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Terms in this set (23)
what are the four different combinations a three transformer bank can be connected into?
2. wye- delta
3. delta- delta
4. delta -wye
primary connections are determined by comparing the _______ with the ______
primary coil voltage on the transformer nameplate with the system voltage.
if a transformer has only one number for the primary voltage rating, it should be used for what connections only?
Delta primary connections
if primary voltage rating of the transformer match the circuits phase to neutral voltage, then connect _____ primary.
if primary voltage rating of the transformer match the circuits phase to phase voltage connect _____ primary
you parallel the secondary coils (alley cat bad dog) when making _____ secondary connections.
Wye Secondary connections.
the secondary connection is determined by the ____.
service voltage of the customer.
if the phase to phase (hotleg to hotleg) voltage of the service needed is 1.732 times higher than the phase (hotleg) to neutral voltage, connect a _____ secondary.
what are four examples of wye secondary voltages?
if the phase to phase (hotleg to hotleg) voltage of the service needed is 2 times the phase to neutral (hotleg to neutral) voltage, connect _______ secondary
what are two examples of delta secondary voltages?
when the two secondary coils in a transformer are connected in series together, their voltages will be ____, but when the two coils are connected in parallel (AC BD) then the secondary voltage will be ____
in series 120/240
in parallel 120
how do you find out the configuration of the secondary coils in a transformer? (two ways)
turns ratio test or manually take of lid and check.
paralleling secondary coils (AC BD) does what to the kVA?
it allows the full kVA of the transformer to be used.
"it is strongly recommended that paralleling be done between" which two bushings?
the x1 and x2
what are the two main advantages of wye connected banks?
1. all three transformers share the single phase load equally.
2. they can be built using single or dual primary Bushing transformers.
what is a disadvantage of having 3 transformers in a bank connected wye?
if one transformer fails, then the customer is down to single phase power until it can be fixed/replaced.
floating the "wye point" on a wye/delta closed Bank can be a hazard to lineworkers because _____.
because it's not grounded.
when a transformer on a closed Bank wye/delta goes bad, what can lineworkers do as a temporary fix for customers?
the bank can be reconfigured into a wye/delta open bank.
wye wye connected transformers are ____ size and kVA.
about the same size and kVA
banks with delta connected secondarys have a ______
what are 3 other names for power leg?
for three phase underground transformers, the lineworkers must rely entirely on the _____ to determine which primary and secondary connections were made at the factory.
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