Lecture 11

Consists of windings, which are usually wound around an iron core.

The turn ratio between the coils dictates the current and voltage relationships between the high and low voltage sides.

Power Transformers

Used on transformers, circuit breakers and other electrical equipment as connection points.

They connect the outside conductors to inside equipment.

It is hollow insulator through which a conductor passes which is basically used to connect at both ends to other equipment.

The conductor inside the bushings is normally a solid copper rod surrounded by porcelain insulation.

Bushings

The inside of the bushing may have an oil or gas as an insulation between the copper conductor and the porcelain housing to improve the insulation.

The figure on the right shows a disassembled bushing.

Bushings

http://en.wikipedia.org/wiki/Bushing_%28electrical%29

Porcelain Structure

Copper Conductor

The figure below gives another view of bushings. Here we can see the hollow part through which the conductor is passed.

Bushings

http://www.wholesale-electrical-electronics.com/p-transformer-bushing-1421191.html

The term instrument transformer refers to current and voltage transformers that are used to scale down actual power system quantities for metering/measurement, protection/control and system monitoring.

Current Transformer: A transformer designed to provide a current in its secondary coil proportional to the current flowing in its primary coil.

CTs are used to scale down the high magnitude of current flowing in high-voltage conductors to a level much easier to work with safely.

Instrument Transformers

Using the CT we can scale down the current in the secondary circuit or winding and easily measure it. Also, after we have measured the value of secondary circuit we can use the ratio of turns to find the value of current in the primary circuit.

The figure shows CT connections.

Current Transformer(Continued)

They are used to scale down very high voltages to levels that are safer to work with.

Potential Transformers