The Technology for Manufacturing Oil-immersed Power & Distribution Transformers

Binary's corporate thinking is driven by the commitment to quality. The complete in house manufacturing process helps us to ensure optimum quality of the transformer. We have complete testing facility to test and check all the major raw-materials used in manufacturing the transformer. CRGO laminations are cut and annealed in house to achieve minimum magnetic flux distortion.
Fabrication section ensure the robustness, quality and fine finish of the tank and radiators of the transformer.
The manufacturing process of Transformer cover the following departments:-
1. Coil Winding
2. Core Assembly
3. Core-Coil Assembly
4. Tank-up
5. Transformer Tank
6. Painting & Finishing

Coil Winding is of two types:-
1. High Voltage Coils: H.V. Coils are the components of finished transformers. They are made on automatic layer setting winding machines.
• A solid cylindrical former of predetermined diameter and length is being used as hase over which is made.
• Generally round insulated wire of either copper (Cu) or Aluminium (Al) is used as basic raw material.
• The coils are made in number of layers.
• The starting and finishing leads of each coil are terminated on either side of the coil.
• These leads are properly sleeved and locked at number of points.
2. Low Voltage Coils:
• L.V. Coils are also one of the components of transformer. The procedure of making low voltage coil is generally same as described earlier.
• The shape of the basic raw-material (Al or Cu) is rectangular.
The Test: The "Turn Test" is carried out on the H.V. Coils as per the specifications.

• The basic raw-material is COLD ROLLED GRAIN ORIENTED (CRGO) Silicon Steel
• It is in the form of thin sheets & cut to size as per design.
• Generally three different shapes of core laminations are used in one assembly.
• Notching is performed to increase the magnetic path.
• The laminations are put through annealing process.
• These laminations are assembled in such a manner that there is no air gap between the joints of two consecutive sheets.
• The entire assembly is done on a frame commonly known as core channel. These frames being used as a clamping support of the core assembly.

• The components produced in the coil winding and core assembly stage are then taken into core-coil assembly stage.
• The core assembly is vertically placed with the foot plate touching the ground. the top yoke of the core is removed. The limbs of the core are tightly wrapped with cotton tape and then varnished.
• Cylinder made out of insulating press board/ pressphan paper is wrapped on all the three limbs.
• Low Voltage Coil is placed on the insulated core limbs.
• Insulating block of specified thickness and number are placed both at the top and bottom of the L.V.Coil.
• Cylinder made out of corrugated paper or plain cylinder with oil ducts are provided over L.V.Coil.
• H.V. Coils are placed over the cylinder.
• Gap between each section of H.V. Coils including top & bottom clearances is maintained with the help of oil ducts, as per the design/drawings.
• The Top Yoke is refilled. Top core frame including core bolts and tie rods are fixed in position.
• Primary and secondary windings are connected as per the requirements. Phase barrier between H.V. phases are placed as per requirement.
• Connections to the tapping switch (if required) are made.
• Finally, the component is placed in the oven.

The core-coil assembly and tank supplied by the fabrication deptt. are taken into tank-up stage. The procedure is :
• The core-coil assembly is taken out of the oven and the "Megger test" is carried out.
• Only if the megger value is as per the specification, the assembly may be taken for tank-up.
• The tanks, supplied by fabrication deptt. are brought to tank-up department duly painted.
• Fittings like drain valves, HV& LV Bushings, conservator, oil level indicator and explosion vent are fitted in the tanks.
• The Core-coil assembly is then placed into the tank and properly locked up.
• Pure filtered transformer oil is filled in the tank to immerse the assembly only.
• Connections of primary and secondary to the terminal bushings are made. Operating handle for ratio switch is fitted, wherever required.

We, at Binary have a state-of-art in-house facility for manufacturing transformer tanks.
All tanks are made of high quality steel and can withstand vaccum as specified by the international standards and the customer. All welds are tested, ensuring 100% leakproof of seems and mechanical strength. Trasnformera with Corrogated Fin-Type radiators can aslo be supplied. The fins are manufactured of Gold-rolled steel.The fin height and length are according to customer's specifications and fins can be plain or embossed. All transformer tanks are given a smooth finishing by using the "SHOT BLASTING" process.

Painting : The entire procedure of painting is done under two stages:
1. Cleaning of tanks
• The cleaning of tank is done normally by chipping/grinding.
• The outside surface of the tank is short blasted to achieve a very fine and smooth finish
2. Painting of tanks
• After cleaning the tanks, a coat of hot oil resistence paint is applied on the internal surface of the tank.
• The outside surface is painted with a coat of Red Oxide primer and subsequently with one coat of enamel paint as per customer's requirement.

• Fittings and accessories as per customer's specification and drawing are checked.
• Air Pressure test is subjected to avoid any leakage and seepage on all transformer.
• Transformers are filled with oil upto the minimum level marking, wherever necessary.
• Loose accessories like, earthing terminals, bimetallic connectors, dial type thermometers are also checked for proper fittings.

WHAT IS A TRANSFORMER?
TRANSFORMER IS A STATIC DEVICE WHICH TRANSFORMS A.C. ELECTRICAL POWER FROM ONE VOLTAGE TO ANOTHER VOLTAGE KEEPING THE FREQUENCY SAME BY ELECTROMAGNETIC INDUCTION.

TYPES OF TRANSFORMER
BY APPLICATION

1. DISTRIBUTION TRANSFORMER
2.POWER TRANSFORMER
3.CURRENT TRANSFORMER
4.POTENTIAL TRANSFORMER
5.FURNACE TRANSFORMER
6.BOOSTER TRANSFORMER
7.RECTIFIER TRANSFORMER
8.LOCOMOTIVE TRANSFORMER
9.MINING TRANSFORMER
10.PHASE SHIFTING TRANSFORMER
11.WELDING TRANSFORMER
12.HIGH VOLTAGE TESTING/SC TESTING TRF.
13.GROUNDING TRANSFORMERS
14.CONVERTER TRANSFORMER

DISTRIBUTION TRANSFORMER
TRANSFORMER WHICH IS USED FOR THE PURPOSE OF DISTRIBUTION OF POWER.
11KV/433V is the standard voltage rating.
STANDARD KVA ratings are
25,63,100,160,200,250,315,400,500,630,750 , 1000? , 1250,1500,2000,2500 KVA.
IS-2026 is the NATIONAL I S STANDARD.

MAIN FEATURES
OUTDOOR,OIL COOLED, 3 PHASE,50HZ
PRIMARY IS DELTA? CONNECTED AND SECONDARY IS STAR CONNECTED.
NATURALY COOLED (ONAN TYPE).
AMONGST ALL THE TYPES OF TRANSFORMERS THIS IS THE MOST REQUIRED AND MOST USED TYPE.
PARTS OF TRANSFORMER
MAIN TANK
RADIATORS
CONSERVATOR
EXPLOSION VENT
LIFTING LUGS
AIR RELEASE PLUG
OIL LEVEL INDICATOR
TAP CHANGER
WHEELS
HV/LV BUSHINGS
FILTER VALVES
OIL FILLING PLUG
DRAIN PLUG
CABLE BOX
TESTING OF TRANSFORMER
TESTING IS CARRIED OUT AS PER IS-2026.
ROUTINE , TYPE TESTS & SPECIAL TESTS

ROUTINE TESTS ( TO BE CARRIED OUT ON EACH JOB)
1.Measurement of winding resistance
2.Measurement of insulation resistance
3.Seperate source voltage withstand test (High Voltage tests on HV & LV)
4.Induced Over voltage Withstand test (DVDF test)
5.Measurement of voltage ratio
6.Measurement of NO LOAD LOSS & current.
7.Measurement of LOAD LOSS & IMPEDENCE.(EFFICIENCY & REGULATION)
8.Vector Group Verification
9.Oil BDV test.
10.Tests on OLTC (if Attached)

TYPE TESTS
THESE TESTS ARE CARRIED OUT ONLY ON ONE TRANSFORMER OF THE LOT.
All routine tests
Additionally following tests are included in type tests
Lightening Impulse test.
Temperature rise test

SPECIAL TESTS
Additional Impulse test
Short circuit test
Measurement of zero Phase sequence Impedance test.
Measurement of acoustic noise level.
Measurement of harmonics of the no load current.
Magnetic balance test.

ROUTINE TESTS
Measurement of winding resistance

This test measures the resistance of the HV & LV winding. The values of resistance should be balance for all three phases and should match the designed values.
Equipment used : Digital resistance meter.

ROUTINE TESTS
Measurement of insulation resistance

Measures the insulation resistance of HV & LV windings with respect to earth (body) ???and between LV & HV winding.
INSULATION TESTER OR MEGGER IS USED.

Recommended Values are
2000Mohms for HV & 500 Mohms for LV.

ROUTINE TESTS
Seperate source voltage withstand test (High Voltage tests on HV & LV)- This test checks the insulation property between Primary to earth, Secondary to earth and between Primary & Secondary.

HV high voltage test : LV winding connected together and earthed. HV winding connected together and given 28 KV ( for 11KV transformer)? for 1 minute.
LV high Voltage test : HV winding connected together and earthed. LV winding connected together and given 3 KV for 1 minute.
Equipment used : High Voltage tester ( 100KV & 3KV)

ROUTINE TESTS
Induced Over voltage Withstand test (DVDF test)- This test checks the inter turn insulation.

????????
For a 11KV/433V transformer,866 Volts are applied at the 433V winding with the help of a Generator for 1 minute. This induces 22KV on 11KV side. The frequency of the 866V supply is also increased to 100HZ. ?
Equipment used : MOTOR GENERATOR SET

ROUTINE TESTS
Measurement of voltage ratio

?This test measures the voltage ratio as per the customer’s requirement.
V1/V2 = N1/N2
The voltage ratio is equal to the turns ratio in a transformer. Using this principle, the turns ratio is measured with the help of a turns ratio meter. If it is correct , then the voltage ratio is assumed to be correct.
Equipment used : Turns Ratiometer

ROUTINE TESTS
Measurement of NO LOAD LOSS & current.

The iron losses and no load current are measured in this test. The 433V winding is charged at 433V supply & the 11KV winding is left open .The power consumed by the transformer at no load is the no load loss in the transformer.
Effect of actual frequency must be taken into account.
Equipment used : Wattmeters or power analyser.

ROUTINE TESTS
Measurement of LOAD LOSS & IMPEDENCE.(EFFICIENCY & REGULATION)
This test measures the power consumed by the transformer when the 433V winding is short circuited and The rated current is passed through the 11KV winding.
Equipment used : Wattmeters or power analyser.

ROUTINE TESTS
Vector Group Verification test

This test verifies the Dyn-11 vector group of a distribution transformer.

Equipment used : voltmeter.

ROUTINE TESTS
Oil BDV TEST.
Oil breakdown voltage is checked as per IS-335.
100 mm L X 70 mm B X 80 mm Ht. glass pot.
500ml Oil sample.
Spherical electrodes with gap of 2.5 mm
Recommended value : 60KV
Equipment used : OIL BDV TEST SET.

TYPE TESTS

LIGHTENING IMPULSE TEST

All the dielectric tests check the insulation level of the job.
Impulse generator is used to produce the specified voltage impulse wave of 1.2/50 micro seconds wave
One impulse of a reduced voltage between 50 to 75% of the full test voltage and subsequent three impulses at full voltage.
For a three phase transformer, impulse is carried out on all three phases in succession.
The voltage is applied on each of the line terminal in succession, keeping the other terminals earthed.
The current and voltage wave shapes are recorded on the oscilloscope and any distortion in the wave shape is the criteria for failure.

SPECIAL TEST

Short circuit withstand ability test.

This tests measures the ability of the transformer to withstand the mechanical and thermal stresses caused by the external short circuit.
HV terminals are connected to the supply bus of the testing plant. The LV is short circuited. The testing plant parameters are such adjusted to give the rated short circuit current.
Supply is made on and closed after specified duration of short circuit. The record of current wave form is noted.
There should not be any mechanical distortion, fire to the transformer during this test. Similarly no wave form distortion. The transformer should also withstand the routine tests after the short circuit test.
The reactance of the winding measured before and after the S.C. test should not vary beyond the limits stated in the IS2026.

MAINTENANCE OF TRANSFORMER

Transformer is the heart of any power system. Hence preventive maintenance is always cost effective and time saving. Any failure to the transformer can extremely affect the whole functioning of the organization.?

MAINTENANCE PROCEDURE OIL :

Oil level checking. Leakages to be attended.
Oil BDV & acidity checking at regular intervals. If acidity is between 0.5 to 1mg KOH, oil should be kept under observation.
BDV, Color and smell of oil are indicative.

MAINTENANCE PROCEDURE

Sludge, dust, dirt ,moisture can be removed by filtration.

Oil when topped up shall be of the same make. It may lead to sludge formation and acidic contents.

Insulation resistance of the transformer should be checked once in 6 months.

Megger values along with oil values indicate the condition of transformer.

Periodic Dissolved Gas Analysis can be carried out.

MAINTENANCE

BUSHINGS

Bushings should be cleaned and inspected for any cracks.
Dust & dirt deposition, Salt or chemical deposition, cement or acid fumes depositions should be carefully noted and rectified.

MAINTENANCE

Periodic checking of any loose connections of the terminations of HV & LV side.

Breather examination. Dehydration of Silica gel if necessary.

Explosion vent diaphragm examination.

Conservator to be cleaned from inside after every three years.

Regular inspection of OIL & WINDING TEMPERATURE METER readings.

Cleanliness in the Substation yard with all nets, vines,? shrubs removed.

PROTECTION OF TRANSFORMERS

The best way of protecting a transformer is to have good preventive maintenance schedule.

Oil Temperature Indicators.

Winding Temperature indicators.

Buchholz Relay.

Magnetic Oil level Gauge.

Explosion Vent.

PROTECTION OF TRANSFORMERS

HT fuse & D.O. fuse.

LT circuit breaker.

HT Circuit breaker with Over load, Earth Fault relay tripping.

Oil Surge Relay for OLTC.

PRV for OLTC.

HORN GAPS & Lightening Arrestor.

Breather.

FAILURES & CAUSES
Insufficient Oil level.
Seepage of water in oil.
Prolonged Over loading.
Single Phase loading.
Unbalanced loading.
Faulty Termination (Improper sized lugs etc)
Power Theft.
Prolonged Short Circuit.
Faulty operation of tap changer switch.
Lack of installation checks.

FAILURES & CAUSES

Faulty design

Poor Workmanship

Improper formation of core.

Improper core bolt insulation.

Burr to the lamination blades

Improper brazing of? joints.

Burr /sharp edges to the winding conductor.

Incomplete drying.

Bad insulation covering.

Insufficient cooling ducts in the winding.

FAILURES & CAUSES

Bad Quality of raw material

Transit damaged transformers.

After failure , transformer is removed and replaced with new/repaired one without removing the cause of failure which results in immediate or short time failure.