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© Siemens AG 2014 All rigths reserved. Answers for energy.

Compact Systems for HVDC Applications Dr. Denis Imamovic

13. Symposium Energieinnovation, 12. -14. February 2014, Graz

13.02.2014

© Siemens AG 2014 All rigths reserved.

2 Dr. D. Imamovic

Agenda

• Main Drivers 3

• Fault Clearing in HVDC Multi-Terminals Systems (VSC full-bridge) 4

• R&D Challenges for DC Compact Systems 8

• Solution for DC insulator 16

• Testing Strategy 19

• Summary 20

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Compact Systems for HVDC Applications

HVDC Solutions: Point-to Point connections for strengthening of grid and

transmission of RES

Onshore applications in a Hybrid Transmission System (OHL, underground Transmission)

Offshore Multiterminal HVDC System

Onshore Multiterminal HVDC System

Overlay (Backbone) Grid incl. Onshore and Offshore HVDC Systems

Main drivers today: Requirements on space

reduction

Interconnection of Standardized HVDC Offshore Transmission Installations

ENERGIEWENDE Shutdown of nuclear and fossil power plants in Germany

That means:

Increasing of transmission capacities

Efficient transmission over long distances

Increasing the grid stability with new generation structure

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Prospects and Research for VSC Overhead Line Transmission

Challenges On-going and Planned System Innovations Exposure to atmospheric conditions with high probability of temporary short circuit faults require fast fault detection, clearing and recovery

Bipolar VSC transmission solutions with similar or even better performance compared to HVDC Classic and AC systems

Application of Full Bridge VSC for DC fault current control, extremely fast recovery and variable DC voltage control

Combined AC and DC towers may allow inter system faults (AC-DC) jeopardising operational security of the HV AC system

Application of Full Bridge VSC for reliable fault current blocking (no additional device necessary, like a possible DC Breaker)

Full Bridge VSC is the most effective solution for VSC overhead line transmission providing: most reliable and fast blocking of all internal and external

short circuit faults

fast and smooth DC transmission restart with power transmission already during voltage ramp up

extreme robustness due to unlimited duty cycles

fast reduction of DC voltage to increase security e.g. under bad weather conditions

future-prove solutions considering integration into possible extended HVDC grids

Source: Elektrizitätswirtschaft (ew), 112 (2013), issue 3, page 53

Amprion Ultranet

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Reliable HVDC Grids need more than a Breaker

Short circuit faults spread at the speed of light (in case of overhead lines) and will affect the entire DC grid (DC voltage will be close to Zero during the fault) Possible solutions include electronic DC Breakers, Hybrid DC Breakers in combination with large

reactors, Full Bridge VSC in combination with Fast Switches

1) Fault detection and localization

algorithms distinguishing normal transients from faults protection relays/functions methods identifying the fault location

w/o communication (if possible) 2) Fault current interruption highly reliable solutions

minimizing interference with AC systems or the other DC pole

backup systems 3) Fault isolation high speed (ultra fast) switches

4) System recovery fast and reliable recovery of remaining system high repetition capability

Future HVDC Grids will be build step by step. Smaller systems comprising a few stations will be integrated into larger HVDC Grids. This requires standardisation of HVDC Grid design and operating principles.

Fault handling has 4 components, all are needed and are related to one another:

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VSC full bridge

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Korridor A

2 GW

Korridor A

2 GW

Korridor C

2 x 1,95 GW

Korridor D

2 GW

= ~

= ~

= ~

= ~

= ~

= ~

= ~

= ~

= ~

— Multi-teminal links using full bridge converters and fast DC switches

Towards a first DC Grid in Germany

Based on

Szenario B-2022 NEP 2012

Highest availability In corridor A:

selective fault clearing and fast recovery

In corridor C: parallel operation of two lines with fast take over in case of a fault on one line

Initial Illustration: Bryan Christie Design. Source: www.entsoe.eu

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Operational stresses in gas insulated systems

DC insulating systems must withstand different electrical stress compared to AC systems

Gas

Gas

Gas

Gas

Grounded Encapsulation

Stresses of insulators in operation Mechanical Stress Chemical Stress Thermal Stress Electric Stress

Current I

Impact on

Why is it NOT possible to directly use existing AC systems for DC voltage?

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Why do we have different conditions under DC voltage?

U

U = 0

C1 C2 R2

R1

Insu

latin

g sy

stem

eq

uiva

lent

circ

uit

U

t t1

Field transition

t > t1

C1 C2

AC

t = t1

DC

R1 R2

t → ∞

AC Insulating system Capacitance C determines voltage distribution C hardly dependent on temperature C hardly dependent on electrical field strength

Stable AC voltage distribution in operation

DC Insulating system Resistance R determines voltage distribution R strongly dependent on temperature R strongly dependent on electrical field strength

Time-dependent DC voltage distribution in operation

Electric stresses on insulating materials

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Physical Effects influencing electric stress

N N

+ +

+

+ +

+ +

+

- -

- - -

- - N

- - - -

- - -

-

Ionization Attachment

Recombination

Field emission

Drift due to electric field Charge transport and accumulation

Diffusion

∆T

Grounded Encapsulation

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Transition from AC to DC electric field

1

0

1

0

1

0

1

0

AC

DC

Norm

alized E-field

Positive space charge density in gas

Negative space charge density in gas

Norm

alized E-field

negative DC voltage

negative DC voltage

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Influence of conductivity κ and temperature T on DC electric field distribution

κ1 < κ2 < κ3

1

0

AC

1

0

DC

∆T ≠ 0

DC

∆T = 0

1

0

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HVDC basic investigations Factors of impact on electric stress in DC Compact Systems

Electric Stress

Electric conductivity of insulators

Gas + Solid Insulator

Voltage Type

Material ageing

Accumulation of space charges

Nonlinearity of insulating materials

temperature electric field

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HVDC basic investigations Exemplary test setups

Long-term testing

Dielectric limits

Surface effects

Artificial protrusions Temperature gradient

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Technical challenges for DC insulators

- Development of insulator design allowing for control of physical effects, particularly charging effects - Development of suitable insulating material for DC gas insulated systems - Careful handling/drying of insulating parts and cleanliness during assembly - Definition of “equipment-specific” high voltage testing procedures

Siemens Solution approach

Application of capacitively graded insulator based on RIP technology

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Solution approach Application of capacitively graded insulator

- More than 30 years of experience with RIP technology - Application of RIP technology at DC voltage levels up to ±800 kV - Field grading realized by metallic foils inserted in RIP material

AC/DC bushing

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Innovative RIP insulator design for DCCS ±320 kV

Benefits of RIP insulator - long-term experience with RIP material

from HVDC bushing available

- Field grading effective for AC, DC and impulse voltage stress

Benefits of RIP Insulator - Comparable electric field distribution for

AC and DC due to field grading

Nor

mal

ized

ele

ctric

fiel

d

Radius

DC field distribution

AC field distribution

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Testing Strategy

There are NO international agreed standards for this kind of equipment First approach: Application of IEC 62219 DC Bushing

Application of CIGRE Recommendations for cable testing

Application of various manufactures specified test (depending on the insulation system)

List of the possible dielectric tests: DC withstand test at higher level

DC voltage with superimposed impulse voltage

Polarity reversal

Long(er) term test with specified voltage, current, temperature and time profile

etc.

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Summary

In Addition to traditional Central Power Generation Large Scale Renewable Energy Sources (RES) have to implemented into Transmission Systems

New Transmission Solutions are needed

Standardization of HVDC Grids has started in Europe

Compact Gas Insulated Systems for HVDC Applications are feasible and ready for use

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Thank You!

Dr. Denis Imamovic E T TS Freyeslebenstr. 1 91058 Erlangen Telefon: +49 (9131) 7-44510 Mobil: +49 (173) – 26 29 144 E-Mail: [email protected]

mailto:[email protected]

Compact Systems �for HVDC Applications�Dr. Denis ImamovicAgendaCompact Systems for HVDC ApplicationsProspects and Research for VSC �Overhead Line Transmission�Reliable HVDC Grids�need more than a BreakerVSC full bridgeFoliennummer 7Operational stresses in gas insulated systemsElectric stresses on insulating materialsPhysical Effects influencing electric stressTransition from AC to DC electric fieldInfluence of conductivity κ and temperature T �on DC electric field distributionHVDC basic investigations �Factors of impact on electric stress in DC Compact SystemsHVDC basic investigations�Exemplary test setups Technical challenges for DC insulators��Solution approach�Application of capacitively graded insulatorInnovative RIP insulator design for DCCS ±320 kVTesting StrategySummaryThank You!

compact systems for hvdc applications - home - tu graz · 2015. 7. 10. · application of iec 62219...

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