points to be considered while selecting the appropriate bypass device for soft starter [ for medium

voltage application ]

Sr.

No.

Parameter Vacuum contactor Vacuum circuit breaker

1 Fault level Up to 9 KA only, not suitable for line

side application due to fault level

limitation.

Upto 63 KA, typically 25 KA, suitable

for line side soft starter application.

2 Max. current

carrying

capacity

Max 400 A available Up to 1600 A, typically 630-1250 A

3 Closing and

tripping

mechanism

Solenoid operated, unreliable due to

dependency upon external

parameters wiz. control supply

quality, voltage dip due to heavy

switching solenoid current.

Motor + spring charged operated,

guaranteed performance independent

of external parameters

4 Aux. contacts Limited due to small size and weak

mechanism of solenoid operated

armature

Flexible and reliable due to strong

mechanism, typically more number of

contacts available

5 Closing time 70mS 40mS

6 Tripping time 50mS 10mS

8 Contact travel 4-5 mm 7-8 mm

9 No of

consecutive

operation

5, limited by thermal capacity of

solenoid coils

25, limited by charging motor duty

10 Documented

total number of

operation

10,00,000 for vacuum bottles,

replace bottles after 10,00,000

operations

20,00,000 for vacuum bottles,

Service breaker every after 1,00,000

operations for spring charging

mechanism

11 Availability and

makes

Local makes available with no service

guarantee

Jayashree make [ manufacturing

outsourced tested and monitored by

Jayashree ] provided long service

support [ design life cycle planned up

to year 2025 ]