
43
In the case of direct current cos is always equal to 1 (no reactive component, no effective
components)
Kilo, k is a factor of 1000; 1 kW = 1000 W.
Milli, m is a thousandth, 1 mA = 0.001 A
Note:
Before a measurement can be performed, the measuring device must be set to the
required measuring method (voltage, current, resistance) and the measuring range expected
for the measurement. Incorrect settings could damage the measuring device.
Measuring the resistance of power semi-conductors
The resistance of the power semi-conductors can be measured at the power terminals: input
and output. Please refer to the circuit diagrams of the power section in the Operating
Instructions; Section 6.4 for the armature circuit and Section 6.5 for the field circuit.
Note:
The following precautions must be taken before measuring the resistance:
1) Clear the line-side supply voltage of the power section
2) Check safe isolation from supply on the input and output of the power section of the
current converter
3) Disconnect the load at the output of the current converter
When measuring the power semi-conductor ensure that they are equipped with an RC
element (snubber circuit). For this, first charge (or reverse-charge if reversing the poles of the
ohmmeter) capacitor C of the circuit via the voltage source of the ohmmeter, this means that
for a certain initial time, a low-resistance display will result before the display shows the
actual high-resistance value. This resulting charging process is also an indication that the
snubber circuit is OK, so the manifestation of this effect can also be used to check the
snubber circuit.
Measurements at the power section for the armature supply:
Measure between all phases of infeed 1U1/1V1/1W1 and
between all phases of the infeed and oututs 1C1/1D1, and
between outputs 1C1/1D1 in both polarities of the ohmmeter.
Ideally, all measurements must show a high-resistance value of > 100 k .
Measurements at the power section for the armature supply:
Between infeeds 3U1/3W1, measurements must be high resistance in both polarities.
Between 3U1 and 3C and subsequently 3 D; measurements must be high resistance in both
polarities.
For 1Q field supply: Between 3W1 and 3C and subsequently 3 D, measurement must be
high polarity in one polarity of the ohmmeter and low resistance in the other.
For 2Q field supply all measurements must show high resistance.
The diode:
The thyristor:
Anode +
Cathode -
Technical current direction
from + to -
Anode +
Cathode -
Gate G
Technical current direction
from + to -