SIEMENS
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Siemens MD 50.8 · 2017
Motor options
Electrical design
Motor protection
6
■
Temperature sensor
The temperature sensor is a
positive temperature coefficient
(PTC) thermistor which offers comprehensive protection against
thermal motor overload. The temperature of the winding can be
accurately monitored thanks to its low thermal capacity and the
excellent heat contact with the winding. The PTC thermistor
exhibits a sudden change in resistance when a rated response
temperature is reached.
A tripping unit is used to evaluate the change in resistance and
to open auxiliary circuits via auxiliary contacts.
The switching hysteresis of the PTC thermistor is low, which
facilitates fast restarting of the drive. Motors with this type of
protection are recommended for heavy duty starting, intermittent
duty, extreme changes in load, high ambient temperatures,
or fluctuating supply systems.
In order to prevent serious damage by impulse voltage peaks to
the sensor and the downstream evaluation electronic circuitry
which can occur in inverter operation as a result of the close
contact between PTC thermistor and winding, the connecting
cables and the PTC thermistor have reinforced insulation
designed to provide "protective separation".
Fig. 6/1
Connection circuit diagram
Fig. 6/2
Temperature sensor characteristic
■
Temperature switch
The temperature switch is a
winding thermostat
(NC contact)
and is suitable as a protection device for slowly increasing motor
temperatures. When the rated response temperature is reached,
it can open an auxiliary circuit. When the motor temperature
decreases, the winding thermostat closes again as soon as the
temperature falls significantly below the rated response temper-
ature.
When the motor current rises quickly (e.g. with a locked rotor),
these switches are not suitable due to their large thermal time
constants.
The temperature switch provides safety isolation in accordance
with EN 61800-5-1 up to max. 500 V.
Fig. 6/3
Connection circuit diagram
Fig. 6/4
Temperature switch characteristic
Order code:
PTC thermistor for disconnection
M10
PTC thermistor for warning and disconnection
M11
=1TP1
P1
=1TP2
P2
1TP1
PE
-
1TP2
1
2
-M
01
1TP1
02
1TP2
1TP1
1TP2
G_D087_XX_00136
R
J
NAT
–20K
1TP1
1TP2
4000
Ω
1330
550
250
–20°C
J
NAT
–5K
J
NAT
J
NAT
+5K
J
NAT
+15K
G_D087_XX_00005a
Order code:
Winding thermostat for disconnection
M12
Winding thermostat for warning and
disconnection
M13
G_D087_XX_00135
=1TB1
P3
=1TB2
P4
1TB1
PE
-
1TB2
~2
~1
-
-
-M
03
1TB1
04
1TB2
1TB1
1TB2
35 °C
NAT
t
G_D087_EN_00006a
Warming-up
time
t
Disconnection time
Cooling-down
time
t
Cool. max.
© Siemens AG 2017