o & m manual of sdt - vidhiya

5/10/2018 O & M Manual of SDT - Vidhiya

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Vidhia Electrotrans Industries

SINGLE PHASE POWERTHROUGH

SPECIAL DESIGN TRANSFORMER (SDT)

SDTMANUAL

Vidhia Electrotrans Industries309, GIDC Engineering Estate, Sector: 28,Gandhinagar : 382 028, Gujarat (India)Phone: (0) 079-23211448 Fax: 079-232 10402Email: [email protected]: www.vidhiatransformer.com
mailto:[email protected]://www.vidhiatransformer.com/http://www.vidhiatransformer.com/mailto:[email protected]


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INDEX

Sr. No. Particulars Page No.1 Object 32 Principal Parameters 33 Design Aspect 34 Protection System 45 Operational Instructions 46 Important instruction for installation & commissioning 57 Winding Connection Diagram 68 Schematic Line Diagram 69 Safety Measures 7(I) General 7(II) While commissioning SOT(A) Earthing 7(8) Change over switch 8(C) SOT Relay 8(D) Current Transformer 8(III) During Operation 810 Conclusion 9

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\III Vidhia Electrotrans Industries1. ObjectTo provide the single phase power supply during the period of planned load shedding on agricultureloads, with restriction on misuse of electricity using phase converter. It is intended to continue withsingle phase supply to scattered residential load through Special Design Transformer.2. Principal parametersThe Special Design Transformer (SOT) is suitable for outdoor installation at 50 Hz, 11 KV system inwhich the neutral is effectively earthed. It is suitable for service under fluctuations in supply voltageup to plus 10% to minus 10%.Sr. No. Item Specification1 Voltage class 11000 V2 No load voltage 6.64/10.12 KV3 Primary current in operating phase 30 Amps4 Phase R GROUND5 Type of cooling ONAN6 Guaranteed maximum temperature rise by 35 C / 40 Coil / winding resistance7 Frequency 50 Hz, 3%8 Winding Aluminum wound andSandwich type9 Reference IS 2026/1977 & 1180 1197210 Require continuous current caring capacity 400 Ampsof gang operated change over switch

3. DesignAspectThe design of SDTis uniq\.le and innovative in its own way and is first of its kind ever used by anyElectricity Utility.Transformer winding is sectionalized in two sections, say A & BSection -A Applied voltage Max. current capacity 11500 I - .J 3 volts. (As 11 KV Bus voltage at sis is almost kept 11500 V)Equal to difference of the ampere of input and output amperes ofSpecial Design Transformer

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Section - B Voltage across winding 3680 volts (for load reduction-cum-energy conservation criteria) Max. current capacity 1/44 times of single phase lighting load of LT side of all DY11 Dist.Transformers.This SOT enables to charge one of the phase of primary Delta Winding at 10120 volts (selectionconsidering criteria for energy conservation) for all the DY 11 Dist. Transformers connected on thefeeder. Accordingly, 230 volts on anyone of the phase is available on LT side for all the dist.Transformers. At the same time, it will be very difficult to operate agricultural pump during 1-phasepower supply hours and any attempt to use the agricultural pump during these hours with the help ofphase converter (Teta) will result either into failure of motor winding or tripping of the feeder breakerby appropriate relay, which prevents misuse of energy by phase converter.4. Protection System11 KV feeder provided with such Special Design Transformer (SOT) should get isolated during faultconditions. The breaker provided at the Sub-Station end should invariably trip in case of fault on theline as usual. In addition to this, it should also trip in case of there is over-loading of earth current.While the breaker is designed to take care of the faults during 3-phase conditions, when SpecialDesign Transformer (SOT) is totally isolated, no additional protection is required. However, duringsingle phase power supply hours, one of the conductor works as extended earth, which helps tostabilize the system. The current.in the earthing is sensed with the help of a CT of appropriate ratioto activate appropriate Over-current Relay. If the earthing current exceeds predetermined setting, itwill trip the breaker. This will ensure tripping of the 11 KV line even during single phasing or heavyover-drawl by consumers during single phase hours. This will not allow any usage of motors duringsingle phase hours, as the line will get tripped, if the earth current exceeds the preset value.Single phase load balancing will be done by installing SOT on different phase for different feeders ofsame load shading group, such as SOT will be connected on R phase for one feeder, on Y phase forsecond feeder and on B phase for third feeder. By this way current through power transformer neutralcan be minimized.

5. Operational Instructions

The entire operation of power supply on the feeders provided with Special Design Transformer (SOT)is to be carried out at the SUb-Station end only in the following order:Note: Total 3 terminals are brought out on the top plate of the SOT and the terminal marking of all thethree terminals are in capital letters : R (Earth), Y (In) and B (Out). The 'R' point terminal is indicatedwith the Earth mark.(A) For 3-phase power supply on the feeder

1. Switch off the breaker from Control Room.2. Isolate the Gang Operated change-over switch and make the contact to the cable side.3. Special Design Transformer (SOT) is, thus, isolated.4. Breaker to be made ON from the Control Room.4


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All the distribution transformers having DY 11 configuration will be energized and catered 3-phasepower supply to agricultural consumers along with the other than Agricultural Consumers.(B) For 1-phase power supply on the feeder

1. Switch off the breaker from Control Room.2. Open the Gang Operated change-over switch and connect it to the Special DesignTransformer (SOT).3. Breaker to be made ON from the Control Room.All other than Agricultural Consumers will get 1-phase power supply. Any attempt of using phaseconverters (Teta) by Agricultural Consumers will result into high drawl of current and the earth currentmay exceed the preset value and trip the breaker.(C) Operation of the Tripped Breaker due to Earth Relay on Special De$ign Transformer (SDT)A Special Design Transformer relay flag indicates, when the breaker trips due to operation of earthrelay on Special Design Transformer (SOT).

1. If this flag appears, the earth relay has operated and is required to be reset manually bypushing reset button.2. After resetting the earth relay, the breaker to be made ON from the Sub-Station for giving 1-phase power supply.(D) Frequent operation of earth relay on special design transformersIn case of tripping for the first time, the breaker to be made ON after operation mentioned at (C)immediately. In case of second tripping, the relay should be set only after one hour of tripping during1-phase power supply hours. In case of third tripping, the relay should be set after two hours. Incase of fourth tripping, no 1-phase power supply should be given for rest of the hours of the day.

6. Important instruction forinstallation&.commissioning1. 11 KV Class CT shall be used2. prQtection class CT shall be ensured 5 P 10 class with 15 VA burden, having ratio 30/1 A3. Prop~r relay current setting shall be ensured and should be matched with rating of SOT4. Time Multiplier Setting (TMS) of relay should be 0.025 seconds5. Connections shallbe ensured as per the schematic diagram

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7.Winding Connection Diagram

REarth

B (OUT)

8. Schematic Line Diagram

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9. Safety MeasurersFollowing safety measures are taken to ensure that the system is safe in its operation:-(I ) General

1. The breaker will trip in fault condition during 3-phase power supply hours by the Sub-Stationend breaker.2. The line will trip during single phase power supply hours, as two conductors are at apotential of 6.35 KV and 4.65 KV with respect to earth. The fault will be sensed by the earth-fault relay of the breaker.3. The third phase during single phase hours is already earthed. In case of phase to phasefault in any of the remaining two conductors, the ElF and ole relay will sense and breakerwill trip.4. The Special Design Transformer (SDT) is located within the Sub-Station premises. Twoseparate earthings will be provided to the transformer with GI earthing strip and pipeearthing. The continuity of earthing, measurement of earth resistance and regularmaintenance of the earthing pit will be easy. These earthings can be connected with theSub-Station earthing grid to ensure solid earthing and reduce earth resistance.5. The transformer earthing will be either separately fenced or within the fence-boundary of theSub-Station preventing any accidental contact by any-human or animal.6. In case of any internal faults on Special Design Transformer (SDD, earth relay provided ontransformer will trip the breaker. The faulty transformer can be easily isolated by the gangoperated switches provided.7. A separate circuitry is provided for measurement of earth current and additional trippingdevice will activate the tripping coil of the breaker to disconnect the line in case of any faulton the line or excessive current than the predetermined value.8. As the conductors on the line are live throughout 24 hours, the theft-hazards will also beminimized.9. In case the breaker has tripped due to the relay provided on earthing, the breaker will notoperate till the earth relay is not reset ensuring safety.10. Operational instructions shall be given to reset these IDMT relay for the first trippingimmediately, than after a time lag of .one hour for the second tripping, two hours for the thirdtripping SlQdor fourth tripping, No single phase supply should for rest of hours of the day, soas to prevent any over..oading during single phase hours or misuse of power for agriculturalpurpose.Lighting loadwill be restricted to design value, so that misuse of energy during single phasehOLjrsis prevented.

II. While Commis$icmingSDT(A) EarthingNote: Earthing is the most important part of the commissioning process.

1. Prepare two separate earthing pits near 11 KV outgoing bay for each sub-station and makeearthing as per the drawing.2. Digging of Earthing pits should be done with proper measurement. (At least 3 ft X 3 ft X 10ftdeep in ground)3. All the earthing will be made parallel by interconnecting them with GI strip having size of 50 x6 mm and make a earthing gride

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4. "R" Earth terminal of SOT must be solidly earthed with above grid with 16 sq.mm. CopperPVC insulated cable5. This earth wire should be covered with insulation like PVC rigid pipe and ensure that earthwire should not touch with any metallic part of the structure6. Earth pit chambers shall be prepared as per standards and GI water pipe line shall be laid forperiodical regular watering for reactivation of earthing7. Ensure that the Earthing pipe has required holes for water outlet so that the water poured inthe pipes can make the surrounding soil wet. (To reduce the earth resistance)8. Earth resistance shall be measured periodically to ensure proper earthing.9. If the earthing pit has sandy soil, replace it with black soil and mix the bentonitepowder while adding water to it. Make sure that mixture is done properly.10. While joining earthing pipe to earthing strip, ensure that the pipe as well as strip iscleaned well with glass paper to remove any rust, color, sand etc. This is importantas if it is not cleaned properly, it will increase the earth resistance.11. CT secondary terminal or control cable Armor should be in isolation and none ofthese should be in contact of transformer structure and earthing. If any of these are incontact, there is high risk of relay being damaged.(8) Change over Switch1. While fixing the change over switch, the leveling should be taken proper care of so that eachphase is connected properly.2. Keep the 0.0 fuse between change over switch and SOT.3. All the jumpers (Change over switch 1 SOT 10.0 Fuse) should be fixed with lug crimping.( C ) SOT Relay (Inverse Definite Minimum Time Relay)1. This is the most sensitive part of the system2. Proper relay current setting shall be ensured and should be matched with rating of SOT.3. Time Multiplier Setting (TMS)of relay should be 0.025 seconds.(D) Current Transformer (CT)1. 11KV class CTshall be used.2. Protection class CT shall be ensured 5 P 10 class with 15 VA burden, having ratio 30/1 Amps.(III)DQ~ingOperation1. Shut down the feeder breaker before operating the SOT change over switch.2. Before operating the SOT

2.1 Ensure that the feeder is isolated2.2 Keep the change over switch in three phase power supply position2.3 Start the operation only after ensuring that the earthing is done properly

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10. Conclusion

The innovative single phase power supply system is very much cost effective and meets the purpose.Over and above, SOT is so designed that required voltage level can be set and no load loss of DY 11Distribution Transformers can be reduced by charging them at controlled voltage level.Drawl of load in terms of KW can be reduced by controlling voltage level. Over heating of fluorescenttube chock and fan core can also be reduced. By this way, less drawl of current will also result in toreduction in line losses. Thus wastage of energy, due to heat dissipation and 1 2 R losses of line can bereduced as well as the failure of distribution transformers can also be reduced.

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o & m manual of sdt - vidhiya

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