2 interlocking scheme

Institut Latihan Sultan Ahmad Shah(ILSAS)

Unit Perlindungan, Seksyen Latihan Penghantaran - 2006

KURSUS LATIHAN KEKOMPETENAN

Unit PerlindunganSeksyen Latihan Penghantaran

Institut Latihan Sultan Ahmad Shah (ILSAS)

PERLINDUNGAN PENGHANTARAN(SETAKAT 132kV)



INTERLOCKING SCHEME



OBJECTIVES• Determine the need/policy for interlocking

scheme correctly• Describe the types of interlocking correctly• Explain the interlocking schemes

operations given the logic diagram correctly

• Draw the interlocking schematic given the logic diagram correctly



1. Where do we apply interlocking?

2. What equipment are associated in an interlocking scheme?

3. What impact would there be if an interlocking fail?

PRE-TEST



BASIC DEFINITION

Interlocking as defined in Oxford dict.:• Engage with each other by overlapping• Connect so that they could not operate

independently or unsafely• Mechanism to interlock switches



POLICY (from PCOP)Interlocking:

• All switching devices within a substation shall be interlocked in a manner that ensures they always operate safely



POLICY (from PCOP)Interlocking:

• The interlocking scheme shall be provided to ensure correct sequence of operation of the switching devices



POLICY (from PCOP)Interlocking scheme requirement:

• Interlocking scheme shall cater fo both operational interlocks as well as maintenance interlock




• All switchgears except circuit breakers shall be prevented to operate on load




• Closing or opening of any earthing switch shall be prevented unless the point of application is disconnected from all possible sources of supply



TYPES OF INTERLOCKING

1. Operational Interlock

- mechanical and electrical interlockingassociated with normal systemoperation and switching, and intended toensure that a pre-determined switchingsequence is satisfied



TYPES OF INTERLOCKING

2. Maintenance Interlock

- mechanical and electrical interlockingassociated with a series of switchingoperations to render equipment orsections of the station safe for accessand maintenance by personnel



INTERLOCKMechanically will prevent:• Racking in/out VCB when the VCB is in

CLOSED position• Closing when the VCB is not aligned

properly• Closing VCB if feeder is earthed



INTERLOCKMechanically will prevent:• Closing of CB if spring is uncharged• Closing line isolator if earth switch is in

ON position• Closing of VCB if not in service position• etc



INTERLOCKElectrically will prevent:• Closing when Master Trip relay is not

reset• Closing when CB spring is not fully

charged• Continuous reclosing due to faulty

closing circuit



INTERLOCK

Electrically will prevent:• Opening of isolator if CB still closed• Closing of earth switch if there is

voltage on the line• etc



INTERLOCK

• Interlock scheme design shouldconsider the status of the relevantdevices



LOGIC GATE

• AND gate• OR gate• NOT gate



LOGIC SCHEME• Using the AND,OR and NOT gate, draw a

conceptual diagram for closing of a feeder CB- example check with:* one of Bus isolator closed* line isolator closed* Master Trip reset* synchronizing checked

• Then draw a schematic presentation of the above



STANDARD APPLICATIONS

• Normally checked during commissioning• Failure due to:

- faulty contacts- wrong termination- loose connection

• Some alarms are useful in detecting interlocking failures e.g.- NER open alarm- LV VT open- Trip circuit supervision etc.



SUMMARY• All switching devices within a substation shall be

interlocked to ensures safe operation.

• The interlocking scheme shall be provided toensure correct sequence of operation of theswitching devices.

• Interlocking scheme shall cater for operationalinterlocks and maintenance interlock.

2 interlocking scheme

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