#Variablespeeddrives #casestudy #preventivemaintenance #630 KW




 

During a break down of a 630 KW Ac drives, we observed the silicone gel leaked out from U phase IGBT’s. Silicone gels provide the dielectric insulation in insulated gate bipolar transistor (IGBT) power modules to prevent partial discharge, inhibit moisture ingress and keep out contaminants from the internal circuitry. The junction temperatures of these power modules are located between 150 o C and 175 o C and these temperatures will increase to 200 o C in the near future. I would like to share our observations of this particular case.

      

A.     Temperature sensors of all 3 phases found proper. Resistance was approx. 4.71 K ohms.

B.     Silicone gel leaked out from 6 IGBTS of U phase.

C.     Drive overheat protection was bypassed. So drive was not tripping at high temperature.

D.    Temperature sensing circuit’s track was damaged. So we replaced the gate drive board of particular section.

E.      Heat sink vents was completely choked. We cleaned it by forced air.

F.      We cleaned DC bus bars, capacitors, blowers, Ac bus bars, Power board.

G.    We observed heat sink compound of IGBT’s dried. Due to this heat generated was not dissipated to heat sink. We applied heat sink compounds to all IGBTs.

H.    We replaced all 8 IGBTS & assembled the VFD & enabled overheat protection. Took trail on 1000 Amps load. VFD working properly.

 

Conclusion:  Excessive temperature leads to leakage of silicone gel of the IGBT. Reason of excess temperature is choked heat sink & dried heat sink compound of IGBT’s.  Preventive maintenance of VFD is essential & it can prevent the failure in future.

         

Looking forward  to hear from  your views about this case study.

Web: www.endeavours.in

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