Transcript Transfer Capability

SOUTHERN REGIONAL LOAD DESPATCH CENTRE
BANGALORE
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 precontingency 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
Cascading Blackouts
Power System
Thermal
Stability
Overloading
Rotor Angle
Frequency
Voltage
Stability
Stability
Stability
Small-Disturbance
Transient
Large-
Small-
Angle Stability
Stability
Disturbance
Disturbance
Voltage Stability
Voltage Stability
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 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
• 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.
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
• “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
CEA
CTU
STU
LGBR
Last
Year
Reports
Weather
Forecast
Last
Year
pattern
Anticipated
Network topology +
Capacity additions
Anticipated
Substation Load
Planning
criteria
Credible
contingencies
Simulation
Analysis
Anticipated
Ex bus
Thermal Generation
Anticipated Ex bus
Hydro generation
Brainstorming
Operating
limits
Operator
experience
TTC
Stakeholders
Reliability Margins
Short Term Open Access
ATC
Long Term Open Access
TTC
Reliability Margin
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 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
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 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
KOLAR SPECIAL PROTECTION SCHEME
Performance of the Scheme
FREQUENCY DIP DURING KOLAR HVDC TRIPING AND DURING SIMHADRI GENERATION LOSS
50.1
TAL-KOL TRIP ON15-09-06 AT 16:52 HRS
LOSS IS 1887 MW
49.9
FREQ IN HZ
49.7
49.5
49.3
49.1
SIMHADRI GEN LOSS OF
APPROX 950 MW ON 16-01-07
AT 1812 HRS
48.9
48.7
48.5
T-30 Minutes
T-25 Minutes
T-20 Minutes
T-15 Minutes
T-10 Minutes
Time
T-5 Minutes
T=0 Minutes
T+5 Minutes
2000
1800
1600
1400
1200
1000
800
600
400
200
0
49.55
Talcher-Kolar power flow
Frequency
49.5
49.45
49.4
49.35
49.3
Time
0:29
0:27
0:25
0:23
0:21
0:19
0:17
0:15
0:13
0:11
0:09
0:07
0:05
0:03
49.25
0:01
Power flow
Frequency Trend during the Tal-Kolar pole 2 trip
St. Clair’s curve
Line loading as function of length
3.25
SIL of different voltage level and
conductor configuration
3.00
Voltage Level (kV)
Number and
size of
Conductor
S.I.L. (MW)
765
4 x 686
2250
765
4 x 686
614
400
2 x 520
515
400
4 x420
614
400
3 x420
560
400
2 x 520
155
220
420
132
132
200
50
2.75
2.50
Op at 400
Times SIL
2.25
2.00
Op at 220
1.75
1.50
1.25
1.00
0.75
0.50
0
1
2
3
4
5
6
7
8
9
10
Length in x100 kM
Source : Reproduced from CEA's Planning Criterion
REGIONAL GRIDS
QUICK FACTS
Area : 889,000 SQ KMS
Population : 307 Million
Peak Demand : 28,000 MW
:560 MU / Day
REGIONAL
GRIDS
NORTHERN
REGION
INSTALLED CAPACITY
NORTHERN :-
36,547 MW
EASTERN :-
17,159 MW
SOUTHERN :-
37,592 MW
WESTERN :-
40,280 MW
NORTH-EASTERN :NORTHEASTERN
REGION
TOTAL
EASTERN
REGION
WESTERN
REGION
Area : 951,488 SQ KMS
Population : 230 Million
Peak Demand : 29,000 MW
:640 MU / Day
Area : 425,432 SQ KMS
Population : 227 Million
Peak Demand : 10,000 MW
:200 MU / Day
SOUTHERN
REGION
Area : 636,249 SQ KMS
Population : 223 Million
Peak Demand : 25,000 MW
:470 MU / Day
2,506 MW
134,084 MW
HYDRO
RESOURCES
RESOURCES
ARE FAR AWAY
FROM LOAD
CENTERS.
NECESSITATES
LONG
TRANSMISSION
LINKS FOR
EVACUATION
DELHI
Source:
Powerline
KOLKATTA
MUMBAI
(Siemens Ad),
Oct-2006
COAL
BELT
BANGALORE
CHENNAI
AREAS SHOWN ARE
APPROXIMATE AND INDICATIVE
THE NATIONAL GRID : PHASE 1
500 MW SASARAM
500 MW VINDHYACHAL
WR-NR HVDC B2B LINK
NORTHERN
REGION
Commissioned in Nov. 1989
WR-NR HVDC B2B LINK
Commissioned in June
2001
NORTHEASTERN
REGION
ER
WESTERN
REGION
EASTERN
REGION
BIRPARA(ER) – SALAKATI(NER)
220 KV AC LINK in April 87
400 KV Siliguri-Boangigaon in April 2000
500 MW GAZUWAKA
ER-SR HVDC B2B LINK
Commissioned in Sep. 1999
500 MW BHADRAWATI
WR-SR HVDC B2B LINK
SOUTHERN
REGION
Commissioned in Sept.
1997
Bhadrawathi 2nd pole
in March, 1998
NATIONAL GRID PHASE-1 COMPLETE
REGION
1
EASTERN
REGION
TALCHER
WESTERNRE
GION
KOLHAPUR
RGM
2
SOUTHERN
REGION
KOLAR
NARENDRAKOLHAPUR D/C
AND BACK TO
BACK 2X 500 MW
HVDC SYSTEM
PROPOSED
SR WOULD BE SYNCHRONOUSLY
CONNECTED WITH REST OF INDIA
THROUGH 765 KV D/C RAICHURSHOLAPUR-PUNE LINK
SR INTERCONNECTION BY 2012
INTER-REGIONAL TRANSFER BY END OF
11th PLAN (2012)
4000 MW
NORTHERN
REGION
11850 MW
5500 MW
NORTHEASTERN
REGION
6050 MW
WESTERN
REGION
EASTERN
REGION
1400 MW
SOUTHERN
REGION
1200 MW
6150 MW
36,700 MW OF INTERREGIONAL POWER BY 2012
Source wise composition of
installed capacity in India
(1,34,084 in 2007)
AS on 30-06-07
4120
3%
9542
7%
86936
65%
33486
25%
Hydro
Thermal
Nuclear
Wind & Others
ALL INDIA GENERATION COMPOSITION
16.8, (3%)
Total Market Size = 587.4 BU
84.5, (14%)
Thermal
Hydro
Nuclear
486.1, (83%)
Total Installed Capacity 1,34,084 MW
Sector wise consumption of
electricity in India
6%
5%
35%
29%
3%
22%
Total Installed Capacity 1,34,084 MW
Industry
Domestic
Railways
Agriculture
Commercial
Others
ALL INDIA MARKET COMPOSITION
(1,34,084 in 2007) AS on 30-06-07
3%
9%
5%
46%
State Sector long term
PPA
Central Sector long
term PPA
IPP generation
Short Term Trading
37%
Balancing market
THE SOUTHERN
REGION GRID
ATC ISSUES AND HOTSPOTS
TWO ELECTRICAL REGIONS w.e.f Aug. 2006
NORTHERN
REGION
1
‘NEW’
GRID
WESTERNRE
GION
MAJOR
INTERCONNECTIONS
NORTHEASTERN
REGION
EASTERN
REGION
TALCHER
HVDC
INTERCONNECTS
2
AC
INTERCONNECTS
SOUTHERN
REGION
KOLAR
1000 MW BACK TO BACK
STATION AT
BHADRAWATI(WR)
2X500 MW BACK TO BACK
STATION AT
GAZUWAKA(SR)
TALCHER-II TO KOLAR
2000 MW BIPOLE LINK
INTER REGIONAL TRANSFER CAPACITY
SR WITH OTHER REGIONS
• WITH ER
• JEYPORE-GAZUWAKA
• TALCHER-KOLAR
1000 MW
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
BHADRWATH
I
160607
SR GRID MAP
252
105155
252
197 187
49.42
RAMAGUN
DAM
406
SIMHAD
RI
242 242 240 236
KALPA
KA 406
P
198 202
GAZUWA
35
43
GAZUWAK
0
KAA
1
408
1
200
VEMAGIRI
0
0
NUNNA
195
197
404
MM
344 329 343 343
205
409
DPL
343 348
GHANA
KHAMMAM
I
402
227
258
P
PUR P
MB
68
225
320
267
N
P
0
123
2
NS
147
0
KN
398
NARENDRA
P 147
RAICHUR
243
403
R
1
406
L
409
SSL
119
272
265
M
52
303
MUNIRABA
406P
407
284
209
D
GOOT
314 v 299
KAIGA N
20
389 381
P
218
Y
232
409
341 229
RAYALASEEMA AXIS
KADAPA
P
108
404
405
GUTTUR HIRI
NELLOR
273
96YUR
278
396
TALGUPP
N 37
E
405
401
1
1542
391
A
110
L
34
318
MADRA
M
410 CHITTO185
397 17
S 386
MA
0
S'HAL
P
401
KOLAR OR
388
71
PS
LI
143 141
395
HOSUR
257
107 403
78
420 419
321
SALEM
NEYVELI
GENERAL DIRECTION
397
300
221 402
OF POWER FLOW IS
133
151
UDUMALPE
404
131
FROM NORTH TO
158
P TRICH
TRICHU
251 T
Y
123
SOUTH
R
P
396
280
253
384
123
MADURA
391
I
403
119
THIRUVANANTHAPURAM
399
122
UI IMPORT BY SR FROM CG ON 05-MAR-07
1800
53.5
53.0
1400
52.5
1200
52.0
1000
51.5
UI IMPORT
CG FREQ
800
51.0
FROM CG
SR FREQ
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
49.0
8
0
7
49.5
6
200
5
50.0
4
400
3
50.5
2
600
HOURS --->
20.31 MUs IMPORTED FROM CG
AMOUNT SAVED FOR SR CONSTITUENTS = 2.20 CRs
FREQ (HZ) ---->
1600
1
MW ---->
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