LINEMAN APPRENTICE TRANSFORMER THEORY
QUESTIONS AND ANSWERS
Why is a Closed Wye - Closed Delta primary neutral floated? - ANSWER To
prevent the backfeed of full primary voltage if a line cutout is blown.
Why would a 4th cutout be installed on the primary neutral of a closed Wye -
closed Delta Bank? - ANSWER To prevent Ferroresonance while switching.
What KVA capacity is the bank rated for on an open transformer bank? -
ANSWER 86.6% of nameplate ratings.
Describe the term "Backfeed" - ANSWER To feed the primary coil through
the secondary coil.
What should be done before climbing above a transformer? - ANSWER Check
the tank ground is intact, deenergize the high side and remove secondary leads.
What determines voltage drop amount when a transformer is at full load? -
ANSWER Impedance
Explain polarity of a transformer. - ANSWER Relative direction of current flow
primary to secondary.
When paralleling or banking transformers, the impedance must be within
_____% of each other? - ANSWER 10%
, What would you have in KVA capacity if you took an open delta bank and
closed it? - ANSWER 57.7% of the original 3 transformers. OR 86.6 of the
remaining 2.
How much capacity would you pick up by operating a closed delta bank vs. an
open delta bank? - ANSWER (57.7 to 100%) = 42.3%
What do you have to do to the neutral connection for a closed wye -closed wye
transformer bank? - ANSWER Tie the primary neutral.
What is the purpose of the case ground on a transformer? - ANSWER To keep
the transformer case from becoming energized and on a single bushing
transformer the case ground is the H2 connection.
Name the types of transformer banks you can make with two or three
transformers. - ANSWER Wye-Wye, Wye-Delta, Delta-Delta, Delta-Wye,
Open Wye-Delta, Open Delta-Delta
What does CSP mean? - ANSWER Completely self protected
On a CSP transformer, what coil is the circuit breaker on? - ANSWER
Secondary
Taps are for two purposes, name them. - ANSWER Control voltage to the
customer and correct low primary voltage *raise the tap to lower the secondary
voltage*
T or F, Two cutouts and arrestors are needed on a wye connected transformer. -
ANSWER FALSE
QUESTIONS AND ANSWERS
Why is a Closed Wye - Closed Delta primary neutral floated? - ANSWER To
prevent the backfeed of full primary voltage if a line cutout is blown.
Why would a 4th cutout be installed on the primary neutral of a closed Wye -
closed Delta Bank? - ANSWER To prevent Ferroresonance while switching.
What KVA capacity is the bank rated for on an open transformer bank? -
ANSWER 86.6% of nameplate ratings.
Describe the term "Backfeed" - ANSWER To feed the primary coil through
the secondary coil.
What should be done before climbing above a transformer? - ANSWER Check
the tank ground is intact, deenergize the high side and remove secondary leads.
What determines voltage drop amount when a transformer is at full load? -
ANSWER Impedance
Explain polarity of a transformer. - ANSWER Relative direction of current flow
primary to secondary.
When paralleling or banking transformers, the impedance must be within
_____% of each other? - ANSWER 10%
, What would you have in KVA capacity if you took an open delta bank and
closed it? - ANSWER 57.7% of the original 3 transformers. OR 86.6 of the
remaining 2.
How much capacity would you pick up by operating a closed delta bank vs. an
open delta bank? - ANSWER (57.7 to 100%) = 42.3%
What do you have to do to the neutral connection for a closed wye -closed wye
transformer bank? - ANSWER Tie the primary neutral.
What is the purpose of the case ground on a transformer? - ANSWER To keep
the transformer case from becoming energized and on a single bushing
transformer the case ground is the H2 connection.
Name the types of transformer banks you can make with two or three
transformers. - ANSWER Wye-Wye, Wye-Delta, Delta-Delta, Delta-Wye,
Open Wye-Delta, Open Delta-Delta
What does CSP mean? - ANSWER Completely self protected
On a CSP transformer, what coil is the circuit breaker on? - ANSWER
Secondary
Taps are for two purposes, name them. - ANSWER Control voltage to the
customer and correct low primary voltage *raise the tap to lower the secondary
voltage*
T or F, Two cutouts and arrestors are needed on a wye connected transformer. -
ANSWER FALSE
