Cutler-Hammer HWT-500, Инструкция по эксплуатации

Страница: 19 / 45

I.B. 35-557
19 of 45
CN-33 SINGLE PHASE REVERSE CURRENT TESTS
Before commencing work, refer to the Safety Information.
Switch Positions
Network protector closed, breaker does not have to be in the automatic mode.
FUNCTION Switch – “RELAY” position
I & PV Switch – AI, BI, CI position
Supp VM Switch – CA position
PHASE switch – 180 position
Single PH Test Switch – A, B, C – must correspond to I & PV sw position
SUPPLY Switch – 216 or 480 position depending on network system voltage
VARIAC – zero position
This test requires that a BN dummy plate or BN jack plate be placed in the position of the BN de-
sensitizing relay.
Having previously determined the three-phase current trip value for the CN-33 master relay, the
single-phase value is determined by
1. Select the phasing switch to the 180-degree position.
2. Select the I & PV switch to the desired phase for current, e.g. AI, BI, or CI position.
3. Rotate the black handle of the single-phase selector switch from the OFF position to A
phase, or the same phase as selected on the I & PV switch.
4. Increase the VARIAC until the relay calls for a trip.
The typical single-phase values should be approximately three times the nominal three-phase setting.
For example, if your nominal three phase reverse current setting is 3.2 amps, then the single-phase
value should be approximately 9.6 amps.
You would repeat this test by changing the position of the I & PV switch as well as the single-phase
selector switch, ensuring that the I & PV selection matched the phase selected on the single-phase
selector switch. Repeat the reverse current test to cover all three phases.
Errors in current transformers (shorted turns or open windings) or errors in current transformer
external harness connections (reverse polarity) can be detected by use of this test. However,
nominal deviations of 5 percent can be expected in phase-to-phase comparisons.
When completed with the single phase testing, ensure that the single-phase test switch is turned to
the “OFF” position.