K
Knobhead
One thing before testing a motor is check the mechanical loading. I’ve had many an argument with fitters who insist the gearbox or what ever is free.
A classic being “Jock” (fitter) insisting the Radicon gearbox was free. I was doing pull ups on a set of 18” stillsons trying to turn the motor shaft. Jock insisted it was an electrical problem, fortunately the manager showed up before we came to blows.
In a production environment you will discover everything is an electrical fault. The conveyor motor won’t run, it’s got nothing to do with the tonnes of spillage burying it.
Bearings:
If the motor is still running use a long screwdriver as a stethoscope to listen to the bearings. Place the blade of the driver on the bearing housing or the motor end bell and put your ear against the end of the handle. A rumbling noise tells you all is not well. You can try a few shots of grease, if that doesn’t quieten it down then it’s time to get the spanners out.
With the motor stopped place a bar under the shaft and see if there is any “lift” in the bearing. With roller or ball bearings you shouldn’t be able to detect any. Sleeve bearings you may get a slight amount, I’m sorry but this is one where there’s no definite answer, experience is needed with them.
Electrical tests:
I was taught to use twice the terminal voltage for IR tests but some don’t agree with this. As for minimum values I use the M&Q test method. Where leakage current should not exceed 1/10,000[SUP]th[/SUP] of the FLC. This then takes in to account that a large motor has a lot more windings than a small one and therefore a higher leakage current. With a motor that’s been in service you can’t expect to be getting infinity readings.
A motor with an internally connected star point there’s only limited tests you can do. But there again they are cheap enough to be more or less disposable.
IR test:
Due to the internal star connection you can only test the windings to earth.
CR tests:
A to B, B to C, C to A. Compare each of the three readings, they should be within a few % of each other.
View attachment 11927
A motor with six terminals whether it’s connected star of delta can be tested the same way.
IR tests:
With the links still connected test to earth. With the links in one test covers all the windings.
Remove the links and test A1 to B1, B1 to C1, C1 to A1. This checks the insulation between the individual windings.
CR tests:
A1 to A2, B1 to B2, C1 to C2. Compare each of the three readings, they should be within a few % of each other.
If the motor tests OK then it’s time to look at the starter, isolator and supply cables.
A classic being “Jock” (fitter) insisting the Radicon gearbox was free. I was doing pull ups on a set of 18” stillsons trying to turn the motor shaft. Jock insisted it was an electrical problem, fortunately the manager showed up before we came to blows.
In a production environment you will discover everything is an electrical fault. The conveyor motor won’t run, it’s got nothing to do with the tonnes of spillage burying it.
Bearings:
If the motor is still running use a long screwdriver as a stethoscope to listen to the bearings. Place the blade of the driver on the bearing housing or the motor end bell and put your ear against the end of the handle. A rumbling noise tells you all is not well. You can try a few shots of grease, if that doesn’t quieten it down then it’s time to get the spanners out.
With the motor stopped place a bar under the shaft and see if there is any “lift” in the bearing. With roller or ball bearings you shouldn’t be able to detect any. Sleeve bearings you may get a slight amount, I’m sorry but this is one where there’s no definite answer, experience is needed with them.
Electrical tests:
I was taught to use twice the terminal voltage for IR tests but some don’t agree with this. As for minimum values I use the M&Q test method. Where leakage current should not exceed 1/10,000[SUP]th[/SUP] of the FLC. This then takes in to account that a large motor has a lot more windings than a small one and therefore a higher leakage current. With a motor that’s been in service you can’t expect to be getting infinity readings.
A motor with an internally connected star point there’s only limited tests you can do. But there again they are cheap enough to be more or less disposable.
IR test:
Due to the internal star connection you can only test the windings to earth.
CR tests:
A to B, B to C, C to A. Compare each of the three readings, they should be within a few % of each other.
View attachment 11927
A motor with six terminals whether it’s connected star of delta can be tested the same way.
IR tests:
With the links still connected test to earth. With the links in one test covers all the windings.
Remove the links and test A1 to B1, B1 to C1, C1 to A1. This checks the insulation between the individual windings.
CR tests:
A1 to A2, B1 to B2, C1 to C2. Compare each of the three readings, they should be within a few % of each other.
If the motor tests OK then it’s time to look at the starter, isolator and supply cables.
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