10/05 AWB8230-1541GB
Monitoring functions
115
Thermal overload
Using an electronically simulated bimetallic strip, the DF51
frequency inverters can provide thermal monitoring of the
connected motor. With PNU b012, match the electronic motor
protection to the motor’s rated current. If the values entered here
exceed the rated motor current, the motor cannot be monitored
with this function. In this case, PTC thermistors or bimetal contacts
in the motor windings must be used.
Adjust the current indicated by PNU d002 to the current drawn by
the motor The current indicated under PNU d002 forms the basis
for calibrating the electronic motor protection.
In PNU b013, set the overload protection according to the
applicable motor load.
.
Caution!
At low motor speeds, the output of the motor cooling fan
is diminished, and the motor may overheat despite its
electronic overload protection. You should therefore
provide protection with PTC thermistors or bimetal
contacts.
Figure 119:Overload protection
60
80
100
5 20 50 100
I
[%]
f [Hz]
b013 = 00
b013 = 01
PNU Name RUN b31=
10
Value Function DS
b012 Thermal
overload,
tripping current
– j 0.2 – 1.2 x Ie
[A]
1)
Setting range of the tripping current as a multiple of the frequency
inverter rated current, i.e. the range is given in amperes (A).
xx
b212
b013 Thermal
overload,
characteristic
(torque curve)
– j The electronic thermal protection of the motor in the low speed range can be increased to
improve thermal monitoring of the motor at low frequencies.
I
2
: Output current
01
b213 00 Reduced torque 1
01 Constant torque
02 Reduced torque 2
1) Frequency inverter rated current
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