Comments on Test Results
31
There are several things that can throw test results off so if
results don’t agree with design values, it is best to verify that
equipment and testing procedures are in order before draw-
ing any conclusions.
1.
Recheck test connections to make sure that they are
correct.
2.
Verify device settings and knob calibration. See Section
“Restoring Lost Calibration.”
3.
Return the knob to the previous setting making sure that
the pointer lines up accurately with the correct calibra-
tion dot (see Section “Static Trip Calibration Marks” and
repeat the test.
4.
If there seems to be error in the same direction for all
settings, the ammeter may be at fault. To check the test
set ammeter, connect an ammeter that is known to be
accurate to terminals 1 and 9 of the seven pin terminal
block select phase 1. Connect an external Variac to the
test set external input terminals and set the input power
selector switch to EXTERNAL. Check the ammeter at
several values of current on both the high and low
ranges. The two ammeters should agree within approxi-
mately 3% of full scale for all readings.
5.
If pick-up settings meet design tolerance and the time
delays do not, the stop clock may be a fault. This can be
checked against a stop watch. The tolerance should be
within 5 seconds in 5 minutes (300 seconds).
6.
As pointed out in the introduction, line voltage fluctua-
tions may cause timing errors. Watch the ammeter
during the timing intervals and adjust the current control
as necessary to hold the current constant.
7.
Electrical noise may interfere with the internal phase
control circuitry and can make testing difficult if not
impossible in some cases. An external Variac (Variable
transformer) can be used as a source for the test set by-
passing the phase control elements. This connection
may overcome some testing difficulties.
