Siemens SINAMICS DCM Operating Instructions Manual page 102

Connecting
6.6 Measurement of the armature current
The values determined for the load resistances can be set by soldering additional resistors
onto the soldering lugs parallel to R701 and R704 and, if necessary, by pulling out R701 and
R704.
The influence of the magnetizing current can be taken into account in order to determine the
load resistances accurately. If the magnetizing current is not taken into account, an excess
current equivalent to "magnetizing current x number of turns" will flow through the cables
over and above the specified value.
The magnetizing current is determined as follows:
The secondary current of the current transformer must flow through its ohmic resistor (at
maximum operating temperature), load resistor, and any rectifier diodes connected in series.
This results in a calculable voltage drop at the rated current (sine-wave). This voltage (50 Hz
sine-wave) is then applied on the secondary side and the magnetizing current measured.
This value is then used to calculate R
It is also important to ensure that current transformers do not experience excessive
saturation in the event of an overcurrent, as the magnetizing current will increase
dramatically. It is also important to take temperature rise into account when operating at
permanent load.
Load resistance taking the magnetizing current into account:
I =
m
Parameter settings
p51822 =
p51823 =
p51824 =
p51852 =
100
Magnetizing current
Rated armature DC current
Load voltage at rated armature current
(on delivery = 1,000.0 mV)
1: Current transformers in phases U and V
2: Current transformers in phases U and W (on delivery)
3: Current transformers in phases V and W
4: Current transformers externally interconnected in a V-circuit
5: Actual current value signal, bipolar (external shunt)
0: Internal measurement of armature actual current value
1: Measurement of armature actual current value via X177.1/2
2: Measurement of armature actual current value via X177.3/4
3: Measurement of armature actual current value via X177.5/6
4: Measurement of armature actual current value via X177.7/8
.
B
Operating Instructions, 12/2018, A5E34888669A
SINAMICS DCM Control Module