Apprentice Lineman Transformer Theory
UPDATED ACTUAL Exam Questions and
CORRECT Answers
Why is a Closed Wye - Closed Delta primary neutral floated? - CORRECT ANSWER - To
prevent the backfeed of full primary voltage if a line cutout is blown.
Why is a 4th cutout installed on the primary neutral of a closed Wye -closed Delta Bank? -
CORRECT ANSWER - To prevent Ferroresonance while switching.
On an open transformer bank, what KVA capacity is the bank rated for? - CORRECT
ANSWER - 86.6% of nameplate ratings.
Expain the term "Backfeed" - CORRECT ANSWER - Feeding the primary coil through the
secondary coil.
What must be done before climbing above a transformer? - CORRECT ANSWER - Make
sure the tank ground is intact, de-energize the high side and remove secondary leads.
What determines the amount of voltage drop when a transformer is fully loaded? - CORRECT
ANSWER - Impedance
Explain polarity of a transformer. - CORRECT ANSWER - Relative direction of current flow
primary to secondary.
When paralleling or banking transformers, the impedance must be within _____% of each other?
- CORRECT ANSWER - 10%
What KVA capacity would you have if you convert a closed delta bank to an open delta bank? -
CORRECT ANSWER - 57.7% of the original 3 transformers. OR 86.6 of the remaining 2.
UPDATED ACTUAL Exam Questions and
CORRECT Answers
Why is a Closed Wye - Closed Delta primary neutral floated? - CORRECT ANSWER - To
prevent the backfeed of full primary voltage if a line cutout is blown.
Why is a 4th cutout installed on the primary neutral of a closed Wye -closed Delta Bank? -
CORRECT ANSWER - To prevent Ferroresonance while switching.
On an open transformer bank, what KVA capacity is the bank rated for? - CORRECT
ANSWER - 86.6% of nameplate ratings.
Expain the term "Backfeed" - CORRECT ANSWER - Feeding the primary coil through the
secondary coil.
What must be done before climbing above a transformer? - CORRECT ANSWER - Make
sure the tank ground is intact, de-energize the high side and remove secondary leads.
What determines the amount of voltage drop when a transformer is fully loaded? - CORRECT
ANSWER - Impedance
Explain polarity of a transformer. - CORRECT ANSWER - Relative direction of current flow
primary to secondary.
When paralleling or banking transformers, the impedance must be within _____% of each other?
- CORRECT ANSWER - 10%
What KVA capacity would you have if you convert a closed delta bank to an open delta bank? -
CORRECT ANSWER - 57.7% of the original 3 transformers. OR 86.6 of the remaining 2.
