Commissioning; Stator Winding Insulation Check Through Polarisation Index - MarelliMotori MJB 160 Nstrucciones Y Advertencias De Seguridad

Supply of leading loads only
It is possible to supply symmetrical leading three phase loads for a maximum (in KVAR) equivalent to 0,25 times the power (in KVA)
indicated on the nameplate.

4.7 Commissioning

Before putting into service it is necessary to check the insulation with a Megger at 500 Vdc after 1 minute of the application of the
test voltage.
For a new generator, the stator winding insulation resistance larger of 100 MΩ represent one of essential safety requirements.
ALREADY OPERATING GENERATORS OR AFTER PROLONGED PERIODS OF INACTIVITY THE MACHINE MUST
NOT BE OPERATED IF THE INSULATION RESISTANCE IS LESS THAN 30 MΩ AT THE TEMPERATURE OF 20°. In
this case, it is suggested to dry the winding previously to the generator star-up.
THE MACHINE MUST NOT BE OPERATED IF THE POLARISATION INDEX IS LESS THAN 1,5. (§ 4.8)
In order to prevent risks of electric shock, connect the windings briefly to the ground immediately after measurement.
BEFORE INITIAL START-UP, MAKE THE FOLLOWING CHECKS:
Mechanical checks
- If fixing bolts are securely fixed.
- That the alignment and coupling is correct.
- That the ventilation air is sufficient and that no impurities are drawn in.
- That the protection grids are in place.
- For single bearing generators, that the bolts of the disks are fixed with the correct torque.
Electrical checks
- The plant is provided with the correct electrical protection devices, according to applicable standards.
- That the connection to the terminal block is correctly performed (bolts of terminals properly tightened).
- That no misconnection or short-circuits are present between generator and external breakers: the generator is normally
not protected against short circuits on the connection between generator and external breaker.
In order to avoid any damage to current transformers and to the generator, all current transformers installed on the
generator have to be connected to proper loads: in case the current transformers were not used, they must be
shortcircuited.

4.8 Stator winding insulation check through Polarisation Index

Qualitative insulation resistance versus time curves:
It is possible to check the generator insulation condition by measuring the polarization index, according to IEEE 43.
Execute the insulation resistance measure and insulation resistance registration at ambient temperature and in different times: T1', T2',
..., T10'. Space the measures of a conventional time (one minute for example).
Insulation resistances have to be measured leaving the 500V DC of "Megger" instrument applied for the full duration of 10 minutes.
The comparison between 10 minutes insulation resistance (R
evaluate the condition of the machine winding insulation.
SIN.UM.805.6
Verify that:
Verify that:
isol20°C T10'
) and 1 minute insulation resistance (R
9
ENGLISH
) may be used to
isol20°C T1'
963857153_F