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AUTO-RECLOSING ON EHV LINES.

By

 Y. k. Pandharipande.

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AUTO-RECLOSING ON EHV LINES

80  – 90% of Over-head Line faults are transient faults.Hence restoration of line can be quickly done by Auto-reclosing C.B. after allowing sufficient de-ionisation time,following tripping.

In case of EHV lines, Auto-reclosing enhances systemstability and maintain synchronism.

 Auto-reclosing is not applied to cable feeders or mixedcable plus over-head feeders where faults are likely to

be permanent.

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AUTO-RECLOSING ON EHV LINES

POWER ANGLE CURVE SHOWING EFFECT OF AUTO-RECLOSING ON EARTH FAULTS

If Angle Ɵ2 at which C.B. Recloses is such that Area 2 isgreater than Area 1, synchronism between the two

systems is maintained.

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AUTO-RECLOSING ON EHV LINES

TYPICAL AUTO-RECLOSE SCHEME LOGIC (SIMPLIFIED)

LEGEND: D.T. - Dead Timer, R.T. - Reclaim Timer I/L – Inter-lock (Permissive), L/O - Lock-out

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AUTO-RECLOSING ON EHV LINES

DEAD TIME - time between fault arc extinguished and C.B. Contactremake.

INFLUENCING FACTORS

1. SYSTEM STABILITY / SYNCHRONISM

Depends upon permissible system disturbance time upto whichsystem stability can be maintained, based on Power Angle Curve.

3 Phase tripping may cause loss of synchronism requiring rapidreclosure.

2. C.B. CHARACTERISTIC

C.B. Duty Cycle C.B. Trip Time Mechanism Reset Time C.B. Closing Time

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AUTO-RECLOSING ON EHV LINES

DEAD TIME – INFLUENCING FACTORS

3. DE-IONISATION OF FAULT ARC

De-ionisation time depends upon:

System Voltage Weather Conditions Capacitive Coupling with Healthy Phase(s) TYPICAL MINIMUM DE-IONISATION TIME

66 KV - 0.10 S.132 KV  – 0.17 S.220 KV  – 0.28 S400 KV  – 0.50 S.

(REF. P.R.A.G. of Areva)

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AUTO-RECLOSING ON EHV LINES

RECLAIM TIME:

Time following successful auto-reclosing (measured from theinstant A/R contact makes), which should elapse, beforesubsequent A/R sequence is initiated in the event of recurrenceof fault.

INFLUENCING FACTORS

1. DUTY CYCLE OF BREAKERTypical Duty Cycle = O  – C  – O  – 3 Minutes  – C  – O  – C

2. RESETTING OF CLOSING MECHANISM TO BE READY FORSUBSEQUENT RECLOSURE

Governed by spring charging time in case of motor wound springcharge breakers.

Time for Air Pressure to recover in case of ABCBs

Time for SF6 reservoir to recharge in case of SF6 Breakers.

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AUTO-RECLOSING ON EHV LINES

2. 1-PHASE TRIP AND RECLOSURE (ON 1-PHASE FAULT) 

Feasible if C.B. has separate closing and tripping mechanism andClosing / Tripping Coils for each phase.

No Loss of Synchronism (Synchronising power can be exchangedthrough healthy phases).

Longer de-ionising time requiring long dead time (effect of healthy phase coupling)

  Mal-operation of E/F relay on healthy circuit likely in case of 

double circuit lines, in multiple neutral earthed systems.

Pole Discripancy time should be set to over-ride dead time.

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AUTO-RECLOSING ON EHV LINES

3-PHASING AUTO-RECLOSING – Supplimented by “Dead Line charging” & “Check Synchronising” at Consegutive Ends.  

End “A” having DLC feature checks for Dead Line/Live Bus Condition, through U/V Relays 27L / 27B & close CB 52A.

Synchronism is checked between I/C Line and Bus voltage at endB, before reclosing CB 52B.

DLC Feature applied at line end having weak source.

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AUTO-RECLOSING ON EHV LINES

PROTECTION CHARACTERISTIC FOR HIGH SPEEDRECLOSURE

Protection initiating A/R should be High Speed (such as DistanceZone1 / Aided trip, Pilot Wire Differential etc)

  Simultaneous tripping at both ends is an essential pre-requisite to

apply High Speed Reclosure. This requires Distance relays to beinter-locked through tele-protection channel to ensuresimultaneous tripping for end section faults.

In case of 1-Phase Tripping & Reclosure, protection needs to be

Phase Selective. If not, separate Phase Selectors (Over Currentor Impedance type) have to be provided.

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AUTO-RECLOSING ON EHV LINES

LOCK OUT If A/R is unsuccessful or not likely to be successful, C.B. is

tripped and Auto-reclosing is blocked.

CONDITIONS FOR LOCK OUT Fault cleared by time delayed backup protection (e.g.

Distance Z2/Z3, IDMT O/C etc).

CB Inter-locks (such as Air pressure, Spring Charge LimitSwitch etc) not permissive.

Fault recurring during Reclaim Time.

CB Switched On To Fault (Manual Closing)  Tele-protection channel out of Service.

Synchronism not regained indefinitely in case of 3 Phase trip& Reclosure.

 Auto-reclose Out of Service (Non-Auto Mode)