Commissioning
of
Transformers
and Reactors
Transportation, Site handling & Commissioning
Content
• Significance of Rating plate details
• Description of equipment and accessories and its role
• Pre Commissioning process and various pre-commissioning
tests
Transformer Basics
The induced voltage (V) in a transformer
V = 4.44 * N * B * A * f volts
Where N = Number of winding turns, B = Flux density value (Tesla)
A = Core limb area (m2),
f = Frequency of applied voltage(cycles/sec)
V1= e1= N1 d / dt
V2= e2= N2 d/ dt
V1 / V2 = N1 / N2
V1/N1 =V2/N2
Mandatory information on rating plate
a) Type of Plate
transformer
Rating
details
b) Number of this standard.
c) Manufacturer's name, serial number & Year of manufacture.
d) Number of phases.
e) Rated power, voltages, currents and frequency
f) Tapping range and designation with connection arrangement
g) Connection and phase displacement symbol
h) % impedance
i) Type of cooling
j) Total mass, Transportation mass
Mandatory information on rating plate-continued..
Rating Plate details
k) Mass and type of insulating liquid with reference to the relevant IEC
standard.
l) Maximum system short-circuit power or current
m) Insulation levels (withstand voltages)
n) Guaranteed maximum temperature rises of top liquid and windings
o) Current Transformer details
Rating
Plate
General Arrangement Layout
Layout of 3 Phase 400kV Transformer
Essential parts of the Transformer
• Magnetic circuit- to carry mutual flux
• Electric circuit- HV and LV windings
• Supporting structure
• OLTC & Bushings
• Insulation system
•
Cooling system
Active Part
The set formed by Core, windings , Clamping Frame, Lead and Support.
Current Transformer
Top clamping frame
HV main lead
Winding
Tertiary lead
Lead Support
Winding support assembly
Bottom clamping frame
HV SIDE
Active Part
LV main lead
Tap-changer
Neutral lead
Top Frame
Tap leads
Bottom Frame
LV SIDE
Shunt Reactors:
Shunt Reactors are used in high voltage systems to compensate capacitive
generation from long lightly loaded overhead lines
The shunt reactor compensates the capacitive generation on power lines to
avoid non-controlled voltage rise especially on lightly loaded lines.
One critical operating parameters like vibrations and noise.
Shunt Reactors:
Insulating Oil
Used as coolant, transfers heat generated in windings and also acts as
insulating medium for Transformer, Reactor, CT and CVT etc.
Mineral Oil:
Most popular due to low cost and easy availability, basically a
fraction, based on carbon type composition
petroleum
Synthetic Oil: Askarels, Silicon fluids etc -Oil with special parameters like high
fire resistance, high permittivity and gas absorbing characteristics
Vegetable Oil: offers the benefit of complete biodegradability and it's also less
flammable than mineral oils. It is extracted from plants like soy, or sunflowers,
which makes it biodegradable.
Bushings in POWERGRID
Based on Condenser CoreOIP
RIP
Solid
Based on Conductor
 Draw Rod
 Draw Lead
 Solid Stem
Bushings in POWERGRID Contd…
Based on Application
Oil-Air OIP bushings
Oil-SF6 RIP Bushings
Oil to Oil RIP bushing
Oil-Air Solid Bushing
OLTC & Driving Mechanism
Conservator Tank
Other Accessories
PRD
OTI & WTI
Buchholz Relay
OSR
MOG
Breather
Step to
commissioning
Contents
of the Presentation
Transportation & Site arrival checks
Storage & Installation
Vacuum drying and oil filling
Pre-commissioning Testings
Post-commissioning activities
Transportation
Mode of Transportation
• By Rail
• By Ship
• By Road
Impact Type
Onboard Rail
•
•
Impacts in longitudinal axis during shunting operations and vertical shocks
due to rail joints
Normally acceleration from 0.5 to 1.0 g in 2-500 Hz band is experienced,
however during shunting operation acceleration up to 4.0g in 2-20 Hz band
can be experienced
Onboard a Ship
•
•
•
Rolling, Pitching and Yawing
low frequency vibrations repeating at regular periods.
Normally acceleration from 0.3 to 0.8 g in 2-30 Hz band is experienced.
Impact Type
Onboard a Trailer
•
•
Impacts in longitudinal axis during braking operations and vertical and lateral
shocks due to road conditions.
Normally acceleration from 0.5 to 1.0 g in 3-350 Hz band is experienced.
During Loading/unloading &Rigging
•
•
Low occurrence, high magnitude impact (like lifting gear failure, dropped
Transformer).
Shock events from 2.5 to 10.0 g in 2-20 Hz band are experienced.
Impact during Transit
Impact Issues
 Visible Damage:- Leading to on site or factory repairs
 Conceal Damage:- Causing out of warranty failure
Damages occur because of :Acceleration Amplitude : a
Change of velocity : Δv
Duration: t
Digital Impact Recorder
TS representation on Impact Recorder
• Transformer to be fitted with Electronic impact recorders (on returnable basis) at
least 2 numbers for 400kV Class Transformer and 1 number for below 400kV
class Transformers
• Could measure the magnitude and duration of the impact in all three directions.
• The acceptance criteria and limits of impact, which can be withstood by the
equipment during transportation and handling in all three directions, shall not
exceed“3g” for 50mSec (20Hz) or as per contractor standard, whichever is
lower
What to check?
Check the setting of Impact Recorder
Setting for range, wake & Alarm
Journey Start date, end date and record duration
Acceptable limit of mechanical shock is ‘ 3g for 50 ms’ on any direction
Downloading and analysis of impact recorder data
Impact Recorder Analysis: Shockwatch
Impact Recorder Analysis: Monilog
Check at site
Transit Damage
Healthy Locating pin and
insulation
Transport Modes
 Oil Filled
 Nitrogen Gas / Dry air filled

When oil filling would exceed the permissible or economical maximum transport
weight
 Customer Requirement
Checks on Transformer upon arrival at site
 Visual external inspection. In case of any abnormality like broken glass on gauges,
broken welds, Paint finish damage, same needs to be referred to manufacturer/ region/
CC
Nitrogen/ Dry air pressure & dew point check or oil level check if transported in oil filled
condition and compare with factory data
Nitrogen pressure to be maintained minimum 0.175 kg/sq cm( 2.5 psi) during
Transportation.
 Measurement of core insulation resistance to ground. (Min. Acceptable value : 500MΩ)
Document to be referred
Contract document & Technical specification
for obtaining detailed scope of work
Manufacturer
Procedures
Installation
Manuals/
For guidance and uniformity across all
substation
in
POWERGRID
“Pre
Commissioning Procedures and Formats for
Switchyard Equipments :D-2-01-03-01-05”
have been made.
Activity Flowchart for commissioning
Oil Filtration plant : Precaution to be taken
Changing of Lubricating oil of vacuum pump
Cleaning of Filter packs
Flushing of whole filter machine with fresh oil
Checking of vacuum obtained without load (milli bar)
Silica gel breather to be provided in the tank
All erection activity to be carried out with continuous purging of dry air in the main
tank
Internal Inspection: Should Include
• Removal of any shipping blocking or temporary support.
• Examination for indication of core shifting.
• Tests for unintentional core or core clamp grounds.
• Visual inspection of windings, leads, and connections including
clamping, bracing, blocking, spacer alignment, phase barriers, oil
boxes, and coil wraps.
• Inspection of Dead End Tap Changer and in-tank LTCs including
contact alignment.
• Inspection of current transformers, including supports and wiring
harness.
• Checks for dirt, metal particles, moisture, or other foreign material.
Internal Inspection: Findings
Leakage Test through pressure
Fill dry N2/ dry air till pressure of 4- 5psi (.3 kg/cm2 ) is achieved and to be kept
for 24 Hrs
In case pressure remain same, record dew point
Proceed for evacuation if no drop in pressure is observed
In case of drop in pressure, attend the leakages by applying soap water
solution in all valve opening and repeat the pressure test
Vacuum drop & Tightness Test
Starting of evacuation on complete unit
Stopping of evacuation near the pressure of 5 kPa (50 mbar)
Note the Pressure as P1 in kPa after 1 hour of stopping evacuation
Note the Pressure Pressure P2 in kPa after half an hour of reading pressure P1
Calculate drop in vacuum = (P2-P1) x V , V= Oil quantity
Allowable Leakage of less than 150 mm Hg liters per minute ( 20 m3 Pa/min).
If the leakage rate exceeds 20 m3 Pa/min or the vacuum does not hold, then the leak
in the transformer system shall be located and arrested
Vacuum drying and N2 purging cycle
• Continue Vacuum till pressure of 0.13kPa(1 Torr) is achieved and then retain it
for the 72-96 hrs for 420 kV and above equipment
• Break of vacuum and purge N2/ Dry air of dew point -50° or better and retain it
for 48 hrs
• Check for dew point
• If acceptable, then proceed for oil filling
Transformer HV
Rated Voltage
(in kV)
Up to 145kV
145 kV and 246
kV
Above 420 kV
Application of Vacuum &
holding for (before oil
filling)*(in Hours)
12 HRS
24 HRS
STANDING TIME After Oil
circulation and before
energising (in Hours)
12 HRS
48 HRS
48 HRS
120 HRS
Oil Filling in Conservator
Oil Filling
Parameter
prior be
to filling
in main
tankto filling in
Each lot Oil
of the
oil shall
tested
prior
main tank at site for the following:
Break Down voltage (BDV)
Moisture content
Tan-delta at 90°C
Interfacial tension
70 kV (min.)
5 ppm (max.)
0.0025 (Max)
0.04 N/m(Min)
Oil Parameter After filtration & settling prior to
energisation
1
2
3
4
5
Break Down voltage (BDV)
Moisture content
Tan-delta at 90°C
Interfacial tension
*Oxidation Stability
a) Acidity
a) Sludge
a) Tan delta at 90 °C
70 kV (min.)
5 ppm (max.)
0.005 (Max)
More than 0.04 N/m
0.3 (mg KOH /g) (max.)
0.05 % (max.)
0.05 (max.)
* Test results can be submitted within 45 days after commissioning
Other Checks on Oil
Furan
Should not be traced
Particle Counts
As per TS
Resistivity at 90 °C
6 X 10 ^12 ohm-cm (min.)
Total Gas Content
< 1%
Pre-commissioning Tests
C & Tan δ measurement on bushings & winding
Variable frequency Tan delta of bushing is mandatory
Frequency response analysis
Voltage ratio test, Vector Group& Polarity checking
Magnetization current test
Magnetic Balance test( for 3-ph unit)
IR measurements-PI & DAI
Core Insulation Tests
Winding resistance measurement
Operational tests on OLTC, Cooler Banks
Tests on Bushing CTs
 IR, Continuity, Polarity
 Current Ratio/ Magnetization curve
Protection & alarm tests
Electrical Tests and DGA Diagnostic Matrix
Bushings
Tap changer
Windings
Core
Insulation equivalent circuit
Conductor equivalent circuit
Re1 Lf1
Lf2
Re
2
Rf
X
CHL
High Voltage
Winding
CH
Low Voltage
Winding
CL
Core & Tank
Ref: CIGRE Brochure No.445
Capacitance and Tan δ measurement
This test provide an indication of quality and soundness of the insulation in bushing
/winding
Dielectric losses in the insulation are caused by:
• Conductive Losses: Transport of Electrons and Ions
• Polarization Losses: Through Interfacial Polarization Effects
• Partial Discharges: Local discharges
Measurement Set up
Frequency dependency of Capacitance and Tan δ
Influence of Conductivity
(Polarization Effects Dominating
Dielectric with Notable
Conductivity Effects
Dielectric Frequency Response
It is used for determining moisture content and aging of press board and
Paper
DFR Application Areas
• Power transformers
• Instrument transformers
• Bushings
International guidelines
Frequency Domain Spectroscopy
•
Capacitance and power factor measurements at variable frequency (1 kHz down to
0.1mHz)
•
•
Same preparation as for capacitance and power factor Measurements
Same procedure as in capacitance and power factor
Measurements
•
Performed at relatively low voltage, typically 140 V(RMS)/ /1.4kV(RMS)
Dielectric Frequency Response
Response of Transformer
Bushing Diagnosis methods
Power frequency Capacitance(C) and Tan 
Acceptance value
Oil Impregnated paper
(OIP)
Insulation Type
Resin Impregnated paper
(RIP)
IEC-60137
< 0.7%
<0.7%
IEEE C57.19.01
< 0.85%
<0.5%
Typical New Values
0.3-0.4%
0.2-0.4%
IEEE 62.1995
0.1%(Rise)
0.1%(Rise)
Above values are corrected to 20° C
Tan  response bushing
Tan delta in %
10
Faulty Bushing
1
Healthy Bushing
0,1
0,022 0,046
0,1
0,22
0,46
1
2,2
4,6
10
Frequency in Hz
20
42
60
90
220
470
1000
Capacitance response of bushing
Capacitance pF
700
650
Healthy Bushing
600
550
Faulty Bushing
500
Frequency in Hertz
X-Wax formation
Bridging of conductive
layers
Frequency Response Analysis:
FRA represents a systems response to a sinusoidal input at varying frequencies
FRA Principle:
Transformer can be modelled as a network of capacitance, resistance, self- and
mutual inductances. Any alteration in these parameters, FRA response will also
change accordingly
IFRA – Impulse Frequency Response Analysis
This uses an impulse voltage source, it is quick but has inherent repeatability problems
and is therefore not the preferred method for general use.
SFRA – Swept Frequency Response Analysis
Uses a swept frequency voltage source, although slightly slower than IFRA is
repeatable and the results are easily comparable between any test equipment used.
Frequency Response
Raw Data
1.1 -> N
Raw Data
1.1 -> N
10
10,000,000
1
0.1
100,000
Impedance [Ohm]
Admittance [mS]
1,000,000
0.01
10,000
0.001
1,000
0.000
10
100,000
10,000
Frequency [Hz]
1,000
100
1,000,000
100
10
10,000,000
100
Impedance
1,000
10,000
Frequency [Hz]
100,000
1,000,000
10,000,000
Admittance
Phase Angle H(θ) = Tan-1 ( Vout/Vin)
Raw Data
1.1 -> N
-15
Raw Data
-20
1.1 -> N
-25
180
-30
160
-35
140
-40
120
-45
100
-50
80
-55
60
40
-60
Phase [°]
Magnitude [dB]
The ratio between the
response
signal
(Vout)
and
the
reference
voltage
(Vin), represented as
Gain (DB’s) plotted
against frequency is
the required SFRA
curve.
-65
-70
20
0
-20
-75
-40
-80
-60
-85
-80
-90
-100
-120
-95
-140
-100
-160
10
100
1,000
10,000
Frequency [Hz]
100,000
Magnitude
1,000,000
10,000,000
10
100
1,000
10,000
Frequency [Hz]
100,000
1,000,000
Phase Difference
10,000,000
Core insulation check
•
•
•
•
To ensure isolation between core-frame and tank
Allows for investigating accidental grounds which results in circulating
currents if there is more than one connection between the core and ground.
Desire value minimum 1000M
To be corelated with DGA results
Insulation Resistance Measurement
Purpose : To check the condition of insulation ( degree of dryness of paper
insulation) and presence of any foreign contaminants in oil
Absorption Coefficient:
IR (60 sec)/ IR(15 sec )
Polarization Index:
IR (600 sec)/ IR(60 sec )
I(t)=Ic(t)+Ia(t)+Ir
Insulation Resistance Measurement
For Class A insulation in reasonably dried condition DAI at 30 C should be more
than 1.3. Even if insulation is dry, IR value may be low due to low resistivity of oil.
Time diagrams of good and bad
insulation tested
Turns Ratio/ Polarity Test
• The turns ratio of a transformer is the ratio of the no. of turns in a higher
voltage winding to that in a lower voltage winding.
• The voltage ratio of a transformer is the ratio of the rms terminal voltage of a
higher voltage winding to the rms terminal voltage of a lower voltage
winding.
• For all practical purposes, when the transformer is on open circuit, its voltage
and turns ratio may be considered to be equal.
• Polarity is determined by the internal connections and is indicated on the
name plate. The polarity of transformer is of interest when it is to be
connected in parallel with one or more other transformers.
Exciting/ Magnetising Current Test
• Exciting/Magnetizing current is the current required to force a given flux thorough
the core.
• Normally done before DC measurements to avoid the effect of residual magnetism
• Transformer under test may be demagnetized before commencement of this test.
Results
•between
similar
single
phase
units/phases:10%
•As compared to previous tests : 25%.
•The test values on the
•outside legs should be within 15 % of each
other, and values for the centre leg should
not be more than either outside for a threephase transformers
Magnetic Balance Test
This test is conducted only in three phase Transformers to check imbalance in
magnetic circuit
V1
V2
V3
Transformer neutral to be disconnected from ground & apply 230V
across one phase and measure voltage in other two windings
Ensure V1 = V2+V3
Very negligible voltage induced to be investigated
Winding Resistance Measurement
• The transformer winding resistance is measured at site to check
• Physical displacement or distortion of winding
• Abnormalities due to loose connections
• Broken strands or short-circuited turns
• High contact resistance in tap changers
• As the transformer resistance is low resistance, the measurement is done with the
help of Kelvin Double Bridge/ Transformer Ohm Meter. Winding resistance at 75deg c
may be calculated
•
R75=Rt(235+75)/(235+t) , Where Rt= Resistance measured at winding temp t
The comparison of readings with other phases, duplicate transformers or previous
measurements should be done and variations under field conditions should not
exceed 5%.