|
1.1 |
Fresh Transformer oil before filling in Transformer |
||
|
Parameters |
Standard Values
(Acceptable range) |
Source |
|
|
(a) Appearance |
Clear and transparent and free from suspended matter or sediments |
IS 335 – 1993 |
|
|
(b) Density
at 29.50 C |
0.89 g/cm3 (Max) |
IS 335 – 1993 |
|
|
(c) Kinematic Viscosity at 270 C at 400
C, Max |
27 cSt (Max) under
consideration |
IS 335 – 1993 |
|
|
(d) Interfacial Tension (IFT) 270 C |
0.04 N/m (Min) |
IS 335 – 1993 |
|
|
(e) Flash point, Pensky
marten (Closed) |
140 0 C (Min) |
IS 335 – 1993 |
|
|
(f) Pour point |
- 60 C (Max) |
IS 335 – 1993 |
|
|
(g) Acidity (Neutralisation Value) |
|
|
|
|
(i) Total
acidity |
0.03 mg KOH/
g (Max) |
IS 335 – 1993 |
|
|
(ii) Inorganic acidity/ alkalinity |
Nil |
IS 335 – 1993 |
|
|
(h) Corrosive Sulphur |
Non – Corrosive |
IS 335 – 1993 |
|
|
(i) Di-electric strength
(Breakdown voltage) |
|
|
|
|
(i) New unfiltered oil |
30 kV, rms
(Min) |
IS 335 – 1993 |
|
|
(ii) After
filtration |
60 kV, rms
(Min) |
IS 335 – 1993 |
|
|
(j) Dielectric Dissipation Factor (Tan ) DDF at 900 C |
0.002 (Max) |
IS 335 – 1993 |
|
|
(k) Specific Resistance (Resistivity) |
|
|
|
|
(i) at 900 C |
35*1012 Ω –cm
(min) |
IS 335 – 1993 |
|
|
(ii) at 270
C |
1500*1012 Ω –cm (min) |
IS 335 – 1993 |
|
|
(l) Oxidation stability |
|
|
|
|
(i) Neutralization value after oxidation |
0.40 mg KOH/g (Max) |
IS 335 – 1993 |
|
|
(ii) Total
Sludge after Oxidation |
0.10% by weight (Max) |
IS 335 – 1993 |
|
|
(m) Ageing Characteristics after
Acceleration ageing (open
breaker method with copper
catalyst) |
|
|
|
|
(i) Specific Resistance (Resistivity) |
|
|
|
|
at 270 C |
2.5*1012 Ω –cm (min) |
IS 335 – 1993 |
|
|
at 900 C |
0.2*1012 Ω –cm (min) |
IS 335 – 1993 |
|
|
(ii) Dielectric
Dissipation Factor ( Tan delta)
at 900 C |
0.2 (Max) |
IS 335 – 1993 |
|
|
(iii) Total Acidity |
0.05 mg KOH/
g (Max) |
IS 335 – 1993 |
|
|
(iv) Total
Sludge |
0.05% by weight (Max) |
IS 335 – 1993 |
|
|
(iv) Total
Sulphur |
0.15% (Max) |
IEC 60296-2003 |
|
|
(n) Water
content of new unfiltered oil |
50 ppm (Max) |
IS 335 – 1993 |
|
|
(o) S. K. Value |
4 to 8% by mass
(Max) |
IEC – 60296,
2003 |
|
|
(q) Presence of Oxidation Inhibitor |
Oil shall not contain antioxidant additives. Value of 0.05% by mass (Max) shall
be treated as absence of |
IS 335 – 1993 |
|
|
|
|
DBPC – Phenolic type inhibitor |
|
|
(r) PCB content (Polychlorinated Bipheyls) |
Not detectable 0.1 mg/kg (Max) |
IEC – 60296,
2003 |
|
|
(s) Dissolved Gas Analysis (DGA) |
Not applicable |
IS 335 – 1993 |
|
|
(t) 2 – furfural (Furan
Analysis, Test method – IEC 61198:1993) |
0.1 mg/kg (Max) |
IEC – 60296,
2003 |
|
|
(u) Furfural (Aging criteria for oil immersed Power Transformer) |
Warning Trouble
1.5 ppm 15 ppm |
CIGRE DOC. No. 227 Life Management Technique for Power Transformer Page – 107 |
|
|
(v) Total
Furan Content |
250 parts per billion (ppb) |
Transformer Diagnostic USBR, june 2003,
Page 15 |
|
|
Additional Requirement for inhibited oil |
|
|
|
|
Inhibitor content (Antioxidation
additive content) DBPC (Ditertiary Butyl Paracersol) DBP (Ditertiary
Butly Phenol) |
Minimum 0.08 % by mass and maximum
0.4% by mass |
Inhibitor content determination
( Test Mehod:IS – 13631) IEC – 60296,
2003 |
|
|
Minimum 0.15 % by mass and maximum 0.3%
by mass |
Nynas and shell Inhibited oil |
|
1.2 |
Transformer oil for in-service Transformer |
|
|||
|
Oil Parameters |
At the time
of first Charging. |
During O&M |
|
||
|
(a) Appearance |
Clear, free from sediment and suspended matter |
Clear without visible contamination |
IS 1866 |
- 2000 |
|
|
(b) Break Down
Voltage (BDV) (GAP – 2.5 mm) min |
40 kV for <
72.5 kV 50 kV for 72.5 to 170 kV 60 kV for >
170 kV |
30 kV for <
72.5 kV 40 kV for 72.5 to 170 kV 50 kV for >
170 kV |
IS 1866 |
- 2000 |
|
|
(c) Water content (Moisture) (Max) |
20 ppm for < 72.5 kV 15 ppm for 72.5 to
170 kV 10 ppm for > 170 kV |
No free moisture for<72.5 kV 40
ppm for 72.5
to 170 kV 20 ppm for > 170 kV |
IS 1866 |
- 2000 |
|
|
(d) Acidity (Neutralization value ( Max) |
0.03 mg KOH/g |
0.3 mg KOH/g |
IS 1866 |
- 2000 |
|
|
(e) Sediment & Sludge (Max) |
0.01% by mass |
0.02 by mass |
IS 1866 |
- 2000 |
|
|
(f) Resistivity |
|
|
|
||
|
(i) Resistivity at 200 C (Min) |
|
1*1012 Ohm-cm |
IS 1866 |
- 2000 |
|
|
(ii) Resistivity at 900 C (Min) |
6*1012 Ohm-cm |
0.1*1012 Ohm-cm |
IS 1866 |
- 2000 |
|
|
(g) Dielectric
Dissipation factor at 900C and 40-60 Hz (Tan Delta/ power factor)
(Max) |
0.015 for < 170 kV 0.01 for ε170 kV |
1.0 for <170 kV 0.2 for 170
kV |
IS 1866 |
- 2000 |
|
|
(h) Inter Facial Tension
(IFT) AT 270 C (Min) |
35 mN/m |
15 mN/ m |
IS 1866 |
- 2000 |
|
|
(i) Flash Point (Min) |
1400C |
Max decrease of 150C from
initial value |
IS 1866 |
- 2000 |
|
|
|
(j) Density at 29.50C (Max) |
0.89 g/cm3 |
Not Essential |
IS 1866 |
- 2000 |
|
(k) Kinematic Viscosity at 270C (Max) |
27 cSt |
Not Essential |
IS 1866 |
- 2000 |
|
|
(l) Pour point (Max) |
-60C |
Not Essential |
IS 1866 |
- 2000 |
|
|
(m)
Oxidation stability of uninhibited
old |
|
|
|
||
|
(i) Neutralization value (Max) |
0.4 mg KOH/g |
Not Essential |
IS 1866 |
- 2000 |
|
|
(ii) Sludge (Max) |
0.1% by mass |
Not Essential |
IS 1866 |
- 2000 |
|
|
Additional requirement for inhibited oil |
|
|
|
||
|
(n) Oxidation Stability of inhibited oil |
Minimum 0.08%
by mass and maximum 0.4% by
mass |
Not Essential |
IEC 60296, 2003 |
||
|
1.3 |
Dissolved Gas Analysis (DGA) |
|
|
|
Typical rates of gas increase for power transformers |
Values in milliliters per day |
IEC: 60599-1999 See note Below |
|
|
Hydrogen (H2) |
<5 |
||
|
Methane (CH4) |
<2 |
||
|
Ethane (C2H6) |
<2 |
||
|
Ethylene (C2H4) |
<2 |
||
|
Acetylene ((C2H2) |
<0.1 |
||
|
Carbon Monoxide (CO) |
<50 |
||
|
Carbon dioxide (CO2) |
<200 |
||
|
Equation to calculate the rate of gas increase as per IEC: 60599
– 1999 Rate – (Y2-Y1)m/{>(d2
– d1)} m1/ day Where Y1 = is the
reference analysis Y2 = is the
last analysis (Y2-Y1) – is the increase in micro litre
per litre. M = is the
mass of oil, in kilograms P = is the mass density,
in kilograms per cubic metre. d2 = is the date for Y1 d1 = is the date for Y2 |
|||
|
1.4 |
Transformers/ Reactors |
||
|
Ten
Delta for bushing at 200C |
0.007 |
IEC – 60137 |
|
|
Capacitance for Bushing |
-5% to +10% Variation |
|
|
|
Contact Resistance of Bushing |
10 Micro – Ohm/Connector |
NGC, UK Recommendation |
|
|
Ten Delta for Windings at 200C |
0.007 |
IEEC/C57.12.90.1999 |
|
|
Ten Delta for
Windings at 200C (Power factor) |
0.005 |
Transformer Diagnostic USBR, June 2003 |
|
|
Rate of Rise of
Tan Delta (Bushing & Winding) |
0.001 Per year
(Max) |
|
|
|
Magnetizing current test (Excitation |
If the excitation current is less
than 50 milli
amperes (mA), the difference between the two higher currents |
Transformer Diagnostic USBR, June 2003 |
|
|
|
current test) |
should be less than 10%. If the excitation
current more than 50 mA, the
difference should be less than 5%. In general, if there is an internal problem, these differences will be greater. |
|
|
|
Magnetic
Balance Test (Three Phase) |
Value of supply voltage (230 V AC) in one phase is equal to sum voltage induced in other
two phase. When
supply voltage in middle limb, voltage induced in outer limbs should equal and roughly half of the supply voltage. |
|
||
|
Winding resistance Transformer and Reactor (Resistance converted to 750C) |
± %5 difference between
phases or from Factory tests. |
|
||
|
Voltage Ratio of Transformer (All Taps) |
± %5 difference from
Factory tests. |
|
||
|
Insulation
Value (Thumb Rule/ Empirical Formula) |
Min
insulation values for one minute resistance
measurement for transformers may be determined by using
the following formuls: R = CE/ √kVA Where R = Insulation resistance, in MΩ C=
1.5 for oil filled transformers at 200C, assuming that the transformer’s insulating oil is
dry, acid free, and sludge free. = 30.0 for un-tanked oil
impregnated transformers. E –
Voltages rating, in V, of one of the single phase windings (ph – to ph for delta connected and ph – to neutral for wye connected transformers) kVA
= Rated capacity of the winding under test ( If the winding under test
is three-phase and the three
individual windings are
being tested as one, the rated capacity of
three-phase winding is used. |
|
||
|
IR Value of Winding (Min) |
Rated Voltage Class
of winding |
Min desired IR value
at 1 minute at 300C (Mega ohm) |
|
|
|
11 kV |
300 |
|||
|
33 kV |
400 |
|||
|
66 kV & above |
500 |
|||
|
Polarization index (Ratio of IR values at 10
min to 1 min) |
Polarization index |
Insulation Condition |
|
|
|
Less that 1 |
Dangerous |
|||
|
1.0-1.1 |
Poor |
|||
|
1.1-1.25 |
Questionable |
|||
|
1.25- 2.0 |
Fair |
|||
|
2.0-4.0 |
Good |
|||
|
Above 4.0 |
Good |
|||
|
CORE INSULATION TEST Min (Between CL
and CC +G with tank grounded) |
1000K Ohms at 2.5/3.5 kV DC for 1 min |
|
||
|
Transformer Neutral Resistance Value |
Below 1 ohm |
|
||
|
Turret/ Neutral Resistance Value |
±3% |
IS – 2705 |
||
|
Vibration level for Reactors |
200 Microns (Peak to Peak) 60 Microns (Average) |
|
||
|
Sweep
Frequency Response Analysis Test (20 Hz
to 2 |
In
general, changes of +/- 3 dB (or more) in following frequency range may
indicate following faults: Frequency Range |
Euro – Double Client Committee Transformer Diagnostic |
||
|
|
MHz) |
Probable Fault 5Hz to 2 KHz Shorted turns, open
circuit, residual magnetism or core movement 50 Hz to 20 KHz Bulk movement of windings
relative to each other 500 Hz to 2
MHz Deformation within a
winding 25 Hz to 10
MHz Problems with winding
leads and/ or test lead
placement. |
USBR, June 2003 |
|||
|
Moisture measurement
of winding (RVM Measurement) |
IEEE Std. 62-1995 |
|
||||
|
Insulation condition |
% Moisture by dry
weight in paper (Wp) |
% Water saturation of oil ( ) |
CIGRE DOC No. 227. Life
management Technique for Power Transformer Page 119 |
|||
|
Dry (at commissioning) |
0.5- 1.0% |
<5% |
||||
|
Normal in operation |
<2% |
|
||||
|
Wet |
2-4% |
6-20% |
||||
|
Extremely wet |
>4.5% |
>30% |
||||
|
Degree of polymerization (DP) |
New insulation |
1,000 DP to 1,400
DP |
EPRI’s
Guidelines for the life Extension
of Substations, 2002 Update, Chapter 3, Table 7 DP Values for Estimating Remaining paper life. |
|||
|
|
60% to 66% life
remaining |
500 DP |
||||
|
|
30% life remaining |
300 DP |
||||
|
|
0 life remaining |
200 DP |
||||
|
1.5 |
CIRCUIT BREAKERS |
|||||
|
Dew Point of SF6 Gas |
Dew point
values as per Annexure
– II |
|
||||
|
Dew Point of operating air |
+450C at Atmospheric Pressure |
|
||||
|
(A) CB Operating timing |
400 kV |
220 kV |
132 kV |
IEC-62271-100 (2001) |
||
|
(a) Closing time (Max) |
150 ms |
150 ms |
150 ms |
|
||
|
(b) Trip time
(Max) |
25 ms |
35 ms |
45 ms |
IEC-62271-100 |
||
|
(c) Close/Trip time pole discrepancy at rated operating pressure |
50 ms 3.33 ms |
5.0 ms 3.33 ms |
5.0 ms 3.33 ms |
2001 |
||
|
- Phase to Phase (Max) close open |
2.5 ms |
2.5 ms |
2.5 ms |
IEC-62271-100 (2001) |
||
|
-Break to Break (Max) of same phase |
35 ms 300 ms |
35 ms 300 ms |
35 ms 300 ms |
|
||
|
(d) CO time (min) |
±5 ms ±3ms |
±5 ms ±3ms |
±5 ms ±3ms |
With simultaneous close & trip command. |
||
|
(e) Trip delay time for
DCRM test (CO operation) – Minimum |
|
|
||||
|
(f) Deviation from standard timings as per GTP
of manufactures – close open |
|
|
||||
|
|
(B) Travel of
operating rod |
ABB CGL BHEL Alstom (Imported) |
200 mm 230 mm 130 mm 184 mm |
IEC-62271-100 (2001) |
|
(C) PIR time - BHEL make - CGL make - ABB mak - NGEF make - M&G make - TELK make - Alstom make
(HVDC) -ABB make
(HVDC) |
400 kV 12-16 ms 8-12 ms 8-10 ms 8-12 ms 8-12 ms 8-12 ms 8-12 ms 8-12 ms |
Manufactures Recommendations. |
||
|
(D) PIR operating time prior to opening of main contacts (ABB, CGL, NGEF make CBs) |
5 ms (Min)
at rated pressure |
|
||
|
(E) PIR and main contacts overlap time (BHEL, M&G, ABB (imported make CBs) |
5 ms (Min)
at rated pressure |
|
||
|
(F) Tan delta
of grading capacitors |
0.007 |
Since temperature correction factor for Tan
Delta depends on make, type and
also again conditions, the correction factors for different types/ makes are different. Hence no standard temperature error
factors can be applied |
||
|
(G) Rate of rise in Tan dalta |
0.001 per year (max) |
|||
|
(H) Capacitance of grading capacitors |
Within ±5% of
the rated value |
|
||
|
(I) Contact Resistance of CB (in Micro-Ohm) |
400 kV 220 kV 132
kV 150 100 100 |
|
||
|
(J) Contact Resistance of CB terminal connector |
10 Micro-Ohm per connector |
NGC, UK Recommendations |
||
|
(K) Evacuation level before SF6 gas filling |
5mbar (min) |
|
||
|
(L) N2 leakage rate from N2 accumulator |
3 bar per
year (max) |
|
||
|
(M) IR VALUE |
|
|
||
|
1. Phase – Earth 2. Across open
contacts 3. Control cables |
1000 M-Ohm (Min) by 5.0/10.0 kV megger 1000
M-Ohm (Min) by 5.0/10.0 kV megger 50 M-Ohm (Min) by 0.5 kV megger. |
|
||
|
(N) PRESSURE SWITCH
SETTINGS - SF6 gas pressure switches |
Within ±0.1 Bar
of set value. |
|
||
|
|
- Operating air pressure switches - Operating oil pressure switches |
Within ±0.1 Bar
of set value Within ±0.1 Bar
of set value |
|
|
|
(O)
BDV of oil used for MOCB - At the
time of filling -During O&M |
40 kV at 2.5 MM
GAP (Min) 20 kV at 2.5
MM GAP (Min) |
Manufactures Recommendations |
||
|
1.6 |
CURRENT TRANSFORMERS |
|||
|
(A) IR Value -Primary – Earth -Secondary – Earth -Control Cables |
1000 M –OHM (Min) 50 M-OHM (Min) 50 M-OHM (Min) |
by 5.0/10.0 kV Megger by 0.5 kV Megger by 0.5 kV Megger |
||
|
Tan delta value |
0.007 |
Since
temperature correction factor
for Tan – Delta depends
on make, type and also ageing
conditions, the correction factors
for different types/ makes are different. Hence, no standard temperature error
factors can be applied. |
||
|
Rate of rise in Tan Delta |
0.001 per year (max) |
|||
|
|
(B) Monitoring of Tan delta · Upto 0.007 (rise @ 0.001) ·
0.007 to 0.011 ·
0.011 |
- Yearly monitoring -
Half yearly
monitoring -
Replace the CT |
|
|
|
Terminal connector contact resistance |
10 Micro-Ohm per connector |
NGC, UK Recommendations |
||
|
CT ratio errors |
±3% protection cores ±1% metering cores |
IS – 2705 - do- |
||
|
|
Pressure 0.10 kg/cm2 0.20
kg/cm2 0.30 kg/cm2 0.40 kg/cm2 0.50 kg/cm2 |
Oil level 10 mm 30 mm 50 mm 70 mm 90 mm |
|
|
|
1.7 |
CAPACITIVE VOLTAGE TRANSFORMERS |
|||
|
(A) Tan Dalta |
0.007 |
Since
temperature correction factor
for Tan – Delta depends
on make, type and also ageing
conditions, the correction factors
for different types/ makes are different. Hence, no standard temperature error
factors can be applied. |
||
|
(B) Rate of rise in Tan Delta |
0.001 per year (max) |
|||
|
(C) Change in Tan from pre commissioning value |
Measurement Value Measurement Frequency Upto +0.002 -
Three yearly +0.002 to +0.003 -
Yearly Above +0.003 - alarming |
|
||
|
|
(D) Capacitance |
Within ±5%
of pre commissioning value |
|
|
|
(E) Contact resistance of terminal connector. |
10 Micro-OHM per connector |
NGC, UK recommendations |
||
|
(F) Change in capacitance from pre
commissioning value |
Measurement Value Measurement Frequency Upto ±2% - Three
yearly ±2% to ±3 - Yearly Above
±6% - alarming (needs replacement) |
|
||
|
|
1000 M-OHM (Min) by 5.0/10.0 kV Megger 50
M-OHM (Min) by 0.5 kV Megger 50 M-OHM (Min) by 0.5 kV Megger |
|
||
|
(G) Drift in
secondary Voltage (to be
measurement in 0.2/0.5 class multimeter) |
|
|
||
|
|
Condition Frequency |
Measurement |
|
|
|
Upto ±0.5 volts ±0.5 to ±0.8 volts ±0.8 to ±1.2 volts ±1.2 to ±2.0 volts above +2.0
volts -0.8 to -4.0 volts less
than -4.0 volts |
Healthy To be monitored Close
monitoring Close monitoring Alarming Close monitoring Alarming |
Six month 03
monthly monthly 15 days replacement 15
days replacement |
|
|
|
(H) EMU tank oil parameters BDV (Min) Moisture
content (Max) Resistivity at 900C Acidity IFT at 270C Tan delta at 900C
Flash Point |
|
IS- 1866 |
||
|
30 kV
(GAP 2.5 MM) 35 PPM |
|
|||
|
0.1*1012 OHM-CM 0.5 mg
KOH gm (Max) 0.018 N/M (Min) 1.0 Max 1250C (Min) |
|
|||
|
(I) CVT voltage ratio errors |
±5% protection cores ±5% metering cores |
IEEE/C93.1.1990 IEC 186 |
||
|
1.8 |
DISCONNECTING SWITCHES |
|||
|
|
(A) Contact resistance (B) Contact resistance of terminal connector (C) IR Value - Phase – Earth - Across Open Contacts - Control cables |
300 Micro – Ohm (Max) 10 Micro-Ohm
per connector 1000 M-Ohm (Min) by
5.0/10.0 kV megger 1000 M-Ohm
(Min) by 5.0/10.0 kV megger 50 M-Ohm (Min) by 5.0 kV megger |
NGC, UK recommendations |
|
|
1.9 |
SURGE ARESTER |
|
|
|
|
(A) Third Harmonic Resistive Current (THRC) – for all makes Elpro/
Alstom / Oblum/ CGL -
For new
Las -
For Las in services |
·
Upto 30 Micro
– Ohm ·
(Upto 150
Micro – Ohm)
– Normal · (150 to 350 Micro-Ohm) – to be tested for insulation test &
if value found
low - to be removed from service. ·
Beyond 350 Micro Ohm (Gapless type) - to be removed from service ·
Beyond 350 Micro Ohm (Gapless type) - to be removed from service |
|
||
|
(B) IR Value |
1000 Mega-Ohm (Min) |
|
||
|
1.10 |
MICELLANEOUS |
||
|
(A) Station Earth Resistance (B) Thermovision Scanning -
Temp upto 150C (above ambient) -
Temp above 15-500C (above ambient) -
Temp above 500C (above ambient |
1.0 Ohm (Max) -
Normal -
Alert -
To be immediately attended. |
IEEE/C37.010.1979 |
|
|
(C) Therminal Connectors |
10 Micro-Ohm per connector |
NGC, UK recommendations, |
|
|
(D) IR Values -
All Electrical Motors. -
Control Cables -
LT Transformer -
LT Switchgears |
50 M-Ohm (Min) by 0.5 kV megger 50 M-Ohm (Min) by 0.5 kV megger 100
M-Ohm (Min) by megger 100 M-Ohm (Min) by 0.5 kV megger |
IS 900 |
|
|
1.11 |
BATTERIES |
||
|
(A) Terminal connector resistance (B)
Specific Gravity |
10 Micro-Ohm ±20% 1200 ± 5GM/L
at 270C |
ANSI/IEEE/450-1987 |
|
|
1.12 |
DG SET |
||
|
(A) Winding IR value (B) Stator winding resistance |
50 M-Ohm Within ± 10% of
STD value |
|
|
DEW POINT OF SF6 GAS
|
Sl. No. |
Make of CB |
Dew Point at
rated pressure |
Dew point at Atmospheric Pressure (Limit) |
Remarks |
|
1 |
BHEL |
-150C |
-360C |
At the time
of commissioning |
|
-70C |
|
During O&M |
||
|
-50C |
|
Critical |
||
|
2 |
M&G |
|
-390C |
At the time
of commissioning |
|
|
-320C |
During O&M |
||
|
3 |
CGL |
-150C |
-350C |
At the time
of commissioning |
|
-100C |
-310C |
During O&M |
||
|
4 |
ABB |
-150C |
-350C |
At the time
of commissioning |
|
-50C |
-260C |
During O&M |
||
|
5 |
NGEF |
-150C |
-360C |
At the time
of commissioning |
|
-70C |
-290C |
During O&M |
||
|
-50C |
-270C |
Critical |
||
|
6 |
For all make |
-150C |
-350C |
To be followed for substations having
ambient temperature less than 00C |