ABB DCS550 Series, Manual

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Fault tracing
3ADW000379R0501 DCS550 Manual e e
calculates the temperature rise of the motor. This is because the motor will reach its end temperature after
the specified time when starting to run the cold motor (40°C) with nominal current. This time is about four
times the motor thermal time constant.
The temperature rise of the motor behaves like the time constant which is proportional with the motor current
to the power of two:
) 1 ( 1 *
2
2




− = Φ
−
τ
t
Motn
act
e
I
I
When the motor is cooling down, following temperature model is valid:
) 2 ( *
2
2
τ
t
Motn
act
e
I
I
−
= Φ
with:
Φ
alarm
= temperature rise == [M1AlarmLimLoad (31.03)]
2
Φ
trip
= temperature rise == [M1FaultLimLoad (31.04)]
2
Φ
= temperature rise == Mot1TempCalc (1.20)
i
act
= actual motor current (overload e.g. 170%)
i
MotN
= nominal motor current (100%)
t = length of overload (e.g. 60 s)
τ
= temperature time constant (in seconds) == M1ModelTime (31.01)
As from the formulas (1) and (2) can be seen, the temperature model uses the same time constant when the
motor is heating or cooling down.
Alarm and tripping levels
Alarm and tripping levels are selected by means of M1AlarmLimLoad (31.03) and M1FaultLimLoad (31.04). If
the levels are exceeded either A107 M1OverLoad or F507 M1OverLoad is set. The motor fan will continue to
work until the motor is cooled down under the alarm limit. The default values are selected in order to achieve
quite high overload ability. Recommended value for alarming is 102 % and for tripping 106 % of nominal motor
current. Thus the temperature rise is:
− Φ
alarm
== [M1AlarmLimLoad (31.03)]
2
= (102%)
2
= 1.02
2
= 1.04 and
− Φ
trip
== [M1FaultLimLoad (31.04)]
2
= (106%)
2
= 1.06
2
= 1.12.
The temperature rise output of the model is shown in Mot1TempCalc (1.20).
Thermal model selection
The thermal models is activated by setting M1ModelTime (31.01) greater than zero.
Thermal time constant
Set the time constant for the thermal model by means of M1ModelTime (31.01). If the thermal time constant of
a motor is given by the manufacturer just write it into M1ModelTime (31.01). In many cases, the motor
manufacturer provides a curve that defines how long the motor can be overloaded by a certain overload
factor. In this case, calculate the proper thermal time constant.
Example:
The drive is designed to trip if the motor current exceeds 170 % of motor nominal current for more than 60
seconds. Selected tripping base level is 106 % of nominal motor current, thus M1FaultLimLoad (31.04) =
106 %.