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Typical limiting values of Sub-station electrical equipments.1. Transformer / Reactor:

SL. NO. EQUIPMENT / TEST DATA PERMISSIBLE LIMITS REFERENCEA) Transformer oil

a) BDV

-At the time of first charging 600 kV (Gap 2.5 mm) IS 1866

-During O&M 50 kV (Gap 2.5 mm) Minimum IS 1867

b) Moisture content IS 1868

-At the time of first charging 15 PPM (Max.) IS 1869

-During O&M 25 PPM (Max.) IS 1870

c) Resistivity at 90 degree C 0.1-1012 Ohm-CM (Min.) IS 1871

d) Acidity 0.2 mg KOH/gm (Max.) IS 1872

e) IFT at 27 degree C 0.018 N/M (Min.) IS 1873

f) Tan delta at 90 degree C 0.20 (Max.) IS 1874

g) Flash point 126 Deg. C (Min.) IS 1875

B) Vibration level for reactors 200 Microns (Peak to Peak) IS 1876

60 Microns (Average) IS 1877

C) Tan delta for bushing at 20 Deg. C 0.007* IEC 137

D) Capacitance for bushing + 5% variation IEC 138

E) IR value for winding 1000 M-Ohm By 5.0/10.0 kV IEC 139

F) Tan delta for windings at 20 Deg. C 0.007* IEEE/C57.12.90.1980

G) Contact resistance of bushing terminal

connectors

10 M. Ohm / Connector NGC.UK

Recommendations

H) Turret Neutral CT ratio errors 39 IS 2705

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