NLC Transformers Final

Whats the purpose of a transformer?

An electrical device that converts voltage from either Hugh voltage to low or low to high voltage.

Whats the source side?

The primary side/High side

Whats the load side?

The secondary side

what is the point of termination?

Where the conductors are attached to the transformer

( AKA the bushings)

What is the order of the secondary bushings in Series?

X1 X2 X3

What are the two main types of overhead transformers?

Conventional and CSP

How do you identify a conventional transformer?

It will have an external cutout fuse as well as a lightning arrestor.

How do you identify a CSP transformer?

It will have a lightning arrestor but no cutout. It has an internal circuit breaker and a current limiting fuse.

Whats a bayonet fuse and what's it do?

Its a fuse used in a pad mount transformer to protect the secondary side.

What are the two types of transformer cores?

Wound type typically for higher voltages

Shell type low voltage but better efficiency

what does the transformer use to keep cool and how does it do it?

It uses oil and convection

approximately what pressure will the transformer pressure relief valve open?

10 PSI

When coils are wrapped around an iron core what happens?

The efficiency increases

The amount of induced voltage can be transformed by changing the number of turns of wire in the ____________ coil

Secondary

What is turns ratio?

Turns ratio is the ratio between the number of turns in the primary coil and the number of turns in the secondary coil of a transformer. IF the primary coil has 100 turns and the secondary has 10 turns the turn ratio is 10:1

How is the turns ratio calculated?

By dividing the primary voltage rating by the secondary voltage rating.

EX: If the primary voltage is 19,900 and the secondary side is 240

19,900/240=82.9. therefore our turns ratio is 82.9:1

On additive polarity transformers, the secondary bushing on the right hand side of the unit is designated as

If additive the X1 will be on the right hand side

On a subtractive polarity transformer the secondary bushing on the right hand side is designated as?

If subtractive the X1 will be on the left hand side

How do we distinguish between additive and subtractive transformers?

Transformers 200 KVA and smaller and with a primary rating of 8660 and below will be additive. anything above those numbers is subtractive.

What are the two main transformer losses called?

Iron and Copper losses or

Load and no load losses

What is the order of the bushings in an additive transformer?

Starting from the left X3 X2 X!

when banking transformers the impedances must be within plus or minus _______ of each other

7.5%

What % do tap changers adjust secondary voltage?

2.5%-4.5%

Where can the nameplate be found on both overhead and underground transformers?

Overhead near the lower mounting bracket

underground inside the door on the face

What does a nameplate do?

Describes the technical aspects of a transformer

A phase to phase connection is what type of transformer?

Delta

Phasse to phase or phase ground connection is what type of transformer?

Cadillac

phase ground connection is what type of transformer?

GRDY

A nameplate with only one number on the primary side means what?

Delta transformer

A nameplate with two primary numbers and the letter Y means what ?

Cadillac

A nameplate with the bigger number first and GRDY means what type of transformer?

A GRDY

When should a dual voltage switch be operated?

When the transformer is de-energized

Whats continuity testing?

An Audible sound should not be heard between the primary and secondary windings of a transformer.

Whats the TLC Test?

Transformer last check, used to make sure transformers do not have shorted or open windings prior to energizing

Whats insulation testing?

Using A "megger" its used in troubleshooting and preventive maintenance to test the insulation in electrical apparatuses

Whats turn ratio testing?

By connecting the low inout voltage to the high voltage windings to verify proper turns ratio.

Whats the purpose of a tap changing transformer?

To change turns ratio to affect our voltage output.

What is more common banking three single phases or one three phase transformer and why?

Banking three single phase units is the most common because its less expensive and more economical.

Whats one very important thing to check when banking three single phases?

Make certain the transformers are all the same polaritys

How would you find in Coil current in a delta if given phase current?

Phase current Divided by 1.732.

Voltage stays the same in a delta

How do you find system voltage if given coil voltage in a WYE?

Coil Voltage Multiplied by 1.732

Current stays the same in a WYE

WYE WYE we ______ Wye Delta We _______

Tie, Float

The secondary coils must be _________ for the WYE secondary connections to utilize the full KVA

Paralleled

Whats the most common wye secondary voltage?

120/208

When paralleling coils internally, use what?

Alley Cat Bad Dog ACBD

What two main advantages do WYE connected banks have?

1. All three transformers can share the single phase load equally

2. They can be built using single or dual primary bushing transformers

Whats a power leg?

A hot leg that exists on delta and open delta secondaries that is 1.73 Times greater that the neutral two hot leg voltage

Define impedance

The total opposition to current flow caused by a transformer