MegOhm meters..

laatsch55

laatsch55

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Ok guys, while checking the 100 horse moter at the WD yesterday wiyth a Fluke 1577 Insulation tester the moter was supposed to be fine. Before changing out wire today we put a 60 horse by the drive, hooked it up and had the drive ramp the motor up and down and no problems. Hooked up the 100 after the new wire and same thing, DC bus overvolt.

Question, it is a TEFC motor that has taken a few saltwater showers, there may/may not be salt deposits in the windings, it will roll the moter for a few seconds till it trips on DC overvolt then a reset of that fault results in not even one revolution. Let things cool down(the drive obviously because the moter has not made a hundred revolutions and is cool to the touch) and it will rotate a few more. further investigation reveals a VERY ROUGH drive end bearing so it appears the motor can be at rest in a place wher it megs ok but a slight movement of the rotor can cause a shorting....The drive is a Yaskawa A1000 and has been running for two months. Can a motor exhibit these symptoms and still have good windings??
 
Gepetto

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laatsch55 said:
Ok guys, while checking the 100 horse moter at the WD yesterday wiyth a Fluke 1577 Insulation tester the moter was supposed to be fine. Before changing out wire today we put a 60 horse by the drive, hooked it up and had the drive ramp the motor up and down and no problems. Hooked up the 100 after the new wire and same thing, DC bus overvolt.

Question, it is a TEFC motor that has taken a few saltwater showers, there may/may not be salt deposits in the windings, it will roll the moter for a few seconds till it trips on DC overvolt then a reset of that fault results in not even one revolution. Let things cool down(the drive obviously because the moter has not made a hundred revolutions and is cool to the touch) and it will rotate a few more. further investigation reveals a VERY ROUGH drive end bearing so it appears the motor can be at rest in a place wher it megs ok but a slight movement of the rotor can cause a shorting....The drive is a Yaskawa A1000 and has been running for two months. Can a motor exhibit these symptoms and still have good windings??
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You sure the bad end bearing isn't leading to run-out that could have worn through a winding on the stator due to contact?
 
laatsch55

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No I'm not Joe. But the good reading on the MO meter would suggest the windings are good. Phase to phase was 550MO, phase to ground on all 3 were 550 MO, resistance phase to phase was .3ohms.... I wasn't running the MOmeter, a tech from Weatherford was, she was in the area and came over to do it....the homeliest woman I have ever seen in the oilfield...after unhooking the motor output wires from the drive after the failed attempt to drive the motor, we got 185 ohms to ground on 2 legs, 55MO on the other. This was after the motor had rotated....but could not get consistent reading after that...
 
laatsch55

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She had a wonderful attitude, kinda bad when a roustabout knew more about their drives than one of their techs did....
 
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laatsch55 said:
No I'm not Joe. But the good reading on the MO meter would suggest the windings are good. Phase to phase was 550MO, phase to ground on all 3 were 550 MO, resistance phase to phase was .3ohms.... I wasn't running the MOmeter, a tech from Weatherford was, she was in the area and came over to do it....the homeliest woman I have ever seen in the oilfield...after unhooking the motor output wires from the drive after the failed attempt to drive the motor, we got 185 ohms to ground on 2 legs, 55MO on the other. This was after the motor had rotated....but could not get consistent reading after that...
Click to expand...
I'm not sure how much clearance you have between the armature and the stator, but it can't be much. The closer they are, the more efficient the motor will be. You've got 185 ohms to ground on two legs. You say that there is a very rough bearing...could there be a foreign object that has found it's way between the armature and stator, shorting out the windings to ground? Joe mentioned the worn bearing leading to runout and wear...it is also possible that the bearing has too much play in the axis perpendicular to the armature, causing rubbing and ruin...The only way you're going to know for sure is to pull it apart.
 
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