PSP_Lab_Experiment_ [AIUB]

8/3/2019 PSP_Lab_Experiment_ [AIUB]

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Power System Protection Lab

Experiment # 01Name of the Experiment : Familiarization with

different kinds of insulators, fuses and

miniature circuit breakers


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Insulators:

The insulators provide necessary insulation

between line conductors and supports andthus prevent any leakage current from

conductors to earth.


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Insulator Materials

Porselin (20% silica, 30% feldspar, 50% clay)


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Insulator Materials Toughened Glass

Processed by controlling thermal or chemical treatment to

increase its strength compared with normal glass


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Advantages of Glass Insulators:

It is easier to detect a damaged glass insulatorthan a porcelain insulator.

Dielectric strength of glass is much higher

than that of porcelain. Glass has a lower co-efficient of thermal

expansion than porcelain.

Glass is mechanically more strong thanporcelain where under compression but intension same as porcelain.


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Types of Insulators

Pin insulators: Pin insulators are used in 11 KV and 33 KVoverhead lines.


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Types of Insulators Spool / Shackle Insulators: These insulators

are used in the 0.4 KV overhead service lines.


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Types of Insulators

Disc Insulators or Suspension type Insulators:

These Insulators are used normally in HV (>33KV)overhead transmission lines. Total Insulation of the string

can be increased by increasing the number of disc unit in

the string.


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Types of Insulators

Strain Insulators:


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Flush over of Insulator In flash over, an arc occurs between the line conductor and

insulator pin and discharge jumps across the air gaps. In case of flash over, the insulator will continue to act in its

proper capacity.


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Puncher of Insulator

In case of puncher, the discharge occurs from conductor to pin

through the body of the insulator.

When such breakdown is involved, the insulator is

permanently destroyed.


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Specification of a Insulator


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Impulse voltage withstand test


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Impulse voltage flashover test


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Dry and wet power frequency voltage

withstands test


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Creepage Distance

Creepage distance is the shortest path

between two conducting parts of an electrical

or electronic circuit measured along the

surface of the insulator.


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Fuse

Fuse is the simplest and cheapest current

interrupting device for protection of the

electrical devices from excessive currents.

It provides two types of protection:

Short circuit protection

Over Load protection


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Types of Fuse

Semi-enclosed or Re-wire able Fuse:These types of fuses are used for the protection of appliances at 0.4 KV

voltage level. and usually called cut-out. The Fuse carrier can be pulled out

and the blown out fuse element can be replaced.


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Types of Fuse

Totally Enclosed or cartridge Fuse:

The Fuse Element (the conductor which melts) is enclosed in a

totally enclosed container and is provided with metal contact

on both side.


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Types of Fuse

Drop out Fuse:

This type of fuse is normally used in 11 KV side

of a 11/0.4 KV distribution transformer.


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Types of Fuse

HRC ( High Rupturing capacity) cartridge

Fuse: A cartridge fuse link having breaking capacity higher then certain specified

value (e.g. above the 16 KA for medium voltage)


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Lightning Arrestor

The main function of a Lightning arrestor is to divert any surge over

voltage caused by lightning to the ground, so that equipment or devices

behind the arrestor are saved from insulation failure and eventually short

circuit fault.


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Miniature Circuit Breaker (MCB)

A circuit Breaker (CB) is an automatically operated electrical switch

designed to protect an electrical circuit from damage caused by overload

or short circuit.

Unlike a fuse, which operates once and then has to be replaced, a CB can

be reset (either manually or automatically) to resume normal operation.

MCBs are used to protect electrical appliances in LV system ( up to 100 A)


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Moulded Case Circuit Breaker (MCCB) Use in 3-phase system.

It also providesShort Circuit Protection

Over Load Protection

Documents

PSP_Lab_Experiment_ [AIUB]