Siemens Energy & Automation, Inc.
40
9.5.2 Test Equipment
The following equipment is used for the functional tests.
1. Portable DC multimeter - volts, ohms, and amperes (analog
type preferred).
2. Insulation tester - 1,000 volt DC megohmmeter (“megger”)
battery operated amp probe AMB-4D or similar.
3. 9-volt battery NEDA 1604.
4. 100-ohm resistor, 1 watt minimum.
5. 20-ohm resistor, 5 watts minimum.
6. Battery clip and clip leads.
Ground or case internal insulation . . . . . . . . . .2500V AC rating
SCR reverse blocking voltage . . . . . . . . . . . .rating 1300V peak
SCR forward off state voltage . . . . . . . . . . .rating 1300V peak
Reverse leakage current and
forward off state leakage
current at room temperature
and operating voltage levels . . . . . .less than one milliamp
Gate junction typical resistance
range as measured with
typical multimeter ohms scales . . . .10 ohms to 50 ohms
Gate trigger voltage to switch on . . . . . . . . . . . . . . . . . .2V DC
Gate trigger current to switch on . . . . . . . . .100 milliamps DC
Anode circuit holding and
latching currents . . . . . . . . . . . . .300 milliamps to 1 amp
9.5.3 Basic SCR Tests
Make sure all power sources are disconnected from controller
and locked out before performing the following test. See figures
27 through 29.
Test 1 - Verify Gate Integrity
1. Disconnect gate circuit wires only from each gate terminal.
2. Use a multimeter to measure each SCR gate junction resis-
tance.
3. Connect one meter lead to gate terminal ‘TG.’
4. Check gate resistance both to power cathode terminal ‘T’
and to the auxiliary cathode terminal ‘TK.’ Typical readings
are 10 to 50 ohms. Open or short readings indicate a dam-
aged or defective SCR.
5. Repeat the measurements from ‘LG’ to ‘L’ and from ‘LG’ to
‘LK.’ All SCR’s in a controller should have similar values.
Test 2 - Verify Module Ground Insulation
1. Disconnect line ‘L’ and motor load ‘T’ power connections
from power terminals or thyristor module.
2. Use the megger 1,000V DC range to test between case
base or heat sink and each power terminal ‘L’ and ‘T.’ A high
megohm reading at 1,000V indicates 2,500V case insulation
is OK.
Test 3 - Verify Off State Blocking and Reverse Blocking Voltage
1. Disconnect the module anode to cathode power terminal
jumper (figures 27 - 29) to test individual SCR’s for reverse
blocking and forward off state voltage.
2. Connect the megger across anode ‘A’ and cathode ‘K’ termi-
nals of one SCR; set megger to 1,000V setting. A typical
reading of greater than one megohm indicates an accept-
able SCR and leakage current of less than one milliamp at
1,000V DC.
3. Reverse the meter polarity and repeat the step 2 measure-
ment.
4. Proceed to the other SCR in the module. Make the anode
and cathode meter connections and measure for both polar-
ities.
5. A short circuit or a measurement below one megohm prob-
ably indicates a defective SCR.
Hazardous voltage.
Will cause death or serious injury.
To avoid electrical shock or burn, discon-
nect and lock out all power sources from
controller before testing.
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