transformer basics

Define transformer

Is an electrical device that converts voltage from either high voltage to low voltage or low voltage to high voltage

Is the primary side always the high voltage side? explain

Yes because the primary bushings have more insulation that the secondary bushings

What is a bayonet fuse?

Bayonet fuses are located above the primary bushing, they are used in pad mount transformers for both energizing and deenergizing the transformer

Explain what KVA means and how it is used

Kilo Watt Rating. It is used to know the rating for the transformer

What are the differences between conventional and CSP Transformers?

A conventional transformer needs an external protective fuse device, also known as a cut out. A completely self protected Transformers (CSP) internally, protected by a current limiting fuse, and is also protected by a circuit breaker that also energize in the energizes the secondary side of transformer

What is the purpose of a transformer core?

It provides a path for magnetic coupling of the two windings

What is the purpose of the insulating fluid?

It cools and insulate the core and coil assembly

Explain induction with any transformer

A coil of wire will become energized if place close to another coil of wire that is attached to a source of alternating current (AC) power

What is terms ratio on how is it calculated?

Is the comparison of the number of terms of wire in each coil. Ex. If the primary coil has 100 turns and the secondary coil has 10 turns the ratio is 10 to 1, (10:1)

Explain the difference between additive and subtracted polarity

Transformers that are 200 kva and smaller with a primary rating of 8660 volts and below will be additive. From left to right secondary bushings will read x3-x2-x1. All others will be subtractive

List five items that can be found on a nameplate

primary voltage, secondary voltage, impedance, weight of transformer, and KVA

Explain the concept of diversity factor

states that a transformer does not have to be sized for total load of customer because the customer never has a light and appliance on at one time

Impedance

Is the total opposition to current flow caused by the transformer and is made up of resistance and inductive resistance. If a transformer has an impedance of 2% the secondary voltage will be limited by 2% when the transformer is at full load

Explain the importance of transformer grounding

Is intended to provide a point of connection to the Earth, where there is zero potential, which provides a path for return current in the event of a fall and ensures that protected devices will operate clearing the fall

What two functions do transformer fuses perform?

1.) prevent damage to the transformer from overloads or short circuit on the secondary side of the transformer.

2.) isolated the transformer that has an internal fault from the circuit of the circuit does not have to clear the fault

Calculating fuse sizes

1.) Coil current = kVA rating x 1000 / coil voltage

2.) Multiply the coil current by 1.25

3.) round to the nearest fuse size

Iron losses

No load losses. Are created by the oscillation of the magnetic field in respect to the core

Copper losses

Load loss. Are caused when a current flows in a conductor (caused by load) this flow creates heat as load increases heat increases. The heat limits current flow