Transformers

Question 1

How does oil cool a transformer?

Answer 1

Heat rises, so cool oil starts at the bottom of the transformer. As it travels through the coils and gets hot it goes to the top of the transformer where the heat radiates into the air through the metal tank or through the fins. As it cools it falls down the tank walls pushing cool oil downward where it once again travels the the transformer

Transformer and metering manual page 7

Question 2

What’s the maximum difference in impedance transformers can have when banking single phase closed delta?

Answer 2

10% difference

Transformer & metering manual page 16

Question 3

What is the maximum difference in impudence you can have when banking transformers together 3 phase?

Answer 3

No more than 25 percent

Question 4

What are the 2 types of transformers used in Edison’s electrical system?

Answer 4

• Laminated core type
• Wound core she’ll type
• second step book transformer design and theory.

Question 5

Describe the difference between power, potential, and current transformers.

Answer 5

• PT’s sense voltage, used for meters, capacity in relays, and control circuits
• CT’s step down high currents to lower current levels used in relay protection and metering services
• Power transformers take a high voltage to a lower usable voltage.
• 2nd step book transformer design and theory

Question 6

What are wound shell type transformers good for?

Answer 6

• low voltage high capacity

Question 7

What’s a vector?

Answer 7

Magnitude and angle

Question 8

Why doesn’t a transformer go phase to phase through the coil?

Answer 8

Because of the inductive reactants.

Question 9

When can you work on the high side of an over head transformer?

Answer 9

When the fuses have been pulled and the taps to the fuse holder have been removed.

*AMP Rule 216

Question 10

Does a straight 240v service have 3 CT’s in the panel?

Answer 10

No
The grounded phase is unmetered

Question 11

What is polarity?

Answer 11

Polarity is the relative direction or induced voltages between the high voltage terminals and low voltage terminals.

Transformer and metering manual page 12