Electrical Engineering ⇒ Topic : IS Specifications
IS Specifications :
(1). Outdoor type distribution transformers (IS : 1180-1964) :
Standard ratings : 16, 25, 40, 50, 63, 80 and 100 kVA
No-load voltage ratios : 3300/433 V, 6600/433 V and 11000/433 V.
Tappings : Shall be provided on h.v. side in 5 steps. The ranges shall be ± 2.5% and + 5% off-load tap changers to be used.
Connections : LVY (Dy 11) with neutral brought out to a separate insulated terminal.
Cooling : By low viscosity transformer oil.
Conservator tank To be provided on transformer of rating 50 kVA or above.
Limits of temperature rise :
The following temperature rises shall be permitted over the ambient temperature of 45°C:
Winding (temperature to be measured by resistance method) 55°C
Oil (temperature rise to be measured by thermometer in the top oil) 45°C
The above temperature rises are for ON, OB, OW type cooling.
Impedance : 4.5°/,2 at 75°C, subject to the tolerance limit of 10%.
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