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Transformers ch 4

Transformer Connections

QuestionAnswer
1. The majority of 3-phase transmission circuits in the US are designed with 3-phase transformers connected together to obtain 3-phase power. T/F False
8. A wye system is also known as a __ system(cross, neutral, open, star) star
9. A wye-to-delta connection may be made with three single-phase transformers T/F True
10. Wye-to-delta connected transformers, with properly marked leads, always have an angular-phase displacement of __(30 degrees,45,60,90) 30 degrees
11. A __connection may also be called a V-connection because only two sides on the delta triangle are included (delta-to-wye,open delta, open wye, wye) open delta
12. The voltage tolerance on most motors is +-__(10%,15,25,30) 10%
13. Today, the majority of dwellings are wired with 3-wire service T/F True
14. A __ is a 3-phase connection method that has the wire from the ends of each coil connected end-to-end to form a closed loop ( autotransformer connection, delta connection, wey connection, wye-to-wye connection) delta connection
15. In the secondary winding of a 1-phase transformer, the neutral wire generally carries a current equal to that of either of the two outside wires. T/F False
21. All phases of a 3-phase transformer have the same relative polarity T/F True
22. __ refers to the voltage-vector relationship of the transformer leads as brought outside the transformer case ( tranformer polarity, vector polarity, voltage ratio, winding ratio) transformer polarity
23. Using an open delta connection, it is possible to remove one unit for repair and keep the system up an running . T/F True
24. In transformers that have both windings wound in the same direction with respect to the core, the polarity is changed from subtractive to additive by interchanging the position of the two X leads. T/F True
25. List three mthods used to test for polarity and check transformer lead markings Transformer comparison, DC use, AC use
26. In a balanced 3-phase, delta-connected system, the line current is equal to __ times the current in one of the coils ( 0.58 , 1.00, 1.73, 2.33 1.73
27. A __ connection is a 3-phase connection that has one end of each coil connected together and the other end of each coil left open for external connections.(closed,delta, open, wye) wye
33. ANSI standardization rules state that high-voltage leads brought outside the transformer case are to be marked with a __ and low-voltage leads are to be marked with a __(A/B,X/Y,H/L,H/X) H/X
34. In a three-phase circuit, the three windings are located within the generator to create three separate voltages which are out-of-phase with each other by __ electrical degrees(30,45,90,120) 120
35. In a wye-conneced system,the only current that flows in the neutral wire is the __ current ( balanced, unbalance, leakage, inrush) unbalanced
36. The polarity of a transformer can be used to deduce the direction of the turns of the high-and-low-voltage windings around the transformer. T/F False
37. A __ winding is a third winding that is often used in power transformations to provide station power requirements or a tie with synchronous condensers. ( hold-over, synchronous,tertiary, triplen) tertiary
38. In a wye-to-delta connection of three single-phase transformers, one unit may be disconnected from the circuit and service maintained with the secondary operation in an open delta at __ of normal bank capacity( 50.0; 57.7; 66.7; 86,6) 57.7
39. Three-phase transformers are seldom connected in a delta-to-delta connection . T/F True
40. In general, distribution transformers of 200 kVA or less having voltages of 7500 V or less have ___ polarity ( additive, subtractive, positive, negative) additive
Do the other ones out of the book with illustrations.
Created by: JoshHampton
 

 



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