1. SOUTHERN REGIONAL LOAD DESPATCH CENTRE BANGALORE
ONE DAY WORKSHOP ON
AVAILABLE TRANSFER CAPABILITY(ATC)
IN INDIAN CONTEXT
WELCOME TO
14TH AUGUST 2007
Power Grid Corporation of India Limited

2. ATC FUNDAMENTALS
WHY ATC?

3. Presentation Road Map What is Transfer Capability
Difference between Transfer Capability and Transmission capacity
Assessment of Transfer Capability
What is reliability Margin why are they required
What are the risks associated with violation of transfer capability in real time
How to Improve Transfer Capability

4. AIM OF POWER SYSTEM ENGINEERS
EARLIER STATEMENT
To provide Reliable, Stable and Secured Power supply to the end user with Least possible cost
PRESENT STATEMENT
To provide Reliable, Stable and Secured Power supply to the end user with Least possible cost WITH Maximizing profit to all stake holders

5. Electricity is a scientific phenomenon
EMF travels at the speed of light
Available ‘just-in-time’
Delivered to the customers fresh
No one get placed on hold
Impartial in its benevolence and wrath
Good servant but a ruthless master
Interconnected systems with thousands of kilometers of transmission lines and hundreds of generators operating with split second synchronism
The largest single machine ever created
Grid operation is a continuous interplay of technical phenomena and natural/ human intervention

6. Power flow characteristics
Is directional
Does not recognize geographical boundaries, asset ownership
Does not check the map to determine the shortest route
Flows are dictated purely by
Impedances of the transmission lines
Point of injection by generators
Point of consumption loads
“Time & Location matter is fundamental to operation”
-Shmuel Oren & Fernando Alvarado

7. Some Definitions
‘TTC is the amount of electric power that can be transferred over the interconnected transmission network in a reliable manner based on all of the following conditions:
1. For the existing or planned system configuration, and with normal (pre-contingency) operating procedures in effect, all facility loadings are within normal ratings and all voltages are within normal limits.
2. The electric systems are capable of absorbing the dynamic power swings, and remaining stable, following a disturbance that results in the loss of any single electric system element, such as a transmission line, transformer, or generating unit.
3. After the dynamic power swings subside following a disturbance that results in the loss of any single electric system element as described in 2 above, and after the operation of any automatic operating systems, but before any post-contingency operator-initiated system adjustments are implemented, all transmission facility loadings are within emergency ratings and all voltages are within emergency limits.

8. Some Definitions continued
4.With reference to condition 1 above, in the case where pre-contingency facility loadings reach normal thermal ratings at a transfer level below that at which any first contingency transfer limits are reached, the transfer capability is defined as that transfer level at which such normal ratings are reached.
5 In some cases, individual system, power pool, subregional, or Regional planning criteria or guides may require consideration of specified multiple contingencies, such as the outage of transmission circuits using common towers or rights-of-way, in the determination of transfer capability limits. If the resulting transfer limits for these multiple contingencies are more restrictive than the single contingency considerations described above, the more restrictive reliability criteria or guides must be observed.’

9. TRANSFER CAPABILITY
Transfer Capability’ is the measure of the ability of interconnected electric systems to reliably move power from one area to another over all transmission lines (or paths) between those areas under specified system conditions
POINT A
POINT B
Transfer Capability is different from ‘Transmission Capacity’, which usually refers to the thermal limit or rating of a particular transmission element or component

10. TRANSMISSION CAPACITY vs TRANSFER CAPABILITY
S No.
Transmission Capacity
Transfer Capability 1
Is a physical property in isolation
Is a collective behaviour of a system 2
Depends on design only
Depends on design, topology, system
conditions, accuracy of assumptions 3
Deterministic
Probabilistic 4
Constant under a set of conditions
Always varying 5
Time independent
Time dependent 6
Non-directional
Directional 7
Determined directly by design
Estimated indirectly through
simulation studies 8
Declared by designer/ manufacturer
Declared by the System Operator 9
Generally Understood by all
Frequently misunderstood 10
Considered unambiguous & sacrosanct
Subject to close scrutiny by all
stakeholders

12. A CHAIN IS ONLY AS STRONG AS ITS WEAKEST LINK
IN A GRID WITH ELEMENTS IN SERIES AND PARALLEL, THE WEAKEST LINK IN SERIES WOULD DETERMIN THE STRENGTH OF THE NETWORK

13. Transfer Capability Limits
Thermal limit
Thermal Limits establish the maximum electrical current that a transmission line or electrical facility can conduct over specified time periods before it sustains permanent damage by overheating or before it violates public safety requirements
Voltage limit
System voltages and changes in voltage must be maintained within the acceptable range as defined in the Grid Codes. For example, minimum voltage limits can establish the maximum amount of electric power that can be transferred without causing damage to the electric system or customer facilities. A widespread collapse of system voltage can result in a black out of portions or the entire interconnected network

14. Stability Limits
The transmission network must be capable of surviving disturbance through the transient and dynamic time periods (from milliseconds to several minutes respectively) following a disturbance. All generators connected to ac interconnected transmission system operate in synchronism with each other at the same frequency. Immediately following a system disturbance, generators begin to oscillate relative to each other, causing fluctuations in system frequency, line loadings, and system voltages. For the system to be stable the oscillations must diminish as the electric systems attain a new, stable operating point. If a new, stable point is not quickly established, the generators will likely lose synchronism with one another, and all or a portion of the interconnected system may become unstable. The result of generator instability may damage equipment and cause uncontrolled, widespread interruption of electric supply to customers.

15. Total Transfer Capability: TTC
Thermal Limit
Power Flow
Voltage Limit
Stability Limit
Total Transfer Capability
Time
Total Transfer Capability is the minimum of the Thermal Limit, Voltage Limit and the Stability Limit

16. “Non-simultaneous Transfer Capability is the amount of electric power that can be reliably transferred between two areas of the interconnected electric system when other concurrent normal base power transfers are held constant.”
“Simultaneous Transfer Capability is the amount of electric power that can be reliably transferred between two or more areas of the interconnected electric system as a function of one or more other power transfers concurrently in effect.”

18. TTC assessment block diagram
Planning
criteria
Credible
contingencies
CEA
CTU
STU
Anticipated
Network topology +
Capacity additions
Simulation
Analysis
Brainstorming
LGBR
Last
Year
Reports
Weather
Forecast
Anticipated
Substation Load
Anticipated
Ex bus
Thermal Generation
TTC
Anticipated Ex bus
Hydro generation
Stakeholders
Last
Year
pattern
Operating
limits
Operator
experience

19. Reliability Margins

20. Short Term Open Access Long Term Open Access Reliability Margin
ATC
TTC

21. Need for Reliability Margins
Peculiarity in Indian power grids
Difference in Planning assumptions and operating conditions
Forecasting errors
Outage of units etc

22. Peculiarity in Indian power grids
Haulage of power over long distances
Resource inadequacy leading to high uncertainty in adhering to maintenance schedules
Pressure to meet demand even in the face of acute shortages and freedom to deviate from the drawal schedules.
A statutorily permitted floating frequency band of 49.0 to 50.5 Hz
Non-enforcement of mandated primary response, absence of secondary response by design and inadequate tertiary response.
No explicit ancillary services market
Inadequate safety net and defense mechanism

23. Difference in Planning assumptions and operating conditions
Planning criteria
The ISTS shall be capable of withstanding and be secured against a selected list of credible contingency outages without necessitating load shedding or rescheduling of generation during Steady State Operation.
The credible contingencies considered are
Outage of a 132 kV D/C line or,
Outage of a 220 kV D/C line or,
Outage of a 400 kV S/C line or,
Outage of single Interconnecting Transformer, or
Outage of one pole of HVDC Bipole line, or
Outage of 765 kV S/C line
Outage of a single largest in feed
Planning is carried out on regional self sufficiency basis
In the proposed Planning criteria six dispatch scenario’s are considered

24. Difference in Planning assumptions and operating conditions
Operating conditions not accounted during planning
Simultaneous outage of more elements like Bus bar operation in a station
Simultaneous outage of generators in a station due to auxiliary supply problem or evacuation line outages
Weather disturbance causing multiple outage of lines in the same corridor
Depletion in Hydro storage and less generation due to fuel shortages
Variations in interregional exchanges
Forecast errors
Transmission lines and generators not coming up as per plan
Re configuration of switching arrangements due to constraints like overloading of lines and transformers
Socio-economic uncertainties in a progressive economy
The above causes the difference in transfer capability in real time compared to Planning assumptions

25. Likely consequences of contingency during various operating conditions
S No.
Scenario
Likely consequences 1
Real time transfers > TTC
System might not survive even a single element outage what to talk of a multiple contingency 2
ATC < Real time transfer< TTC
System might survive a single element tripping. But the chances of a cascading failure are high in case of a multiple contingency. 3
Real time transfer < ATC
Chances of survival are high for single contingency and moderate for multiple contingency.
Providential escape from ‘the valley of death’ on certain occasions cannot be a justification to operate the system at that edges. Luck is a not a part of operating procedure

26. Methods to improve TTC We should of strong defence mechanisams like
System Protection schemes
Effective under frequency and under voltage protections
Auto re-closing schemes
Tools for damping the oscillations like TCSC’s
Wide area monitoring and measurement equipment for quick action taking
Improved visualisation to the system operator to take immidiate corrective action
Empowerment of SLDC/Generator operators to take immidiate corrective actions

27. Effect of Series Compensation on SIL

28. KOLAR SPECIAL PROTECTION SCHEME

29. Performance of the Scheme

31. St. Clair’s curve

32. REGIONAL GRIDS QUICK FACTS
400 MU CONS IN A DAY-1.5% IS 6 MU, 2190 MU IN A YEAR, 2/UNIT IS 4400 MILLION RUPEES IS 440 CRORE RUPEES

33. REGIONAL GRIDS INSTALLED CAPACITY TOTAL 134,084 MW
Area : 889,000 SQ KMS
Population : 307 Million
Peak Demand : 28,000 MW
:560 MU / Day
REGIONAL GRIDS
INSTALLED CAPACITY
NORTHERN :- 36,547 MW
EASTERN :- 17,159 MW
SOUTHERN :- 37,592 MW
WESTERN :- 40,280 MW
NORTH-EASTERN : ,506 MW
TOTAL ,084 MW
NORTHERN REGION
NORTH-EASTERN REGION
EASTERN REGION
Area : 425,432 SQ KMS
Population : 227 Million
Peak Demand : 10,000 MW
:200 MU / Day
WESTERNREGION
Area : 951,488 SQ KMS
Population : 230 Million
Peak Demand : 29,000 MW
:640 MU / Day
SOUTHERN REGION
Area : 636,249 SQ KMS
Population : 223 Million
Peak Demand : 25,000 MW
:470 MU / Day

34. HYDRO RESOURCES DELHI Source: Powerline (Siemens Ad), Oct-2006
RESOURCES ARE FAR AWAY FROM LOAD CENTERS.
NECESSITATES LONG TRANSMISSION LINKS FOR EVACUATION
HYDRO RESOURCES
DELHI
Source:
Powerline
(Siemens Ad),
Oct-2006
KOLKATTA
MUMBAI
COAL BELT
BANGALORE
CHENNAI
AREAS SHOWN ARE APPROXIMATE AND INDICATIVE

35. THE NATIONAL GRID : PHASE 1
NORTHERN REGION
THE NATIONAL GRID : PHASE 1
500 MW SASARAM
WR-NR HVDC B2B LINK
Commissioned in June 2001
500 MW VINDHYACHAL
WR-NR HVDC B2B LINK
Commissioned in Nov. 1989
NORTH-EASTERN REGION ER
WESTERNREGION
BIRPARA(ER) – SALAKATI(NER) KV AC LINK in April 87
EASTERN REGION
400 KV Siliguri-Boangigaon in April 2000
500 MW GAZUWAKA
ER-SR HVDC B2B LINK
Commissioned in Sep. 1999
SOUTHERN REGION
500 MW BHADRAWATI
WR-SR HVDC B2B LINK
Commissioned in Sept. 1997
Bhadrawathi 2nd pole in March, 1998
NATIONAL GRID PHASE-1 COMPLETE

36. THE NATIONAL GRID : PHASE II
NORTHERN REGION
THE NATIONAL GRID : PHASE II
GORAKHPUR(NR) - MUZZAFARPUR(ER) 400 KV AC D/C Commissioned in Aug. 2006
500 MW VINDHYACHAL
WR-NR HVDC B2B LINK
Commissioned in Nov. 1989
500 MW SASARAM
WR-NR HVDC B2B LINK
Commissioned in June 2001
PATNA(ER) - BALIA(NR) 400 KV A/C D/C Commissioned in Jun. 2007
NORTH-EASTERN REGION
GWALIOR(WR) - AGRA(NR) 400 KV A/C S/C Commissioned in Jun. 2007 ER
WESTERNREGION
BIRPARA(ER) – SALAKATI(NER) 220 KV AC LINK in April 87
(400 KV Siliguri-Boangigaon in April2000)
EASTERN REGION
500 MW GAZUWAKA
ER-SR HVDC B2B LINK
Commissioned in Sep. 1999
SOUTHERN REGION
GAZUWAKA 2nd pole in March, 2005
500 MW BHADRAWATI
WR-SR HVDC B2B LINK
Commissioned in Sept. 1997
(2nd pole in March, 1998)
RAIPUR(WR) – ROURKELA(ER) 400 KV AC D/C Commissioned Mar. 2003
2000 MW TALCHER(ER)-KOLAR(SR)
HVDC LINK comissioned in SEP 2002
TALCHER(ER)-KOLAR(SR) HVDC LINK
CAPACITY ENHANCED TO 2500 MW in JUL 2007

37. Inter Regional Links – Till March 2006
Name of the Link
Capacity (MW)
East-North
Dehri-Sahupuri 220kV S/c
150
Sasaram HVDC back-to-back
500
Sub-Total
650
East-West
Budhipadar-Korba 220kV T/c
450
Rourkela-Raipur 400kV D/c
1200
1650
West-North
Vindhyachal HVDC back-to-back
Existing 220kV AC Lines
200
700
East-South
Gazuwaka HVDC back-to-back
1000
Talcher-Kolar HVDC bipole
2000
3200
West-South
Chandrapur HVDC back-to-back
300
1300
East-North East
Bongaigaon-Siliguri 400kV D/c
800
Birpara-Salakati 220kV D/c
Total
8500
700 MW
650 MW
36,547 MW
1650 MW
2506
17,159
1000 MW
40,280 MW
1300MW
1200 MW
2000MW
39,592 MW
IR Capacity = 8,500 MW

38. Inter Regional Links – Till July 2007
Name of the Link
Capacity (MW)
East-North
Dehri-Sahupuri 220kV S/c
150
Sasaram HVDC back-to-back
500
Muzaffarpur-Gorakhpur 400kV D/c (Quad)
2000
Patna-Balia 400kV D/c (Quad)
Sub-Total
4650
East-West
Budhipadar-Korba 220kV T/c
450
Rourkela-Raipur 400kV D/c
1200
1650
West-North
Vindhyachal HVDC back-to-back
Existing 220kV AC Lines
200
Gwalior-Agra 765kV S/c
1500
2200
East-South
Gazuwaka HVDC back-to-back
1000
Talcher-Kolar HVDC bipole (Enhanced)
2500
3700
West-South
Chandrapur HVDC back-to-back
300
1300
East-North East
Bongaigaon-Siliguri 400kV D/c
800
Birpara-Salakati 220kV D/c
Total
14500
2200 MW
4650 MW
36,547 MW
1650 MW
2506
17,159
1000 MW
40,280 MW
1300MW
1200 MW
2500MW
39,592 MW
IR Capacity = 14,500 MW

39. IR Links – Till 2007 – 08 Till 2007 – 08 IR Capacity = 19,700 MW
Name of the Link
Capacity (MW)
East-North
Bihar Sharif(ER)-Balia 400kV D/c (Quad)
2000
Barh(ER)-Balia 400kV D/c (Quad)
Sub-Total
4000
East-West
400kV Ranchi(ER)-Sipat(WR) D/c Line with Series Compensation
1200
Total
5200
Name of the Link
Capacity (MW)
East-North
Dehri-Sahupuri 220kV S/c
150
Sasaram HVDC back-to-back
500
Muzaffarpur-Gorakhpur 400kV D/c (Quad)
2000
Patna-Balia 400kV D/c (Quad)
Sub-Total
4650
East-West
Budhipadar-Korba 220kV T/c
450
Rourkela-Raipur 400kV D/c
1200
1650
West-North
Vindhyachal HVDC back-to-back
Existing 220kV AC Lines
200
Gwalior-Agra 765kV S/c
1500
2200
East-South
Gazuwaka HVDC back-to-back
1000
Talcher-Kolar HVDC bipole (Enhanced)
2500
3700
West-South
Chandrapur HVDC back-to-back
300
1300
East-North East
Bongaigaon-Siliguri 400kV D/c
800
Birpara-Salakati 220kV D/c
Total
14500
2200 MW
8650 MW
36,547 MW
2850 MW
2506
17,159
1000 MW
40,280 MW
1300MW
1200 MW
2500MW
39,592 MW
Till 2007 – 08 IR Capacity = 19,700 MW

40. NARENDRA-KOLHAPUR D/C AND BACK TO BACK 2X 500 MW HVDC SYSTEM PROPOSED1
TALCHER
SR WOULD BE SYNCHRONOUSLY CONNECTED WITH REST OF INDIA THROUGH 765 KV D/C RAICHUR-SHOLAPUR-PUNE LINK
RGM
NARENDRA-KOLHAPUR D/C AND BACK TO BACK 2X 500 MW HVDC SYSTEM PROPOSED
KOLHAPUR
TALA PROJECT-LARGE CENTRAL GRID ARUNACHAL TO GUJARAT ON SAME FREQ
KOLAR
SR INTERCONNECTION BY 2012

41. INTER-REGIONAL TRANSFER BY END OF 11th PLAN (2012)
SOUTHERN REGION
WESTERNREGION
NORTHERN REGION
NORTH-EASTERN REGION
INTER-REGIONAL TRANSFER BY END OF 11th PLAN (2012)
4000 MW
11850 MW
1200 MW
6050 MW
5500 MW
1400 MW
6150 MW
EASTERN REGION
36,700 MW OF INTER-REGIONAL POWER BY 2012

42. Source wise composition of installed capacity in India (1,34,084 in 2007) AS on 30-06-07

43. ALL INDIA GENERATION COMPOSITION
Total Market Size = BU
Total Installed Capacity 1,34,084 MW

44. Sector wise consumption of electricity in India
Total Installed Capacity 1,34,084 MW

45. ALL INDIA MARKET COMPOSITION
(1,34,084 in 2007) AS on

46. THE SOUTHERN REGION GRID
ATC ISSUES AND HOTSPOTS

47. ‘NEW’ GRID 1 2 TWO ELECTRICAL REGIONS w.e.f Aug. 2006
NORTHERN REGION 1
NORTH-EASTERN REGION
‘NEW’ GRID
EASTERN REGION
TALCHER
WESTERNREGION
MAJOR INTERCONNECTIONS
HVDC INTERCONNECTS
TALA PROJECT-LARGE CENTRAL GRID ARUNACHAL TO GUJARAT ON SAME FREQ 2
SOUTHERN REGION
AC INTERCONNECTS
2X500 MW BACK TO BACK STATION AT GAZUWAKA(SR)
KOLAR
1000 MW BACK TO BACK STATION AT BHADRAWATI(WR)
TALCHER-II TO KOLAR
2000 MW BIPOLE LINK

48. INTER REGIONAL TRANSFER CAPACITY SR WITH OTHER REGIONS
WITH ER
JEYPORE-GAZUWAKA MW
TALCHER-KOLAR MW
WITH WR
RAMAGUNDAM-CHANDRAPUR MW
TOTAL CONCURRENT CAPACITY IS 4000 MW
220 KV LINKS ARE IGNORED BECAUSE THEY ARE NOT IN ACTIVE USE

49. GENERAL DIRECTION OF POWER FLOW IS FROM NORTH TO SOUTH
SR GRID MAP
GAZUWAKA
RAICHUR
GOOTY
SALEM
UDUMALPET
TRICHUR
MADURAI
TRICHY
MADRAS
NEYVELI
GUTTUR
KAIGA
BHADRWATHI
MUNIRABAD P N
KOLAR
HOSUR
THIRUVANANTHAPURAM
NELLORE
NLM
SIMHADRI
HIRIYUR
TALGUPPA
KADAPA
NARENDRA
CHITTOOR
MAPS
KALPAKA
VEMAGIRI
NUNNA
KHAMMAM
RAMAGUNDAM
MBN
KNL
GHANAPUR
SSLM
MMDPLI
NSR
S'HALLI
HOODY 35
160607
105155
49.42 43
197 1
195
225
227
258
242
240
236
303 2
147 96
108
318
110 37
218 34
278
252
229
341
107
267
123 20
119 52
320 68
388
420
419
143
141 71
265
122
280
401
151
158
221
321
300
257 17
389
381
209
243
272
187
343
329
344
205
348 78
133
131
251
253
198
202
v 299
314
200
273
185
RAYALASEEMA AXIS
404
402
395
405
408
409
391
403
232
406
410
396
397
386
407
384
399
398
1542
284
GENERAL DIRECTION OF POWER FLOW IS FROM NORTH TO SOUTH

50. UI IMPORT BY SR FROM CG ON 05-MAR-07
PEAK IMPORT OF 3670 MW FROM ‘NEW’ GRID
UI IMPORT
FROM CG
CG FREQ
SR FREQ
20.31 MUs IMPORTED FROM CG
AMOUNT SAVED FOR SR CONSTITUENTS = 2.20 CRs

51. AREAS OF CONSTRAINT HYDERABAD URBAN AREA HIGH 400/220 KV ICT LOADINGS
220 KV LINE OVER LOADING
DEC TO FEB
SENSITIVE TO IMPORT FROM WR AT RAMAGUNDAM
NEW STATIONS PLANNED………..WOULD BE IN PLACE BY
SRISAILAM EVACUATION PROBLEMS
DEPENDS ON RAINFALL IN CATCHMENT AREA (N KARNATAKA, SW MAHARASHTRA)
OVERLOADING OF SRISAILAM-KURNOOL AND KURNOOL-GOOTY 400 KV S/C LINKS
SENSITIVE TO IMPORT FROM GAZUWAKA AREA
NO TIME FRAME AS YET FOR AUGMENTATION
NUNNA-NELLORE D/C LINK
WOULD BE SOLVED WITH NEW GENERATION COMING UP SOUTH BY 2009
GOOTY-BANGALORE CORRIDOR
FULL GENERATION AT RAICHUR, ALMATTI, BTPS AND IMPORT FROM WR/ER
WIND ENERGY EVACUATION ISSUES IN SOUTH TAMILNADU
2000 MW WIND IN TN, PARTICULARLY ALONG KERALA BORDER AND IN KANYAKUMARI AREA
EVACUATION PROBLEMS AS NETWORK WAS NOT DESIGNED FOR THIS
DEDICATED SS AND TL IN PROGRESS
WOULD SATURATE AT MW
SEASONAL AND UNPREDICTABLE
CONSTRAINT – KERALA HAS TO MAINTAIN HYDRO TO PREVENT LINE OVERLOADING

52. HOT SPOTS COIMBATORE AREA MADRAS CITY BANGALORE CITY SUBTRANSMISSION
LINE OVERLOADING PROBLEMS
MADRAS CITY
110 KV GMR VASAVI EVACUATION
ROW PROBLEMS
BANGALORE CITY SUBTRANSMISSION
RELIABILITY ISSUES