TROUBLESHOOTING
TESTING AND ADJUSTING
A circuit continuity tester, similar to the 8S4627 (circuit
continuity tester) can be used for checking low
resistance continuity. This tool can also be used to
check rectifiers and controlled rectifiers. It uses a 3-volt
battery source. This is all that is needed to activate the
gate of a controlled rectifier.
A Kelvin or Wheatstone bridge can be used to
measure the resistance of the revolving field and stator
winding of the generator or the exciter armature.
A 500 to 1000 volts megohmeter is needed to
measure the insulation resistance of the generator
stator, revolving field, exciter armature, and exciter field.
A DC ammeter with the correct current shunt is used
to measure the current of the exiter field.
A clamp-on volt-ammeter with a 0 to 600 volts and 0 to
600 amperes scales is used to measure line voltage and
line current. Some generators are rated higher than 600
amperes, but these units are normally connected with
two or more conductors in parallel per phase. To
measure line current for these generators, measure the
current in each conductor per phase and add the
currents together.
NOTE: See WARNING below, if generator is
rated over 600 volts.
A direct-reading tachometer is used to measure rpm.
When exact frequency control is needed, a direct
comparison can be made with outside line power.
On generators with higher than 600
volts rating do hot use direct-reading
test equipment to measure line
voltage or line current, (even though
the instrument has higher voltage
capacity).
Voltage
and
current
transformers with a high voltage
rating must be used. On power
circuits higher than 600 volts, direct-
reading meters CAN have failure of
insulation.
Where the same adjustments are necessary on two or
more units, (as in parallel operation) use the same
instrument for measuring all voltages.
In many of the following resistance test procedures,
the ohmmeter connecting polarity (positive or negative)
is given for testing the respective component.
NOTE: The identification of lead polarity on
ohmmeter instruments is not necessarily the
same.
POLARITY CHECK OF OHMMETER TERMINAL
1. Selector switch. 2. Selector switch. 3. Mark to
show polarity of ohmmeter cables.
Volt-ohm-milliameter cable polarity must be known.
The red, positive “+”, color on the cable of an ohmmeter
can be either positive (+) or negative (-) and
identification of each cable is needed.
A second volt-ohm-milliameter (multimeter) can be
used with the test ohmmeter to find the correct polarity of
the connecting cables.
Turn one instrument selector switch (1) to DC volts,
and turn the test ohmmeter selector switch (2) to ohms
(RX1). Connect the cables of both instruments together
until both instruments have a meter indication at the
same time. (Change the cables if necessary).
The red, positive “+”, lead from the instrument with
selector switch (1) on DC volts is connected to the
positive lead of the test ohmmeter. Put a mark on the
ohmmeter to show the polarity of the ohmmeter cables
(3). the correct positive and negative identification of the
cables has been made.
On the digital multimeter, the above procedure is not
necessary. Polarity is indicated on the readout.
For further information on using the digital multimeter,
see Special Instruction, Form SEHS7734.
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