38
In braking operation (voltage and current have different signs), with negative rated motor
speed, positive current, discontinuous current operation, without smoothing reactor;
Firing angle 143 degrees.
Measurement of current characteristic of line-side current:
During the positive half-wave
of the line-to-line line voltage, two positive current peaks occur, then a pause for the duration
of the current maximum value, then two negative current maximum values during the
negative half-wave of the line voltage. If the two positive or negative current maximum values
are missing, the thyristor does not fire.
The advantage of current measurement on the infeed side is that an AC probe can be used
for current measurement with the oscilloscope or recorder, which is more readily available
than a DC probe for measurement in the DC circuit.
The measurement can also be performed on the R805 load resistors (for current converters
in line phase U) and R806 (for current converters in line phase W) of the current converters
on the power interface module with an oscilloscope (measurement of voltage drop at the load
resistor).
Example below: Measurement current at point of transition from discontinous to continuous
current
U-Last (Motor)
-600
-500
-400
-300
-200
-100
0
0
2
4
6
8
10
Zeit in [ms]
U
in
[
V
]
Laststrom
-20
0
20
40
60
80
100
120
140
0
2
4
6
8
10
Zeit in [ms]
Id
c
in
[
A
]
Time in [ms]
Time in [ms]
Load current
Motor armature voltage
