Week 3 Flashcards
Which type of connection is phase-to-neutral? DELTA or WYE?
WYE
What is a “power leg” and what is it used for?
It is the third phase in a DELTA bank; its phase-to-ground voltage serves nothing, but its phase-to-phase voltage feeds the three-phase load.
What consideration should be given to the X2 on the “power” transformer?
Check to see if it has a ground strap to the case. If it does, remove it or you will short the secondary windings out.
What type of connection is phase-to-phase? DELTA or WYE?
DELTA
Can an Open-WYE/Open-WYE serve a three-phase load?
No; it only provides two phases and is useless.
What does the term “open bank” mean?
One leg of the DELTA or WYE configuration is gone; two transformers are supplying three-phase power
In a WYE system, the coil voltage is 7,200 volts. What is the system voltage?
12,470 volts
Every effort should be made to select transformers with the same when paralleling or banking.
Impedances
In a DELTA system, the coil voltage is 7,200 volts. What is the system voltage?
7,200 volts
Proper transformer selection starts by comparing two things. What are they?
The circuit and service voltages (on the work order) and the transformer voltage/kVA ratings
What is meant by “Sames-Opposites?”
In an Open-WYE/Open DELTA, if the primary connects sames (H2s are tied and grounded), then the bottoms must connect opposites (X3 connects to X1); must be sames-opposites or vice versa.
In an open bank, why would one transformer be bigger, and how is that transformer referred to?”
It is larger in kVA because it provides power to the three-phase and the single-phase load; it is called the “lighter” or “lighting” pot
What is the “power” transformer?
The smaller of the transformers in the DELTA bank; it provides the third phase
There are two ways to deliver a three-phase service to a customer. What are they?
Either with a three-phase transformer or interconnected single-phase transformers.
