Transformers and Distribution Systems Flashcards
7 cards from real CEA practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Transformers and Distribution Systems flashcards as text
What advantage does a delta-wye transformer secondary provide over a delta-delta secondary?
Answer: A neutral point allowing both single-phase and three-phase loads
The wye secondary's neutral point allows the system to supply both single-phase line-to-neutral loads and three-phase loads from the same transformer bank.
What standard secondary voltage does a center-tapped single-phase distribution transformer supply for typical US residential service?
Answer: 120/240V single-phase
The standard US residential distribution transformer provides 120/240V single-phase service via a center-tapped secondary, delivering both 120V and 240V.
In a three-phase delta transformer connection, how does the line voltage compare to the phase (winding) voltage?
Answer: Line voltage equals phase voltage
In a delta connection, each winding is connected directly between two line conductors, so line voltage equals phase voltage.
What is the primary purpose of voltage taps on a distribution transformer?
Answer: To adjust the turns ratio and compensate for supply voltage variations
Transformer taps provide multiple connection points on the primary winding, allowing the turns ratio to be adjusted to maintain proper secondary voltage despite supply variations.
A 480V to 208Y/120V transformer is best described as which winding configuration?
Answer: Delta-wye
The 480V primary has no neutral and is connected in delta; the 208Y/120V secondary with a neutral is connected in wye, making it a delta-wye transformer.
What does transformer polarity (indicated by dot notation on a nameplate) describe?
Answer: The instantaneous voltage relationship between primary and secondary terminals
Transformer polarity indicates the instantaneous voltage relationship between primary and secondary terminals, which is critical when connecting transformers in parallel or in a bank.
Which three-phase transformer connection is most commonly used for commercial and industrial power distribution in the United States?
Answer: Delta-wye
The delta-wye connection dominates US commercial and industrial distribution because the wye secondary provides a neutral for single-phase 120V loads alongside three-phase service.