SITE INSTRUCTIONS FOR TRANSFORMERS (PART 3)

Further to our previous blogs for site instructions now we are giving some details about schedule for maintenance which will be helpful for site personal to take care the installed transformers.

RECOMMENDED MAINTENANCE SCHEDULE:

The hourly and daily inspection recommended is applicable for attended substations only.  However, for unattended substations these items should be inspected as frequently as possible. 

Sl. No.	Inspection Frequency	Items to be inspected	Inspection Notes	Action required if inspection shows unsatisfactory conditions
1	Monthly	i.  Oil level in transformer ii.  Connections iii. Loading cycle	Check transformer Oil level Check tightness Check if more than rated	If low, top up with dry oil.  Examine transformer for leaks If loose, tighten
2	Quarterly	i. Bushings	Examine for cracks and dirt deposits.	Clean or replace
3	Half-yearly	Gasketted Joints, Gauges and General Paint Work	Check of moisture under cover inspects.	Improve ventilation, check oil.
4	Yearly	i.  Oil in transformer ii.  Oil in tap changer, if provided iii. Connections iv. Breather	Check for dielectric Strength and water content.  Check for acidity and sludge.                          --- Colour of silica gel	Take suitable action to restore quality of oil. Take suitable actions if earth resistance is high If colour of silica gel is observed from blue to pink, silica gel shall be replaced.
5	5 Yearly	For large power transformers, check oil for DGA	----	-----
6	Occasionally	For fiber optic sensor	Signal strength	Clean through kit

TROUBLE SHOOTING CHART

Faults observed during the periodic maintenance schedules are to be rectified as per the suggested action required.  However, certain chance troubles and major faults in performance of the transformer shall have to be attended to in a desired sequence, as per manufacturer’s instructions (or) ready reference manuals.  Guidance to manage electrical and mechanical troubles normally encountered in all types of transformers are provided as follows:

Trouble Shooting (1)	Cause (2)	Remedy (3)
Rise in temperature/ High temperature Winding & oil	Over Load	If possible, reduce load.  Heating can often be reduced by improving power Factor of load.
	Insufficient Cooling	1. Check if all the radiator valves are      open 2. If unit is forced cooled, make sure fans are functioning.
	Sludged oil	Use filter press to wash off core and coils.  Filter oil to remove sludge.
Audio Noise	Leaky gaskets and joints.  Accessories and external transformer parts are set into resonant	Make certain all joints are tight.  Tighten loose parts.  In some cases parts may be stressed into resonant state.  Releasing pressure and shimming will remedy this condition.
Fractured metal or porcelain parts of bushings	Unusual strains placed on terminal connections	Cables and bus-bars attached to transformer terminals should be adequately supported.  In the case of heavy leads, flexible connections should be provided to remove strain on the terminal and bushing porcelain.
Gases and Buchholz Relays	Due to incipient fault	Action required according DGA analysis
Oil level	Due to leakages or pilferage in gasket and welded joints	Cause of leakages to be checked and proper action to be taken

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