Annex 3

Preventive Maintenance Schedule for Current Transformers

S. No.	Tasks assigned	Shut Down (SD) Or Without Shut Down (WSD)	Periodicity
A.	I R MEASUREMENT
a.	I R measurement (Pl. DAR)	SD	In case of requirement
b.	Measurement of Tand and Capacitance	SD	3 Yearly*
c.	Measurement of CT Secondary resistance	SD	In case of requirement
d.	Magnetization Chracteristics	SD	In case of requirement
e.	CT ratio test	SD	In case of requirement
f.	DGA and testing of other parameters of oil	SD	In case of requirement
g.	Thermovision Scanning of CT and Top dome	WSD	Yearly
h.	Checking of Bellow Expansion	WSD	Monthly
i.	Visual inspection CT for oil leakage and crack in Insulator etc.	WSD	Monthly
MARSHALLING BOX
a.	Checking of oil leakage	WSD	Monthly
b.	Checking of healthiness of gaskets	WSD	Monthly
c.	Checking of space heater & Illumination	WSD	Yearly
d.	Checking the tightness of all connections including earthing	SD	Yearly
e.	Cleaning of marshalling box and junction box	SD	Yearly
B.	VISUAL CHECKING OF EARTHING HF POINT
a.	Visual checking of earthing HF point (in case it is not being used for PLCC)	SD	Yearly
b.	Checking for any breakage or cracks	SD	Yearly
c.	Checking of oil leaks	WSD	Monthly
d.	Cleaning of CVT capacitor stacks and tightness of terminal connections	SD	Yearly
e.	Capacitance and Tand measurement CVT	SD	3 Yearly
f.	Measurement of voltage at metering points in control Room	WSD	Monthly
g.	Testing of EMU tank oil for BDV	SD	6 Yearly
h.	Thermovision Scanning of Capaacitor stacks	WSD	Yearly
MARSHALLING BOX
a.	Checking of spacer heater & Illumination	WSD	Yearly
b.	Checking and tightness of all connections including earth connections	SD	Yearly
c.	Clearning of marshalling box and junction box	SD	Yearly
d.	Checking of healthiness of gaskets	SD	Yearly

*First time after one year from commissioning and then once in every three years.