Cause of fault and break down of electrical machine | Cause of fault and break down of motors | MAINTENANCE OF MOTORS/GENERATOR & CONTROL EQUIPMENT

 MAINTENANCE OF MOTORS/GENERATOR& CONTROL EQUIPMENT

➤ Introduction to Maintenance :

Maintenance is an activity carried out to

👉  to restore a machine /equipment/appliance to normal working condition
👉  to maximize availability &reliability
👉  to extend useful  life
👉  to improve the accuracy/performance
👉  to ensure safety of personal

➤ Classification of electrical m/cs :

For maintenance of any machine first we have to knowledge about classification of machine

➤ Statics machines : Transformers

 👉 No moving/rotating parts

 👉 Only electrical  losses

 👉 More efficiency

 👉 Less maintenance

 

➤ Rotating machines : Motors & generators

 

👉 Moving/rotating parts

👉 Both mechanical & electrical losses

👉 Comparatively less efficiency 

👉 More maintenance

➤ Cause of fault and break down of electrical machine :

Due to-

1. Mechanical wear-   friction

2. Electrical wear-    weakening of insulation

 

1. Mechanical wear-   friction

Parts which undergo mechanical wear

1       Bearings

2       Shaft, key way, key

3       Carbon brushes

4       Commutator

5       Slip rings

1. Bearings undergo mechanical wear due to

•       Mis -alignment-vertical/horizontal

•       Vibration-loose foundation

                        -Mis-alignment

                        -unbalanced rotor

•       Over load

•       High belt tension

•       Improper lubrication

•       Coolant/water/dust entry

•       Improper assembly

•       Wrong replacement

•       Improper design

•       Ageing

2. Shaft, key way, key

  • Sudden/jerky load,

  • Improper key size

  • Over load

   • Mis alignment

3. Carbon brush

Under goes mechanical wear due to

•       Heavy sparking- brush not in MNA

                                     - projected mica

                                     - overload

                                     - defective rotor

                                     - low spring tension

                                     -improper seating

•       Burrs on Commutator

•       Brush too soft

•       High spring tension

•       Inferior quality

4/5. Commutator/slip ring

 Under goes mechanical wear due to-

•       Heavy sparking

•       Spring tension too-high

•       Brush too hard

➤ Electrical wear (weakening of insulation resistance)

Causes:

•       Over heat- over load

                        - Over/under voltage

                        - Frequent starting

                        - Improper cooling

                        - High ambient

•       High voltage

•       Moisture absorption

•       Accumulation of dust/dirt

•       Exposure to chemicals

•       Ageing

➤ Effects of weak insulation :

Electrical faults :

•       Earth fault

•       Inter turn fault

•       Coil short

•       Shock

If any of the above fault occurs, the motor needs rewinding

Symptoms for failure:

•       Unbalanced current

•       Abnormal current

•       Abnormal sound

•       Abnormal smell

•       Abnormal heat

•       Abnormal mater readings

•       Abnormal vibration

•       Frequent tripping of mcbs/olr

•       Frequent fuse blowing

•       Low insulation resistance

     Neglecting the above symptoms may lead to major breakdowns

 

 

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