BRIEF ON THE REPORT OF CIGRE WG B4-45 – TECHNOLOGICAL ASSESSMENT OF 800KV

HVDC APPLICATIONS

(Authors: R N Nayak, Mohammed Rashwan, R P Sasmal)

UHV Symposium Delhi, Jan 2009

Background: Formation of WG

Converter Configuration

Ground electrode station

Insulation Co-ordination

External Insulation

Reliability and Availability

Interference Levels

Conclusion

PRESENTATION SUMMARY

Background

• WG14.32 formed to review the current state of HVDC converter stations up to 600kV and requirement to expand the technology to voltages above 600kV and specifically to 800kV.

• Several studies and meetings confirmed 800 kV HVDC transmissions - a feasible voltage step (IEEE and Cigré in the late 80’s, Cigré 2002, Power Grid Corporation of India Ltd. Workshop in Delhi, February 2005)

• New WG B4-45 formed in 2005 for “ Technological Assessment of 800kV HVDC Applications “

The main driving forces for 800 kV HVDC systems:

Cost of power losses on overhead lines. Need for Bulk power evacuation over very long

distances. Technological constraints of other EHV options. Right of way constraints. Techno-economic drive necessitates development of 800

kV HVDC

Background

The amount of power to be transmitted The transmission distance Staging consideration of the project Location of converter station The amount of power to be transmitted at the different

stages of the project Reliability and availability requirements Loss evaluation Size and weight of the converter transformers for

transport

Converter Configuration

Decided by Utilities / planners

3,000 MW

3,750 A400 kV

800 kV

400 kV

3,000 MW

800 kV 3,750 A

1,875 A1,875 A

Possible 800 kV Arrangements- Series and Parallel

• Two similar rating parallel 12 pulse converters per pole

• Two dissimilar rating parallel 12 pulse converters per pole.

• One single 12 pulse converter per pole

• Two similar MW rating series connected 12 pulse converters per pole

• Two dissimilar MW rating series connected 12 pulse converters per pole

Converter Configuration

3,000 MW

3,750 A800 kV

600 kV

400 kV

200 kV

12 x 300 MVA

The advantages/disadvantages one of the valve groups insulated for

400 kV only;

only one among four transformer groups have full insulation at 800 kV

In case, one 12 – pulse bridge fails, half of the pole power can still be

transmitted (no ground return), voltage level will be half of nominal losses would be high;

No practical staging scheme; installation at full power done at once;

4 spare units needed per station unless provisions made for 600 KV and 800 KV units to fit in the space of 200 KV and 400 KV units

Series converters

Converter Configuration

3,000 MW

800 kV

Advantages / disadvantages:

loss of a converter means still the operation at 800 KV; with unbalanced ground current

Metallic return can not be used unless the same polarity parallel converter is removed from service

The staging in power, possible by installing one 12 – pulse bridge for each pole, later on, a second one

Possible to make rectifiers and inverters at different location i.e Multi-terminal stations.

2 spare units required, as minimum, per station;

Parallel convertersConverter Configuration

Earth Electrode station Design Criteria

Life expectancy : 50 yrsUnbalance current during normal operationPole outage condition Due consideration for parallel /multi-terminal operationPossibility of Metallic return to avoid ground current

Selection of Suitable site Close to HVDC terminal to reduce cost Soil resistivity upto the depth of 10 kms.

Ground Electrode

Natural sources located in the magnetosphere and ionosphere,

Earth being conducting natural sources, induce secondary fields in the earth.

Vector nature of electromagnetic fields enables to estimate the tensor form of the resistivity structure by measuring five components time series data consisting of three magnetic (Hx, Hy , Hz ) and two electric (Ex, Ey ) components.

Magnetotelluric (MT) measurement based on natural electromagnetic (EM) fields & it delineate the electrical structure of the earth

Natural EM fields contain a wide spectrum of signals Deeper resistivity information by recording low frequency

content of the signal for a longer duration of MT time series recording

Magnetotelluric measurement Ground Electrode

Good Conductivity up to the depth of 4150m except the top layer of about 100m

Typical result of Soil Resistivity

Ground Electrode

neutral

800 kV DC

D

10

E1

V3

V3

V2 72

V1

92

valve hall boundary

C2

C1

V3

V3

V3 71

V3

valve hall boundary 81

AC Bus- 1

A

52

62 A

- 1

A

51

61 A

91

A2

E2

400 kV DC

82

M

SR

AC Bus

• Converter transformer arrester “A2”

• Converter group arrester type “C1” and “C2”

• Mid point arrester type “M”

• Smoothing arrester type “SR”

Provide higher safety and reliability to the equipment.

Insulation Co-ordination

Arrester arrangement for series Converters

E1

9

valve hall boundary

V2

V2

V2

7

V1

C

AC-Bus 1

A

5

6 A

AC-Bus 1

A

5

6 A

A2

V2

V2

V2

7

V1

valve hall boundary

81

M

800 kV DC

D

10 SR

neutral

E2

82

800 kV DC

D

10 SR

neutral

E2

82 81

E1

9

Converter transformer arrester “A2”

• Converter group arrester type “C”

• Mid point arrester type “M”

• Smoothing arrester type “SR”

Provide higher safety and reliability to the equipment.

Insulation Co-ordination

Arrester arrangement for parallel Converters

SIWL kVpk 1600

LIWL kVpk 1900

DC withstand test voltage

kV 1200

Polarity reversal test voltage

kV 1020

Insulation Co-ordination

Insulation levels depends upon:

Particular layout, arrester arrangement arrester datasystem parameters

Typical Minimum Insulation Values:-

External Insulation

External insulation Creepage distance

• Pollution level• Surface material of insulators or equipment

housing Shed profile

Corrections for Altitude

Converter station equipment: The conditions well defined

Transmission line: conditions vary along the route ( 2000 – 3000 km) as the line pass through all kinds of terrain, including polluted areas and high altitudes > 1000 m.

Established procedure of calculation of availability and reliability for HVDC projects already established and being monitored and reported Worldwide

Characteristics of a reliable HVDC project: long continuous operations without fault

being fault tolerant, that is, being able to recover from faults quickly

only partial and acceptable loss on major faults

well integration in the AC system.

Availability and Reliability

Availability and Reliability

Typical forced outage rate used as design base in the recent HVDC projects: • Pole outage : 5 – 6 per year per pole• Bipole outage: 0.1 per year

Possible target values with series valve group :• 12 pulse bridge (Converter) outage: 2 - 2.5 per

year per converter • Pole outage : 2 – 3 per year per pole• Bipole outage: 0.1 per year or less

Possible target parallel valve group converters :• Pole outage : 5 – 6 per year per pole• Bipole outage: 0.1 per year

Interference Levels

Electric Field : 25kv/m – 30 kV/m

Ion current Density : 100 na/ m2

Minimum conductor height: 18 / 20 mtrs

Magnetic Field limit• Occupational exposure: 200 mT• Public Exposure: 40 mT

FOR HVDC TRANSMISSION LINE

FOR HVDC TERMINAL Electric Field : 30kv/m

Ion current Density : 100 na/ m2

Conclusion

Availability and reliability of Large HVDC system plays a major role in system stability, Needs proper planning for converter configuration

Experience gained from the initial 800 kV HVDC projects must be suitable incorporated in future projects

R & D activities must be continued to reduce the overall cost of the HVDC systems

Converter transformer design, wall bushing and external insulations needs special care during design.

THANK YOUTHANK YOU