MarelliMotori MJB 250, Руководство по эксплуатации и обслуживанию

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ENGLISH
963857101_G
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4. INSTALLATION AND COMMISSIONING
Check before installation
Before installing the generator
- make sure that name plate data corresponds to the power supply and operating conditions and that the installation
complies with the manufacturer’s recommendations
- clean any protecting varnish from all connecting surfaces (such as surface of couplings and flanges and shaft
extension for two-bearing generators).
The single support generators come supplied with a bracket that holds together the coupling flange and the adapter flange or with
a bolt that blocks the rotor to the non drive side end-shield. Before installation, remove the bracket and/or the bolt.
Install the generator in a ventilated room. If installed in closed areas the alternators should have a possibility to exchange the cooling air
directly with atmosphere.
Air outlet and inlet openings should not be obstructed: provisions should be taken to prevent obstacles from obstructing ventilation
openings. The inlet of warm air should be avoided.
Provision should be taken to make inspection and maintenance easy when the generator is installed or during operation.
4.1 Insulation test
On the premises of the constructor of the group, if the alternator has remained inactive for a long period of time (more than one month)
it is opportune to execute an insulation test towards ground of the windings of the main stator, before putting it into service. Before
executing this test, it is necessary to disconnect the connections leading to the regulation devices (Voltage regulator or other devices).
The insulation resistance of windings to heart should be measured using a suitable DC instrument (“Megger” instrument or a
similar one), which output voltage (test voltage) is equal to 500 V for low voltage generators and not less than 1000 V for
medium voltage generators.
Reading of insulation resistance will be done after having applied Megger output for 1 minute to winding.
For a new generator, the stator winding insulation resistance larger of 100 M
Ω represent one of essential safety requirements.
Do not touch power terminals during and immediately after the insulation resistance check because the winding is in
voltage.
To measure the insulation resistance, proceed in the following way:
Concerning the windings of the main stator (see diagram), the insulation resistance measurement must be conducted taking care to
detach the connections leading to the regulation devices (voltage regulator or other devices) or to any other group devices. The
measurement is taken between one phase and ground with the remaining two phases also connected to ground (the operation must be
conducted on all three phases).
Concerning the exciter-stator, detach the + and – cables from the regulator and measure the insulation resistance between one of
these two terminals of the winding and ground.
Concerning the rotor windings, measure the insulation resistance between one terminal of the winding of the main rotor on the rectifier
bridge and the rotor ground (shaft).
The values measured are recorded. If in doubt, also measure the polarisation index. (§ 4.7)
In order to prevent risks of electric shock, connect the windings briefly to the ground immediately after measurement.
In order to be able to make a correct comparison of the measured insulation resistance values, they are referred to 20°C.
A correction coefficient is applied for different temperatures:
T
winding
(°C) T 15 20 25 30 35 40
K
correction
K
c
0.69 1 1.42 2 2.82 4
Example: R
mis
= 50 M
Ω
at the winding temperature of 30°C; (R
isol
)
20°C
= K
c
⋅
(R
mis
)
30°C
= 2
⋅
50 = 100 M
Ω
( )
( )
T
mis
c
C 20
isol
R K R
⋅ =
°