technology considerations for cross border power
TRANSCRIPT
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Technology Considerations for
Cross Border Power Interconnections
SAARC Dissemination Workshop Lahore, Pakistan | 30 September – 01 October 2015
“The Past, Present and Future of High Voltage DC
(HVDC) Power Transmission”
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Objectives of Cross Border Power Transmission
• Import of cheaper electricity from
neighbouring country: Save investment on
local costlier generation
• Export of surplus power to neighbouring
country: earn revenues
• Reserve sharing: save investment on adding
generation capacity for peaking and
maintain reserves
• Enhance system strength to allow more
penetration of renewable energy and gain
environmental benefits
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Technical Considerations
• For Exporting Country (Source system)
• Enough Surplus Generation for export without causing
shortage in its own system
• Adequate Transmission System Capacity to bring the
exportable surplus power to the export point of Tie Lines
• Strong Regulatory Framework on Technical Reliability Criteria
to sustain all types of contingencies
• For Importing Country (Sink system)• Enough spinning reserve in generation or an automatic
loadshedding scheme in place to avert system collapse in
case of loss of Full or partial Tie-Lines
• Adequate Transmission System Capacity to absorb the
imported power deep into its network
• Strong Regulatory Framework on Technical Reliability Criteria
to sustain all types of contingencies
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Technical Issues with Fixed Power Export/Import
(Unidirectional or Bidirectional)
• Frequency Regulation and maintaining constant flow of
power on Tie-Line
• Source System:
• Maintain enough hot active spinning reserve (ASR) margins so that
loss of generation (Under-frequency) should transiently recover the
frequency of its own system and restore constant flow on Tie Line
• Control of over-frequency in case of load rejection in its own
system or due to loss of Tie Line (partial or total) through governor
action or trip-scheme of some specific generators
• Sink System:
• Maintain enough hot active spinning reserve (ASR) margins or
automatic loadshedding scheme so that loss of generation or loss
of Tie-Line (partial or total) should transiently recover the frequency
of its own system and restore constant flow on Tie Line without
overburdening the source system
• Control of over-frequency in case of load rejection in its own
system or due to loss of Tie Line (partial or total) through governor
action or trip-scheme of some specific generators
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Technical Issues with Fixed Power Export/Import
(Unidirectional or Bidirectional)
• Voltage Regulation and Reactive Power Management
• Source System:
• Must have enough reactive power reserve (in generators, SVCs or
other FACTS devices) to properly compensate the Tie Lines’
reactive consumption to maintain acceptable voltage profile at
sending end
• Control of over-under voltage through fast acting devices (TCR,
SVCs or FACTS devices)
• Sink System:
• Must have enough reactive power reserve (in generators, SVCs or
other FACTS devices) to properly compensate the loads’ reactive
power demand to maintain acceptable voltage profile at receiving
end
• Control of over-under voltage through fast acting devices (TCR,
SVCs or FACTS devices)
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Technical Issues with Reserve Sharing
• Dynamic Reserve Power Sharing (DRPS)
• Under normal condition, minimum or no power flows on the Tie-Lines
• Loss of generation or load rejection in any of the two or more countries
interconnected through Tie Lines would immediately trigger the DRPS to
rise to the occasion and redress the system need accordingly
• An optimum capacity of Tie Lines is determined through analysis by running
iterative simulations using Generation/Transmission Planning Software
specially meant for this analysis which bring out the tentative tie line
capacity for reserve sharing using LOLE criteria and Reserve Margins
criteria
• For frequency and voltage control, more fast response of controllers for
active power (AFC or AGC) and reactive power (SVC or FACTS) is required
than in fixed power transfer interconnections.
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Other Common Issues
• Inter Area Oscillations (Small Signal Stability Issues)• The inter-area oscillatory modes may be excited
• Even in a large system of one country
• but they are quite common when it comes to interconnected
systems of two or more countries
• These modes are inherent in the large systems and may result into
• Poor damping of oscillations after transient faults
• Oscillatory instability leading to system collapse
• Slow voltage recovery in a certain country gradually
leading to voltage collapse especially if the systems
are synchronised through AC Tie-Lines
• Cascading effect originating in one country may lead
the whole interconnected system to collapse if
automatic stability control strategy is not in place, an
acceptable brown out may avoid a blackout
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alSelection of Tie Lines
(Technology and Voltage Level)
• What is required of Tie Lines to be decided • The power to be transfered (MW)
• The distance (line length) of line route
• The terrain, high or medium or low altitude, mountainous or
plain or a sea
• Tie-Line Options• HVAC (400 kV, 500 kV or 765 kV)
• Shunt and or Series compensated HVAC• Switched Shunt compensation, SVCs, STATCOMs etc.
• Fixed Series compensation (FSC) or Thyristor Controlled Series
Compensation) (TCSC) or SSSC
• HVDC (ranging from ± 250 kV to ± 800 kV Bipoles or Single
Poles)
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Selection Preferences of Tie Lines
(Technology and Voltage Level)
• Short Distance – High Power Transfer• HVAC with shunt compensation
• HVDC Back to Back
• Long Distance – High Power Transfer• HVAC with Series Compensation (FSC or TCSC or SSSC)
• HVDC Bipole (in the range of ± 400 kV to ± 800 kV depending
on power to be transfered)
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Series Compensation
Sending
GMW
MVAR
MW
MVAR
Receiving
VsVR
XC
)Sin (12
q-q=
XL -- XC
VR . VS
PR)Sin (12
q-q=
X
VR . VS
PR
• Line reactance compensation device for long distance transmission
• XC can be connected in the mid-point or at both ends as 0.5 XC each
• Enhances power transfer capacity
• Decreases effective electrical length of transmission a line
• Reduces overall losses
• Influence Reactive Power Conditions of the system
• Automatic control of MVAR in proportion to line current squared (I2XC)
It increases with the increase of transmitted power and thus increases reactive
power balance of the system
• Prevents voltage collapse particularly on heavily loaded lines
• Thyrister controlled series capacitor banks for damping of oscillations and active
power flow control
• The degree of compensation lies between 20 to 70 %
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HVDC Line
DC to AC
ConverterAC to DC
Converter
POWER FLOW
DC LineTransformer
Receiving
Network
Sending
Network
Transformer
i
Direct CurrentAlternating Current
i
Alternating Current
i
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Comparison of HVAC and HVDC Lines
HVDC HVAC
HVDC is economical for long distance
large transfer of power
HVAC Series compensated circuits for
long distance transmission may cause
subsynchronous resonance (SSR)
Filter circuits, damping circuits and
Thyristor Controlled FACTS devices
(TCSC or SSSC) avoids SSR
Firewall against disturbances Disturbance travels quickly from one
system to another
Smaller right of way Bigger Right of Way
Upgradeable schemes Upgrading requires lot of space
Linking asynchronous networks Not Applicable
Control power flow: Electronic Control
of active/reactive power
Requires additional investment on
SVC or FACTS devices for faster
control of active/reactive power
Very fast response: high speed power
transfer possible
Not so fast because of mechanical
switching
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Comparison of HVAC and HVDC Lines
HVDC HVAC
Does not contribute in increasing fault
levels as much as an HVAC system
does, therefore does not increase
system strength
Larger contribution in fault levels
helps system strength especially
required for penetration of
Renewables
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Case Studies:
Gulf Cooperation Council Interconnection Authority
(GCCIA)
Based on Reserve Sharing between 6 countries of GCC i.e. Kuwait, Saudi
Arabia, Qatar, Bahrain, UAE and Oman
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Case Studies:
Gulf Cooperation Council Interconnection Authority
(GCCIA)Tie-Line Power, MW
Kuwait-Saudi
Arabia
1200 MW
Saudi Arabia B-B
HVDC
1200 MW
Saudi Arabia-
Bahrain
600 MW
Saudi Arabia-
Qatar
700 MW
Saudi Arabia-UAE 900 MW
UAE-Oman 400 MW
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•
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Case Studies:
Interconnection of 10 countries of
Economic Cooperation Organization (ECO)
• ECO comprises of 10 countries:
1. Pakistan
2. Iran
3. Afghanistan
4. Turkey
5. Turkmanistan
6. Tajikistan
7. Qazaqistan
8. Azerbaijan
9. Kyrghizia
10. Uzbekistan
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Case Studies:
Economic Cooperation Organization (ECO)
• The interconnection study was carried out jointly by
NTDC, NESPAK and PPI in 2008-09
• Six Central Asian Countries shyed away to provide
their system data, and Afghanistan also could not
provide its inputs due to civil war situation
• Study was finally completed only for three countries,
Pakistan, Iran and Turkey
• The spot year of study was 2013
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Case Studies:
Economic Cooperation Organization (ECO)
Supply-demand balance analysis had shown that Iran
would have huge surplus power for export mostly
during the winter season in future years.
Turkey and Pakistan will have most of the deficits in the
winter season.
Load in Iran was light in the winter season with
maximum surplus of generation capacity and deficits in
Turkey and Pakistan to be high in the same season.
Load flow, short circuit and transient analysis was
carried out by modeling winter peak load conditions
(2013) of the three countries.
Generation surplus in the Iranian system was around
16000 – 18000 MW during winter season in 2013
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Case Studies:
Economic Cooperation Organization (ECO)
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Case Studies:
Economic Cooperation Organization (ECO)
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Case Studies:
Economic Cooperation Organization (ECO)
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Case Studies:
Economic Cooperation Organization (ECO)
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Case Studies:
Economic Cooperation Organization (ECO)
Two Alternatives of interconnection between Iran and
Pakistan through HVAC and HVDC have been studied.
Zahidan–Quetta 500 kV double circuit, with 50 % series
compensation provided at the mid-point switching station
alongwith ArgBam N-Zahidan double circuit of 400 kV,
Quetta-D.G. Khan 500 kV single circuit and Quetta R. Y.
Khan 500 kV single circuit will facilitate transfer of 1500 MW
from Iran to Pakistan (Alternative-I).
Alternative – II for Iran-Pakistan has been based on HVDC for
transfer of 2000 MW which envisage N-Kerman-Quetta ±500
kV HVDC Bipole with Quetta-D.G. Khan 500 kV single circuit
and Quetta R. Y. Khan 500 kV single circuit as the
reinforcements.
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Case Studies:
Economic Cooperation Organization (ECO)
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Case Studies:
Economic Cooperation Organization (ECO)
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Case Studies:
Economic Cooperation Organization (ECO)
Load flow analysis of all the above Alternatives show that transfer of
2000 MW each to Turkey and Pakistan from Iran is at optimum level. All
the intact circuits are loaded within the rated limits and there is no
violation of voltage profile under normal as well as contingency
conditions under N-1 criteria.
In short circuit analysis there is some increase in the 3-phase fault
levels in the substations on the receiving-end i.e. those importing power
in Turkey and Pakistan.
Increase is not as much as it could cause any violation of exceeding
the fault levels above the short circuit ratings of the equipment of these
substations.
For Iran, as the interconnection alternatives are for its light load
conditions, the fault levels are lesser than what they would be during
the peak load conditions.
No concerns or limitations are foreseen related to the short circuit
levels in case of interconnection between the three power systems with
transfer of 2000 MW each to Turkey and Pakistan from Iran.
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Case Studies:
Economic Cooperation Organization (ECO)
Transient stability analysis carried out for the interconnected
systems of Turkey, Iran and Pakistan with 2000 MW transfer
each to Turkey and Pakistan from Iran shows that the
proposed inter-ties between power systems of Turkey, Iran
and Pakistan, are strong enough to keep the three systems
intact under disturbed conditions occurring in either system.
Impact of disturbance in one system is mitigated to travel to
the other system because the inter-ties are HVDC bipoles
that allow each system to maintain its own equilibrium.
Swings of rotor angles are wider for the generating units
which are at or close to fault locations but all
swings/oscillations damp down to maintain the three systems
in synchronism.
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Case Studies:
1000 MW Import from Iran to Pakistan
• Three Alternatives were studied:
• Alternative –1 based on HVAC of two 500 kV single
circuit transmission lines between Zahedan and
Quetta 678 km, with 50 % series compensation
provided at the midpoint switching station
• Alternative –2 based on HVAC of two 765 kV single
circuit transmission line between Zahedan and Quetta
678 km, with midpoint switching station provided with
reactors to mitigate midpoint overvoltage.
• Alternative – 3 based on Zahedan-Quetta ±500 kV
HVDC with 678 km long bipolar line and converter
station of 1000 MW capacity at each end.
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Dispersal of Power to the National Grid
Quetta 500/220kV Substation
Double Circuit 220kV Transmission Line
Quetta Industrial
Mid Point Switching Station
(50% Series Compensation)
Two Single Circuit 500kV HVAC
Transmission Lines
N-Zahedan 400/500kV Substation
Two Single Circuit 400kV HVAC
Transmission Lines
N-Zahedan 1000MW Power Plant
Case Studies:
1000 MW Import from Iran to Pakistan
Alternative-I: 500 kV HVAC
50 % Series Compensated
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D.G.Khan R.Y.Khan
Single Circuit 500kV HVAC Single Circuit 500kV HVAC
Transmission Line Transmission Line
Quetta 765/500/220kV Substation
Double Circuit 220kV Transmission Line
Quetta Industrial
Mid Point Switching Station
Two Single Circuit 765kV HVAC
Transmission Lines
N-Zahedan 400/765kV Substation
Two Single Circuit 400kV HVAC
Transmission Lines
Edimi 1000MW Power Plant
Case Studies:
1000 MW Import from Iran to Pakistan
Alternative-II: 765 kV HVAC
Mid-Point Switching Station
to install Reactors to
mitigate overvoltage at
midpoint
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Case Studies:
1000 MW Import from Iran to Pakistan
Alternative-III:
± 500 kV HVDC Bipole
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Case Studies:
1000 MW Import from Iran to Pakistan
• In all the three alternatives, the voltage and frequency excursions
and swings of rotor angles of the generating units are not wide and
they are damped down quickly to maintain synchronism and keep
the two system stable under all events of sever disturbances;
• The proposed three alternatives of interties between power systems
of Iran and Pakistan are technically strong enough to keep the two
systems intact under disturbed conditions occurring in either system;
• The 3rd Alternative has an edge over the other two in view of the fact
that impact of disturbance in one system is mitigated to travel to the
other system because the interties are HVDC bipolar line that allow
each system to maintain its own equilibrium;
• There appears to be no issues or concerns regarding transient
stability of the interconnected systems of Iran and Pakistan with
import of 1000 MW from Iran to Pakistan.
• Costs of both 500 kV HVAC and HVDC were comparable but due to
Iran’s preference for HVDC , Alternative-III was recommended
“SAARC Energy Ring” - (1) Power Grid
Planned 500 kV AC lines for CASA-1000
Existing 500 kV AC lines and substations
Existing 220 kV lines and substations
Proposed CASA-1000 DC line and converters
Proposed Delivery Point
Peshawar
Quetta
Gawadar
Mand Jackigur
Existing 70 MW
Under Construction 100 MW
Planned 1000 MW Amritsar
Planned 500 MW
Zahidan
Lahore
Khudzhent
Dushanbe
Sangtuda Shurkhan
Pol-e-Khomri
Kabul
Datka
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Case Studies:
An Overview of SAARC Interconnection Potential
Multiple Systems in SAARC Countries
• Internal Asynchronous Multiple Systems in some countries
Afghanistan
o Kabul and surrounding network (local generation)
o Kandahar and Hilmand system (local generation)
o Herat (Import from Iran)
o Balkh and Jowzjan (Import from Uzbekistan and Turkemanistan)
o Qunduz (Import from Tajikistan)
Bhutan
o Thimphu and surrounding (local generation)
o Chhukha and surrounding network (import from India)
o Trongsa, Mongar and surrounding network (import from India)
o Export of power to India
Nepal
o Internally synchronised from Mahendranagar to Anarmani with importing
interties from India at many places
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Case Studies:
An Overview of SAARC Interconnection Potential .)
Internally Synchronised Multiple Systems at SAARC Level
Bangladesh: with import of 500-1000 MW power from India through
back-to-back HVDC (Bheramara-Behrampur intertie with BB station
at Bheramara)
Pakistan: with little import from Iran for feeding Gawadar-Pasni Isolated
system
Sri-Lanka: Externally isolated
Maldive: Externally isolated
India: Exporting power to Bangladesh (HVDC-BB)
Exporting to Nepal and Bhutan radially (internally
asynchronous)
Importing from Bhutan
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Case Studies:
An Overview of SAARC Interconnection Potential
• CASA 1000 Multiple-Terminal HVDC will interconnect Afghanistan
and Pakistan
• Nepal, Bhutan and India should preferably interconnect through AC
because it will strengthen the networks of Nepal and Bhutan.
HVDC may be an option if High Hydel Power Potential in Bhutan is tapped
and the bulk of power requires HVDC intertie.
• Bangladesh-India BB-HVDC intertie capacity may be enhanced for
more power exchange as planned
• Sri Lanka-India submarine HVDC intertie seems quite a costly
proposition and not winning on Benefit/Cost Ratio
• Pakistan-India BB HVDC between Lahore and Amritsar has a good
potential and may be tapped. Would be in the interest of both
countries
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Thank You for Your Kind Attention