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