Siemens SENTRON 3VL System Manual page 140

Parameter assignment/addressing
10.2 Setting the protection parameters for motor protection (ETU10M, ETU30M and LCD-ETU 40M)
Setting the time-lag class/trip class
The SENTRON VL circuit breaker offers the option of selecting from various time-lag classes
or trip classes for different motor applications.
One version (ETU10M) contains a thermal memory and phase failure sensitivity based on a
fixed trip class 10.
With the
the short-circuit release are set in combination with the right rotary encoding switch.
Another version (
30. The setting in accordance with CLASS 5 is only used on motors with an extremely low
overload capacity. In CLASS 30, by contrast, the motor must be suitable for starting under a
heavy load. That is, the trip class must be adapted to the start-up time of the motor.
Definition of the trip class
The trip class specifies the start-up times during the motor start in accordance with
IEC 60947-4-1. The trip class is defined by the tripping time at 7.2-times the set current level
(in the cold state). Combinations with CLASS 10 are generally used.
The tripping times are as follows:
● CLASS 10 A between 2 and 10 secs,
● CLASS 10 between 4 and 10 secs,
● CLASS 20 between 6 and 20 secs,
● CLASS 30 between 9 and 30 secs.
Applications such as fans, require longer start-up times.
Phase failure sensitivity
The "phase failure sensitivity" function is also integrated into the releases for motor
protection ETU10M, ETU30M and ETU40M. This ensures that the motor is reliably protected
against overheating if a phase interruption or a large fluctuation occurs. The phase failure
sensitivity protects 3-phase AC motors against overheating while only 2 phases are active.
The specified operating current IR is automatically reduced to 80% of the set value if the
r.m.s. values of the operating currents in the three phases in the case of the ETU10M and
ETU30M trip units differ by more than 40%. If an adjustable phase unbalance of 5 to 50% is
set on the ETU40M trip unit, the set operating current I
the set value.
Thermal memory
The trip units for motor protection ETU10M, ETU30M and ETU40M have a "thermal
memory" that takes account of the pre-loading of the motor (tripping in the case of overload).
The function of the fixed "thermal memory" cannot be switched off (except on the ETU40M).
Following an overload trip of the circuit breaker, the tripping time is reduced by the thermal
pre-loading of the circuit breaker in such a way that further overloads cannot harm the motor
windings.
After an overload trip, the tripping times are reduced in accordance with the tripping
characteristic curves so that even the inrush current can result in a trip. A cooling time
dependent on the size of the motor is required before the motor can be switched on again.
140
ETU30M
overcurrent trip unit, both the time-lag class TC and the tripping current of
ETU40M
) with an LCD trip unit permits step by step setting from class 5 to
is automatically reduced to 87% of
R
3VL molded-case circuit breakers
System Manual, 03/2009, 110 0110 - 02 DS 01