REF 542plus switchbay protection and control unit
Manual Part 3: Installation and Commissioning
1VTA100004-en DMS,2001-10-04
REF542
plus
: Installation and Commissioning
35 / 80
5.5
Determining the transformer direction
The connection of the measuring inputs and the correct polarity of the current and
voltage transformers or sensors is very important for distance, comparison and direc-
tional functions.
In addition to testing the polarity, the transformation ratio and the magnetizing charac-
teristic, the wiring of the transformers/sensors must also be checked during these
test.
5.5.1
Current transformer
The transformers must have a positive winding.
This can be easily checked with a 9 V battery and an analog DC voltmeter. If the pri-
mary coil of the current transformer is connected to the battery, the analog voltmeter
connected on the secondary side must show positive. When the battery is discon-
nected, the voltmeter must measure a negative impulse.
The positive terminal of the battery must be connected to P1 of the primary coil and
the positive input of the voltmeter to s1 for this test. The same applies for the negative
terminal at P2 of the primary coil and the voltmeter negative input at s2 of the secon-
dary coil.
The test setup for checking the direction of a core is shown in the following figure.
V
+
–
+
–
P2
P1
1s1
1s2
2s1
2s2
3s1
3s2
Figure 16:
Setup for the polarity test of current transformers
This polarity check, also referred to as patch test, must be run for every core. To
guarantee correct operation even with a multi core current transformer with different
cores such as protection and measuring cores, it is recommended that the magnetiz-
ing characteristic (hysteresis) be recorded. A Variac with appropriately high voltage is
connected to the secondary terminals. The flowing current is measured while the out-
put voltage is rising. The characteristic of the measured values, voltage over current,
yields the magnetizing characteristic of the core, which can then be compared with
the manufacturer's data.
The transformation ratio of the current transformer cores is checked with a special
primary current feed device. The feed device is primarily connected to the current
transformer and the secondary value is measured at the secondary terminals of the
transformer or at the protective cabinet with an ampere meter.
