southern regional load despatch centre bangalore
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SOUTHERN REGIONAL LOAD DESPATCH CENTRE BANGALORE. WELCOME TO. ONE DAY WORKSHOP ON AVAILABLE TRANSFER CAPABILITY(ATC) IN INDIAN CONTEXT. 14 TH AUGUST 2007. Power Grid Corporation of India Limited. ATC FUNDAMENTALS. WHY ATC?. Presentation Road Map. What is Transfer Capability - PowerPoint PPT PresentationTRANSCRIPT
SOUTHERN REGIONAL LOAD DESPATCH CENTREBANGALORE
ONE DAY WORKSHOP ON
AVAILABLE TRANSFER CAPABILITY(ATC)
IN INDIAN CONTEXT
14TH AUGUST 2007
Power Grid Corporation of India Limited
ATC FUNDAMENTALS
WHY ATC?
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
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
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
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
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.
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.’
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
Transfer Capability is different from ‘Transmission Capacity’, which usually refers to the thermal limit or rating of a particular transmission element or component
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
Power System
Stability
Thermal
Overloading
Rotor Angle
Stability
Small-Disturbance
Angle Stability
Transient
Stability
Frequency
Stability
Voltage
Stability
Large-
Disturbance
Voltage Stability
Small-
Disturbance
Voltage Stability
Cascading Blackouts
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
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 limitSystem 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
• Stability LimitsThe 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.
Total Transfer Capability: TTC
Voltage Limit
Thermal Limit
Stability Limit
Total Transfer Capability
Total Transfer Capability is the minimum of the Thermal Limit, Voltage Limit and the Stability Limit
Time
Power Flow
• “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.”
TTC assessment block diagram
TTC
AnticipatedNetwork topology +Capacity additions
Anticipated Substation Load
Anticipated Ex bus
Thermal Generation
Anticipated Ex busHydro generation
LGBR
Last Year
Reports
WeatherForecast
CEACTUSTU
Last Year
patternOperator
experience
Planning criteria
Operating limits
Credible contingencies
Simulation
Analysis
Brainstorming
Stakeholders
Reliability Margins
Short Term Open Access
Long Term Open Access
Reliability Margin
TTC
ATC
Need for Reliability Margins
– Peculiarity in Indian power grids– Difference in Planning assumptions and
operating conditions– Forecasting errors– Outage of units etc
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
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
Difference in Planning assumptions and operating conditionsOperating 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
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
Methods to improve TTCWe 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
KOLAR SPECIAL PROTECTION SCHEME
Performance of the SchemeFREQUENCY DIP DURING KOLAR HVDC TRIPING AND DURING SIMHADRI GENERATION LOSS
48.5
48.7
48.9
49.1
49.3
49.5
49.7
49.9
50.1
T-30 Minutes T-25 Minutes T-20 Minutes T-15 Minutes T-10 Minutes T-5 Minutes T=0 Minutes T+5 Minutes
Time
FR
EQ
IN
HZ
TAL-KOL TRIP ON15-09-06 AT 16:52 HRS LOSS IS 1887 MW
SIMHADRI GEN LOSS OF APPROX 950 MW ON 16-01-07
AT 1812 HRS
Frequency Trend during the Tal-Kolar pole 2 trip
0200400600800
100012001400160018002000
0:01
0:03
0:05
0:07
0:09
0:11
0:13
0:15
0:17
0:19
0:21
0:23
0:25
0:27
0:29
Time
Pow
er fl
ow
49.25
49.3
49.35
49.4
49.45
49.5
49.55Talcher-Kolar power flow
Frequency
Line loading as function of length
0.50
0.75
1.00
1.25
1.50
1.75
2.00
2.25
2.50
2.75
3.00
3.25
0 1 2 3 4 5 6 7 8 9 10
Length in x100 kM
Tim
es
SIL
Voltage Level (kV)Number and
size of Conductor
S.I.L. (MW)
765 4 x 686 2250
765 4 x 686 614
Op at 400
400 2 x 520 515
400 4 x420 614
400 3 x420 560
400 2 x 520 155
Op at 220
220 420 132
132 200 50
SIL of different voltage level and conductor configuration
St. Clair’s curve
REGIONAL GRIDS
QUICK FACTS
SOUTHERN REGION
WESTERNREGION
EASTERN REGION
NORTHERN REGION
NORTH-EASTERN REGION
INSTALLED CAPACITY
NORTHERN :- 36,547 MW
EASTERN :- 17,159 MW
SOUTHERN :- 37,592 MW
WESTERN :- 40,280 MW
NORTH-EASTERN :- 2,506 MW
TOTAL 134,084 MW
REGIONAL GRIDS
Area : 889,000 SQ KMSPopulation : 307 Million
Peak Demand : 28,000 MW :560 MU / Day
Area : 951,488 SQ KMSPopulation : 230 Million
Peak Demand : 29,000 MW :640 MU / Day
Area : 636,249 SQ KMSPopulation : 223 Million
Peak Demand : 25,000 MW :470 MU / Day
Area : 425,432 SQ KMSPopulation : 227 Million
Peak Demand : 10,000 MW :200 MU / Day
Source:
Powerline
(Siemens Ad),
Oct-2006
HYDRO RESOURCES
COAL BELT
MUMBAI
DELHI
CHENNAIBANGALORE
KOLKATTA
RESOURCES ARE FAR AWAY FROM LOAD CENTERS.
NECESSITATES LONG TRANSMISSION LINKS FOR EVACUATION
AREAS SHOWN ARE APPROXIMATE AND INDICATIVE
EASTERN REGION
SOUTHERN REGION
WESTERNREGION
NORTHERN REGION
NORTH-EASTERN REGION
THE NATIONAL GRID : PHASE 1
ER
500 MW VINDHYACHAL
WR-NR HVDC B2B LINK
Commissioned in Nov. 1989
BIRPARA(ER) – SALAKATI(NER) 220 KV AC LINK in April 87
500 MW SASARAM
WR-NR HVDC B2B LINK
Commissioned in June 2001
500 MW GAZUWAKA
ER-SR HVDC B2B LINK
Commissioned in Sep. 1999
500 MW BHADRAWATI
WR-SR HVDC B2B LINK
Commissioned in Sept. 1997
NATIONAL GRID PHASE-1 COMPLETE
400 KV Siliguri-Boangigaon in April 2000
Bhadrawathi 2nd pole in March, 1998
SOUTHERN REGION
WESTERNREGION
EASTERN REGION
NORTHERN REGION
NORTH-EASTERN REGION
‘ELECTRICAL’
REGIONS
1
2SOUTHERN REGION
WESTERNREGION
EASTERN REGION
NORTHERN REGION
NORTH-EASTERN REGION
‘ELECTRICAL’
REGIONS
1
2
1
SR INTERCONNECTION BY 2012
KOLAR
TALCHER
RGM
NARENDRA-KOLHAPUR D/C AND BACK TO
BACK 2X 500 MW HVDC SYSTEM
PROPOSED
KOLHAPUR
SR WOULD BE SYNCHRONOUSLY CONNECTED WITH REST OF INDIA THROUGH 765 KV D/C RAICHUR-
SHOLAPUR-PUNE LINK
11850 MW
1200 MW6050 MW
5500 MW
1400 MW6150 MW
36,700 MW OF INTER-REGIONAL POWER BY 2012
EASTERN REGION
SOUTHERN REGION
WESTERNREGION
NORTHERN REGION
NORTH-EASTERN REGION
INTER-REGIONAL TRANSFER BY END OF 11th PLAN (2012)
4000 MW
41203%
95427%
3348625%
8693665%
HydroThermalNuclearWind & Others
Source wise composition of installed capacity in India (1,34,084 in 2007) AS on 30-06-07
ALL INDIA GENERATION COMPOSITION
16.8, (3%)
486.1, (83%)
84.5, (14%)
ThermalHydroNuclear
Total Market Size = 587.4 BU
Total Installed Capacity 1,34,084 MW
Sector wise consumption of electricity in India
22%
29%
5%
35%
6%
3%
IndustryDomesticRailwaysAgricultureCommercialOthers
Total Installed Capacity 1,34,084 MW
ALL INDIA MARKET COMPOSITION
5%9%
3%
46%
37%
State Sector long termPPACentral Sector longterm PPAIPP generation
Short Term Trading
Balancing market
(1,34,084 in 2007) AS on 30-06-07
THE SOUTHERN REGION GRID
ATC ISSUES AND HOTSPOTS
SOUTHERN REGION
WESTERNREGION
EASTERN REGION
NORTHERN REGION
NORTH-EASTERN REGION
1
2
TWO ELECTRICAL REGIONS w.e.f Aug. 2006
‘NEW’ GRID
HVDC INTERCONNECTS
AC INTERCONNECTS
MAJOR INTERCONNECTIONS
2X500 MW BACK TO BACK STATION AT
GAZUWAKA(SR)
1000 MW BACK TO BACK STATION AT
BHADRAWATI(WR)
TALCHER
KOLAR
TALCHER-II TO KOLAR
2000 MW BIPOLE LINK
INTER REGIONAL TRANSFER CAPACITY SR WITH OTHER REGIONS
• WITH ER• JEYPORE-GAZUWAKA 1000 MW• TALCHER-KOLAR 2000 MW
• WITH WR• RAMAGUNDAM-CHANDRAPUR 1000 MW
TOTAL CONCURRENT CAPACITY IS 4000 MW
220 KV LINKS ARE IGNORED BECAUSE THEY ARE NOT IN ACTIVE USE
SR GRID MAP
GAZUWAKA
RAICHUR
GOOTY
SALEM
UDUMALPETTRICHU
R
MADURAI
TRICHY
MADRAS
NEYVELI
GUTTUR
KAIGA
BHADRWATHI
MUNIRABAD
P
P
P
P
P
P
P
P P
P
P
N
KOLAR
HOSUR
THIRUVANANTHAPURAM
NELLOREN
LM
SIMHADRI
HIRIYURTALGUPP
A
KADAPA
NARENDRA
CHITTOOR MA
PS
KALPAKA
GAZUWAKA
VEMAGIRI
NUNNA
KHAMMAM
RAMAGUNDAM
MBN
KNL
GHANAPUR
SSLM
MMDPL
I
NSR
S'HALLI
HOOD
Y
35
160607
105155
49.42
43
197
1
195
225
227258
242 240242 236
303
21471471
96108
318110
37
218
34
0
278
252252
229341
107
267123
20
11952
32068
388
420 419
143 14171
265
119 122
280
0
1 401
151158
221
321
300
257
17
389 381209
243
272
197 187
343329 343344 205348343
78
133131
123123
251
253
0198 202
v 299314
200
1
0 0
273
185
RAYALASEEMA AXIS
404
402
395
405
408
409
405391
403
232
406409
410
409
403
0
406
396
402
404
406403
397
406
386
407
401
384396
399
391
398
397
404
1542
284
GENERAL DIRECTION OF POWER FLOW IS
FROM NORTH TO SOUTH
0
200
400
600
800
1000
1200
1400
1600
1800
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
HOURS --->
MW
---
->
49.0
49.5
50.0
50.5
51.0
51.5
52.0
52.5
53.0
53.5
FR
EQ
(H
Z)
---
->
UI IMPORT BY SR FROM CG ON 05-MAR-07
CG FREQ
SR FREQ
UI IMPORT
FROM CG
AMOUNT SAVED FOR SR CONSTITUENTS = 2.20 CRs
20.31 MUs IMPORTED FROM CG
PEAK IMPORT OF 3670 MW FROM ‘NEW’ GRID
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 2008-9
• 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 4000-5000 MW– SEASONAL AND UNPREDICTABLE– CONSTRAINT – KERALA HAS TO MAINTAIN HYDRO TO PREVENT LINE
OVERLOADING
HOT SPOTS• COIMBATORE AREA
– LINE OVERLOADING PROBLEMS
• MADRAS CITY– 110 KV GMR VASAVI EVACUATION– ROW PROBLEMS
• BANGALORE CITY SUBTRANSMISSION
• RELIABILITY ISSUES