Applications
3.3 Motor protection applications of 3VA molded case circuit breakers
3VA molded case circuit breakers with IEC certificate
154
Manual, 03/2019, A5E03603177010-03
Blocking protection
The 3VA2 molded case circuit breakers with the ETU860M motor protection trip unit now
have blocking protection integrated in the circuit breaker for the first time.
If the motor is blocked (or if it falls short of the breakdown torque), a high motor current -
almost as high as the starting current but still not as high as a short-circuit current - is
generated. Without blocking protection, it can take up to 30 s or even longer (depending on
the current and T
P
settings) for the molded case circuit breaker to trip. This results in
unnecessary thermal stress.
Blocking protection is automatically deactivated during startup until the motor reaches
operating speed (t
start
).
t
start
is equal to t
b
.
Typical application examples for this include:
●
Rock crushers (rock too large or too hard)
●
Conveyor belts (transported goods jammed)
1)
Adjustable I
b
over 0.4 in firmware version 4.3 and higher
2)
Adjustable t
b
over 0.5 s in firmware version 4.3 and higher
Idle running protection
The 3VA2 molded case circuit breakers with the ETU860M motor protection trip unit now
have idle running protection integrated in the circuit breaker for the first time.
When the load on the motor is removed, e.g. when the drive chain or drive belt snaps, the
current falls below the normal motor operational current. The integrated idle running
protection detects this condition, trips and thus shuts down the application.
