Insulation Resistance; Safety Instructions; General Considerations; Measuring The Stator Winding - WEG GPW Series Installation, Operation And Maintenance Manual

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4.5 INSULATION RESISTANCE

4.5.1

Safety instructions

DANGER
Before measuring the insulation resistance,
the alternator must be stopped and
disconnected from the charge and the
voltage regulator disconnected.
The winding being tested must be
connected to the frame and to the ground
for a period until removing the residual
electrostatic charge.
Failure to observe these procedures may
result in personal injury.
4.5.2

General considerations

When the alternator is not immediately put into operation,
it must be protected against moisture, high temperature
and dirt, thus avoiding damages to the insulation.
The insulation resistance of the windings is measured
before commissioning.
If the environment is too humid, it is necessary to check it
periodically during storage. It is difficult to determine rules
for the real value of the insulation resistance of a
machine, since it varies with environmental conditions
(temperature, humidity), conditions of machine cleaning
(dust, oil, grease, dirt) and quality and conditions the
insulating material used.
The assessment of the periodic monitoring records is
useful to conclude whether the alternator is able to
operate.
NOTE
The insulation resistance must be measured
using a MEGOHMMETER.
4.5.3

Measuring the stator winding

The test voltage for the stator windings of the alternator
must be as per Table 4.1 in accordance with standard
IEEE43.
Table 4.1: Voltage for measuring the insulation resistance
Rated voltage of the
winding (V)
< 1000
1000 - 2500
2501 - 5000
5001 - 12000
> 12000
Before making the measurement on the stator winding,
check the following:

If all cables are disconnected from the charge;

If the voltage regulator is disconnected.

If the alternator frame and the windings not measured
are grounded;

If the temperature of the winding was measured;

If all temperature sensors are grounded.
The measurement of the insulation resistance of the
stator windings must be done in the main terminal box.
20 l Installation, operation and maintenance manual
Insulation resistance test
Continuous voltage (V)
500
500 -1000
1000 - 2500
2500 - 5000
5000 - 10000
The meter (megohmmeter) must be connected between
the alternator frame and the winding. The frame must be
grounded and the three phases of the stator winding
remain connected to the neuter point, as shown below:
Figure 4.5: Measurement on the three phases
When possible, each phase must be isolated and tested
separately. The separate test allows a comparison
between the phases. When a phase is tested, the other
two phases must be grounded on the same ground of
the frame, as shown below.
Figure 4.6: Measurement in separate phases
4.5.4 Measurement on the winding of the
rotor, exciter and accessories
Measurement on the rotor winding:

Disconnect the cables of the rotor from the diode
cluster;

Connect the insulation resistance meter
(megohmmeter) between the rotor winding and the
shaft of the alternator. The measurement current
cannot pass through the bearings.
Measurement of the stator winding of the main exciter.

Disconnect the power cables from the exciter;

Connect the insulation resistance meter
(megohmmeter) between the exciter stator winding
and the alternator frame.
Measurement on the rotor winding of the main exciter.

Disconnect the cables of the exciter rotor from the
diode cluster;

Connect the insulation resistance meter
(megohmmeter) between the rotor winding and the
shaft of the alternator. The measurement current
cannot pass through the bearings.
Measurement of the stator winding of the auxiliary exciter
(PMG) - alternators model GP-:

Disconnect the cables that connect the auxiliary exciter
to the voltage regulator;

Connect the insulation resistance meter
(megohmmeter) between the stator winding of the
auxiliary exciter and the alternator frame.
ATTENTION
The test voltage for the rotor, main exciter,
auxiliary exciter and space heaters must be
500 Vdc and 100 Vdc for other accessories.
It is not recommended to measure the
insulation resistance of thermal protectors.
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