substation protection

7/30/2019 substation protection.

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SUBSTATION PROTECTION

Atul sontakke.


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OUTLINE

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Introduction

Nature and Causes of faults

Components of Protection

Fuse and its types

Relay and its types Circuit breaker

Earthing

Isolator


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Introduction

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A Substation covers various equipment such as Circuit Breakers,

Isolators, Earth Switches, Lightning Arresters, Grounding System and

etc. Protection scheme is designed to limit the effects

of disturbances in the power system which is allowed to persist, may

damage plant and interrupt the supply of electric energy. The

greatest threat to the security of a power supply station is short

circuit which imposes sudden and violent change in he power

system. Rapid isolation of the fault by nearest switchgear will

minimize the damage. It covers various types of protection used inswitchyard such as relays, circuit breakers and etc.


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NATURE AND CAUSES OF FAULTS

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Insulation failure.

Conducting path failure.

Overvoltage's due to lightening or switching surges.

Puncturing or breaking of insulators.

Failure of conducting path due to broken conductors.

Faults due to poor quality of system components or because of faulty

system design. System design.


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COMPONENTS OF PROTECTION

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FUSES

MCB/MCCB

RELAYS

CIRCUIT BREAKERS

EARTHING

ISOLATOR


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FUSES

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Fuse-Fuse is a piece of wire of a material with avery low melting point. When a high current flows

through the circuit due to overloading or a short

circuit wires gets heated and melts. As a result, the

circuit is broken and current stops flowing.

Types of fuses. Low voltage fuse.

KIT-KAT fuse.

HRC (High rupturing fuse).

Semiconductor fuse.

High voltage fuse.

Drop out fuse.


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MCB (Miniature Circuit Breaker)

Type Tripping Current perating Time

Type B 3 To 5 time full load current 0.04 To13 Sec

Type C 5 To 10 times full load current 0.04 To 5 Sec

Type D 10 To 20 times full load current 0.04 To 3 Sec


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Application of MCB

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B Curve MCB-This type MCB is used for resistive load.

e.g. Heater, Oven.

C curve MCB- This type MCB is used for inductive load.

e.g. Fan, Washing M/C, Fridge, motor, AC, Transformer,

D Curve MCB- This type MCB is used where High inrush current is

available.

e.g. Induction motor, Transformer.


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MCCB (Moulded Case Circuit Breaker)

MCCB is used for protecting of low-voltage electrical wires and

connected equipment, against overloads and short-circuits.

Rated current up to 1000 A.

Trip current is adjustable. The advantage of MCCBs for very large ratings is their compact size.

An ACB is physically larger, but more cost-effective for higher ratings.


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RCCB(Residual Current Circuit Breaker)

Phase (line) and Neutral both wires connected through RCCB.

RCCB trips the circuit when there is earth fault current.

The amount of current flows through the phase (line) should return

through neutral.

Any mismatch between two currents flowing through phase andneutral detect by -RCCB and trip the circuit within 30Miliseconed


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ELCB (Earth Leakage Circuit Breaker) An ELCB had a current sensing coil in series with the ground cable, so

the supply would be tripped if current occurred in the ground lead.

This was often combined with a voltage sensing coil on the frame

also, which used a separated ground some distance away.

The original use was for larger motors and generators/transformers,

where the insulation can fail, and the voltage on the frame of the

machine can rise dangerously above ground due to the ground

resistance and fault current.


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Relays

Relays are electrical switches.


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Types of Relay. Over current relay.

Under voltage relay.

Earth fault relay.

Phase sequence relay.

Time delay relay.

Buchholz Relay.

Frequency Relay.


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Buchholz Relay.


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High voltage circuit breakers

open or close a circuit under all conditions. Viz. no load full load and

fault condition.

it can be operate manually and automatically under fault conditions.

Under normal operating condition, the contact remains close and thecircuit breakers carries the full load-current continuously.


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Classification of circuit breaker.

Oil circuit breaker- Which employ some insulating oil for arc extinction.

Air-blast circuit breaker- in which high pressure airblast is used arc extinction.

SF6-Sulferhexafluoride gas is used for arc extinction.

Vacuum CB- Vacuum is used for arc extinction. 33kV.


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Oil circuit breaker.

Advantages of Oil Circuit Breaker (OCB)As an Arc extinguishing medium oil has the following

advantages:

1. Oil produces hydrogen during arching. The hydrogen helps

extinguish the arc.

2. Oil provides insulation between the contacts after the arc

has been extinguished

Disadvantages of Oil Circuit Breaker (OCB)

1. Oil is inflammable and may cause fire hazards. When a

defective circuit breaker fails under pressure, it may cause an

explosion

2. The hydrogen generated during arcing, when combined with

air, may form an explosive mixture

3. During arcing, oil decomposes and becomes polluted by

carbon particles, which reduces its dielectric strength. Hence,

it requires periodic maintenance and replacement.


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Vacuum Circuit Breakers

Advantages

Very long lifetime of the contacts (This

provides longer breaker life.)

Less maintenance required

Less moving parts in mechanism

Less force needed to separate thecontacts (since the distance between them

is shorter.)

Environment friendly. Since interruption

takes place in vacuum medium, VCBs do

not require

gas or liquid addition. This reduces thepossibility of leakage of gas (or any

material) that can

be harmful for environment.


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Air blast Circuit breaker.


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SF6 circuit breaker.

Advantages

Simple construction, less cost.

SF6 gas is non flammable, non toxic

Maintenance free

Ability to interrupt low and high fault

Excellent Arc extinction.


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EARTHING

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Types of Earthing -

Plate Earthing Pipe Earthing


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Measurement of Earth Resistance

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ISOLATOR

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Circuit--Isolator Isolators are available in

ratings from 11 kV to 132kv.

in 1200 A, 1600 A, and 2000 A versions.

Style like Side--break, vertical- break,

centre break styles. can be furnished, to

suit almost any substation layout.


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ELECTRICAL SLD

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Thank you

substation protection

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