765kV Training Ppt

Design Aspects, Major Challenges and Our Expérience ofand Our Expérience of

765 kV Substations

Purshottam KalkyNTPC NoidaNTPC ,Noida

25.03.10

Index

Development of HVAC in world and Areva T&D Experience of765kV System.

Design Aspects and Major Challenges of 765kV System.B i D i tBasic Design parameters .State-of-the-art –technologies.

Future Major Challenges.Future Major Challenges.Return of Experiences –Case Studies.

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Development of Voltages Levels for AC Power TransmissionWorld

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Development of Voltages Levels for AC Power TransmissionWorld

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Development of Voltages Levels for AC Power TransmissionIndia

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765kV Substations – Areva Presence

S N S b i C SS.No. Substations Customer Status

1 765 KV in Venezuela EDELCA’s,Brazil Commisioned

2 765kV Sipat NTPC Commisioned

3 765kV Anpara –C Lanco Infratech Ltd. (LITL) Ongoing

4 765kV Bina and Satna PGCIL Ongoing4 765kV Bina and Satna PGCIL Ongoing

5 765kV Lucknow and Balia PGCIL Ongoing

6 765kV Jatikala and Moga PGCIL Ongoing6 765kV Jatikala and Moga PGCIL Ongoing

7 765kV Bhivani PGCIL Ongoing

8 765kV Anpara - D UPPTCL Ongoing

9 765kV Sasaram PGCIL To Start

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Basic Design Parameters

System Operating Voltage 765 kV 400 kVSystem Highest Voltage 800 kV 420 kVLightning Impulse withstand Voltage (kV) ± 2100 ± 1500Switching Surge withstand Voltage (kV) ± 1500 ± 1050Power Frequency Withstand Voltage q y gr.m.s. (kV) 830 630Max. Fault Level for 1 sec. (kA) 40 40/50/63Minimum Creepage Distance (mm) 20000 10500Minimum Corona extinction voltage (kV) 508 320Clerances (mm)

Phase to Phase 7600 4200Phase to Earth 4900 3500

Sectional Clearances 10300 6500

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Basic Design ParametersConductorConductor

Rigid Conductor 4.5 Inch (120mm) or

higher 4 InchMoose (31.77mm

Flexible Conductor Bull (38.24mm Dia)(

Dia)Per Phase Flexible conductor Arrangement 4 X Bull 4 X MooseSub Conductor spacingSub - Conductor spacing (mm)

At Main Bus and Jack Bus Level 450/457 450/457

At Equipment Level 300 450/457

Equipment Level (m) 14 8Jack Bus Level (m) 38/39 22Jack Bus Level (m) 38/39 22Main Bus Level (m) 26/27 15Phase to Phase spcing (m) 14/15 6 / 7

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Bay Width (m) 51.5 24 /27

State-of-the-art technologies

»The detail study was done to find an acceptable balancebetween parameters impacting in the bundle design in EHV likecorona, short circuit pinch effect and electrical field in a 765 kVNTPC India substationNTPC India substation.

»Short circuit mechanical criteria

» Corona –RIV criteria

Size of bare stranded conductor bundle»Electrical field

& health

criteria

»Fig 1: balance between the different phenomenon's.

»SELECTED WORKING

AREA

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»Fig 1: balance between the different phenomenon s.

State-of-the-art technologies

»Electric and Magnetic Field Consideration relatedto the 765 kV Substations.The advent and increasing use of higher voltage lines has increased

the relative importance of field effects such as induced voltage andcurrent in conducting bodies.

During the past 20 years the general public has become increasinglyDuring the past 20 years the general public has become increasinglyconcerned about potential adverse health effects of exposure toelectric and magnetic fields at extremely low frequencies (ELF).

Such exposures arise mainly from the transmission and use ofl t i l t th f i f 50/60 Helectrical energy at the power frequencies of 50/60 Hz.WHO's International EMF Project has been established to work

towards resolving the health issues raised by EMF exposure.Scientific reviews have been conducted and gaps in knowledgeScientific reviews have been conducted and gaps in knowledge

identified.A formal task group meeting to assess the results was held by IARC

in 2001. WHO adopted IARC's conclusions after assessment of non-h lth i k i 2002

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cancer health risks in 2002.

State-of-the-art technologies»The International Commission on Non-Ionizing Radiation Protection(ICNIRP) has p blished g idelines on e pos re limits for all EMF(ICNIRP) has published guidelines on exposure limits for all EMF.»The guidelines provide adequate protection against known healtheffects and those that can occur when touching charged objects in anexternal electric field.»Limits of EMF exposure recommended in many countries are broadlysimilar to those of ICNIRP, which is a non-governmental organization(NGO) formally recognized by WHO and a full partner in theInternational EMF Project.International EMF Project.

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State-of-the-art technologies»The electric field and magnetic fields were calculated for the»The electric field and magnetic fields were calculated for thefollowing geometry based on the layout :

S.No. Variable Qualifier

1 Umax 800 kV

2 Height above ground for field calculation 1 8 m2 Height above ground for field calculation 1.8 m

3 Conductor bundle 4 X Bull

4 Conductor Diameter 38.25 mm

5 Sub-Conductor Spacing 450/300mm

6 Phase conductor separation 14 m

7 Phase conductor height above ground 14,26 & 38 m

8 Busbar Current 600 A

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State-of-the-art technologiesThe mean value of the electrical field along the switchyard in theThe mean value of the electrical field along the switchyard, in themost exposed area (lower connection level) is 7.20 kV/m < 10kV/m…taken into account all future extension with 300mm quad bullbundle for equipment at 14m level.

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State-of-the-art technologies

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State-of-the-art technologies

» Equipotential lines

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State-of-the-art technologies

» Magnetic field in 765 kV substations

Ball

»In any cases the magnetic fields in this the working area is 67 µT < 500 µT.

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State-of-the-art technologies

»The corona effect on conductor and connectors.»The Corona effect (disruptive discharge) is due to importantelectrical field in the very close area of the bare conductor / bareyaccessories). For 765 kV it’s a main criterion.»Due to increment of the corona effect with the proximity of theground, the management of the bundle design needs deepi ti ti f ti b t tinvestigations for connection between apparatuses.»The critical surface gradient of a cylindrical cable has beenevaluated using Peek's formula (inception of Corona effect).

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State-of-the-art technologies

»Following observation was made during corona study.»The ratio of operating conductor surface gradient to coronainception gradient should Eops/Ec < 0.90»The optimum conductor spacing for the minimum conductorsurface gradient (adjacent conductor spacing , not diagonaldistance ) is seen from the range of 300 to 400 mm .»Continuous corona will also generate high levels of radio noiseand corona losses in dry conditions. The extraneous radio noisewill increase background noise levels and so pollute the localradio frequency spectrum.radio frequency spectrum.

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State-of-the-art technologies

»Following observation was made during corona study forconnectors

»Limitations of RIV / corona performance are mainly link to»Limitations of RIV / corona performance are mainly link toconnectors and equipment limitations / design.»Test have been carried from 200mm to 450mm cable spacing,up to 130% of Um (i.e. 660 kV phase-ground) based on a coronap ( p g )design optimised initially for 457mm cable spacing.»As expected extinction voltages are quite similar from 300mmand 450 mm spacing, except for the spacer.

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State-of-the-art technologies

»The spacer design is the most critical material in this case, a redesignof spacer had carried and tested again to meet requirement.

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State-of-the-art technologies

»Some Important design issue in terms of Corona for Non –CeramicInsulators (NCI).»The presence of corona activity is a good indication of trouble withnonceramic insulators and other transmission line equipmentnonceramic insulators and other transmission line equipment.»Corona in such situations is common and not only results in customercomplaints about audible noise and radio interference but also degradesthe polymeric rubber material of the NCI, which in turn can cause

t f il f th i l tipremature failure of the insulation.»Hence proper corona shielding shall be provided for NCI in 765 kVSubstations.

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State-of-the-art technologies

»Corona Issue with NCI

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State-of-the-art technologies

Short Circuit force for Towers and Equipment terminals.

At first simplified methods for calculation by hand had beendeveloped for typical cases based upon International standard IEC60865.

In the past only the static behavior of the support has been takeninto account.

Design loads suggested in IEC 60865 1 take the maximumDesign loads suggested in IEC 60865-1 take the maximuminstantaneous values of short-circuit tensile force Ft, drop force Ff,pinch force Fpi as static load for design purposes.

This methodology is not feasible as well as economical for highersystem voltages.

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State-of-the-art technologies

We find to alternate advance methods as International standardIEC 60865 is applicable for voltage class up to 420kV.Now days analytical and numerical methods or a combination ofboth on computers developed based on Advanced methods useboth on computers developed based on Advanced methods usefinite element or finite difference modeling.These software further based upon combination of Internationalstandard IEC 60865 and CIGRE 214 : “The Mechanical effects ofshort-circuit currents in open air Substation” Part-II working groupshort-circuit currents in open air Substation Part-II working group23.03.Recent development concerns a more on true impact of dynamicloading .

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State-of-the-art technologies

Some SCF videos which exactly can simulate in today’s software's.

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State-of-the-art technologies

Taken a 450mm bundle as reference 100% for traction load atapparatus terminals, a 300mm arrangement reduce the short circuitstress of 20%

Stress on equipment terminal120%

80%

100%

MainBF

40%

60%

0%

20%

200 250 300 350 400 450

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200 mm 250 mm 300 mm 350 mm 400 mm 450 mmBundle spacing

State-of-the-art technologies»Control Switching of Circuit Breakers.g»Optimizing a circuit breaker’s closing or opening moment is of utmostimportance when switching reactive loads because random switchingcan sometimes result in high transient overvoltage's and inrushcurrentscurrents.»These transients generate stresses for all substation and networkequipment, leading to accelerated aging or – in the worst case-destruction of equipment.»The RPH2 provides a reliable , low – cost way to reduces theseswitching transients to an acceptable level. Serving as a control unit , itdelays the switching order – phase by phase –until the pre- definedswitching time (depending on current / voltage network characteristics)that reduces switching transients to minimum level.»The RPH2 is particularly important element when switching largetransformer , shunt reactors, capacitors and uncompensated lines.

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State-of-the-art technologies»Insulation Coordination

»The study shall be carried out using ELETROMAGNETICTRANSIENT PROGRAM (EMTP), which is a well established programf h t difor such studies.

»The study shall be carried out in accordance with IEC71-1 andIEC71 2IEC71-2.

»The switchyard along with the transmission lines shall be modeledin accordance with the proposed layout plan diagram. Thein accordance with the proposed layout plan diagram. Theequipments as well as the distances between the equipments shallbe taken from this diagram.

»Various configurations (open close status of breakers) of theswitchyard shall be considered to arrive at the maximum overvoltagelevels at different points in the switchyard.

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»Switching overvoltage study shall be carried out due to switchingof incoming line breakers at remote end.

State-of-the-art technologies»Insulation Coordination

»The study shall be carried out using ELETROMAGNETICTRANSIENT PROGRAM (EMTP), which is a well established programf h t difor such studies.

»The study shall be carried out in accordance with IEC71-1 andIEC71 2IEC71-2.

»The switchyard along with the transmission lines shall be modeledin accordance with the proposed layout plan diagram. Thein accordance with the proposed layout plan diagram. Theequipments as well as the distances between the equipments shallbe taken from this diagram.

»Various configurations (open close status of breakers) of theswitchyard shall be considered to arrive at the maximum overvoltagelevels at different points in the switchyard.

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»Switching overvoltage study shall be carried out due to switchingof incoming line breakers at remote end.

Future Major Challenges

Online Switching for Spare ICT

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Future Major Challenges

Online Switching for Spare Line reactor with Single phase CB

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Return of Experience- Sipat»Flashover at GT-4 Suspension Insulator.

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Return of Experience- Sipat»Flashover at GT-4 Suspension Insulator. - Proposal

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Return of Experience- Sipat»RPH2 – Alarm Indication

»On Rph2 following alarm indications shown on display“command time” min. and “operating time max.”» Investigation carried out and final conclusion was to separateInput /output signal in separate cable.

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Conclusion

According to our experience,EHV Projects require aminutious consideration ofminutious consideration ofkey-factors which may not beas important as for loweras important as for lowervoltage Projects.

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Thank you for your attention!a you o you atte t o

We would be most pleased:We would be most pleased:»to provide additional information at the end of this lecture onany other topic of interest to you.»to provide in the future our support and advise if requested»to provide, in the future, our support and advise, if requestedby you.

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