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southern grid
1. Know about Southern Grid
M. G. Morshad , ADGM / Electrical
TPS II ( 7 x 210MW) NLC India Ltd
2. Indian Power Grid
1. Electrical power system consist of – Generation, transmission , Distribution
& Consumption.
2. The transmission network (interconnections) that transmits the electrical
power generated by various generating station to the distribution point for
the customers is know as power grid.
3. In India there are five regional power grids – Northern Region
( NR), Western Region (WR), Eastern Region (ER), Southern Region (SR) &
North East Region (NER)
4. For proper distribution of power and grid stability all regional grids are
interconnected through HVDC links
Standard Generating
Voltage ( KV)
10.5 KV
15.75 KV
21 KV
26 KV
Standard Transmission
Voltage ( KV)
110 KV
132 KV
220 KV
400 KV
765 KV
Standard Distribution
Voltage ( KV)
11 KV
33 KV
66 KV
16. Southern Grid – Installed capacity
MW %
Tamil Nadu 17,222 32%
Andhra Pradesh 14,057 26%
Karnataka 11,603 21%
Kerala 2,818 5 %
Central Sector (ISGS) 8,810 16 %
Total Installed capacity ( As on 30.1.2013) 54, 510 MW
32%
26%
21%
5% 16% Tamil Nadu
Andhra Pradesh
Karnataka
Kerala
Central Sector (ISGS)
20. Typical SR Demand with Frequency
17000
18000
19000
20000
21000
22000
23000 12:00AM
2:00AM
4:00AM
6:00AM
8:00AM
10:00AM
12:00PM
2:00PM
4:00PM
6:00PM
8:00PM
10:00PM
Time (In Hrs)
Demand(InMW)
48.5
49
49.5
50
50.5
Demand Frequency
21. DailyConsumption of Southern Region for 2003-07
280
330
380
430
480
530
580
Apr
May
Jun
Jul
Aug
Sep
Nov
Dec
Jan
Feb
Mar
Months ---->
Consumption(InMUs)---->
2003-04 2004-05 2005-06 2006-07
22. Generation cluster
around Ramagundam
(2600 MW)
Generation cluster
around Neyveli
(2490 MW)
Generation cluster
around Simhadri
(1000 MW)
Southern zone
( Karnataka, Tamil Nadu , Kerala)
(High Load demand)
Northern zone
(Andhara Pradesh)
(Low Load demand)
Southern Grid – Inter Grid connection
23. Southern Grid – HVDC Link ( Asynchronous )
HVDC
LINK
TYPE
CAPACITY
(MW)
PURPOSE
Talcher (ER) -
Kolar (SR)
Bi polar
(1367 Km
line)
2500
To draw power from eastern grid to
southern grid
Jeypore (ER ) -
Gazuwaka (SR)
Back to
back
1000
Bidirectional power flow between
Eastern & Southern grids for
exchanging surplus power
Chandrapur (WR ) -
Bhadrawati (SR)
Back to
back
1000
Bidirectional power flow between
Western & southern grids for
exchanging surplus power
24. Grid Stability criteria
1. Frequency Stability
a) Short-term frequency stability
b) Long-term frequency stability
2.Voltage Stability
a) Large-disturbance Voltage Stability
b) Small-disturbance Voltage Stability
3. Load Angle Stability
a) Small-disturbance Angle Stability
b) Large-disturbance Angle Stability (Transient Stability)
25. Grid stability – Frequency
Frequency instability occurs due to mismatch between load
demand and generation
a. High Frequency : High generation but low load demand due to
improper load demand forecasting
b. Low frequency : High load demand but low generation due to non
availability of generator / sudden tripping of generator / HVDC link
supplying power to the grid.
Frequency stability is ensured by taking following steps
a. Implementing ABT ( Declaration of generator availability based on
load forecasting & imposing of strict UI mechanism)
b. Running generation unit with free governing mode so that unit can
automatically increase / decrease generation depending on the grid
frequency.
c. Installing protection for automatic under frequency load shedding
and islanding
26. Grid frequency band and MW
correction in FGMO
Frequency ( In Hz) MW Correction (In MW)
49.6 +30.0
49.7 +25.2
49.8 +16.8
49.9 + 8.4
50.0 0.0
50.1 -8.4
50.2 -16.8
50.3 -25.2
50.4 -30.0
27. Grid stability – Low Voltage
Voltage Instability in grid causes mainly due to lack of adequate
reactive power support . It could be due to
(a) Sudden change in the network topology redirecting the power flows.
(b) Gradual increase of power demand in such a way that VAR requirement
of some of the buses may not be met locally.
Voltage collapse getting initiated from a node/set of nodes could
result Into wide area voltage instability and can be classified as
a. Transient (varying from 1 to 3 sec.)
Transient voltage instability remedial measures require fast and automatic
actions viz. power system stabilizers and static VAR Compensators
b. Steady-state (varying from tens of seconds to several minutes).
Steady-state voltage instability which occurs mainly due to gradual VAR deficit
can be controlled to a large extent by the timely and prompt intervention of the
system operator and utilities.
28. Basic function of power System Stabilizer ( PSS) provided in
excitation system (I)
Sudden changes in load cause grid to oscillate at very low frequency.
Since rotor inertia acts as weight connected to the grid through spring
force - this frequency induced in the machine and causes low
frequency (o.2 to 2.5 Hz) power oscillation.
This phenomenon is known as Dynamic Oscillations and it gets
damped within one second by the inherent damping forces, friction and
windage force present in the system.
The power oscillation will be stronger and may cause the machine to
go out of steps when machine is
a. Delivering high active and reactive power to the grid
b. Connected with tie line having high reactance
c. Having high AVR gain and low time constant
29. Basic function of power System Stabilizer ( PSS)
provided in excitation system (II)
This phenomenon of power oscillation in machine caused by minor
disturbance in grid is known as dynamic instability or oscillatory instability.
It can be damped and improved the stability of the grid & machine by
introducing power system stabilizer (PSS) or slip stabilized for all large
size machine connected to large network.
Power swing equation for any machine connected to the grid is
MA - ME = H (d2δ/dt2)
Where -
MA = Mechanical torque delivered by prime mover
ME = Electrical torque delivered by generator
H (d2δ/dt2) = Acceleration
H = Inertia constant of the rotor (Stored kinetic energy in MJ at
synchronous speed / Machine rating in MVA)
δ = Load angle
30. S
N
R
DC source for
excitation current
Y
B
Stator axis
Rotor axis
Load
angle (δ)
Synchronous speed of
the rotor at operating
frequency
Oscillatory motion of rotor due to
power swing
Damping force
31. Basic function of power System Stabilizer ( PSS)
provided in excitation system (III)
Power swing due to incremental changes in ME causes oscillatory motion in rotor.
Friction & windage force and magnetic attraction force between stator & rotor act
in opposite direction and damp this oscillatory motion after a time gap depending
on the magnitude of oscillation.
Since the magnetic attraction force between stator and rotor can be controlled by
changing excitation voltage therefore total damping force acting on rotor motion
can be controlled effectively by imposing excitation voltage proportional to the
incremental power ME.
PSS acts on this principle and damps the dynamic oscillation of the machine
within a shortest possible, which help to keep the machine stable even during
minor disturbance in the grid.
Power oscillation without PSS Power oscillation with PSS
32. Basic function of power System Stabilizer ( PSS)
provided in excitation system (III)
Automatic
Voltage
Regulator
Generator
PT
Set
Voltage
Actual
Voltage
Error
Voltage
Power System
Stabilizer (PSS)
Gen Field
ΔP (Active power)
Δf (Gen frequency)
During power swing, power system stabilizer (PSS) senses the incremental changes in active
power & frequency at generator terminal and converts it to electrical signal for input to AVR.
Influenced by the input signal AVR impose the excitation voltage proportional to the
incremental active power across the field winding so that magnetic attraction between
stator and rotor gets increased and damps the oscillatory motion of rotor within the
shortest possible time.
@ PSS is made for damping oscillation within the limited range. Beyond this range limiters
and protection are taken care of the situation
@ PSS is kept activated only when generator load is more than 50%, because the magnitude
of oscillation increases with the increase of generator load.
33. Grid stability – Over Voltage
Reasons for over voltage
1. Low demand & high supply of VAR
2. Light loading / idle charging of long lines
Disadvantages of over voltage
1. Running generator at leading PF with possibility of pole slipping
2. Possibility of failure of system insulation due to over voltage stress during switching /
line to ground fault
Measures for avoiding over voltage
1. Decreasing the Tap position of Transformers
2. Switching off capacitor banks
3. Disconnecting lightly loaded / idle charging long lines .
4. Switching on reactors .
Calculation of reactive power Formula Data
System Voltage Skv 420 KV
Fault Current level FkA 40 KA
Short Ckt MVA Scc= 1.732 X Skv X FkA 29097 MVA
Max Bus voltage V1 = 441 KV or (441/420) PU 1.05 PU
Acceptable Bus voltage V2 = 416 KV or (416/420)PU 0.99 PU
Total reactive power Sr = Scc{ ( V2 – V1)/V1} 1763 MVAR
Standard capacity Sst 63 MVAR
Nos of reactor required Sr / Sst 27 Nos
34. Reactors in southern grid
* BUS REACTORS
PGCIL
1. Hosur
2. Kolar
3. Hiriyur
4.Salem
5. Munirabad
6. Hyderabad
7. Sriperumbudur
NTPC
8. Ramagundam
NPCIL
9. Kaiga
NLC
10. TPS II
11. TPS II Expn
* BUS REACTORS
KPTCL
12. Raichur TS
13. Talaguppa
14.Devanagere
15.Neelamangala
APTRANCO
16. Simhadri
17. Srisailam
18. Kurnool
19. Vizag
* LINE REACTORS
PGCIL
1. Neyveli – Trichy I
2. Madurai – Trichy I
3.Salem – Udumalpet II
4.Madurai – Trivandram I
APTRANCO
5. Khammam - Hydrabad
Existing Reactors = 8 Bus + 56 Line = 64 Nos ( 3500 MVAR)
* New addition (2008-11) = 19 Bus + 5 Line = 24 Nos ( 1763 MVAR)
35. Maximum – Minimum operating voltage limit for
transmission & distribution - as per Indian grid
code
36. Grid stability – Load angle
Angular instability is mainly responsible for power oscillations in the system. It
occurs as a result of
Transient angular instability (varying from 1 to 3 sec.) due to sudden tripping
of load/generator .
Measures : it can be prevented only by automatic actions like fast auto
reclosing, dynamic breaking, switching of series capacitors, power system
stabilizer and static VAR compensators
Steady state angular instability is mainly experienced when power flow
through the long tie lines interconnecting two large networks increase
beyond its capacity limits. In such cases frequency oscillations of low
intensity is observed. But if this low intensity frequency oscillation is not
controlled, it may trip the tie line leading to grid disturbance.
Measures : Continuous monitoring the load angle and initiating corrective
measures accordingly to the situation
37. Load Angle
Sending end
Bus voltage = V1
Load Angle = δ1
Receiving End
Bus Voltage = V2
Load Angle = δ2
Power transfer = P
Line Impedance = X
V1 . V2
P = Sin (δ1 - δ2)
X
V1 . V2
= Sin δ
X
-1 P . X
Load Angle δ = Sin
V1.V2
•Load angle increases with the decrease
of voltage & frequency resulting in
increase of lagging MVAR
•Load angle decreases with the increase
of voltage & frequency resulting in
increase of leading MVAR
38. Monitoring Load Angle
Loadangle and Voltage (Receiving end) relation for different line lengths
3
5
7
9
11
13
15
17
19
21
400 390 380 370 360 350 340 330 320 310 300
VOLTAGE AT RECEIVING END
LoadAngleindegrees
350KM line
200KM line
100KM line
39.
40. Indian Grid – Institutions
Central
Government
State
Government
Private sector –
(Indian and
International)
Ministerial Institutions
Ministry of Power,
Ministry of New & Renewable
Energy
Planning Commission,
Central Electricity Authority,
Bureau of Energy Efficiency
Central Electricity Regulatory
Commission
Appellate Tribunal for Electricity
Corporations
Generation,
Transmission,
Trading, Financing,
Manufacturing
National and Regional Load
Dispatch
Ministerial Institutions
Ministry of Energy,
State Renewable Energy
Agency
State Regulatory
Commission
Corporations
Generation,
Transmission,
Distribution
State Load Dispatch Centre
Generation,
Transmission,
Distribution,
Trading, Financing
Manufacturing,
Services
41. Indian Grid – Functions of the Institutions
Ministry Of Power
(MoP)
Legal provisions (EC Act 2003),
Policy directions
Guidelines for competitive bidding, etc
Central Electricity Authority
(CEA)
National Electricity plan,
Monitoring of projects,
Maintaining data and statistics,
Demand forecast,
Feasibility analysis of Hydro projects
Regulatory Commission
(CERC,SERCs)
Regulates all players in the sector,
Decides tariff,
Approves capital expenditure,
Monitors supply and service quality
Ensure implementation of various
provisions of EC Act 2003
Load Despatch Centre
(PGCIL )
Scheduling and accounting of power at state level.
Responsible for maintaining grid stability and
discipline
Generation Company
(NTPC,NLC,DVC, NHPC, SEBs ,Privates)
Subject to provisions of act, can generate power
based on contracts or independently.
Needs to abide by Load Dispatch directions for
scheduling its generation
Transmission Company
(PGCIL,SEBs)
Builds and operates the transmission network and
infrastructure
Distribution Company
(SEBs , Private)
Maintaining and building distribution network
Metering & billing
Collection from consumers
42. Indian Grid – Legal Structure
Public / Citizen of India
Legislature
MoP
EC ACT 2003
Policy
CERCSERCs
Regulation &
Orders
Executives
• Tariff
• Capacity Addition
• Customer service