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Testing Static Trip III Devices
The ZSI output is an isolated transistor that can be checked
with an ohmmeter, or by using a dropping resistor and
connecting both the devices positive and negative power
supply and detecting turn-on of the transistor with a voltme-
ter. This transistor turns ON when either SHORT TIME or
GROUND elements have picked-up.
A resistor of approximately 220 ohms should be used to limit
the current through the transistor during testing. Connect the
resistor from pin 3 to pin 8, connect pin 7 to pin 1 or 2.
Measure the voltage between pins 7 and 8.
To check the operation of the ZSI input circuit set the SHORT
TIME and GROUND TIME BANDS to .40, so that a difference
in timing can be detected. Open the SHORT TIME 12t SLOPE
switch. Run the time delay test as described previously, then
at the 15 pin connector connect pin 5 to pin 4 and pin 6 to pin
1 or 2 and repeat the timing tests. The time delay should then
change to the selected band.
If the 12t slope switch is are closed the incoming ZSI signal
will not change the time delays unless the current used in the
test is above the range where the SLOPE circuits affect the
delay.
Long Time Cool Down Tests (Thermal Memory)
The cool down integrator accumulates the LONG TIME signal
and provides a cool down function for the LONG TIME delay.
Closing the thermal memory switch disables the integrator
and allows the long time delay elements to reset whenever
the long time signal drops below pick-up. When the thermal
memory switch is open the long time delay elements are not
reset when the signal drops below pick-up, but is decreased
slowly with time
To check the operation of the circuit set LONG TIME PICK-
UP on .5 LONG TIME BAND on 1, close the thermal memory
switch. Apply 0.5 amperes to one phase input, allow the
device to time out, record the time. Open the thermal
memory switch and repeat the same test, again record the
time, it should be the same as the first test.
Repeat the test but this time momentarily lower the current
to 0.15 to 0.2 ampere for approximately 5 seconds every 10
seconds. Be very careful to not drop below 0.15 amperes.
Again measure and record tripping time, this should be
approximately the same as for the first two tests. Close the
thermal memory switch and repeat this test, in this case the
device should never time out, and it should be possible to
continue the cycle indefinitely.
Remote Indicator Output Tests
All STATIC TRIP Ill trip devices have a nine pin connector on
the front of the device to connect to the remote indicator unit.
If the remote indicator is available it can be used to test the
output signals, if there is a malfunction between the two
assemblies, substitution of either unit is the best field test to
isolate the defective assembly.
The output signal is a four bit, latched, parallel binary word
representing the calculated RMS current in the highest phase
that is provided to the remote indicator. This word is on pins
2 through 5 of the nine pin connector, with the following code:
Current, in Multiples of
Binary Word
Switch
Long Time Pick-Up
0000
0001
1
0.6X
0010
2
0.7X
0011
3
0.8X
0100
4
0.9X
0101
5
1.0X This is Long Time
Pick-Up Current
0110
6
1.1X
0111
7
1.2X
1000
8
1.3X
1001
9
1.4X
The connector also co 5 volts on pin 1 to power the
remote indicator. The negative or common line is on pin 9. Pin
8 is a signal called NOT RESET this signal is used to enable
the remote indicator and is + 5 volts DC when current above
approximately 100 milliamperes is supplied to the trip device,
below this input level none of the data is valid. All pins can be
checked with a voltmeter, while the current is adjusted as
desired, some dithering of the LED is normal and should be
ignored .
The remote indicator assembly decodes the number and
drives a light emitting diode bar display, to indicate the
magnitude of current. The indicator also contains a switch
and circuitry that selects any one of the current levels
indicated and closes a solid state contact when that level is
exceeded. The table lists the switch marking and the current
levels.
The solid state contact is rated 1 ampere max. 125VDC or
AC, nominal.
It is not necessary to operate the circuit breaker for any static
trip device tests. If it is desired to test the operation of the
circuit breaker, the tests can be run with the circuit breaker
closed and allowing the trip device to open the breaker.
