1 EMT6 Thermistor Overload Relays for Machine Protection
1.2 System overview
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EMT6
10/16 MN03407006Z-DE/EN
www.eaton.com
1.2 System overview
1.3 Description of device
To protect the machinery from overload, direct temperature monitoring
systems can be used in addition to current-dependent protective devices.
The EMT6 overload relays monitor the thermistor sensors used for
monitoring temperature and switch off the power relay in the event of
overheat in the machinery.
1.3.1 Direct temperature monitoring using thermistors
The motor current can also be used to monitor motor overtemperature in
addition to the indirect method of temperature monitoring. For this, the
motor manufacturer implements integral thermistors in the motor windings.
Apart from the sole purpose of motor protection, thermistors are also used
to monitor the temperature of motor and machine bearings. They are also
commonly used for temperature monitoring of heating systems, heating
circulation fans, in the windings of various sizes of transformers, for
generator protection as well as for monitoring gaseous or liquid coolants, and
temperature monitoring of non-electrical mechanical equipment.
Thermistors are step-action temperature sensors, also referred to as PTC
resistors or positive temperature coefficient resistors. Their resistance
changes sharply when a defined temperature is exceeded.
The thermistors are monitored by the thermistor overload protection relay
EMT6.
Figure 1: Overload protection relays EMT6,
EMT62 (left) and EMT6-DB, EMT6-DBK (right)
