Dry Transformer Course.pptx

Operation and maintenance of dry transformers

1. Mapna Group | Slide 1 Dry Type Transformers

2. Mapna Group | Slide 2 Content

3. Mapna Group | Slide 3 What is a dry transformer? A dry transformer does not utilized any kind of liquid for cooling , it has windings encapsulated under Vacuum , in epoxy resin reinforced with glass net. It is the most technologically advanced design for extreme conditions. These transformers meet strict parameters with respect to electrical system demands , are virtually maintenance free and are manufactured in accordance with industry and international standards including, IEC 60076-11.

4. Mapna Group | Slide 4 Main advantages: safe and environmental friendly Reduced environmental contamination . Zero risk of leakage of flammable or contaminating substances. Environmental safe in production. Well suited to damp and contaminated areas. No fire hazard. Transformers are non flammable and self-extinguishing. High resistance to short circuits. High capacity to support overloads. High performance in dealing with seismic phenomenon. Capable of withstanding the most severe of rolling and vibrating conditions.

5. Mapna Group | Slide 5 Main advantages: The most economical Less space needed. Less civil work needed. No special safety features required. (fire detection) Maintenance free. Longer transformer life due to low thermal and dialectic ageing. Can be installed closer to the point of consumption reducing load cable losses. Optimal design subject to constant improvements in design as new materials become available.

6. Mapna Group | Slide 6 Environmental, climatic and fire classes Environment E0 Normal indoor installation, no condensation, no considerable pollution. E1 Limited pollution, occasional condensation eg off circuit periods. E2  Heavy pollution, frequent condensation . Climate C1 Lower ambient temperatures: Operation -5 °C Storage and transport -25 °C C2  Lower ambient temperatures: Operation -25 ºC/-25 ºC Storage and transport Fire F0 No special requirements except typical characteristics for dry type transformers . F1  Increase demands. All material practically free of halogens Limited formation of fumes Limited contribution with calorific energy to the source of fire Self extinguishing transformer fire

7. Mapna Group | Slide 7 Dry transformers VS Oil transformers The best alternative due to: Suitable to operate in humid or heavily polluted environments (E2). Suitable for operation, transport and storage at ambient temperatures down to -25 ºC (C2). Restricted flammability, self fire extinction (F1). Emission of toxic substances and opacity of fumes is minimized (F1). Withstand the same impulse test even for exposed situation. Have more ability to withstand thermal and dynamic short circuit effects. Mechanically stronger, safer against vibrations, earthquakes, etc.. No liquid, neither leaks and no risk of polluting spills. Fire hazard Safety for people and property Respect for natural life

8. Mapna Group | Slide 8 Types and Designs Types: Standard three phase transformer. Multi winding transformer. Low Voltage transformer. Autotransformer. Drive systems transformers. Excitation systems transformers. Standard designs: High Voltage winding material: foil disks. Low Voltage winding material: aluminum/copper foils. Insulation class: F (155°), H (180°).

9. Mapna Group | Slide 9 Dry Transformer Components 1 2 3 4 5 6 7 8 9 1 1 2 3 4 5 6 7 8 9 1 Wheels Foundation Lower clamp High-voltage connecting rod Insulating cylinder iron core Neutral bar Low-voltage winding High-voltage winding Upper clamp

10. Mapna Group | Slide 10 Dry Transformer Components 1. Magnetic Core: The magnetic core is made from laminations of grain-oriented silicon steel insulated with 0.25- 0.3 mm thickness . The choice and grade of steel and the 45 degrees cutting pattern and method of step-lap assembly minimize the loss level and the no-load current with the effect of a very low noise level.

11. Mapna Group | Slide 11 Dry Transformer Components 2. Low Voltage Winding: The low voltage winding is made of aluminum or copper foil to achieve zero axial stresses under short circuit conditions; the foil is insulated by a class F or H inter-layer film , pre-impregnated with heat-activated, epoxy resin. The ends of the winding are protected and insulated using a class F or H insulator. The whole winding is polymerized by being placed in an autoclave for 2 hours at 130°C which guarantees: Outstanding resistance to industrial atmosphere aggression , Excellent dielectric withstand , Excellent resistance to radial stresses under bolted short circuit conditions. Each LV winding terminates in a tin-plated aluminum or copper connection point, enabling connections to be made without using a contact interface (grease, bi-metal strip). Assembly is carried out according to current practices, including using spring pressure washers under nuts and screw heads.

12. Mapna Group | Slide 12 Dry Transformer Components 3. High Voltage Winding: The high voltage winding is usually made and wounded by series aluminum foil. This kind of wounding method is because of the high turn numbers and small cross-section in high voltage winding. These methods are used to obtain very low stress levels between adjacent conductors . This winding is cast and moulded under vacuum in a class F or H loading and fireproofed resin

13. Mapna Group | Slide 13 Dry Transformer Components Spacer strips (LV) Glass random non-woven with B-stage epoxy resin impregnation Polyester non-woven with B-stage epoxy resin impregnation  Support and spacers (LV) dog bones Layer insulation (LV) Multi-layer insulation with B-stage epoxy resin coating Glass fabric with B-stage epoxy resin impregnation NOMEX with epoxy resin coating Outer bandings (LV) Thread reinforced polyester non woven with B-stage epoxy resin impregnation   Insulation cylinders PET Folie   NOMEX  PET Vlies   Polyester folien-Laminat   Cast-resin reinforcement (HV) Glass roving fabric with cured epoxy resin

14. Mapna Group | Slide 14 Dry Transformer Components 4. Voltage regulation Some tap voltages are designed at high voltage side to control the voltage at the low voltage side and keeping it constant. The variation step voltages are ±2 × 2.5% according to the rated voltage. The variation of tap voltages is done via a piece of brass or copper at the high-voltage side. The variation of tap voltages in dry transformers is off-circuit type , and the transformer must be turned off. Low Voltage (V) High Voltage (V) Tap Number Connection Status 400 21000 1 6-5 20500 2 7-5 20000 3 7-4 19500 4 8-4 19000 5 8-3 5 4 3 7 6 8 5 4 3 7 6 8

15. Mapna Group | Slide 15 Dry Transformer transportation guidelines Handling lifting with slings Lifting is carried out using the 4 lifting holes for a transformer without an enclosure and by 2 lifting lugs in the case of a transformer with an enclosure. The slings should not form an inside angle greater than 60 °. lifting with a fork lift truck The lifting capacity of the fork lift truck should first be checked. If suitable, the forks should be inserted inside the base channels after removing the rollers . towing. Towing the transformer with or without enclosure should be done from the under base. For this purpose hole of 27 mm diameter are provided on every side of the under base. owing can be done in two directions : in the axis of the under base and perpendicular to that axis.

16. Mapna Group | Slide 16 Dry Transformer Maintenance guidelines Storage The transformer should be protected in storage from water drops and dust generating work (masonry, sanding, etc.). The transformer can be stored at a temperature down to - 25°C. The place of transformer storage should be protected from water drops , and if the transformer is delivered with a plastic cover , it should be kept over the equipment while it is in storage. It is better to place a dehumidifier such as silica gel close to the windings in humid environments and provide proper ventilation. The dry transformer is resilient against fire. It means that no anti-fire precautions are necessary .

17. Mapna Group | Slide 17 Dry Transformer Installation Installation and Commissioning It's not the dry transformer manufacturer's responsibility to install it basically, but it's recommended for commissioning to take advice from the manufacturer's professionals. For installation, the following guidelines are followed : The transformer should be installed on a flat surface and indoor (IP 00), and for outdoor installation, use an enclosure with appropriate IP ( eg . IP 35). the altitude should not be above 1000 meters unless a higher altitude is specified at the time of enquiry ; the ambient temperature for the transformer to be within the following limits : -minimum : – 25°C ; -maximum : + 40°C (unless a higher temperature is designed for based on information provided at the time of enquiry).

18. Mapna Group | Slide 18 Dry Transformer Installation Installation and Commissioning For an altitude and a daily average temperature higher than 1000 meters above the sea and 30° C respectively, the dry transformer must be de-rated according to IEC 60076 and IEEE C57.91: Type of cooling % of kVA rating Decrease load for each °C higher temperature Increase load for each °C lower temperature Decrease load per 100m (330 ft ) AN, AF, AN/AF 1.0 1.0 2.0 Type of cooling % of kVA rating Decrease load for each °C higher temperature Increase load for each °C lower temperature Decrease load per 100m (330 ft ) AN, AF, AN/AF 1.0 1.0

19. Mapna Group | Slide 19 Installation and Commissioning Ground the transformer and all metal parts including the enclosure. Check the terminal connections and the similarity of all taps in three phases Check the connection of thermal sensors via ohmmeter from the terminal box All steel and brass bolts should be tightened with the recommended torques below. Thread size Torques steel bolts ( N.m ) brass bolts ( N.m ) M8 20 10 M10 40 20 M12 75 35 M12 140 70 Dry Transformer Installation

20. Mapna Group | Slide 20 Installation and Commissioning (forced ventilation ) In the event of temporary overloading , to avoid overheating of the windings, it is possible to install forced ventilation. For powers equal or greater than 1000 kVA, it is possible to install forced ventilation to achieve a temporary increase in power of 40%, without any special modification. However, if an increase in power is requested , account must be taken of the impact of this choice on the following points : - Sections of cables and of Prefabricated Busbar Trunking (PBT), -The rating of the transformer's protective circuit breaker, -The size of inlet and outlet openings for air in the transformer room, -The life span of fans in service , which is considerably shortened compared with that of the transformer Dry Transformer Installation

21. Mapna Group | Slide 21 High voltage side cable connection The cable connection holes are reserved at the upper and lower ends of the connecting rod on the high voltage side of the transformer. Taking the delta connection as an example, the phase sequence at the upper end is U-V-W and the phase sequence at the lower end is V-W-U . Attention should be paid to correct phase sequence when connecting high voltage cables. Fasteners shall be used during the connection, and loosening preventive measures shall be taken to fix the cable at the terminal of the high-voltage connecting rod of the transformer. Dry Transformer Installation High voltage cable junction Corresponding connection phase sequence Upper terminal U-V-W Lower terminal V-W-U

22. Mapna Group | Slide 22 Low voltage side bus-bar or cable connections The low-voltage terminal of the transformer has reserved cable connection holes, and fasteners with loosening preventive measures are required to fix the cable or bus bar. If it is required to be equipped with copper- aluminium composite foil ( cupal ) as specially specified in the contract, the copper- aluminium composite foil ( cupal ) shall be installed between the low-voltage terminal of the transformer and the cable, or between the low-voltage terminal of the transformer and the bus bar. Please refer to the figure. In the installation of copper-aluminum composite foil, the copper surface should be in contact with the copper bars, and the aluminum surface should be in contact with the aluminum bars. Dry Transformer Installation

23. Mapna Group | Slide 23 Cable installation layout (with enclosure) For the transformer with protective enclosure , cables in its high-voltage side and low-voltage side can be imported to internal part of the enclosure through the top or bottom of the enclosure, which can be connected to the corresponding wiring site of the transformer. • The bending radius of the cable needs noting, to prevent force on end of cable connection. Dry Transformer Installation

24. Mapna Group | Slide 24 Cable installation layout (without enclosure) The high voltage side cable can be connected to the transformer after layout in the bottom cable tray or after layout the top cable tray . Cable or bus bar can used for the low-voltage side connection. If the bus bar connection is used, soft connection transition is recommended to avoid mechanical impact on the low-voltage winding and reduce noise level due to structural reasons. • High-voltage cables are not allowed to pass through the high-voltage connecting rod (delta connection) of the transformer. Dry Transformer Installation

25. Mapna Group | Slide 25 Electrical safety clearance Sufficient space must be ensured around the transformer to ensure a smooth connection of the cable and the necessary electrical distance. The minimum clearance value for flashover protection is as below. These electrical distances are for installation equal to or below 1000 m above the sea level, and for each 500 m increase above the 1000 m, the mentioned distances must increase by 10%. After the transformer is installed, ensure that the transformer body and enclosure are reliably grounded. Dry Transformer Installation Maximum voltage of the equipment (kV) Minimum clearance value A (mm) B (mm) C (mm) 12 125-150 50 40 24 225-280 100 50-70 36 325-400 160 90-110

26. Mapna Group | Slide 26 Commissioning of temperature control system The transformer may be equipped with a temperature control system to monitor the temperature of the winding to prevent abnormal temperature rise of the winding, thereby protecting the transformer. The temperature control system includes a temperature controller and a temperature sensor (PT100). The temperature sensor (PT100) is placed in the three-phase winding of the transformer. When the temperature reaches the set value, the temperature sensor (PT100) feeds back the corresponding temperature change to the temperature controller. After the temperature controller receives the corresponding feedback signal, it corresponds to different functional responses. The over-temperature alarm and over-temperature trip functions need to be connected with the relay protection system of the front-end equipment so that the higher-level equipment can be linked when the temperature controller acts. Dry Transformer Installation Temperature controller function description Parameter settings Over-temperature trip 140˚C Over-temperature alarm 130˚C Fan on 90˚C

27. Mapna Group | Slide 27 Ventilation of the Transformer Room In the case of natural cooling(AN ): the ventilation of the substation or of the enclosure must ensure by natural convection the dissipation of the heat produced by the transformer’s total losses. In the case of a sufficiently ventilated substation, appropriate ventilation will consist of a fresh air intake opening of S section at the bottom of the substation and an outgoing air opening S ’ located above on the opposite wall at height H metres above the intake opening. To ensure efficient cooling of the transformer and sufficient air circulation, it is essential to maintain a minimum height of 150 mm under the live section, by installing rollers or an equivalent booster. It must be noted that restricted air circulation reduces the transformer’s continuous and short term overload capacity . Dry Transformer Installation     = Sum of the transformer’s no-load and load losses expressed in kW at 120°C. S = Area of the lower air intake opening (allow for mesh factor) expressed inm 2 . S ’ = Area of the air outlet opening(allow for mesh factor) expressed in m 2 . H = Height difference between the two openings expressed in metres .  

28. Mapna Group | Slide 28 Ventilation of the Transformer Room In the case of Air cooling(AF): Forced ventilation of the substation is necessary for ambient temperatures above 20°C , or small or badly ventilated rooms for applications with frequent overloads. The fan can be thermostat controlled and operate as an extractor in the top part of the room. Dry Transformer Installation   = Sum of the transformer’s no-load and load losses expressed in kW at 120°C.   Ventilation (AN) of the Transformer Room (Example) - T ransformer 1000kVA, -Po = 2300 W , Pcc at 120°C = 11000 W, i.e. P= 13.3 kW. If the distance between the grills = 2 m, then S = 1.7 m 2 of net surface area necessary. If we imagine a grill obstructing the air inlet by 30 % ; the air inlet grill surface area should then be 1.5 m×1.5 m, and that of the air outlet should be 1.5 m×1.6 m.

29. Mapna Group | Slide 29 Pre-commissioning test Voltage ratio test: Measure the voltage ratio of the winding under all taps and the connection group. The allowable deviation of rated tap voltage ratio s hall not exceed ± 0.5%, except for special transformers. Tips: Earth the transformer Dry Transformer Commissioning   : Base Temperature : Ambient Temperature : Base Resistance : Ambient Resistance   DC Current source/ DC Battery Varying Resistor Ampere meter Volt meter Dry Transformer Wingding resistance test: Measure the DC resistance of the winding at all taps and records the winding temperature. (Measure the DC resistance shows the accuracy of transformer connections) Tips: DC current for low voltage winding : 10 A DC current for high voltage winding : 1A Maximum DC current: 10% rated current Minimum DC current: 1.2 times the maximum of no- load HV winding LV winding 200 V- 380 V

30. Mapna Group | Slide 30 Pre-commissioning test Insulation resistance test: Measure the insulation resistance values of the windings and cores and record ambient temperature and humidity. Tips: The insulation resistance is measured at ambient temperature of - 25 º C ~ 50 º C, humidity ≤ 90% If the insulation resistance is not less than 2 MΩ , a voltage can be applied to the low-voltage side of the transformer and the transformer can be dried by no-load heating. If the insulation resistance value is less than 2 MΩ , it can be dried by air drying or baking with heat lamp . Dry Transformer Commissioning HV Winding LV winding Body Megger Test position Test equipment (1 min) Test value requirements HV- E 2500 V ≥100 M Ω LV- E 2500 V ≥50 M Ω HV- LV 2500 V ≥100 M Ω 1 2 3 4

31. Mapna Group | Slide 31 I. Voltage regulation If the actual grid voltage deviates from the rated voltage of the transformer, the tapping gear of the transformer can be adjusted appropriately to control the output voltage value. For no-load voltage regulation, the transformer gear tap shall be adjusted to the appropriate gear to keep in line with the grid voltage. Tips: The gear of transformer is set at rated gear (4-7) by default when it leaves factory. Make sure that the transformer is powered off before adjusting the gear. The three-phase tap must be adjusted at the same time. The rear gear bolt must be tightened after adjustment and the torque value must be restored. Dry Transformer Operation

32. Mapna Group | Slide 32 II. No load operation When large capacity no-load transformers are put into operation , visible sparks may be generated at the joints of external components (especially at the core and clamps), but this phenomenon will soon disappear. This is due to physical reasons, and will not affect the safe operation of the transformer, so it is not a product defect. III. inrush current There is inrush current when the transformer is switched on , and the peak value can reach 6-8 times of rated current. The setting value of current quick protection for the transformer shall be larger than the peak value of inrush current, and the time limit shall be ≤ 0. 5 s. Therefore, no-load inrush impulse test shall be carried out before operation to check whether the relevant protection of the transformer is malfunction or not. If the protection value is set improperly, it will cause the tripping phenomenon in the later closing. IV. long-term storage or overhauled For long-term storage (storage time more than 3 months) or overhauled transformers or transformers to be used at ambient temperature below 0 ℃, it is recommended to operate without load for 12 hours before putting the transformers into load , and the load shall be gradually increased. Dry Transformer Operation

33. Mapna Group | Slide 33 V. overload operation The transformers are designed to operate at rated power at ambient temperature defined by IEC 60076 : 40 °C maximum 30 °C monthly average of the hottest month 20 °C annual average If operated normally, the transformer should attain its expected lifetime consumption. In particular, the average annual temperature and the load significantly affect the lifetime consumption. Environment temperatures differing from the annual average have an effect on the system’s load capacity. The three-phase voltage, current and temperature values shall be recorded periodically during the operation of the transformer so that the historical data of the transformer can be consulted in case of overhaul or fault. Dry Transformer Operation Ambient temperature (Average Annual temperature) Load rating –20 °C 124 % –10 °C 118 % 0 °C 112 % +10 °C 106 % +20 °C 100 % +25 °C 97% +30 °C 93 % +35 °C 90% https://www.worldweatheronline.com/

34. Mapna Group | Slide 34 Maintenance Cast-resin transformers are maintenance-free. Routinely inspect and clean the windings, bolt connections, alarm devices and all fan functions once a year . If the transformer is in dusty environment or close to the pollution source , it is recommended to clean the equipment every six months. It is recommended to fully inspect and clean the transformer every 5 years . Before maintenance, the transformer must be powered off and all terminals must be short-circuited and grounded. Transformer cleaning Blow off the transformer with dry compressed air or wipe with dry cloth and alcohol (concentrations above 85%) to prevent the formation of creepage paths and blockage of cooling air passages. Dry Transformer Maintenance Sediment Cleaning method Oily 2 Carbonaceous 1+2 Metal-containing 1+2 Saline 1+2 Dry dust 1+2 Wet dust 2 Cleaning method 1 Use compressed air to blow the transformer. The compressed air must be oil-free and water-free, and the air pressure ≤ 6 bar. Vacuum cleaners can also be used instead of compressed air for dust collection. Cleaning method 2 Wipe with a dry rag and alcohol (concentrations above 85%).

35. Mapna Group | Slide 35 Dry Transformer Maintenance S/N Maintenance items Maintenance cycle (recommended) Use Tools Methods: 1 Clean the surface stains of windings, pads and cores and stains at the heat dissipation holes of the enclosure Normally, each year or more. Every 6 months for dusty and other polluted environment Dry compressed air, pressure ≤ 3 bar, dry rags and alcohol Select cleaning method according to Form 1 2 Check winding surface condition Normally, each year or more. Every 6 months for dusty and other polluted environment Visual inspection No blackening or cracks on the surface of the winding (if any, please contact the manufacturer) 3 Check bolt and nut tightening status at cable connections Each year or after maintenance Torque wrench According to the torque table 4 Check correct tapping connections and bolt tightening Each year or after maintenance Torque wrench According to the torque table 5 Check grounding condition of transformer body and enclosure Each year or after maintenance Torque wrench and visual inspection According to the torque table

36. Mapna Group | Slide 36 Dry Transformer Maintenance S/N Maintenance items Maintenance cycle (recommended) Use Tools Methods: 6 Check whether temperature controller settings, temperature probe and PT100 are normal. Each year or after maintenance Heat gun, power supply The temperature of the temperature controller can be displayed normally by blowing the temperature probe with a heat gun. 7 Check the cooling fan Each year or after maintenance Power supply Turn on the power supply, start the operation according to the manual of the temperature controller, and observe whether it rotates 8 Insulation resistance test Each year or after maintenance or 5 years Insulation resistance tester Refer to for test values

37. Mapna Group | Slide 37 Dry Transformer Maintenance S/N Maintenance items Maintenance cycle (recommended) Use Tools Methods: 9 Transformation ratio test Every 5 years or after maintenance Transformation ratio tester Refer to test 10 DC resistance test Every 5 years or after maintenance DC resistance tester Refer to test 11 Power frequency withstand voltage test* Every 5 years or after maintenance Power frequency withstand voltage tester Refer to test * Applied withstand voltage test: The withstand voltage strength of the transformer is tested. The on-site tested withstand voltage value is 80% of the factory test voltage value. The factory test withstand voltage value can be shown in the factory test report and nameplate.

38. Mapna Group | Slide 38 Dry Transformer Maintenance (Frequently asked questions guidelines (chart)) S/N Question Possible cause Corrective measure 1 Temperature controller does not display Temperature controller power cord is not connected Measure whether the temperature controller power interface is energized and required to reconnect the power supply (85 ~ 250 V) It is internal failure of temperature controller, power interface of temperature controller is energized, but panel indicator lamp is not on Contact Service Center to replace with a new temperature controller 2 Temperature controller three phase temperature display FOC or FCC Wrong or poor connection or loose connection of temperature sensor Check and press the temperature sensor wiring and tighten it according to the auxiliary wire diagram on the transformer certificate of conformity Temperature sensor probe is damaged Contact Service Center to replace with a new temperature controller

39. Mapna Group | Slide 39 S/N Question Possible cause Corrective measure 2 Three-phase temperature display of temperature controller differs greatly Temperature sensor probe is not fully inserted into thermometer tube (three-phase probe is inserted at different depths) Check the position of the temperature probe and place it correctly Cooling fan is damaged Contact Service Center to replace with a new temperature controller Temperature sensor probe is damaged Contact Service Center to replace with a new temperature controller Three-phase load of transformer is not balanced Check three-phase load and voltage, current 3 The temperature controller cannot communicate properly with the monitoring device Wrong address setting for temperature controller Please refer to the use manual for the temperature controller The communication cable of the temperature controller and the strong electric cable are arranged together, which causes the interference of the communication signal Properly lay out the cables

40. Mapna Group | Slide 40 S/N Question Possible cause Corrective measure 4 Noise is abnormal Primary side voltage exceeds tapping rated voltage Disconnect the power of transformer and adjust tap gear The bus bar is not fixed well and there is resonance. The transformer is not well fixed with the ground, and the resonance enclosure plate is not fixed tightly, and there is resonance Bus bar, enclosure board and transformer base are well fixed There are unclamped free ends in the iron core or clamping parts, and there are high frequency vibrations during the excitation of the iron core, resulting in abnormal noise Check the fastening core and clamping piece and press the free end tight with insulating material Within the same power distribution room, multiple devices are placed close together, causing wall reflections and noise overlapping Reasonably lay out equipment position in power distribution room In the transformer load, equipment such as frequency converter produces large harmonics in the system, which makes the core excitation uneven and causes noise* Filter device is designed in low voltage system Transformer is under overload operation state Check the load and distribute the load reasonably *De-rating the Transformers according to non sinusoidal currents (Slide 44)

41. Mapna Group | Slide 41 S/N Question Possible cause Corrective measure 5 Cooling fan is not running Temperature does not reach fan start temperature value Refer to factory temperature setting value and setting method Cooling fan is damaged Contact Service Center to replace with a new cooling fan 6 Low side output voltage is high or low Grid input voltage is high or low Adjust the tap gear of transformer 7 Transformer over-temperature alarm, trip Transformer overload (overvoltage, over current) operation Check transformer load Cooling of transformer fails Check whether the cooling fan is working properly and check whether the cooling air duct is blocked 8 Winding surface discharge Severe stains (dust, etc.) on the surface of the winding Clean stains on windings, pads, etc. Short circuit on high and low voltage lines Check high-voltage lines High and low voltage transmission lines suffer from overvoltage impulse Optimize system protection functions

42. Mapna Group | Slide 42 S/N Question Possible cause Corrective measure 8 Winding surface discharge There is insufficient distance between metal structure and winding minimum insulation clearance requirements 9 Winding ablation and blackening Upon the service life of the transformer and natural damage; poor heat dissipation; long-term overload; short circuit of external wiring; system overload; wrong cable connection; metal foreign body falling into the cooling air duct of the winding; unscrewed torque of tap gear bolt; short circuit fault inside the winding, etc. On-site inspection is required. Please contact service center for such inspection. Dry Transformer Maintenance (Frequently asked questions guidelines (chart))

43. Mapna Group | Slide 43 Loading transformers with non sinusoidal currents All ratings for transformers are based on sinusoidal rms values, rated power, rated voltage, losses, temperature rise, etc. Dry Transformer Operation   : Rated Power : Rated Voltage : Rated Current   Load losses and temperature rise are based on sinusoidal rms rated current. + +   : DC losses produced by a DC current of the same value that rms fated current. : Winding eddy losses at the rated frequency produced by circulation current (eddy) in the windings due to leakage flux. : Other stray losses, produced in bus bars and steel parts due to leakage flux, these losses have not any influence on winding temperature rise.   All losses referred to the reference temperature. When transformer supply a non sinusoidal load current with the same rms value than rated current, DC losses remain constant but winding eddy losses increase due to the higher frequency of the harmonics, as a result, winding temperature rise increases and temperature limits can be exceed.

44. Mapna Group | Slide 44 Loading transformers with non sinusoidal currents A transformer requested to supply non sinusoidal loads, shall be oversized in order to guarantee that windings temperature limits are not exceed in service. Total Harmonic Distortion: Dry Transformer Operation It is a measurement of the  harmonic distortion  present in a signal and is defined as the ratio of the sum of the powers of all  harmonic  components to the power of the fundamental frequency. T   K- factor: K-factor defines the non-linear load a transformer can tolerate without overheating or damage. The basis for K factor is seen in the ABB Document ( Loading transformers with non sinusoidal currents ). This document identifies the method for correctly de-rating transformers for non-linear loads.   ( pu ): rms current for harmonic “h” in pu of rms rated current I rated h : is the harmonic number    

45. Mapna Group | Slide 45 Loading transformers with non sinusoidal currents Dry Transformer Operation * Remark: this equivalence list is valid up to 3150kVA transformers

46. Mapna Group | Slide 46 Loading transformers with non sinusoidal currents (Example) Dry Transformer Operation Fundamental Power – 2MVA Net harmonic content – K-17 => Factor K equals to 1.28 Equivalent Power – 2000 × 1.28 = 2560kVA As a result of this, the transformer shall be physically sized as 2560kVA rated power and the temperature rise limit shall be guaranteed at such equivalent power as well. Therefore, should the temperature rise test is requested, during the full load part of the test the current must be equal to the rated current multiplied by the proper Factor-K, i.e. assuming the no load voltage level on LV side is 417V (Dyn11), rated current will be 2000/ (417×√3) = 2.77kA, however test must be run at 2.77×1.28= 3.54kA (corresponding to 2560kVA).

47. Mapna Group | Slide 47 Excitation Transformer Dry Transformer

48. Mapna Group | Slide 48 Excitation Transformer Dry Transformer Electrostatic shielding Electrostatic shielding is a metallic barrier (aluminum or copper foil  ) built into a transformer between the primary and secondary winding. The shield is grounded. Providing an electrostatic shield between the primary and the secondary windings thus avoiding transfer of surge/impulse voltages passing through inter-winding capacitance . The stray capacitance between windings can generate asymmetry currents and could lead to high common mode noise and is found to emphasize the noise transmission in a converter,.

49. Mapna Group | Slide 49 Excitation Transformer Dry Transformer

50. Mapna Group | Slide 50 Excitation Transformer Dry Transformer Power (kVA) Height (m) Temperature ( °C ) THD (%) 2410 1650 40 29.7 2770.11 1000 40 29.7 2541.39 1000 40 I. Height: =2770.11 kVA      

51. Mapna Group | Slide 51 Dry Transformer The First Indoor 110KV/35KV 31.5MVA Cast Resin Transformer (CRT) and GIS Substation Layout

52. Mapna Group | Slide 52 Dry Transformer Useful References 1. Electric Power Transformer Engineering, Second Edition Edited by James H. Harlow 2. Spotlight on Modern Transformer Design by  Pavlos S. Georgilakis   3. Transformer Engineering: Design and Practice by   S.V.Kulkarni & S.A.Khaparde 4. Transformer Design Principles: With Applications to Core-Form Power Transformers, Second Edition by  By  Robert M. Del Vecchio , Bertrand Poulin , Pierre T. Feghali ,  Dilipkumar M. Shah,  Rajendra Ahuja 

53. Mapna Group | Slide 53 Dry Transformer Useful References 5. The J & P Transformer Book b y Martin Heathcote 6. Transformer and Inductor Design Handbook by Colonel William T. McLyman 7. ABB Transformer Handbook 8. ترانسفورماتور یک‌فازه و سه‌فازه (جلد 1 و 2) تالیف دکتر علی مطلبی

54. Mapna Group | Slide 54 Dry Transformer Useful References 8. الکترونیک قدرت هانس بولر ترجمه دکتر قدیر عزیزی قنادی Useful Telegram channel & Web site https :// t.me/transformermag_group ادمین گروه : مهندس آرش آقایی فر- مدیر مسئول فصلنامه ترانسفورماتور https :// electrical-engineering-portal.com

55. Mapna Group | Slide 55 Dry Transformer Learn from yesterday, live for today, hope for tomorrow. The important thing is “Not to stop questioning” Albert Einstein Thank you Question ?