420KV SF 6 CIRCUIT BREAKER .pdf

7/27/2019 420KV SF 6 CIRCUIT BREAKER .pdf

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420KV SF6

CIRCUIT BREAKER

OPERATION AND TESTING


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CONTENT:

Introduction

Classification of circuit breakers

Advantages of SF6 circuit breaker

Technical data

Constructional details

Arc phenomenon

Operating principle

Conclusion


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ABSTRACT:

This project is titled 420 KV SF6 CIRCUIT BREAKER OPERATION AND TESTING .The operation of

420KV SF6 circuit breakers was explained. The various routine tests recommended by IEC 62271-100 standard is

described and the results of the test are compared with the specified values.

The first deals with the basic introduction to a circuit breaker, types of circuit breaker, the properties and

advantages of SF6 circuit breaker, its disadvantages, technical data, constructional features of the breaker in which

various parts of the circuit breaker are explained, It also deals with the basic working principle, arc phenomenon,

arc extinction and modes of operation of 420 KV SF6 circuit breaker.

The second part covers introduction to IEC 62271-100 standards and various types of tests. A list of various types

and routine test is also included.


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INTRODUCTION:

With the ever-increasing demand for energy, power generation, transmission and distribution have become very

important and circuit breaker is a vital component in the transmission system achieves greater significance.

A circuit breaker is a device which can make or break a circuit manually or by remote control under normal

conditions, break a circuit automatically under fault conditions and make a circuit either manually or by remote

control after fault cleared.

The circuit breaker serves two basic purposes:

1. Switching during normal operating conditions for the purpose of operation

and maintenance.

2.Switching during abnormal conditions such as short circuit and interrupting

fault currents.


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CLASSIFICATION OF CIRCUIT BREAKERS:


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CLASSIFICATION BY LOCATION:

Switchgear based on where it is located is classi ied as indoor and

out-door type.

Medium and low voltage switchgear and high voltage as

Insulated Switchgear ( IS) are categorised as indoor type

Where as the out- door switchgearwhich has air as an external

insulating medium is categorised as air insulated switchgear ( IS)


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CLASSIFICATION BY EXTERNAL DESIGN:

Out-door circuit breakers can be identified as either dead-tank or live-tank

type circuit breakers, from the point of view of their physical structural

design.

In Dead tank circuit breaker, the switching device is located with suitable

insulator supports inside a metallic vessel(s) at ground potential and filledwith insulating medium.

In Live tank circuit breaker the interrupter(s) is/are located in an insulator

bushing/s and are at a potential above the ground. The live tank circuit

breakers are cheaper and they require less mounting space.


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CLASSIFICATION BY INTERRUPTING MEDIA:

Depending upon the interrupting media the circuit breakers are classified into

Air Blast Circuit Breaker

Oil circuit breakers

Vacuum circuit breaker

SF6 gas circuit breaker


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ADVANTAGES OF SF6

GAS CIRCUIT BREAKERS:

SF6 is an electro-negative gas and has a strong tendency to absorb free electrons , so it has very short arcing time.

The dielectric strength of SF6 gas is 2 to 3 times that of air, such breakers can interrupt much larger currents.

There is no risk of fire because SF6 gas is non-flammable.

The SF6 circuit breakers requires low maintenance .

Since SF6breakers are totally enclosed and sealed from atmosphere , they are particularly suitable where

explosion hazard exists e.g coal mines.


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TECHNICAL DATA:

Electrical data:

Rated voltage KV 420

Rated insulation level

- Lightening impulse withstand

voltage(1.2/250us)

KVp 1425

- One minute power frequency

withstand voltage

KV 520-610

Rated frequency HZ 50

Rated normal current A 3150

Rated short -circuit breakingcurrent

KA 40

Rated short-circuit making

current

KA 2.5 times rated short-circuit

breaking current

Rated short- circuit current

duration

Sec 3

Rated duty cycle--

O- 0.3sec-CO-3mins-CO


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OPERATI TI I :

Closing time ms 100 max

Opening time ms 22 max

Arcing time ms 18 max

Break time Cycles 2


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CONSTRUCTIONAL ETAILS:

The main parts of the SF6 circuit breaker are:

Interrupt assembly

Bell-crank mechanism

Support insulator

Hydraulic mechanism

Control cabinet


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ARC PHENOMENON:

When short circuit occurs, a heavy current flows through the contacts of the circuit breaker before they are opened

by the protective system.

At the instant when the contacts begin to separate, the contact area decreases rapidly and large fault currents

causes increased current density and hence rise in temperature.

The heat produced in the medium between contacts is sufficient to ionise the air or vaporize and ionise the oil.

The ionised air or vapour acts as conductor and an arc is struck between the contacts.

The p.d between the contacts is quite small and is just sufficient to maintain the arc.

The arc provides a low resistance path and consequently the current in the circuit remains uninterrupted so long as

the arc persists.


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OPERATING PRINCIPLE:


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CONCLUSION:

Thus in our presentation we are explained about basic introduction of circuit breaker, classification

of circuit breakers depending upon different consideration, technical data , advantages of SF6circuit breaker, constructional features circuit breaker, Arc phenomenon operating principle of SF6circuit breaker and the process of arc extinction.


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REFERENCES:

TEXT OOKS:

1.PRINCIPLES OF POWER SYSTEM - V.K.MEHTA

ROHIT MEHTA

2.OPERATION & MAINTANCE OF SF6 CIRCUIT BREAKER BHEL,HYD.

WEBSITES:

1.WWW.GOOGLE.COM

2. WWW.BHEL.COM

3. WWW.ABB.COM.


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THANK YOU


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420KV SF 6 CIRCUIT BREAKER .pdf