Current Transformer and Current Input
RTHC-SVD01B-EN 31
10. To perform the following test, you will need to use a digital voltme-
ter with a diode test function. With the transformer’s Phoenix con-
nector disconnected and the power off to UCP2, perform a diode
test across the corresponding pair of current transformer input
pins on the Starter module (header J5). The meter should read
from 1.0 to 1.5 volts for each current transformer input. Repeat
using the opposite polarity. The same reading should result.
Extreme errors suggest a defective Starter module. If the diode
voltage drops prove accurate, reconnect the transformers to the
Starter module and re-power the unit.
11. With the CTs reconnected to the Starter module, attempt a restart
of the chiller. As the compressor is started, and the inrush locked
rotor transient has passed, (locked rotor transient should last less
than one second) simultaneously monitor the actual compressor
phase current(s) (using a clamp-on type ammeter) and the volt-
age developed at the respective current transformer's termination
at the Starter module (using a digital volt-meter on a 0-20 VAC
scale). Refer to Table 4-3 for the compressor phase current to
output voltage relationship for each extension current transformer.
Using 4-3, look up the current that corresponds to the output volt-
age read by the voltmeter and compare to ammeter reading.
Assuming relatively accurate meters, the values should agree to
within 5%.
12. If the measured current and the output voltage from the CT agree
within the tolerance specified, the CT is good. If diagnostics, over-
load trips, or other problems potentially involving current sensing
continue to occur with all phase currents to the compressors veri-
fied to be within the normal range, then the problem is either with
the CT selection, Current Overload Settings #1 and #2, or the
starter module’s current input. Since the first two items were veri-
fied above, that leaves only the Starter module circuitry as an
issue. It is advisable to replace the Starter module.
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