone interference.
28. Disadvantages of a wye-to-wye connection include what? Transformer Principle and Applications, 2006: Transformer Connections, PP 82
Harmonics.
29. In a Wye to Wye connection the voltage of each single-phase unit connected to form a wye-to-wye connection is _____percent of the line voltage: an advantage. Transformer Principle and Applications, 2006: Transformer Connections, PP 83
57.7 percent
30. The difference between a Delta Wye and a Wye to Delta connection voltage is what? Transformer Principle and Applications, 2006: Transformer Connections, PP 83 & 84
• The primary is 4160V on a Delta or Wye primary. 277V/480V is available on the Wye-Wye secondary.
• 480 is available on the Wye-Delta secondary.
• Wye to Delta above
• Wye to Wye above
31. A Wye to Delta must have what done with the neutral? Transformer Principle and Applications, 2006: Transformer Connections, PP84
The neutral on the primary side and the neutral of the supply source for the primary must be grounded.
32. Delta to Delta systems are used where? Transformer Principle and Applications, 2006: Transformer Connections, PP 85
In industry where old equipment is used on new high-voltage 480 V bus duct systems.
33. What is more common.... a three phase system or three single phase units? Transformer Principle and Applications, 2006: Transformer Connections, PP 85
Three single phase units in an industrial delta to delta system.
34. One of the disadvantages of a Delta to Delta connected system is what? Transformer Principle and Applications, 2006: Transformer Connections, PP 86

To obtain a grounded system, what must be done? PP 87
The absence of an intentional connection to ground on the secondary of the transformer.

One of the corner of the delta secondary must be grounded.
35. When a Delta to Delta system has no neutral, and one is derived to give a reference to ground, this system is also referred to as a? Transformer Principle and Applications, 2006: Transformer Connections, PP 87
grounded B phase.
36. In a Delta to Delta grounded B phase system the center conductor is identified as what? What must be done with fusing. Transformer Principle and Applications, 2006: Transformer Connections, PP 87
As a neutral conductor, and fusible clips must have a shunt, usually a copper tube, installed if used as a serviceable disconnect.
37. A transformer configuration that allows for low cost install for future expansion is what? Transformer Principle and Applications, 2006: Transformer Connections, PP 88

The primary on an Open Delta is _____volts and the secondary is ______volts. Transformer Principle and Applications, 2006: Transformer Connections, PP 88
An open delta, or two single phase transformers.

Primary voltage is 2400V and the secondary voltage is 240 volts with a voltage vector relationship at 60 degrees.
38. What type of connection makes it possible to maintain operation in an emergency? Transformer Principle and Applications, 2006: Transformer Connections, PP 89
An open delta connection.
39. The load on an open delta must be reduced by how much from that of a closed delta. Transformer Principle and Applications, 2006: Transformer Connections, PP 89
42.3 percent
40. When an open delta connection supplies a large single-phase load and a small 3-phase load, the two transformers should have different what? Transformer Principle and Applications, 2006: Transformer Connections, PP 89
KVA ratings.
41. One of the more popular Delta to Delta connections is the ________. Transformer Principle and Applications, 2006: Transformer Connections, PP 89

The advantage of a hi-leg to ground is what?
120/240V 4 wire system with high leg to ground.

120/240V versus 120/208V which is not adequate for 240 volt motors having a voltage tolerance of +/- 10 percent. Low voltage will result in overheating.
42. A wye to wye connection may have an angular-phase displacement of ______ or _____ degrees. Transformer Principle and Applications, 2006: Transformer Connections, PP 91
0 or 180 degrees.
43. A Wye to Delta connection always has an angular phase displacement of _____ degrees, with properly marked leads. Transformer Principle and Applications, 2006: Transformer Connections, PP 91
30 degrees.
44. A disadvantage of a delta connection is? Transformer Principle and Applications, 2006: Transformer Connections, Chapter 4 summary
that the coil is rated for the line voltage and thus makes the high voltage required for transmission difficult.
45. Wye connection offer what? Transformer Principle and Applications, 2006: Transformer Connections, Chapter 4 summary
lower voltage-to-ground combined with the higher phase-to-phase voltage for long-distance power distribution.
46. What does the 30 degree difference in phase displacement mean regarding a wye and delta transformer on the same feeder? Transformer Principle and Applications, 2006: Transformer Connections, Chapter 4 summary
It means it is impossible to parallel a wye and delta transformer on the same feeder.
47. What makes it difficult to maintain good balance from phase-to-phase in a wye connection? Transformer Principle and Applications, 2006: Transformer Connections, Chapter 4 summary.
The ability to take single phase loads from line to neutral in a wye connection make it difficult to maintain good balance from phase-to-phase.

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