Electrical Maintenance - DC Motor Maintenance

You know that electric motors can be divided in two main classes: AC and DC. This training film uncovers basic knowledge of direct current (DC) electric motors: how they work, main principles, functions, physical processes, construction, as well as preventive maintenance and troubleshooting. To understand what makes the electric motor turned, we will go through electromagnetic induction and current-carrying conductors. It will be useful for students, who just started learning electrical machines, and for experience electricians, who wasn't working with electric motors, to refresh their knowledge.
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Timeline:

Segment 1
00:35 PRINCIPLES OF OPERATION AND PARTS IDENTIFICATION
02:04 Motor Action
02:16 An Elementary Motor
02:22 Why Motor turns
02:35 Main Magnetic Field and Conductor
03:00 Commutator Segments and Brushes
03:35 How Motor turns
03:40 Magnetic Field and Magnetic Flux
04:15 Armature, Shift and Armature Reaction
04:31 Position of Neutral Plane
05:07 Sparking
05:46 Small Poles
06:44 Construction of Electric Motor
07:29 EMF and CEMF
07:59 Voltage Supply. Electromotive Force Induction
08:05 How Counter Electromotive Force are produced. Explanation
08:50 Parts of Typical Compound DC Motor
09:00 Frame
09:20 Field Pole Pieces
09:47 Shunt Field and Series Filed Coils
09:55 Interpole Coil
10:08 End Bells
10:24 Brush Rigging and Holders
10:38 Brush Tensioning Device
10:43 Brush Pigtail
10:54 Armature Shaft, Armature Core, Armature Windings and Commutator

Segment 2
11:45 IDENTIFICATION AND CLASSIFICATION
12:41 Illustration of Series Motor
12:59 Simple Schematic Diagram
13:36 Overspeed
13:49 Resistance and Current Flow
14:23 Shunt Motor
15:18 Compound Motor
15:44 Importance of Marking
16:00 Manual and Diagram
16:40 Nameplate
16:56 Motor Leads Marking

Segment 3
17:45 BRUSHES AND BRUSH RIGGING MAINTENANCE
18:31 Before you start
18:58 Common Source of Trouble
19:50 Sparking, Arcing and Heating
20:12 Commutator Problems
20:34 Cleaning the Motor is the first order in any Maintenance Procedure
20:49 Commutator Check
21:32 How Good Brush Looks
22:18 Brush Holders Check
22:38 Adjustment of Brush Holders
23:28 Maintenance and Repair Parts Manual
23:34 Preferable Distance from the Surface
23:50 Stagger of Rigging Adjustment
24:30 Sign of Wear
24:56 Brush Replacement
25:10 All New Brushes must be seated
26:57 Pressure Setting for Tension Devices
27:17 Brush Tensioning Scale

Segment 4
28:00 COMMUTATOR MAINTENANCE
28:38 How to reduce electric motor problems
28:47 Good-looking commutator
29:09 What to use to clean any commutator
30:07 Bearing end of the commutator and the area behind the risers for carbon dust and dirt
30:52 Threading and grooving
31:22 Low brush pressure, contamination or the wrong type of brush
31:58 About grooving in details
32:38 Damage commutator. Copper drag
33:01 What causes copper drag?
33:46 What is flashover and what causes it?
35:18 Extreme overload and sparking or arcing
36:09 Result of flashover
36:21 If you do or not do your job well
36:59 Preventive maintenance performed periodically and thoroughly will prevent flashover
37:11 Dirt and other type of contamination on electrical equipment

Segment 5
37:39 TROUBLESHOOTING
38:15 Identifying the problem
38:23 What you need to know about the motor to look for a ground
38:41 Insulation test for grounded motor
39:07 Locate the grounded parts
39:36 Where the ground can be happened
39:45 If raise the brushes off the armature
39:57 Series field check
40:13 Shunt filed check
40:28 Armature field might be grounded too. Check it!
40:56 Continue elimination process
41:24 Determining which coil is damaged
42:06 Check the circuits
43:51 If no readings
44:11 Difference in the readings
44:37 No reading on brush due to holder tension
45:54 Check the readings on the brushes after tension adjustments
46:05 When all brushes on the armature
46:44 A short circuit problem
47:56 If a fuse doesn't blow or the breaker doesn't trip the short will quickly become an open
48:09 Observation first

Segment 6
48:48 DISASSEMBLY AND ASSEMBLY
49:35 First remove the brushes and field coil leads from the brush rigging
49:54 Then mark the end bells and remove them
50:32 Now armature can be removed
50:50 Bearing removal technique
50:59 Inspection of commutator
51:31 Armature winding inspection
51:56 Armature banding check
52:04 Pay attention to condition of the insulation
52:08 Cleaning
52:26 Growler
53:26 Field poles and coils checking
54:15 Remove dust and dirt
54:26 Megatest
54:53 End bells checking and cleaning
55:00 Brush rigging and holders cleaning and inspection
55:38 Motor reassembling
57:47 Turn the shaft by hand. It should and must move freely
58:00 Bad bearing
58:28 Condition of brushes
58:48 Set the tensioning device
58:57 Take a ground reading on it and check it for opens
59:11 Summary
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Produced by NUS Corporation
A Halliburton Company
1980

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