Motor Start Protection; Setting Parameters - ABB REF542plus Manual

4.2.1 Setting parameters

1VTA100114-Rev. 04 en
Valid from Version V4D02
Multifunction Protection and Switchgear Control unit REF542plus
Manual: Motor Protection with ATEX-Certification

4.2 Motor start protection

Overloading of the motor may occurred if the duration of the starting process is ex-
tended due to heavy load condition. The startup behavior is impacted by the con-
nected load. Such overloads are normally more critical for the rotor (rotor-critical mo-
tors) than for the stator. Manufacturers of the motor usually specify a permissible cur-
rent / time starting integral I
cate the magnitude of the maximum permissible starting current and the maximum
permissible starting time.
The current/time starting integral is proportional to the thermal short-time loading of
the motor. It is derived by integrating the current curve i(t) into the time interval from 0
to T :
starting
T
Starting
∫
2 ⋅ =
I T t i (
0
Where:
I: Admissible starting current
T: Admissible duration of the motor start
i(t): Current as a function of time t
In order to simplify the calculation process, it is assumed that the starting current dur-
ing heavy startup until the generation of the fast tripping is constant. Under this condi-
tion, the above equation can be approximated by the equation below:
2 2
⋅ =
I T I T
Starting
where:
I Motor startup current
starting
T Motor startup time
starting
The motor start protection function in the REF542plus can therefore supervised the
motor startup behavior for temperature overload conditions using the calculation
method based on equation (2). The current/time starting integral is calculated as soon
as the preset response value of the starting current is exceeded within the first
100 ms during the motor starting process. The tripping signal is generated if the cur-
rent/time starting integral exceeds the specified value of I
A startup is registered if the motor current changes from values below 0.10 of the
rated motor current up to values above the preset threshold value of the starting cur-
rent within 100 ms.. The starting signal is reset again as soon as the motor current
falls below the preset threshold value of the starting current. If the motor current drops
below 0.10 of the rated motor current, the motor is assumed to be at standstill. This
definition is necessary for determining the thermal model later.
For operation, the parameters need to be set as shown below the following illustra-
tion:
PTMV, 19.01.05
2
for their motors. Alternatively, a special note may indi-
T
2
) dt
Starting
(1.)
(2.)
2 T.
Motorprotection 12 / 66