Motor Protection - Eaton DS7 Manual

2 Engineering

2.8 motor protection

2.8 motor protection
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DS7 Soft starter 09/16 MN03901001Z-EN www.eaton.com
The motor protection protects the three-phase asynchronous motor from
thermal overload due to a mechanical overload or the failure of the motor
cooling (fan) or the failure of a connection cable.
There are two basic ways of protecting the three-phase asynchronous motor
from overload during operation: By
• monitoring of current consumption (motor-protective circuit-breaker,
overload relay or bimetal relay),
• direct temperature monitoring in the motor winding (PTC, thermistor).
L1
L2
L3
PE
①
I > I > I >
②
③
M
3 ~
Figure 20: Possible motor protection variants
a Motor-protective circuit-breaker (PKZ, PKE, NZM) - disconnection with manual release
b Overload relay (ZB, ZEB) – here in combination with a contactor
c Overload relay (ZB, ZEB) for indication of the thermal overload –
can alternatively (①, ②) also be arranged on the mains side
d Thermistor, PTC or semiconductor contactor protection in the motor winding with external signalling relay (EMT)
￫
The combination of the motor protection variants ①, ② or ③
with the temperature monitoring variant ④ is also called full
motor protection.
M1
④