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Case Study What could go wrong During Lubrication of HT / LT Motors
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Hello Friends / Sirs, The Today I am going to present a Case of Induction Motor, which might be rare in Industries. Hence want to share the experience, so that the problem they faced must not be faced by others or can be avoided. In a plant, there was a HT Slip Ring Induction Motor in which there was a Motor of 2000 KW, 6.6 kV & 988 RPM. The motor was commissioned in 2011 and was running well till when we found out some issues. After running for more than 1.0 year, approx. 2000 hours (1.5 years), it was time to do Relubrication of bearings of both DE and NDE Side. Technician went for it and started greasing the motors from greasing inlet on Both DE & NDE Side. On NDE Side it greased 8 pumps of grease gun. But when he started greasing on DE side, after 2 pump grease started coming back out of greasing inlet. So we went and checked again what was happening. We tried it too with force but the grease was coming back out of inlet. But as the plant was running we couldn’t do more. We also look for possibility, if the greasing inlet was left open or inlet cover got missed and some foreign materials might have gone inside the inlet as the greasing inlet was found not covered during checking. Due to production demands, we couldn’t do much for next 4 months despite monitoring the DE Side bearing temperature closely. After 4 months we got a 6 day planned shutdown So during this 6 day shutdown we planned to check what is the exact issue in the DE Side greasing inlet. Shutdown started on 3rd day of shutdown we got to check our motor DE side after it was decoupled. We knew greasing is not going into bearing through greasing inlet. We thought obviously some foreign material has entered into Greasing inlet, as greasing inlet was not covered.
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So we started removing unwanted material from greasing inlet through fine stick and tools which we had. But after removing what could have been visible we started greasing again, but the problem persists. Now we brought drill machine to remove the foreign particles, which has become the Headache in last 12 hours. When drill bit went inside and started drilling, to our surprise drill bit got damaged and broken. Now everyone was surprised. What can be inside which can break the drill bit? We removed that broken drill bit. Now we started soft hammering on the outer side of End cover near greasing inlet, so that the foreign particles move out or change its position (Soft hammering to avoid damage to end cover of HT Motor) after trying it for 4 hours nothing happened. One of my senior with -around 17-18 yrs of experience took the End cover and hit it with ground with greasing inlet down (Hit was more than soft and less than hard). And what come out of the greasing inlet surprises everyone. “It was a broken piece of Drill Bit” not the one which was broken by us. Now we check whether the greasing hole is through or not, and yes it was not through. We got / assumed what could have happen during manufacturing of End Cover for this HT motor. The workman might have been drilling hole for greasing and the drill bit might have broken during that. Instead of telling his seniors, they kept as it is and packed Motor with good amount of grease in it, so it can run for couple of years freely. He would have thought it, Let it go as who checks “Greasing Inlet” during commissioning also motor is kept around 6 – 8 months at site Packed before commissioning and it take around one month for commissioning. And Engineer will do greasing in Motor obviously after 2000 hours till that timer around 2 years will be gone.
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Now the problem was over. We make the inlet grease through, so that grease can go to bearing. Fixed the motor, coupled it, trial taken and greasing done. (Sigh of relief at 3 AM Midnight) We knew what was Maintenance Engineers next target, to check if the same problem is there in rest of motors were greasing nipple is there.
We (Maintenance team) mostly believe that “Whatever OEM has done, might have done as per design�, but the above case was saying something else, mistakes can happen from OEM too and that’s why maintenance engineer are there to correct it. Also we must make a maintenance practice to cover Motor grease inlet to avoid entering of foreign materials into grease inlet.
Below is the Pictorial Representation of HT Motor for Better understanding.
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+91-265-2225137