220-66-kv-xmer-on-line-nifes-r4-sept-08 - Gujarat Electricity Board

GETCO/E/TS – XMER01power/R4 Sept 08
1.12.1 The dielectric strength of winding in insulation and of the bushings shall conform to
the values given in IS:2026-1962 (as amended up to date).
1.12.1.1 The partial discharges in the transformer at the time of dispatch shall not be
more than 500 pC.
1.12.1.2 The Maximum Limit of value of tan delta shall be 1% for windings, 0.5% for
bushings and 0.2 % for oil.
1.12.2 For rated system voltage of <strong>220</strong> and <strong>66</strong> kV, the following impulse test voltage may
be offered
System Voltage Impulse Test Voltage Power frequency voltage
<strong>220</strong> kV 1050 kV 460 kV
<strong>66</strong> kV 350 kV 160 kV
1.12.3 The H.V. winding of the transformer shall have graded insulation. The insulation
class of the neutral and or the windings shall be graded to 95 kV (Impulse) and 38 kV
(Power frequency) withstand.
1.13 TEMPERATURE RISE:
1.13.1 The transformer shall be installed out-door without any protection from sun and rain.
The maximum hot spot temperature rise shall be limited to 105 0 C with Class-A
insulation. Each transformer shall be capable of operating continuously at its normal
rating without exceeding the temperature rise limits specified as under
Winding (measured by resistance)
Temp. rise in 0 C
ONAN 55
ONAF / OFAF 60
Top oil (measured by thermometer).
Temp. rise in 0 C
ONAN 45
ONAF / OFAF 55
Cores Not to exceed that
permitted for the adjacent
part of the winding.
Note: The reference ambient temperature for the purpose of temperature rise shall be
40 0 C.
1.13.2 The transformer shall be free from abnormal noise (other than humming) and
vibration.
1.14 FREQUENCY:
1.14.1 The transformer shall be suitable for continuous operation with a frequency variation
of ±3% from normal of 50 Hz. without exceeding the specified temperature rise.
1.15 PARALLEL OPERATION:
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