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SF6 VS VCB - A COMPARISON

 

Sl. No.

1

Criteria

2

SF 6 circuit breaker

3

Vacuum circuit breaker

4

  1. SWITCHING DUTIES

1.

Summated breaking current capacity

To 50 times rated short circuit breaking current

To 10,000 times continuous rated current.

To 100 times rated short circuit breaking current

To 20,000 times continuous rated current.

2.

Critical switching

  1. Motor, Reactors small inductive current.

Very well suited Over voltage generally under 2.5 p.u. Normally no action necessary to limit over voltages.

Well suited. Under certain circumstances steps may be necessary to limit over voltages because of possibility of virtual current chopping. Use of surge arrestors recommended

 

  1. Capacitors

Well suited. Restrike free. In special cases reactors may be necessary to limit in rush current – Low over voltage.

Suited. Generally Restrike free. In special cases reactors may be necessary to limit in rush current-Reignition and restrikes possible in certain cases due to statistical scatter of breakdown voltage in vacuum.

 

  1. Over head and cable feeders.

Very well suited – Restrike free.

Very well suited Restrike free.

 

  1. Switching of arc furnaces.

Only suitable in applicable with comparatively low number of operations per day.

Suitable also for applications with very high number of operations (over 100 co-per day.)

3.

Suitability of single and multi shot auto reclose cycles..

Very well suited

Very well suited

 

SI. No.

1

Criteria

2

SF 6 circuit breaker

3

Vacuum circuit breaker

4

II. MAINTAINABILITY

1.

Number of operations between servicing, referred to operating mechanism.

500 to 20,000 C-O Operations

10,000 to 20,000 C-O operation

2.

Service life of interrupters

5000 to 20,000 Co-operations (Between over hauls)

20,000 to 30,000 Co-Operations or (manufacturers guidelines)

3.

Service interval

Lubrication of operating mechanism after 5 to 10 years (if limiting number of operations not reached)

Lubrication of operating mechanism after 10 years (if limiting number of operations not reached.)

4.

Expenditure on overhaul of interruptors.

Overhaul involves complete dismantling of interrupter.  Labour costs high, material costs low.

Tester used to check vacuum level. If necessary replace interrupter. Low labour costs. High material costs.

5.

Supervision of Circuit breaker condition.

Supervision of SF 6 gas pressure possible (Pressure guage with contacts for remote signaling.)

Checking the insulation and quench media not easily possible-But generally supervision of vacuum level not necessary (sealed for life)

6.

Refilling of arc quenching media

Possible

Not possible

III. REALIABILITY

1.

Failure rate

Lowest

(7-13 per 1000 CB-Yrs.)

Lowest

(7-13 per 1000 CB-Yrs.)

2.

Mechanical life

Good

Excellent

3.

Fire Hazard

Zero

Zero

4.

Interrupting capacity in case of leakage.

Switching of rated current still possible.

Not possible

IV. COST

1.

Cost of production

Slightly higher than VCB

-

2.

Maintenance cost

Lowest negligible cost for minimum 10 years.

Lowest negligible cost for minimum 10 years.

 

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