Introduction to auto-reclosing

The extra high voltage transmission lines transmit a large quantity of electrical power. Hence, it’s perpetually fascinating that the continuation of power flow through the lines mustn’t be interrupted for an extended time. There is also a brief or permanent fault within the lines. Temporary faults get mechanically cleared, and these don’t need any try for fault rectification. it’s traditional to apply by the operators that once every initial faulty tripping of the road, they shut the road. If the fault is transient, the road holds once the second try of closing the fuse, however if the fault persists, the protection system once more visits the road and so it’s declared as permanent fault.

Faults on overhead lines fall under one in every of 3 categories: transient, semi-permanent and permanent. 80-90% of faults on any overhead line network area unit transient in nature. The remaining 10%-20% of faults area unit either semi-permanent or permanent. Transient faults area unit usually caused by lightning and temporary contact with foreign objects. The immediate tripping of 1 or a lot of circuit breakers clears the fault. later re-energization of the road is typically productive.

A small limb falling on the road might cause a semi-permanent fault. The reason for the fault wouldn’t be removed by the immediate tripping of the circuit, however, may well be burnt away throughout a time-delayed trip. HV overhead lines in forest area units are vulnerable to this sort of fault. an additional profit, notably to EHV systems, is that the maintenance of system stability and synchronizing.

Auto-reclose example schemes
Auto-reclose facilities in common use for a number of standard substation configurations are described in the following sections.

  1. Double Busbar Substation.

         a. Basic scheme – banked transformers omitted.

        b.  Scheme with banked transformers

2. Single Switch Substation.

3. Four-Switch Mesh Substation.

1. Double Busbar Substation Scheme

A typical double bus station is illustrated within the pic:1 below. every of the six EHV transmission lines brought into the station is below the management of a breaker, CB1 to CB6 inclusive, and every line may be connected either to the most or to the reserve busbars by operated by hand isolators. Bus section isolators alter sections of the bus to be isolated within the event of the fault, and bus coupling breaker B.C.

a. Basic scheme – banked transformers omitted: Each line fuse is given associate degree auto-reclose relay that recloses the suitable circuit breakers within the event of a line fault. The operation of either the bus protection or a Vermont Buchholz relay is organized to exclude the auto-reclosing sequence. within the event of a persistent fault on Line one, the road circuit breakers trip and resistance when one try at reclosure.

b. Scheme with banked transformers: 

Some utilities use a variation of the fundamental theme during which Transformers T1 and T2 area unit banked off Lines one and a couple of, as shown in pic:1 . This provides some economy within the variety of circuit breakers needed. The corresponding electrical device circuits one and a couple of area unit teed off Lines one and a couple of severally. The electrical device secondaries area unit connected to a separate HV bus system via circuit breakers CB1A and CB2A.

Auto-reclose facilities will be extended to hide the circuits for banked transformers wherever these area unit used.

Fault on line 1…

For example, a fault online one would cause the tripping of circuit breakers CB1, CB1A, and therefore the remote line electrical fuse. once Line one is re-energized, either by auto-reclosure of CB1 or by the remote electrical fuse, whichever is about to reclose 1st, electrical device T1 is additionally energized.

CB1A won’t reclose till the looks of electrical device secondary voltage, as monitored by secondary Vermont. It then recloses on to the HV busbars once a brief time delay, with a synchronization check if needed.

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Fault on transformer T1…

In the event of a fault on electrical device T1, the native and remote line circuit breakers and breaker CB1A trip to isolate the fault. An automatic gap of the bimotored electrical device isolator IT1 follows this. the road circuit breakers then reclose within the traditional manner AND gate breaker CB1A locks out.

2. Single Switch Substation

The arrangement shown in Figure two consists primarily of 2 electrical device feeders interconnected by one electrical fuse one hundred twenty. every electrical device, therefore, has another supply of provide within the event of loss of 1 or different of the feeders.

For example, a transient fault on Line one causes tripping of circuit breakers one hundred twenty and B1 followed by reclosure of CB one hundred twenty. If the reclosure is palmy, electrical device T1 is re-energized gate breaker B1 recloses once a brief time delay.

If the road fault is persistent, one hundred twenty journeys once more and also the motorized line isolator 103 is mechanically opened. electrical fuse one hundred twenty recloses once more, followed by B1 so each transformers T1 and T2 square measure then provided from Line two.

3. Four-Switch Mesh Substation

The mesh station illustrated in Figure three is extensively utilized by some utilities, either fully or half. the fundamental mesh contains a feeder at every corner, as shown at mesh corners MC2, MC3, and MC4. One or 2 transformers can also be banked at a mesh corner, as shown at MC1.

Mesh corner protection is needed if quite one circuit is fed from a mesh corner, no matter the CT locations. goodish issues will are encountered within the application of auto-reclosing to the mesh station. as an example, circuit breakers a hundred and twenty and 420 in Figure three ar tripped out for a range of various kinds of fault related to mesh corner one (MC1), and everyone needs totally different treatment as way as auto-reclosing is bothered. more variations occur if the faults are persistent.

A outline of facilities is currently given, supported mesh corner MC1 to indicate the inclusion of banked transformers. Facilities at different corners ar similar however omit the operation of kit alone related to the banked transformers.

Transient fault on Line 1

Tripping of circuit breakers a hundred and twenty, 420, G1A and G1B is followed by reclosure of a hundred and twenty to offer deadline charging of Line one. Breaker 420 recloses in sequence, with a synchrony check. Breakers G1A, G1B reclose with asynchrony check if necessary.

Persistent fault on Line 1

Circuit breaker one hundred twenty visits once more when the primary reclosure and isolator 103 is mechanically opened to isolate the faulted line. Breakers one hundred twenty, 420, G1A and G1B then reclose in sequence as on top of.

Transformer fault (local transformer 1A)

The automatic gap of isolator 113A to isolate the faulted electrical device follows tripping of circuit breakers a hundred and twenty, 420, G1A and G1B. Breakers a hundred and twenty, 420 and G1B then reclose in sequence, and breaker G1A is latched out.

Transformer fault (remote transformer)

For a distant electrical device fault, associate entomb trip signal is received at the native station to trip breakers a hundred and twenty, 420, G1A and G1B and inhibit auto-reclosing till the faulted electrical device has been isolated at the link-attached station. If the entomb trip persists for sixty seconds it’s assumed that the fault cannot be isolated at the link-attached station.

Isolator 103 is then mechanically opened gate breakers a hundred and twenty, 420, G1A and G1B are reclosed in sequence.

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