ABB REF542plus - Setting the Temperature

Multifunction Protection and Switchgear Control unit REF542plus
Manual: Motor Protection with ATEX-Certification
Thus, the value for TCOverheat (the time constant for motor operation at overload
above 2 times the rated motor current) can be calculated on the basis of equation
(11.1). The temperature rise time constant TCNormal for non-rotor-critical motors
could, in principle, be chosen larger than the above temperature rise time constant. If
this parameter is unknown, however, the same value can be set, as it is safe to ex-
pect a timely tripping in this case. As experience has shown, the cooling-off time con-
stant while the motor is at zero rotation TCOff should be set within 3 times to 5 times
the value of TCNormal.
4.4.1.2 Setting the temperature
After the time constants have been determined, the thermal capacity needs to be de-
fined. For this purpose, it is necessary to define the maximum overtemperature for the
thermal memory respectively thermal capacity. According to [DIN1, DIN2] the condi-
tion for the environment temperature for operation is 40°C. The maximum overtem-
perature K for normal operation or the temperature of operation under nominal condi-
tion respectively, is given by the corresponding thermal class and the temperature
class according to the following table 2.
Table 2: Maximum overtemperature in K during normal operation at 40°C ambient temperature
Thermal Class Temperature Class
T1 T2 T3 T4 T5 T6
A 50 50 50 50 50 40
E 65 65 65 65 65 40
B 70 70 70 70 70 40
F 90 90 90 90 55 40
H 115 115 115 90 55 40
If, for example, a motor with a thermal class F and a temperature class T3 is certified,
so the allowable maximum overtemperature is according to the table above 90°K. As
a consequence, the environment temperature ϑ
U
respectively Tenv of the thermal
protection function must be set to 40°C and the nominal or rated temperature TMn
ϑ
Mn
to 130°C. The difference of above temperature respectively the maximum over-
temperature of 90°K or 90°C is equal to 100% thermal capacity. In general the trip-
ping of the thermal protection may be set at thermal capacity greater then 100%. Ac-
cording to [DIN1] the constant k may be selected up to 1.2. Consequently the thermal
capacity of 144% may be 144% before the tripping of the thermal protection is gener-
ated.
Table 3: Maximum overtemperature in K during short time overload operation at 40°C
ambient temperature
Thermal Class Temperature Class
T1 T2 T3 T4 T5 T6
A 120 120 120 90 55 40
E 135 135 135 90 55 40
B 145 145 145 90 55 40
F 170 170 155 90 55 40
H 195 195 155 90 55 40
1VTA100114-Rev. 04 en PTMV, 19.01.05 Motorprotection 22 / 66
Valid from Version V4D02