Concept of Electrical Interlocks

Electrical Equipments Interlocks (Concepts) .

Interlocks. 

Interlocks in a substation is used to ensure the safety of the equipments , operating personal and to prevent the wrong sequence of operations.

Why interlocks are used? 

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Suppose interlocks are not present and an operating person close the earth switch without opening the isolator then it can be the cause of phase to earth fault. Which is an example of wrong sequence of operation or human error this is also hazardous for human life and equipments. Opening of isolator without opening of circuit c ircuit breaker cause damage to the isolator. “hence interlocks are required and used”

Bay operation/Switching. 

Bay opening

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Bay closing

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Protection trip(Bay opening due to protection)

Sequence of operation. 

De-energization of a bay (Opening of a bay)

Circuit breaker open II. Isolator open III. Earth switch close I.

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Energization of a bay(Closing of a bay)

Earth switch open II. Isolator close III. Circuit breaker close I.

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Protection trip At the time of fault f ault circuit breaker will open instantaneously .

Interlocks required between following equipments. 

Isolator

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Circuit breaker

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Earth switch

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Isolator. Bus isolator close interlocks:

Bus earth switch open II. Associated earth switch open III. Circuit breaker open IV. Earth switch after CB open V. Isolator switch in remote position I.

. Bus isolator open interlocks:

Circuit breaker open II. Associated earth switch open III. Earth switch after CB open IV. Isolator switch in remote position I.

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. Line isolator close interlocks:

Associated earth switch open II. Circuit breaker open III. Earth switch after CB open IV. Isolator switch in remote position I.

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. Line isolator open interlocks:

Circuit breaker open II. Associated earth switch open III. Earth switch after CB open IV. Isolator switch in remote position I.

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Circuit breaker interlock Circuit breaker close interlocks: Close permit received I. II. Circuit breaker not lockout III. Protection trip not issued IV. Switch in remote position V. Charging conditions a. b. c. d.

dead bus and dead line live bus and dead line dead bus and live line live bus and live line Continued….

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Circuit breaker open interlocks: 

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Direct open command from the BCU or Through TNC switch available in panels

Earth switch interlock Bus earth switch close interlocks: 

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All the isolator associated to that particular bus are open. Bus is under voltage

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. Line earth switch close interlocks: 

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Associated line isolator open Line under voltage

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