dr audih - bau.edu.jo isolator for circuit breaker maintenance circuit breaker isolator feeder...

Download Dr Audih - bau.edu.jo  isolator for circuit breaker maintenance Circuit Breaker Isolator feeder Isolator Dr Audih 16

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  • Dr Audih 1

  • Introduction:

    Sub-stations are important part of power system ,its

    responsible to transfer some characteristic such as (voltage,

    frequency, p.f. etc.) of electric supply.

    The important points must take in consideration while laying

    out a sub-station ,the substation should be:

    Located at a proper site ( At the load centre ).

    Provide safe and reliable arrangement.

    Safe clearances.

    Easily operated and maintained.

    Minimum capital cost.

    The sub-station has many components (e.g. circuit breakers,

    switches, fuses, instruments etc.) which ensure continuous

    and reliable service.

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  • Low tension oil circuit breaker

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    The sub-stations are classified as :

    1- Pole-mounted sub-station

  • 2-Underground sub-station

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  • Underground Sub-Station:

    The underground sub-station requires more careful

    consideration than other types of sub-stations:

    (i) The size of the station should be as minimum as possible.

    (ii) Reasonable access for equipment and personnel.

    (iii) Lighting secured and protection against fire.

    (iv) Good ventilation.

    (v) Remote indication of the rise in temperature so H.V.

    supply can be disconnected.

    (vi) The transformers, switches and fuses should be air


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  • Dr Audih 6

    3- Outdoor sub-station

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    4- Indoor sub-station

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  • Symbols for Equipment in Sub-Stations

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  • 1- Security of supply:

    Security of supply (reliability) : In terms of the effect of the loss

    of supply. The British Code for the design of high voltage open

    terminal substations BS 7354 categorizes substation service

    as the following categories:

    Category 1: No outage (maximum security of supply).

    Category 2 : Short outage to transfer the load to an alternative

    circuit in case of maintenance or fault conditions.

    Category 3: Loss of a circuit or section.

    Category 4: Loss of substation.

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  • Three switch mesh

    Mesh arrangement (three switch mesh.)

    1-only three circuit breakers controlling

    four circuits.

    2-Any circuit breaker may be maintained

    at any time without disconnecting that

    circuit. **Note: (all busbars, circuit breakers (CB)and

    disconnectors must be capable of carrying the

    combined loads of both transformers and line circuit

    power transfers).

    3-Normal operation is with the bypass

    disconnectors and optional circuit

    breaker open so in case of

    maintenance or fault we transfer using

    optional breaker.


    CB2 CB3





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  • 4-In case of a fault on one transformer circuit, we can disconnect,

    and the healthy transformer circuit continue the supply without

    affecting the feeders.

    5-A fault on the bus section circuit breaker causes complete

    substation shutdown until isolate the fault and power restored.

    full mesh circuit:

    Is composed from three switch's arrangement for multiple

    circuit sub-stations is the full mesh layout as shown in Fig.

    Full mesh

    section circuit breaker

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  • 1- Operation of two circuit breakers is required to connect or

    disconnect a circuit and disconnection involves opening

    the mesh.

    2- Line or transformer circuit disconnectors may then be

    used to isolate the particular circuit and the mesh


    3- Circuit breakers may be maintained without loss of supply .

    4- Busbar faults will only cause the loss of one circuit.

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  • Ring circuit:

    The ring busbar offers increased security compared to the

    single busbar arrangement. A typical scheme which would

    occupy more space than the single busbar arrangement is

    shown in Fig.

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  • Category 1 :

    For maximum security of supply within the substation for

    maintenance or fault , the ( one and half ) 1 and 12 circuit

    breaker scheme is used .

    Bypass isolator for circuit breaker maintenance

    Circuit Breaker




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  • GIS 132kV substation double switchyard arrangement indoor

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  • This scheme is used at important high voltage sub-stations

    and large generating.

    1- Additional costs of circuit breakers are involved together

    with complex protection arrangements.

    2- It is possible to operate with any one pair of circuits, or

    group of the circuits separated from the remaining circuits.

    3- The circuit breakers and other system components must be

    rated for the sum of the load currents of two circuits.

    4- High security against loss of supply.

    5- High cost

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  • Category2

    Tow schemes are Used :

    1-Double busbar arrangement with transfer busbar

    arrangement . This arrangement consists of:

    Two bus-bars, a main bus-bar and a spare bus-bar. Its

    the most popular open terminal outdoor substation. Which

    offering the flexibility to allow the grouping of circuits onto

    separate busbars to transfer one busbar to another for

    maintenance .

    -When circuit breakers are

    under maintenance the

    protection is arranged to

    trip the bus coupler


    -The system less flexibility.



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  • 2- Double busbar scheme with bypass disconnector and bus-

    coupler switch

    Each circuit may be connected to either busbar using the

    busbar selector disconnectors.

    On-load busbar selection may be done using the bus-coupler

    circuit breaker.


    ass d











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  • - Motorized busbar selector disconnectors may be used to

    reduce the time to reconfigure the circuit arrangements.

    - Busbar and busbar disconnector maintenance may be

    carried out without loss of supply to more than one circuit.

    - The use of circuit breaker bypass isolator facilities is not

    considered to offer substantial benefits since modern

    circuit breaker maintenance times are short and in highly

    interconnected systems alternative feeder arrangements

    are normally possible.

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  • Category 3

    Single busbar scheme is use

    Simple to operate, in figure we illustrates a five circuit breaker

    single busbar arrangement with four feeder circuits, one bus

    section and ten disconnectors.

    - Each circuit is protected by

    its own circuit breaker.

    - A fault on a feeder or

    transformer circuit breaker

    causes loss of the

    transformer and feeder

    circuit which may be

    restored after isolating the

    faulty circuit breaker.

    bus section

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  • bus section

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  • O.C.B oil circuit breaker C.T current transformer L.A lightning arrester P.T. Power transformer

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  • - A fault on a bus section circuit breaker causes complete

    shutdown of the sub-station. All circuits may be restored

    after isolating the faulty circuit breaker .

    - A busbar fault causes loss of one transformer and one

    feeder. Maintenance of one busbar section or disconnector

    will cause the temporary outage of two circuits.

    - Maintenance of a feeder or transformer circuit breaker

    involves loss of that circuit. The introduction of bypass

    isolators between the busbar and circuit isolator as in

    ( Fig.a) allows circuit breaker

    maintenance without loss of the

    circuit. Bypass may also be

    obtained by using a

    disconnector on the out-going

    ways between two switchgear

    bays (Fig. b). Fig.a Fig. b

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  • Category 4

    Single bus bar without by pass section in busbar is used.

    - Radial busbar arrangement is used this decreased security

    compared to the double busbar arrangement since no

    alternative power flow routes are available.

    - This scheme occupy less space than the

    other arrangements and is cheaper.

    - A fault on a feeder or transformer circuit breaker

    causes loss of the transformer and feeder circuit.

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  • 2 Extendibility :-

    The design should allow for future extendibility (bays known

    as skeleton bays for switchgear ,overhead line or cable


    Note :Gas insulated switchgear (GIS) not permit to add any

    future extension work.

    In open terminal switchyard arrangement allows the user a

    choice of switchgear for future extension work.

    3- Maintainability

    The design must take into account the electricity supply

    company system planning and operations procedures of

    reliability and maintenance requirements for the proposed

    substation equipment.

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  • Portable earthing points and earthing switch/interlock requirements will

    also need careful consideration. Similarly standard minimum clearances


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