VOLTAMP TRANSFORMERS LIMITED (An ISO 9001 Company)
Installation, Operation & Maintenance Manual for “VOLTAMP” make Cast Resin & Vacuum Resin Impregnated Dry Type Transformers
Registered Office & Works VOLTAMP TRANSFORMERS LIMITED, MAKARPURA, VADODARA - 390 014, GUJARAT, INDIA. Tel. : 0265 - 3041423, 2642011, 2642012 Fax : 0265 - 2648454, 2646774 E-mail :
[email protected] [email protected]
-Revision 02, Nov. 2007-
INDEX Sr. No.
TITLE
Section – I
General Description of the Dry Type Transformers
1.0 2.0 3.0
4.0 5.0 6.0 6.0 7.0
General Description of Dry Type Transformers Benefits of Dry Type Transformers Details of Construction & Assembly 3.1 Core 3.2 Windings 3.3 Winding Temperature Indicator (W.T.I.) 3.4 Tap Changer 3.5 Enclosure 3.6 Packing and dispatch Inspection on receipt at site Storing the Transformer at site Handling precautions at site Installation Checking the Electrical clearances
Section – II 8.0
COMMISSIONING
Pre-commissioning checks & tests for Dry Type Transformers
Section – III 9.0
PAGE NO.
MAINTENANCE
Maintenance of Dry Type Transformers
Annexure-I Annexure-II Annexure-III
Pre-commissioning tests Ventilation requirement for Dry Type Transformers Check List for Dry Type Transformers
1.0 General Description of Dry Type Transformers The Dry Transformers type Transformer consists of following major parts : Active Part : It consists of Core, LV winding, HV winding, Frame Parts. Core : The transformer core is made from cold-rolled grain-oriented silicon steel sheets (CRGO). Windings (HV and LV) : Windings are made from electrolytic-grade copper having either fiber glass or super enamel insulation. Frame Parts: The frame parts are made from M. S. channels and are powder-coated. The frame parts hold top and bottom yokes of the core-assembly and also hold the windings under required level of compression. Enclosure : Enclosure is made of CRCA sheet steels and it is pre-treated and powder-coated / epoxy liquid painted (NOTE: In case of IP 00 installation, Enclosure is not provided). Winding Temperature Indicator : Each Dry Transformers type transformer is supplied with digital winding temperature scanner having alarm (HIGH) and trip (TOO HIGH) contacts.
2.0 Benefits of Dry Type Transformers: The Dry Type Transformers do not require much maintenance except for periodic cleaning of the active part and the enclosure from inside for removal of the dust and foreign matters such as cobwebs, fiber particles etc. The Dry Type Transformers do not require any coil level adjustments. There is no fire hazard and hence is ideal for indoor installation. The total losses of Dry Type Transformers are lower as compared to the Oil filled transformers and hence are energy efficient. Oil related maintenance such as checking the BDV, oil levels, checking of the dielectric strength of oil, oil leakages, etc. is not required. The Cast Resin windings do not absorb moisture, except due to surface condensation when stored long. In comparison to Oil immersed transformers, in case of a cast resin transformers the windings have better dynamic short circuit strength, since the conductors are cast. The insulation materials glass fiber and reinforced epoxy resin are having better strength against temperature variations. The insulation materials used are self extinguishing, on removal of the electrical supply to the transformer. Since the thermal time constant is higher as compared to the oil filled transformer, it can take higher short duration overloads. The cast coil transformer complies with the I ndian Standards IS 2026 and IS 11171.
3.0
Details of Construction & Assembly:
3.1
CORE
The transformer core is made of high-grade alloy, low loss CRGO sheets with Carlite Insulation. The core limbs and yoke is cruciform shape with and inter leaved at the joints to reduce the losses. The completed core assembly is coated with resin to prevent corrosion on the cut edges. The core bots and yoke bolts are used to reduce the noise level and minimise the no-load current and no-load losses. The completed core assembly is tested for the No Load losses and the excitation current. Core-bolts are provided with fiber-glass insulation. The core-coil assembly is provided with vertical supports in form of either tie-rods or flitch plates to ensure rigidity of the active parts during transportation as well as during short circuits.
3.2
WINDINGS
The transformer windings are made from electrolytic grade copper with fiber glass or superenamel insulation on the copper conductors. The resin used for casting the coil has high electrical and mechanical strength. The insulation materials are fire retardant. The individual coils are cast under vacuum in M/s. Hedrich make German casting plant. The casting process is controlled by computer and this ensures high quality. The HV and the LV windings are pre-heated to remove the moisture from the surfaces and the insulations prior to the further processing. In case of Cast Resin Dry Type Transformers, the HV and LV windings are separately cast under vacuum and in case of Resin Impregnated Dry Type Transformers, the HV and LV windings are vacuum impregnated. The windings are oven-baked as per the process cycle given by our Collaborators. All the insulation materials which are used for inter-turn and inter-layer insulation are either fiber glass or super enameled. The insulation materials used are non-inflammable and are having self-extinguishing characteristics. The top and bottom of windings are supported with either fiber-glass blocks or epoxy insulators.
3.3
WINDING TEMPERATURE INDICATOR (WTI)
Each Dry Transformers type transformer is supplied with digital winding temperature scanner having alarm (HIGH) and trip (TOO HIGH) contacts. The ALARM & TRIP settings are factory set as per the insulation class. The temperature settings of alarm and trip contacts are user adjustable. In case of three-channel scanner, each LV winding is equipped with one No. RTD PT-100 sensor. The WTI scanner displays the temperatures of three phases sequentially. The Temperatures displayed on the Scanner consist of winding temperature rise + ambient temperature. For single phase application, single-channel WTI with one No. PT-100 type RTD sensor is provided instead of three-channel scanner. Temperature sensors i.e. RTDs are inserted into the cast coil, to measure the temperature of the low voltage windings in each phase. The WTI is operative either with 230 V AC or 110 V AC or suitable DC voltage as per the requirement of the control voltage. The alarm contact is normally set to operate at 130 Deg. Centi. and trip contact at 140 Deg. Centi. for F-class insulation.
The Winding Temperature Indicator is mounted in the Marshalling Box. The RTD (Resistance Temperature Detector) PT 100 sensor is a sensor whose resistance value is directly proportional to the Winding Temperature. (It has 100 ohms resistance between its two leads, at zero degree centigrade temperature). The change in its resistance is sensed by the WTI, which in turn, indicates the temperature of that winding. The WTI has following facilities: a) Alarm Temperature adjustment. Trip Temperature adjustment. b) Maximum Temperature Recording. The WTI has a memory, through which Maximum Temperature attained by the DRY TRANSFORMER winding is recorded. This can be reset, with which the WTI erases the previously recorded maximum winding temperature and is ready for recording the maximum temperature attained thereafter. 3.4
Tap Changer: Normally the Dry transformers are supplied with off-circuit tap links. The tap changing links are generally provided on the HV windings. For specific requirements the transformers are also supplied with a Tap Switch (off-circuit), or On Load Tap Changer. Please refer the G.A. drawing of the specific transformer for the type of the tap changing device.
3.5
Enclosure:
Enclosure is made of CRCA sheet steels and it is pre-treated and powder-coated / epoxy liquid painted (NOTE : In case of IP00 installation, Enclosure is not provided). The enclosure is provided with perforated sheet at the bottom and louvers backed by perforated sheet on enclosure doors for free air circulation. Flat Bi-directional Rollers are provided to support the enclosure assembly.
3.6
PACKING AND DISPATCH
The Dry Type Transformers are dispatched from our works as : a) b) C) D)
The active part is enclosed in CRCA steel sheet enclosure, and covered with polythene bag, when the order is for Indoor / out door installations. When the order is without enclosure (IP00), the active part is dispatched, it is covered with polythene bag and packed in wooden casing. Loose parts such as rollers are wooden packed Parts like appended cable box with disconnecting chambers, busducts etc. are supplied loose to meet size restrictions of the transport vehicle.
4.0
INSPECTION ON RECEIPT AT SITE
Handling and Inspection: Use crane etc. of adequate capacity. Lift only at the holes / hooks provided for the purpose. Please do not use the eye bolts of the canopy at the four corners for lifting the transformer. All the holes / Hooks must be used for lifting. For movement on the floor, fit rollers in the required direction. Please check the following on receipt of the Dry Transformers type Cast Resin Transformer / Vacuum Resin Impregnated Transformer and its components: 1) 2) 3)
4) 5)
Any transit damage to the enclosure, HV / LV coils and their support blocks, cable box, bushings, Marshalling Box and its WTI, loose bolts, (OLTC if provided) etc. Any damages, pilferages of copper busbars / bushings and the tap links, rollers, with reference to Delivery challan. The details of the shortages / damages to be marked on the reverse of the LR and the signature of the transporter / driver with the name of the driver to be obtained on the consignee copy and the transporter copy of the LR. The insurance claim is to be lodged with the insurance company through whom the transit insurance is arranged by you. For this please contact nearest Branch – of M/s. Voltamp Transformers Limited / our Works at Vadodara. The information required by our sales department in such a case will be : 1. 2. 3. 4. 5.
6. 7. 8. 9.
Project name / Client name / site address. Details of Transformer such as Sr. No. & Name Plate details. Purchase Order Number. Present Location of Transformer. Consignee copy of the Lorry Receipt having remarks for damages / pilferages etc. by the material receiving authorities with name , designation & signature, Customer’s Stamp and date of receipt. Details of damages / shortages of the Pilfered item / items and quantity. Sketch and photographs of the damages as required. Open Delivery Certificate taken from the Transporter. If the damage is caused by an accident to the vehicle – place of accident, date of accident, photographs, FIR No. / Police Panchanama and the required legal documents.
5.0
STORING THE TRANSFORMER AT SITE
The best place to store the transformer, when necessary, is indoors in a Dry Transformers, well ventilated place. Polythene sheet removed for inspection should be wrapped in position. If stored outdoors, the unit has to be protected against dust and rain water by storing under covered shed, duly covered with polythene sheet and Tarpaulin. If the Dry Transformers transformer is stored in a damp place, it may require drying before charging. Please consult us before charging. If the site has any chemical fumes or gases, such conditions should be advised to us before the Ordering. The Dry Transformers type transformer is non-inflammable and selfextinguishing after ignition, hence no special fire protective measures are required. 6.0 HANDLING PRECAUTIONS AT SITE The active part of the transformer (Core Coil Assembly) is provided with for solid lifting lugs, can be used for lifting the active part. The enclosure canopy has four nos. (two nos. in case of smaller ratings) heavy duty lifting hooks. The same are to be used for lifting the transformer. Rollers are provided for shifting of the transformer. The rollers are bi-directional and can be rotated by 90 Deg. (Please jack up the unit by a few cm for fitting / changing the direction of the rollers). During the pulling or pushing of the unit please ensure that there is no damage to the enclosure due the crow bar. The crow bar has to be positioned under the base channel and not to the enclosure body. Also, be careful to avoid any stress/ strain on the active part. Please ensure proper tying of the body by ropes while transporting in truck, to avoid the danger of toppling.
TRANSPORTATION AT SITE The active part assembly is such that the HV & LV coils are positioned around the limbs of the core and are locked to the frame parts by supporting blocks. Please handle it carefully. Lifting by crane is only permitted by means of the lifting lugs on the top of the transformer. The smaller rating transformers with weight of less than 1000 KGS., can be handled by a forklift truck. In this case the arms of the forklift are to be positioned under the base channels. All the movements of the unit are to be slow. Avoid jerks and swing while lifting / transporting and lowering operations, to avoid damage to the transformer or injuries to personnel and the adjoining objects.
7.0 INSTALLATION Transformer with minimum IP 44 degree of protection only is suitable for outdoor installation. Those with lesser degrees of protection e.g. IP 21, IP23, IP 33 are suitable for indoor installation only. When they are installed in closed rooms, the room must have openings of adequate area at: i) ii) iii)
Bottom for inlet of cool air and Top for outlet of hot air The size and the location of the openings can be calculated as per the example given in the Annexure - B
Ensure the following during installation : a. Remove all packing material and fixing / lifting accessories b. Lock the rollers to prevent any accidental movement of transformer. c. Open the doors / covers of the transformer. Core coil assembly now becomes accessible. d. Clean by dust-blowers spaces between between HV & LV windings, LV windings and core. Clean the coil surfaces by cloth. Clean the insulators and check for cracks. Avoid applying pressures to windings. e. Check that windings have not moved and pressure blocks are duly clamped. f. Check that there are no loose parts inside the enclosure or on core coil assembly. g. Ensure that the Delta formation lead of the HV coils (which connect the U,V,W phases) are not loose or moved and the clearances as per t he relevant voltage class are maintained. Please ensure that delta leads are not disturbed while doing the HV cable connections. h. All electrical connections must be tight. They must have sufficient cross-section and contact surface area. Contact surfaces must be thoroughly clean. Avoid sharp bends in HV conductors. All cables and connections must be at a safe distance from live parts. i. At factory, the tap changing links are set on the normal voltage position. THEY ARE SET IN THE SAME POSITION ON ALL THE THREE PHASES. Check that they are positioned accordingly. Please refer to the Rating & Diagram plate for the position of the Tap Links terminal numbers. If the supplied unit has Tap Switch or On Load Tap Changer , please ensure that the contacts of the tap changing device are fully engaged and at the desired position. j. Check that the transformer enclosure is properly earthed. Also ensure the connection of the Additional neutral to the ground. k. Check that Winding Temperature Indicator is properly wired and are properly functioning, where provided. Check that the RTD wires and the control cable bunch are not loose or any where near the HV coils. Check the Alarm and the Trip contacts of the WTI are connected to the respective control circuits of the control panel and the HV Breaker.
l. The RTDs are provided in the cooling duct of the LV coils only. Please check and ensure that the same are not put by mistake in the gap between the LV and HV coils, or in the cooling duct of the HV Coils. m. When the transformer is provided with fans/ blowers, check functioning of control circuits and correct direction of rotation. n. When the transformer is provided with fans / blowers, check functioning of control circuits and correct direction of rotation. q) Use channels embedded in the concrete for guiding the rollers. r)
s) t) u) v)
w)
The Dry Transformers type transformer is to be installed on an elevated Plinth / Platform, in areas having considerable fine sand / dust and also to prevent the entry of water during rainy season water logging. The plinth height has to be decided based on the maximum water logging at the site during monsoon. Fix the cable boxes when supplied loose as per the G.A. drawing. Connect the HV and LV cables/ Busducts as per the G.A. drawing. Ensure to put a whether shade for outdoor installations, this will ensure protection from sunlight and rain, and also save the Copper losses during the summer. Marshalling Box - The Marshalling box is mounted on the transformer enclosure (if applicable), it contains the WTI and control terminals blocks. Connect power supply of 230 V / 110 V, single phase, 50 c/s AC or 240 V DC etc, as per the wiring diagram. The air clearances between the enclosure body and the HV coils, between the HV coils of two phases and between HV and LV coils of individual phases are maintained, during the manufacturing as per its design / and the relevant standards. They should not be changed. Before closing the doors and the covers of the enclosure, check that no foreign materials and loose items such as cut cable strands, copper / M.S. chips etc. metal parts, nuts, bolts, electrical cut wire pieces, cotton waste, tools / spanners, live / dead insects/ rodents, or any other small animals etc. are left inside the enclosure / on core / on or inside the coils. This may cause accidents and failure of the Dry Transformers transformers.
WARNING:
DANGER TO LIFE
Do not go near the coils while in operation or during testing, since they carry high voltages. Maintain safe distance from the coils and the live parts, such as busbars, HV and LV terminals, cable termination points etc. The transformer coils and the cable / busduct terminations are carrying High and dangerous voltage and the same should not be touched while testing or after the charging. The charged transformer will retain the voltage due to capacitance effect even after tripping. It is necessary to ground the HV and the LV coils terminals using an insulated discharge pole connected to ground with a safe distance maintained.
8.0 Checking the electrical Clearances. The clearances are as per the respective voltage class and are factory set. Please ensure the following clearances while erecting and doing the HV and the LV cables/ or the busducts as per the respective voltage class of the transformer. Insulation Class (KV) 3.0 7.2 12 17.5 24 36
Min. distance to earth in mm. 20 90 120 220 220 320
SECTION II COMMISSIONING 1.
Following the Transformer installation in accordance with Section I, the transformer is ready for Pre-Commissioning Checks.
2.
Sequence of Pre-Commissioning checks is as per the Annexure A.
3.
DO NOT CONDUCT HIGH VOLTAGE TEST ON THE TRANSFORMER UNLESS IT IS PERMITTED BY U
4.
After the pre-commissioning tests and results are satisfactory, the Dry Transformers type transformer is ready for commissioning
5.
The transformer shall be put under observation at No Load, for any abnormality, through WTI readings, the protective relays on the HV switchgear for 24 hours. The transformer can be gradually loaded after this period. In case of any abnormal behavior the same has to be reported and the help of our service team will be taken.
6.
Voltamp commissioning Engineer can be present during Commissioning only if, it is under the scope of contract.
SECTION III MAINTENANCE OF DRY TYPE TRANSFORMERS 1.0
MAINTENANCE VOLTAMP Dry Transformers type transformer requires only a nominal maintenance during service. Following is the recommended schedule:
After switching off the transformer, it is necessary to ground the HV and the LV coils terminals using an insulated discharge pole connected to ground with a safe distance maintained. a) b) c) d) e) f) g)
h)
i)
Take proper care of the Dry transformer for trouble free operation. Maintain records / logbook of the test results for the transformer, for future comparison of the results. Any abnormality observed is to be recorded, and informed to us. The transformer is dry type and the insulation condition has to be maintained in good condition. Avoid overloads beyond the guaranteed KVA ratings and agreed over loading. Maintain proper circulation of the air in the place where the dry transformers are installed. Please refer the Ventilation requirements given in the Annexure – B. Please ensure that the ventilation louvers and the perforated sheets behind the louvers and at the top and the bottom of the enclosures are clean and not blocked by dust/ fibers/ cobwebs etc. Please follow the safety requirements during the maintenance. - de-energise the transformer. - isolate the HV supply & rack–out the HV breakers and the LV breakers. In case there is no HV breaker, isolate the Drop out fuses on the pole. Solidly earth the HV and t he LV terminations. - never attempt to work on the energized transformer, as this is dangerous. Please read the manual carefully, and follow the correct procedure. In case of any clarifications, kindly contact our branch or H.O.
CAUTION : Violation of the above instructions may lead to fatal accident to persons working on the DRY TRANSFORMERS. 2.0 Schedule of Maintenance :
a)
Monthly: i) Remove dust from the external surface, OF THE ENCLOSURE. If the doors / covers of the transformer are to be opened, the transformer has to be switched-off and the associated circuit breakers need to be in the off & racked out. Please follow the discharge procedure for removing and grounding the HV and LV termination described above. ii) Check up winding temperatures (when indicator is provided)
c) Half Yearly: (With transformer de-energised) : i) Clean the coils and remove any deposits within the ventilation passage through which cooling air flows. ii) Check that connections and clamping blocks are tight. NOTE :
If at a particular location, pollution is high, the frequency of maintenance may have to be suitably increased.
REPLACEMENT OF HV COIL AT SITE: In case it is required the HV coils can be replaced at site and the same has to be carried out by skilled and trained technicians.
In the event of an occurrence of a sustained external fault or an untoward incidence of HV coil failing the same has to be reported and a new HV coil will be supplied and replaced at site by our factory trained technician. It is advisable to take the help of our technician for this work. The procedure for replacing the HV coil can be furnished on request.
3.0 Annexure - I Pre-Commissioning Tests A) Measurement of the IR value (INSULATION RESISTANCE VALUE). Please use 2.5 kV MEGGER for the test. Do not use a 5 kV MEGGER for LV coils.
1 Minute IR values required
HV to Earth
LV to Earth
Between HV & LV
> 100 M ohms
> 20 M ohms
> 100 M ohms
In case the values are lower due to the humidity, the transformer has to be cleaned and dried using Halogen lamps / space heaters in the cubicle. One can also use a 415 V supply connected to the HV coils and short the LV coils for about 24 hours and recheck the IR values. B) VECTOR GROUP TEST : The example of the vector group Dyn11 is given below. For other vector groups please follow the standards or contact us. Connect main lead 1U to 2u and give 433 V, 3 ph., 50 Hz AC supply to HT, main terminals i.e. 1U, 1V, 1W and measure relevant voltages applicable for the vector group in subject. This should fulfill the requirement of the particular vector group. A typical example is given below. e.g. For Dyn11 Vector Group three conditions to be met are: 1V2w = 1V2v,
1W2w < 1W2v,
Volts 1V2w= ______ 1W2w= ______ 1U2N = ______1V2N = ___
1U2N + 1V2N = 1U1V
Volts 1V2v= _______ 1W2v= ______ 1U1V = _______
Requirements 1V2w = 1V2v 1W2w< 1W2v 1U2N + 1V2N = 1U1V
C) VOLTAGE RATIO TEST (BY VOLTMETER) / RATIO METER: The ratio of the voltage measured is to be compared with the desired voltage ratio of the transformer. e.g. For 11000/0.433 kV, Dyn11 the voltage ratio at the rated tap is = 11000/ SQRT(0.433) = 11000/250 = 44 HVTap No.
1U1V / 1U1N
HV Volts 1V1W / 1V1N
1W1U / 1W1N
2u2v
LV Volts 2v2w
2w2u
LV Volts 2u2n 2v2n 2w2n
1 2 3 4 5 Preferably use digital multi meter of reputed make. In case the transformer is with higher number of taps, please extend the table as required.
D) MAGNETIC CORE BALANCE TEST: This test is to be conducted by applying the low voltage to the HV coils. (DO NOT APPLY VOLTAGE TO LV TERMINALS. THIS WOULD INDUCE HIGH VOLTAGE ON THE HV COILS/TERMINALS). Please use 230/ 110 volts, 50 Hz. AC source for the magnetic balance test. Applied Voltage on HV coil Between 1U1V 1V1W 1W1U
Measured Voltages 1U1V
HV (Volts) 1V1W
1W1U
2U2V
2V2W
LV (Volts) 2W2U 2U2N
2V2N
2W2N
E) MAGNETISING CURRENT MEASUREMENT: Apply 433V, 3 ph., 50 c/s, AC supply to HV Main leads and measure input current with LT open, at Min., Normal, Max.Tap. Measure the following currents using a suitable digital multimeter Tap Links Position Min. Normal Maxi.
Voltage Applied to HV Winding (In Volts) 1U1V 1V1W 1W1U
Magnetising Current Drawn by HV Winding (in milli amps.) U Phase V Phase W Phase
ANNEXURE – II VENTILATION REQUIREMENT FOR THE ROOM WHERE THE DRY TYPE TRANFORMERS ARE INSTALLED: Calculations for 1000 KVA Dry Transformer: FORMULAE : Sb =
1000 11.55
P =
0.18*P
KVA KW
2
Sb =
1.200311
M
2
St =
1.320342
M
V/t =
52.668
M
2
√Η St =
1.1 X Sb
M
P x 45.6
M/ min.
2
3
V/t =
3
M / min.
∆θ
2
Sb = St = P= H=
AREA OF BOTTOM AIR INLET in M 2 AREA OF TOP AIR OUTLET in M TOTAL TRANSFORMER LOSSES in KW HEIGHT DIFF. BETWEEN TOP & BOTTOM OPENINGS IN METERS (assumed as 3 meters )
∆θ
TEMP. DIFF. IN BETWEEN OUTLET & INLET AIR ( Assumed as 10 ° C) 3 AIR VOLUME PER UNIT OF TIME in M / MINUTE
V/t =
ASSUMED AIR TEMP. = AVERAGE AIR AMBIENT OF 40°C & ALTITUDE UP TO 1000 METERS
Annexure - III Check List for Dry Transformers A) Use Lifting hooks (with latch) / ‘D’ shackles and proper slings to lift the T/R. Please ensure that the lifting hooks are of appropriate size as per the weight of the transformer. The weight of the transformer is given in the GA drawing and also on the Rating & Diagram plate fixed on the transformer. Use only those lifting lugs, which are meant for lifting complete T/R. Do not use the small eye bolts on the four corners of the enclosure canopy. B) Provide adequate and strong fencing around T/R & Danger Boards at proper locations, in case it is without enclosure. Never store T/R in open to sky if it is without enclosure. C) Check and ensure that enough electrical clearances are maintained between HV/LV live terminals & from enclosure, while connecting the cables. D) Check & ensure that the primary & secondary supply voltages on the system & name plate of the T/R are same. E) Check and ensure the correct temperature settings of WTI Alarm & Trip contact. The WTI will read the final Temperature. e.g. For site ambient temp. of 50° C, F – class insulation & permissible temperature rise of 90° C, the maximum allowable temperature will be = 50+90+15 = 155° C. The factory settings for the WTI are 140° C (Trip) & 130° C (Alarm). Check the tap changing link for all the three phases are at proper position, according to the system voltage. Also, check that, tap links of all the three HV windings at same positions and are properly tightened. Do not try to over tighten the links, it may damage the threads of the hardware and particularly the nuts in the castled coils. F) Check the Winding Temperature Indicator (WTI) by giving 220 / 240 Volts AC; 1 Phase; 50 Hz or the required DC supply as per the WTI aux. voltage given in the specific job drawings as supplied. G) Ensure that the Alarm and Trip contacts of WTI are properly connected to HV/LV circuit breaker having shut trip coil. H Check the T/R enclosure ventilation perforated sheet, for cobwebs / dust for free circulation of air & effective cooling of T/R. I) Check enough circulation of fresh air, for proper cooling of T/R. In case the T/R is installed in closed room, any deviation can cause overheating of T/R & the same shall be damaged. Use blower or soft non-fibrous cloth for cleaning of T/R surface. II) Check all the electrical connections are tightened before charging the T/R. III) Check provision of proper capacity circuit breaker on HV/LV side of T/R, having shunt trip arrangement. IV) Check the Marshalling Box & Secondary of CT (if CT is provided) are not open. V) If T/Rs are being operated under parallel operation, check all the conditions of parallel operation are satisfied as per IS 2026. VI) Check the connected load on T/R is within the permissible limit. Overloading of T/R may cause failure & permanent damage. Check all the pre-commissioning tests are done & found Ok. VII) At any time during the use if the circuit breaker has tripped on HV/LV of the T/R, VIII) please check the transformer and conduct pre-commissioning tests (Megger & Magnetic Balance tests) before charging the s ame.
