What Tests Required After Motor Re-wedge 2

[andrewwalsh]

We are planning to remove and replace the stator coil wedges on a 5400 HP 2/60/4160V Laurence Scott (UK) SCIM. What testing should we do prior to placing this motor back in service. Thanks in advance.
AWalsh

 

[edison123]

AC Hipot at least at rated voltage after rewedge. Check whether old wedges are magnetic wedges. If so, replacement wedges should also be the magnetic wedges to prevent excess no load losses and current.

 

[andrewwalsh]

Thanks Edison and yes, we are replacing magnetic wedges with magnetic wedges.

 

[aolalde]

To test the general condition of the machine winding:
Measure the Winding Resistance of each phase; it should be into 0.5% balance.
Do a core loop test and get the watt/kg core losses and check for lamination hot spots.
Before Attempting a High-potential test, ensure that the insulation is dry. Make an insulation resistance test (IR) and polarization index (PI). IEEE STD 43.
Finally make a Controlled DC Over-Voltage test (or step voltage test, IEEE STD 95) if possible to each phase and up to 1.25 to 1.5 of nominal line to line voltage. The initial step is 1/3 of the test selected voltage taking readings of leakage current at 1 and 10 minutes. Calculate the PI, if satisfactory (PI>2), increase in steps not larger than 3% of the final test voltage per 1 minute up to the final test voltage. Take readings of the leakage current and look for proportional leakage current increase. Sudden increasing changes of leakage current could be indication of breakdown.
If the test is made to each individual phase, connect to ground those phases not under test. After the each phase is tested, discharge to ground the winding tested at least for 1.5 hrs.

 

[powerjunx]

andrew,
5400HP is obviuosly a large machine.
Ways to test the stator winding wedges is;
1. Wedge tightness test, this apparently test the tightness of the stator winding free movement against the core slot.
i had encounter this problem on the past few years, which found out the looseness of the wedges, instead rewedging.. we dip down the stator core to the varnish tank to save down time and cost of maintenance..and it works!
but i never recommend this alternative, if you have time and money it is better to RE-WEDGE.

2.El-CID test(electromagnetic Core Imperfection Detection)
used to detect the whole stator core and winding integrity.
this would be follow after conducting wedge tightness test to ensure the good quality result.

i dont think other test would conclusively define the replacement option, since PI and hi-pot test quantitatively refers the machine suitabily and fitness thru taking insulation resistance, and refers the voltage withstanding of the winding insulation, respectively. BUT NOT WEDGE DEFECTS such as looseness and aging.

However, i agree to used such test after re-wedging works to ensure the quality and workmanship excellent!