Materials:

1. Three-Phase motors (3) with internal faults for troubleshooting, 1/2 to 2 HP
   1. Motor #1:  Internal open winding in lead 8  (Open)
   2. Motor #2:  Internal high resistance connected from ground to lead 5 (Grounded)
   3. Motor #3:  Internal shorted windings, lead 7 tied to 6 (Shorted)

   

2. Multimeters and Megger
   1. Continuity tests
   2. Insulation tests

Motor #1

Purpose:
The trainee will troubleshoot a problem(s) in a three-phase motor created by the Electrical Power instructor.  Using the correct meters, the trainee will diagnose, locate, and verify the problem(s).
 
Procedure:
Troubleshoot the three-phase motor according to the given information.
 
Motor # 1 Situation:
Your supervisor pages and asks you to troubleshoot a motor taken off the production line that is causing down time.  He tells you that it will start and run for a short time before tripping the heaters on the starter.  The motor was connected 230 Volt 3 Phase.
 
Use the correct meters to troubleshoot the motor.  Show below on the diagram exactly where you find a problem, if any.  Use the correct terminology to describe any problems.

Motor #2

Purpose:
The trainee will troubleshoot a problem(s) in a three-phase motor created by the Electrical Power instructor.  Using the correct meters, the trainee will diagnose, locate, and verify the problem(s).

Procedure:
Troubleshoot the three-phase motor according to the given information.

Motor # 2 Situation:
Your supervisor pages and asks you to troubleshoot a motor that has been taken off the production line because it is running hot and sometimes trips the heaters or blows a fuse.

Use the correct meters to troubleshoot the motor.  Show below on the diagram exactly where you find a problem, if any.  Use the correct terminology to describe any problems.

Motor #3

Purpose:
The trainee will troubleshoot a problem(s) in a three-phase motor created by the Electrical Power instructor.  Using the correct meters, the trainee will diagnose, locate, and verify the problem(s).
 
Procedure:
Troubleshoot the three-phase motor according to the given information.
 
Motor # 3 Situation:
Your supervisor pages and asks you to troubleshoot a motor on the line that is causing down time.  He tells you that it blows fuses when the starter pulls in.
 
Use the correct meters to troubleshoot the motor.  Show below on the diagram exactly where you find a problem, if any.  Use the correct terminology to describe any problems.

Troubleshooting Motors Key

1. Motor #1 lead 8 open
2. Motor #2 lead 5 grounded
3. Motor #3 lead 7 tied to lead 6
4. Fuse blown at motor fuse block and same line fuse blown in feeder disconnect.

Quiz:  Troubleshooting Electrical Motors

1. When troubleshooting a three phase motor, if the check for open or shorted windings reads __________, a coil is shorted
   1. infinity
   2. zero
   3. either A or B
   4. neither A or B
      
      
2. A(n) ___________ circuit is a circuit in which current leaves its normal path and travels to the frame of the motor.
   1. open
   2. close
   3. grounded
   4. full
      
      
3. When troubleshooting an electric motor, which of the following meters is best for measuring the insulation resistance of the windings?
   1. Ammeter
   2. Voltmeter
   3. Ohmmeter
   4. Megohmmeter
      
      
4. When troubleshooting a possible problem with the stator windings of a three-phase squirrel-cage motor and with the power lines disconnected from the motor leads, what are the first two checks you should do using an ohmmeter?
   1. Check for an open rotor
   2. Check for an open stator
   3. Check for proper lubrication
   4. Check for a grounded stator winding
   5. Check the amp draw
   6. Check for motor shaft currents
   7. Check for a grounded rotor winding
      
      
5. When a motor has failed due to overloading, _____________.
   1. all motor windings will be blackened evenly
      
   2. there will be obvious damage to the insulation
      
   3. there will be isolated areas of damaged
      
   4. A, B, and C
      
      
6. Single phasing can be reduced by using the ___________.
   1. proper size dual-element fuse
   2. correct heater sizes
   3. both A and B
   4. neither A or B
      
      
7. Whenever more than _________% voltage unbalance is measured, the power company should be notified.
   1. 2
   2. 4
   3. 6
   4. 10
      
      
8. Voltage measured at the motor terminals should be ± ________% of rated value.
   1. 2
   2. 4
   3. 6
   4. 10
      
      
9.  If the meter below displayed 1.6 megohms, the 2&5 coil of the three phase motor is considered __________.
   1. good
   2. bad
   3. shorted to ground
   4. none of the above
      
      
10. If the meter below displayed 20 ohms, it indicates that the three phase motor ________.
    1. is good
    2. open
    3. has shorted coils
    4. is wet