!

SAFETY

FOR LIFE

Testing Fault Block Operation

!

WARNING: Hazardous voltage caused by back-

feeding transformers. Isolate potential transform-

 

ers from source bushings using potential transformer dead-break disconnect switches located on the source-side panel. Failure to do so will result in risk of possible contact with high voltage at the source bush- ings, which may cause death or severe personal injury.

T273.0

The operation of the fault block accessory can be checked by backfeeding a 500:5 (or other available ratio) current transformer, located in the primary loop of one phase of the preferred source high-voltage switch, from a variable 120 Vac source. The 500:5 ratio provides approximately 1 Amp of output test current for every 10 mA of input current. However, to eliminate error due to CT satu- ration, a separate metering CT and meter should be used to read the actual test current.

Test Circuit and Equipment

A suggested test setup is shown in Figure 22. If the control is equipped with the plug and receptacle accessory, use the existing cables to interconnect the motor operators of both high-voltage switches and the CT sensing circuits of the preferred source switch to the S control. If plugs and receptacles are not provided, wire the switches directly to the appropriate terminal blocks as shown in Figures 6 or 8.

S260-75-1

Test Procedure and Troubleshooting

Phase Minimum Actuating Current

IMPORTANT: When checking the phase minimum actuating current the ground fault sensing portion of the accessory must be disabled. Testing on an individual phase basis without disabling ground fault sensing will cause the accessory to activate at the ground fault level.

1.Disable the ground sensing circuit by shorting the ground fault resistor (Figure 22).

2.Set the inrush current multiplier at X1.

3.Close test circuit switches SW2 and SW3 to apply voltage to the control.

The preferred source high-voltage switch (HV1) will close.

4.Close test switch SW1 and slowly raise the test current until the FAULT BLOCK OPERATED light goes on.

The test current should be within the limits specified in Table 7. If FAULT BLOCK OPERATED light fails to come on at the expected level, proceed as follows:

A.Check lamp with LAMP TEST switch (S6).

B.Recheck calculations for proper meter reading.

C.Is ground resistor cleanly shorted out?

D.Did latch relay R1 transfer position?— lamp is only an outward indication of relay position.

E.Are all cable connections secure?

F. Voltage from Accessory Tie Board, Tab D to Ground, Tab L, should be approximately 15 Vdc, average, at actuating level. If observed voltage is approximately 6 volts too low, trouble is probably in the Trip Reset Board; if voltage is too high, trouble is probably in either Diode or Resistor Boards.

G. AC rms voltage from “IN” to “IA” (or whatever phase is energized) should be about 17 V at actuating level. If correct voltage is observed, the CT input is correct.

TABLE 7

Test Current Values for Fault Block Accessory

Figure 23.

020082KM

Actuating

Actuating Current Limits

Current

 

(Amps)

Setting

 

 

 

 

(Amps)

Minimum

Maximum

10

9

11

Disabling ground sensing circuit.

14

12.6

15.4

20

18

22

28

25.2

50.8

40

36

44

56

50.4

61.6

80

72

88

112

101

123

160

144

176

274

247

301

320

250

352

448

403

493

33