Reasons for Developing Electrical and Magnetic Fault.

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Reasons for Developing Electrical and Magnetic Fault.

Q.Give the reasons for developing electrical and magnetic fault.

Reasons for Developing Electrical and Magnetic Fault.
Electrical Faults :

Sr. No.

Faults

Reason

Remedial measures

1

Wrong electric connections

Field winding connections may be
wrong. Field-Armature winding connections might be wrong. 3-phase motor phase
sequence connection R-Y-B may be wrong.

Check the connection. Check direction
of rotation. Interchange connections for proper working.

2

Contact, connections opening.

Dry soldering, improper and loose soldering
of joints. Melting of contact. Break due to opening of soldering.

Resolder the joints etc. clean the
contacts. Dry soldered joints be opened are again to be joint.

3

Damaged Insulation

Over voltage stresses, long running,
overloading, entry of moisture.

Dry the insulation. Check voltage, reduce
load. Stop the machine intermittently for some time.

4

Commutator darkning, Burning

Due to dirt/ Dust accumulation. Offering
low resistance path to the flow of current from positive brush. Improper
brush tension on commutator or on the sliprings. Shape less brushes creating
gap between brush and commutator surface/slip- ring surface.

Clean the commutator. Adjust and check
the brush tension. Replace shape less brushes.

Magnetic Faults :

Sr. No.

Faults

Reasons

Remedial Measure

1.

Misalignment of poles

Due to mechanical injuries, blows, wrong storage of machine sometimes
distance between pole is disturbed. Pole fitting with nut-bolts may not
proper. This disturbs flux distribution.

Necessary alignment should be done be. Nut-bolt fitting should be
proper.

2.

Loose Poles

Due to excessive vibration created by abnormal speed, loose foundation
fittings. The poles become  w.r.t. yoke.
This disturbs flux-distribution.

Steps be taken to correct the position and make tight fitting of
poles with yoke.

3.

Non-uniform air-gap

If rotating part is not true then it creates a non uniform air-gap.

Make true the shaft of rotor or replace it.

4.

Abnormal heating of core.

Magnetic losses increase if there is gap between stamping of core,
core insulation damaged, over heating of insulation due to overload or excessive
voltage. This results in non-uniform flux distribution.

Tighten the core stampings Adjust the voltage to its normal voltage,
load the machine properly avoiding overloads.

5.

Warped and dented core and burns.

At some spots the insulation on the core is burnt, causes sharp rise
of losses in core.

Necessary repairs, rewarnishing core. Replacing same stampings and
re- coring.

 

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