Section 4. Configuration of the frequency converter
default 0.5 Hz). If par. 2.14 is set up on value "YES" par. 2.13 determines the blocking frequency. If value of
frequency decrease under level from parameter 2.13 blockade is activated (STOP). If frequency increases above the
limitation set with par. 2.13 will result in repeated start of a drive. The mode of switch on / off will be coordinated due to
the characteristic such as “loop of hysteresis” (see fig. 4.16).
SLEEP blocking of PID controller –
see section 8.
4.4.4. Thermal protections of the motor
4.4.4.1. Protection limit I
2
t
The built-in thermal model of the motor enables to calculate temperature of the motor in the theoretical way.
The Model is developed on the basis of the following assumptions:
the temperature of windings changes according to exponential law,
the electric motor achieves the maximal temperature for continuous work at a rated current
change of temperature depends on a ratio (I/In)
2
,
the constant of time of cooling for stopped electric motor is four times more than a constant of time of heating
during operation
Frequency converter MFC710 type. TWERD Power Electronics
39
Fig. 4.16 - Operation principal of blocking from “F STOP”
BLOCKING
STOP
START
fselected
Time
0
Par. 2.13
Fig. 4.17 - Definition of area of long operation (a),
Dependence of calculated temperature from motor's current (b) and (c)
I [%] In
f [Hz]
25 Hz
0
Par. 3.4
Par. 3.3
Area of long-time operation
I / In of the drive
Time
0
50%
100%
125%
Ts
Time
Constant of heating time,
par. 3.5
0
63%
100%
105%
b)
a)
c)
Current temperature of the
drive. Ts can be counted
with par. 0.9
