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

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Nov 16, 2013 (3 years and 11 months ago)

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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 A

400 kV

800 kV

400 kV

3,000 MW

800 k

V

3,750 A

1,875 A

1,875 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 A

800 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 converters

Converter Configuration


Earth Electrode station


Design Criteria

Life expectancy : 50 yrs

Unbalance current during normal operation

Pole outage condition

Due consideration for parallel /multi
-
terminal operation

Possibility 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



V

3



V

3



V2



72



V1



92



valve hall boundary



C

2



C

1



V

3



V

3



V

3



71



V

3



valve hall boundary



8

1



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 data


system 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 YOU