Power ground cases.

There have been a few line failure cases due to power ground.

Details of Power ground cases are given below:

Year	L	N	M	S
2009-2010	10	8	5	6
2010-2011	8	7	3	7

Sheds are requested to take following steps to control power ground cases en route.

ROTATING MACHINES:-

Ø  Check the IR Value; it should not be less than 1 mega ohm for individual circuits separately.

Ø  Generator components should be free from dust and oil.

Ø  Check the commutator surface condition & condition of mica depth.

Ø  Check chamfering of commutator segment and sign of copper spreading.

Ø  If  attention is required due to poor TG condition on above accounts then,

Ø  Initially cut mica up to 2.5 mm depth.

Ø   Then chamfering of the commutator segment should be done.

Ø   After chamfering rub hacksaw blade inside mica depth one round for clearing the copper dust trapped between the segments.

Ø  Check the IR value of armature it should be more than 1 mega ohm.

Ø  Check the IR Value of the inter pole as well as excitation field. Check the IR value of starting field and excitation field.

Ø  Check the carbon brush holder saddle for ease of movement. If saddle is hard then explosive power ground will be experienced.

Ø  Mixed grade carbon should not be used in traction machines. Carbon brush grade should be identical.

Ø  Holder insulator IR should not be less than 50 mega ohms.

Ø  All TG holder clearance should be 0.090”.

Ø  The alignment of carbon brush pocket should be parallel with the commutator segment.

Ø  The fitment of holder should match with rocker arm marking.

Ø  Possibility of shifting of rocker arm neutral axis should be checked. Though rarely observed.

Ø  Check VDP, WSR.RP & EXCP for low IR.

Ø  All power switches I.R should not be less than 100 mega ohms.

Ø  The Ground Relay mechanical latch and resetting lever should lock properly failing which latch will disengage at higher speed due to vibration without actually energizing the relay coil.

Ø  Check TM arc ring condition. Arc ring holding bolts should be of suitable size and from approved source. DPT of bolts should be carried out during OVH. Thread locking compound should be used.

Power Cables, Power Control Cables &Power Panels:-

Ø  Check the cable cleat for sign of cable damage.

Ø  Check the cable hoses. The hoses should be replaced in M24 and above schedule.

Ø  Check the cable condition for rubbing, damage and tear.

Ø  Ensure that cables are not rubbing with loco body or the traction motors.

Ø  Check the IR Value of the backing piece of the power contactors. The backing piece should be replaced in M48 schedule. Provide additional nomex sheet in every major schedule.

Ø  Dynamic braking grid should be checked for insulation condition and additional P.U. sleeve should be put over insulator.