Today's challenges for transmission • HVDC advantages over ... · Cross Border Electricity...

1 09-2011 Power Transmission Solutions E T PS Zadoo

Cross Border Electricity Transmission with High Voltage Direct Current (HVDC) -

Executive Exchange Dhaka

Day 1

• Today's challenges for transmission

• HVDC advantages over AC transmission

• What the future holds for HVDC in improving the grid

• HVDC for Renewables




Power Transmission Solutions

Challenges for transmission




World Power Scenario

• World wide electrical power consumption projected to increase by >70% by 2030

investments in power generation

• Tendency to a global energy market need of national and international grid interconnections

• Generation and consumption centers separated by long distances Need to transfer power over long distances




Issues concerning Transmission Systems

Utilization of existing resources and systems to the maximum extent

Transmission of bulk power over long distances efficiently

Severe Right of Way constraints

Uncertainty in Generation

Control of flow of power

Stability




What‟s needed?

Option of up-gradation / allow implementation in stages

Transfer of allocated power / long-term contractual requirement

Should have margin for transfer of operational surplus in addition to committed

power

Meet system requirements – active and reactive power following variations in

load demand and contingencies

High Availability & Reliability

Low cost to consumers




Development of Power Systems

Extensions of Interconnected Systems

Increased Power Exchange among the

Interconnected Systems

Transmission of large Power Blocks over long

Distances (Hydro Resources, Solar Energy,

Wind Energy)




The Vision: Paradigm Shift in the Future

Technology

Economics

Prio

rity

Technology

Economics

Economics

Socio-

Environmental

Socio-

Environmental

Technology

Socio-

Environmental

Today Future Past




Choice of voltage level

Voltage level

Tra

ns

mis

sio

n c

os

ts

Cost of lost energy

Fixed costs

Total costs

Optimum economic

voltage level




0

50

100

150

200

250

300

350

1970 1980 1990 2000 2010 2020

Sources: Cigre WG B4-04 2003 - IEEE T&D Committee 2006

Expected development of DC Transmission:

worldwide installed capacity

Additionally, over

250 GW are expected

up to 2020 !

GW




HVDC is the unique solution to interconnect asynchronous systems, e.g. different grid frequencies.

Solution: HVDC Back-to-Back

HVDC represents the most economical solution for distances greater than approx. 600 km /

400miles

Solution: HVDC Long Distance

HVDC is an alternative for submarine transmission. Economical even for shorter distances

such as a few 10 km / miles Solution: HVDC Cable

HVDC Applications

Up to 1000 MW

Back-to-Back Station

AC AC

50 Hz 60 Hz

Up to 3000 MW

Long Distance Transmission

AC AC

DC line

Up to 800 MW

Long Submarine Transmission

AC AC

DC cable





HVDC advantages over AC transmission




Benefits: HVDC

DC line has lower construction costs than an AC line For equivalent transmission capacity

A double HVAC 3-Ø circuit with 6 conductors required to get reliability of

a 2-pole DC link

DC losses are less compared to AC For the same conductor

DC link is asynchronous Can be used to interconnect grids with different frequencies

HVDC systems are more reliable Cannot be overloaded by outage of parallel AC lines

Right of way for DC line is 41% lower Compared to AC Line designed to carry 2,000 MW

DC systems are modular can be built in stages if the generation is being added over a longer period either at same or different

locations along the line & investments can be deferred

Overload and power modulation features of HVDC could be used to cater

to grid emergencies in case of outage of AC lines




Typical tower structures and rights-of-way. Capacity: 2000 MW

Right of Way Comparisons

± 500 KV DC 800 KV AC 2 X 500 KV AC

50 m 85 m 100 m




Economical Considerations

Capitalised Losses / Break-Even-Distance

total AC cost

DC line

DC terminals

costs

transmission distance

break- even-

distance

DC losses AC losses

AC terminals

AC line

total DC cost




Economic Considerations

HVDC HVAC

Terminal Cost higher lower

Line Cost lower higher

Right-of-Way Cost lower higher

Comparison

Conclusion

HVDC is more economical for transmission distances longer than

the break-even distance

If capitalisation of losses and right-of-way cost are included in

the cost comparison, the break-even distance is further reduced




Comparison of Losses-Case Study

Parameter HVDC System AC System

Voltage ±500 kV 400kV (1D/C+1S/C)

Power 2250 MW 2250 MW

Line Configuration Quad Bersimis Quad Moose

Line Length 970 km 970 km

Losses 135 MW (inc terminal

losses)

216 MW

Capitalisation of diff with 97%

Availability and 60%

utilisation); tariff @10 cents

USD 41 million




Technical Considerations

Typical HVDC Short-Time Overload Characteristics

40°C ambient temperature

20°C ambient temperature

1

1,1

1,2

1,3

1,4

1,5

1,6

0,01 0,1 1 10 100 1000 minutes

Overload in pu




Technical Considerations

Inherent Continuous HVDC Overload vs. Ambient Temperature

1

1,1

1,2

1,3

1,4

-5 0 15 10

Ambient Temperature in Degree Celsius

5 20 25 30 35 40

with redundant cooling

without redundant cooling

Overload in pu





HVDC – High-Voltage DC Transmission: It makes P flow

Three HVDC Options available: PLUS (VSC), “Classic” and “Bulk”

With DC, Overhead Line Losses are typically 30-50 % less than with AC

For Cable Transmission (over 80 km), HVDC is the only Solution

HVDC can be integrated into the AC Systems

HVDC supports AC in Terms of Stability

Summary: Features and Benefits of HVDC 1





System Interconnection with HVDC and Integration of HVDC:

DC is a “Firewall” against Cascading Disturbances

Bidirectional Control of Power Flow – quite easy

Frequency, Voltage and POD Control available

Staging of the Links – with DC quite easy

No Increase in Short-Circuit Power

DC is a Stability Booster

Summary: Features and Benefits of HVDC 2






HVDC-LDT – Long-Distance Transmission

HVDC “Classic” with 500 kV (HV) / 660 kV (EHV) – up to 4 GW*

HVDC “Bulk” with 800 kV (UHV) – from 5 GW* up to 7.2 GW / 7.6 GW**

HVDC comprises V-Control

HVDC PLUS (Voltage-Sourced Converter – VSC)

HVDC can be combined with FACTS

Advanced Power Transmission Systems

B2B – The short Link

Back-to-Back Station

AC AC

DC Cable

AC AC

Submarine Cable Transmission

800 kV for minimal Line

Transmission Losses

Long-Distance OHL Transmission

DC Line

AC AC

Option UHV DC 1,100 kV: 10 GW * LTT = Light-Triggered Thyristor – up to 4 kA

** ETT = Electrically-Triggered Thyristor – up to 4.5 / 4.75 kA, depending on Basic Design




HVDC “Classic” / ”Bulk” versus HVDC PLUS

~

= =

~

AC Grid 1 AC Grid 2

G ~G ~G ~G ~ DC

8 kV Thyristors – IDC ≤ 4.5 / 4.75 kA *

Up to 7,600 MW @ 800 kV DC OHL

MI Cable up to 600 kV

22 Power Transmission Solutions

4.5 kV Transistors (IGBT) – IDC ≤ 1.4 kA

Up to 1,100 MVA

XLPE Cable up to +/- 320 kV DC * depending on Basic Design

HVDC “Classic”

HVDC PLUS

Line-Commutated Current-Sourced

Converter (LCC / CSC)

Self-Commutated Voltage-Sourced

Converter (SCC / VSC)

Thyristors with Turn-on Capability only

Semiconducting Switches with Turn-On

and Turn-Off Capability, e.g. IGBTs




Line-Commutated Converters

Current Sourced, e.g. HVDC; use of Reactor for keeping the

DC Current constant (L is the “Smoothing” Element)

Voltage Sourced – e.g. for Drive Systems, Custom Power and

Traction Supplies; use of Capacitor for keeping the DC

Voltage constant (C is the “Smoothing” Element)

Features: robust Technology, low Losses, high Ratings (up

to ≤ 10 GW for new HVDC Schemes in China)

Switching Frequency is defined by the System Frequency

Converter Technologies – LCC

“Turn-On” Capability only,

System Frequency is the

“Driver” Thyristors

Source: Cigré Task Force B4.43.02 – Future Ratings and

Topologies of Power Electronic Systems





What the future holds for HVDC in

improving the grid




Ultra High Voltage (UHVDC)




Ultra High Voltage

Applications

= HVDC 800 kV

Very high power capacity (5,000 MW

and higher) of a single system

25% lower total transmission cost

compared to 500 kV HVDC

Smaller footprint and lower overhead

transmission line costs as only one

bipole is needed




Ultra High Voltage

Technical Challenges

Enlarging existing

components to increase

the distances between

them

Technological challenges

The key challenge is to control

internal and external insulation

In the Ultra HV range, some

insulation aspects become

highly non-linear

Thorough material selection

and electrode design is

essential

Two possible approaches:

Complete redesign of all

components to optimally

balance their electrical

fields and dimensions




Ultra High Voltage

Composite Housing

Unwanted discharges could

occur in an outside

environment when dust –

combined with water – settles

on the components

Unsuitability of porcelain-

based insulators, that are

commonly used with 500 kV

HVDC

Selection of composite

insulators with silicone housing

avoiding conductive layers

Siemens is the trendsetter in

the use of silicone for HVDC




Ultra High Voltage

Prototype 800kV Transformer

total length: 26 m

total weight: 515 t




HVDC PLUS©

Power electronic devices:

GTO /IGCT IGBT in PP IGBT Module

Topology of VSC:

Two level Three Level Multilevel

J

V ac

J

V ac

M

+

–

Vd

2

Vd

2

Vac

M

+

–

Vd

2

Vd

2

Vac

Vac

+

Vd

2

–

Vd

2Vac

+

Vd

2

–

Vd

2

J

V d

2

V d

2

V ac

J

V d

2

V d

2

V ac

J

V d

2

V d

2

V ac

J

V d

2

V d

2

V ac

IGCT: Integrated Gate-Commutated Thyristor GTO: gate turn-off thyristor




Self-Commutated Converters (IGBT etc.)

Voltage-Sourced Converters

The “popular” Solution: 2 or 3-Level Configuration

Multilevel Converters

Submodules

Diode clamped

“Flying” Capacitors

Series Connected H-Bridge Cells, Chain Links

Resonant Converters

Current-Sourced Converters

Matrix Converters

Combinations of Technologies

High Switching Frequencies

up to several kHz possible,

however, with an Increase in

Losses


Classification of Converters:

Source: Cigré Task Force B4.43.02 – Future Ratings and

Topologies of Power Electronic Systems

Siemens: Advanced VSC

with MMC *

* Modular Multilevel Converter

IGBT: insulated gate bipolar transistor




HVDC PLUS©

Converter Station




New Developments in HVDC Technology

6 inch Thyristor




Actual Status

State of the art is the 8kV, 5 inch thyristor

Current rating up to 3500A

Suitable for HVDC Transmission up to 5500MW (per bipole)

Future Demand

HVDC Transmission System with rating up to 7000MW

Thyristor with current capability up to 5000A

(including overload)

-> development of 6inch Thyristor became necessary

6 inch Thyristor




New Developments in HVDC Technology

Combination




FACTS & HVDC – Overview of Functions & “Ranking”

36 Power Transmission Solutions E T PS S/Re

HVDC LDT **

B2B ** / GPFC

FACTS

TCSC

SVC** SVC**

System A

System B

System C

System E

System F

System D

Voltage Power Flow

Control of Limitation of

Faults SCP *

Power Swing Damping

Spread of Voltage Collapse

* SCP = Short-Circuit Power (System MVA)

FCL

Risk

Barrier

Barrier

Risk of Spread of Voltage Collapse Risk Barrier Barrier

** “Classic” or PLUS

01-2011

Fault-Current Limiter





HVDC for Renewables





HVDC for Wind Power

HVDC for mini solar plants – distant from consumption centers

HVDC for „other‟ renewable sources namely wave, tidal, large Hydro

stations etc....

Transmission for various alternatives





Generation

Presently the costs of setting up Generation plants is prohibitively

expensive

However some break evens have been achieved in wind generation

Solar energy harnessing is largely supported by state subsidies

Other forms are still on ‚drawing boards„ or in prototype mode

However, the encouragement to such developments can largely

come by combining the overall economy by having OPTIMUM

transmission system

Every KW saved in transmission will go a long way towards

boosting the early onset of Renewable power across the globe

Please see details overleaf .............

The need of the hour!





Type of Tech Cost now

Expected Cost

2050

Present Installed

Capacity

Expected

Installed

Capacity 2050

per KWh in Euro as a % of World Capacity

Osmosis Power 0.1 0.05 0.01% 4%

Solar Thermal 0.18 to 0.25 0.05 <0.01% 25%

Tidal 0.1 to 0.2 0.03 <0.01% 2%

Wave 0.15 to 0.50 0.07 <0.1% 15%

Geothermal 0.03 to 0.2 0.05 0.3% 2%

Source: Assorted trade journals / science magazines

With Capacity addition in wind + above

Renewables, the Transmission of Power has to be

effective, economical and controllable

Future Energy - a scenario

HVDC appears to be the most

promising till …….

…… the future develops

alternate technologies !!!!





focused on

Green Energy

and

CO2 Reduction

Shunt Compensation SVC PLUS

[STATCOM]

HVDC “Bulk” – UHV

HVDC PLUS – VSC

Technology‟s answer ……….




Grid connections for Wind Farms

The wind turbines used in offshore installations are separated by

distances up to 500 meters or more.

An underwater medium-voltage cable grid (often 24 or 36 kV AC)

connects the turbines to each other and pools the power, which is then

transmitted to a suitable connection point in the transmission grid on

land.

Depending on the size of the park and its distance from the shore, this

connection can be made at a medium or

high-voltage level using HVAC or HVDC techniques




AC Interconnection




AC or DC Transmission?

AC transmission is not suitable for the transmission of power from large parks located a significant distance from the shore because of high cable capacitance which would lead to high charging currents.

A high-voltage direct current (HVDC) solution utilising Siemens HVDC

Plus system can be used to overcome this problem. HVDC Plus is based on voltage source converter (VSC) technology, in

which power transistors connected in series allow VSCs to connect to networks. This setup can be used for power transmission and reactive power compensation.




AC vs DC Transmission




HVDC System




Typical DC-Transmission for Offshore Wind Park

G ~

G ~

G ~

Platform

Switchgear Platform HVDC PLUS

Onshore

HVDC PLUS

Platform

SVC PLUS

Grid




HVDC PLUS Onshore Layout

AC Busbars

Converter

Transformer:

3 phase /

ODAN

Converter AC

Switchyard:

Insertion Resistor

Star Point

Reactors

Converter Hall

DC Chopper

Converter

Reactors

DC Switchyard

Cable Sealing

End

Control&Protecti

on

Auxiliaries,

Spares

400 MW

+/-200 kV




Grid Access of Green Energy with HVDC PLUS:

WIPOS® – Advanced self-lifting Offshore Platform Layout




On a macro level, the wind farms / parks have maximum productivity along

wind-zones e.g. North sea, some coastal regions along developed and

developing nations

There is an abundand solar energy available in deserts e.g Noten Africa

(Sahara) & other similar reliefs

Same is with wind and tidal energy etc.

These sources are not available on a continuous basis and dependent on

diurnal cycle!

Generation is possible, but is „too far“

However, the consumption centres are hundreds and even thousands of

miles away

Hence an efficient and reliable [‚available„] transmission system provided

by alternate technologies is the need of the hour!

The need of the hour!




Thank you for your attention!

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