Table of Contents
Advertisement
Amperage should never exceed the
nameplate rating when running the intended
load. (Amperage may go above nameplate
momentarily when starting large motors.)
When measuring exciter field amps (Fl and
F2 leads) a D.C. meter is required. The
maximum field current under full regulator
forcing is 6.5 amps D.C.
MEASURING RESISTANCE
The generator windings can be measured
and compared to the values shown in the
service specifications.
Main Stator
The main stator winding resistance is very
low. A meter capable of readings in the
milliohm range would be required.
However, a standard V.O.M. can be used to
check for continuity, shorts, or grounds.
Example: With leads disconnected, a
measurement from T1 to T4 should be very
low (continuity most V.O.M's). Measured
from T1 orT4 to any other lead should be
infinite. Measure from the 'T' lead the
generator frame to check for grounds
(reading should be infinite).
Normal full load reading is approximately 3
amps.
The exciter stator resistance is measured by
disconnecting the Fl and F2 leads at the
regulator. Measure the resistance between
the leads (this value is 22-24 ohms on
standard generators). Measure from the
leads to the frame to check for grounds.
Note markings and disconnect the main
rotor leads (Fl leads and F2 leads) from the
rectifier assembly. Measure the resistance of
the main rotor winding. Compare reading to
value shown in service specification section
12. Measure from the leads to the exciter-
mounting bolt to check for grounds.
Exciter Rotor
Disconnect the exciter rotor leads at the
diodes (leave leads disconnected if
proceeding to check diodes). Measure
resistance between phases. Compare value
to service specification section 12. Measure
from the leads to the exciter-mounting bolt
to check for grounds.
TESTING DIODES (RECTIFIERS)
Diodes perform the function of an "electrical
check valve". They conduct in one direction
only and are used to "rectify" ac current into
dc current. To test, measure the resistance
first in one direction and then reverse the
leads and test in the other direction. The
reading should be high in the reverse
direction and low in the forward direction. A
shorted diode will read low in both
directions. An open diode will read high in
both directions.
NOTES:
1. Two different polarities of diodes are
used. The only difference is in the way the
device is mechanically placed in the case.
When changing diode, be sure the correct
polarity is used.
Refer to section 6 figure 6-34.
2. Some meters do not have enough voltage
output from their internal batteries to turn
the diode on (about 0.6 volts is required),
and the voltage can change with different
58
Advertisement
Table of Contents
