Standard requirements for Insulating Oil

Characteristics	Equipment Voltage	Permissible Limits
Dielectric Strength	145 kV and above	30 kV (Min)
Break down voltage	Below 72.5 kV	40 kV (Min)
	72.5kV and <145kV	50 kV (Min)
Water content	Below 145 kV	35 ppm (Max)
	145 kV and above	25 ppm (Max)
Specific resistance (Ohm-cm) at 90 deg C	All voltages	0.1 x1012 ohm-cm (Min)
Dielectric dissipation factor (tan d) at 90°C	All voltages	0.005 (Max:)
Neutralisation value (Total acidity)	All voltages	0.4 mg KOH/g (Max)
Interfacial tension at 27 deg C	All voltages	0.018 N/M (Min)
Flash point	All voltages	Min.-125°C Max -15 °C decrease of initial value
Sediment or precipitable sludge	All voltages	No sediment or precipitable sludge should be detectable
Dissolved gas analysis	145 kV and above	Refer IS 10593-1993 & DGA study chart