16
Current peaks can also be caused by commutation problems on old motors. On old motors
set p50157 = 1 and p50158 = approx. 0.04 seconds.
Even a weak network can cause current fluctuations if the undervoltage threshold p50351 is
reached when the automatic restart time p50086 is set to a value greater than zero. For test
set p50086 = 0.
Motor speed oscillates when stopping in the opposite direction via:
This is due to the I-component of the speed controller; because it must first integrate down
toward zero, this must cause overshooting in the other direction of rotation.
Remedy: Activate automatic switchover to P control for low speeds. Setting:
Set switchover threshold p50222 = 2 to 5 %. The content of the binector, the parameter
number of the binector set in p50698 must be 1, e.g. set p50698 = 1. You can selectively
activate automatic switchover with this binector selection, for example, to suppress it during a
positioning action.
The motor produces no torque although the necessary armature current is flowing:
Check the current load current with r50019 and measure with an ammeter, any deviations
may point to a fault in SINAMICS DCM. Check current controllers, load resistors (R805
phase U, R806 phase W, see Section 6.4 Operating Instructions) of the current
measurement, check voltage drop at the load (device-specific and dependent on p50076[0]).
Possible fault on the Power Interphace Board.
Perform trace recording.
Check field supply, measure field current and if existent, measure field voltage. If field current
OK and field voltage not OK, an interturn fault in the field winding, which means that the
motor flux is too small could be the cause.
Approx. 25% deviation from the rating plate data for the motor field as a function of the
winding temperature is normal.
Any ground fault of the field winding can have a similiar effect.
Check armature circuit of motor.
Measure insulation resistance field circuit and armature circuit.
Motor does not reach voltage:
The SINAMICS DCM device only generates so much output voltage that the current actual
value does not exceed the set current limit.
The motor voltage is proportional to the product of speed and motor field (flux Phi: ). If the
speed is low for the rated flux of the motor, a relatively low motor voltage will result.
However, if the speed is high and practically no motor flux exists, for example, because of
a fault in the field winding, in this case, too, a low motor voltage will result. The physical
relationship is explained below.
Motor turns several percent too slowly when an analog tachometer is used:
The high-resistance input for the analog tacho (terminal 103/104) may mean that the load on
some tachometers is too low and so therefore output a voltage that is too high compared with
the rating data. As a remedy, an additional base-load resistor can be placed parallel to the
tacho output – observe the rating plate data on the tachometer.
Module replacement:
Before installing the replacement module, compare its part number with the old number.
C98043-Axxxx-Ly-zz; xxxx: Number of the module, e.g. 7100; y: L number.
The number up to the L number y must be the same. The version zz of the module is
irrelevant; all previously supplied versions of the module bearing a part number identical up
to the L number are compatible.