Insulation Resistance; Safety Instructions; General Considerations; Measurement Of The Stator Winding - WEG G Serie Manual De Instalación, Operación Y Mantenimiento

4.5 INSULATION RESISTANCE

4.5.1

Safety instructions

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

General considerations

When the alternator is not immediately placed into
operation, it must be protected against moisture, dirt and
high temperature, thus avoiding that the insulation
resistance
The insulation resistance of the windings must be
measured before entry into operation.
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 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 evaluation 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

Measurement of the stator winding

The test voltage to the stator windings of the alternators
must be as Table 4.1 in accordance with standard IEEE43.
Table 4.1: Voltage for measurement of the insulation resistance
Winding nominal
voltage (V)
< 1000
1000 - 2500
2501 - 5000
5001 - 12000
> 12000
Before measuring the stator winding, check the following:

If all load cables are disconnected;

If the voltage regulator is disconnected;

If the frame of the alternator and the windings not
measured are grounded;
 If the temperature of the winding has been measured;

If all temperature sensors are grounded;
The measurement of the insulation resistance of the
stator windings must be made in the main terminal box.
10680382 Installation, operation and maintenance manual – Synchronous Alternator – G line - Horizontal
Insulation resistance test
Continuous voltage (V)
500
500 -1000
1000 - 2500
2500 - 5000
5000 - 10000
The meter (Megohmmeter) must be connected between
the frame of the alternator and the winding. The frame
must be grounded and the three phases of the stator
winding remain connected to the neutral point, as shown
in Figure 4.3:
Figure 4.3: Measurement in the three phases
Whenever possible each phase must be insulated and
tested separately. The separate test allows the
comparison between the phases. When a phase is
tested, the other two phases must be grounded on the
same grounding of the frame, as shown below.
Figure 4.4: Measurement in separate phases
4.5.4 Measurement in the rotor winding,
exciter and accessories
Measurement of the rotor winding

Disconnect rotor cables of the set of diodes;

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 main exciter.

Disconnect the power cables from the exciter;

Connect the Insulation resistance meter
(Megohmmeter) between the stator winding of the
exciter (terminals I and K) and the frame of the
alternator.
Measurement of the rotor winding of main exciter.

Disconnect exciter rotor cables of the set of diodes;

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 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 frame of the alternator.
ATTENTION
The test voltage for the rotor, main exciter,
auxiliary exciter and space heater must be
500 Vdc and other accessories 100 Vdc.
It is not recommended the measuring of
insulation resistance of thermal protectors.
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