Speed-Dependent Evaluation Of The Motor Current - Lenze i950 Commissioning Manual

Configuring the motor control
Motor protection
Motor overload monitoring (i²*t)
13.9.1.2

Speed-dependent evaluation of the motor current

WARNING!
Fire hazard by overheating of the self-ventilated standard motor
Possible consequence: destruction of system parts
▶ Protect self-ventilated standard motors especially at low speeds by sufficient cooling or
from impermissibly high motor currents. Carry out a speed-dependent evaluation of the
permissible motor current.
WARNING!
Fire hazard by overheating of PM synchronous motors
Possible consequence: destruction of system parts
▶ Please check for every individual case which r.m.s. value can be used to permanently oper-
ate the motor at standstill. In case of some motors, a derating I1/In < 100 % is required
when n1/nn = 0 %. This serves to prevent an overload of individual motor phases as their
power loss doubles with continuous DC current load. (It is called DC current load as the field
frequency amounts to 0 Hz at standstill.)
When you select a Lenze motor from the catalogue and transfer its parameters
into the i700 servo inverter a typical characteristic is automatically set for the
selected motor. A deviating parameterisation is only required if the motor is
operated in ambient conditions which demand a general derating. Example: use
in site altitudes > 1000 m. In case of motors of other manufacturers, the operat-
ing points have to be parameterised based on the data sheet information.
By selecting a characteristic, the permissible motor current is evaluated depending on speed
for calculating the thermal motor utilisation. For this purpose, up to four operating points on
the S1 characteristic of a motor can be used.
The S1 characteristic can be found in the technical data sheet/catalogue of the respective
•
motor.
The representation in the objects /characteristic is carried out as relative values with refer-
•
ence to rated values.
The speed-dependent evaluation of the permissible motor current can actually be switched
off by parameterising all 8 characteristic points to "100 %".
Operating points
①
②
③
④
268
Standstill n01-I01
Reference point n02-I02
Rated point (n03=nN)-(I03=IN)
Field weakening n04-I04
For motors, this operating point is often descri-
bed with the no-Io values.
If the value falls below the speed n02, a derat-
ing in the current is required because:
• the motor cooling of self-ventilated motors
deteriorates considerably.
• a DC current load causes an increased power
loss in a winding.
• For motors, this operating point is also
described with the no-Io values.
Rated values of the motor are the reference for
2
all operating points of the i xt monitoring.
This operating point should be parameterised
irrespective of the use in the current applica-
tion.