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THE CU HVDC SCHEME

 

 

 

 

 

 

Between:      Coal Creek, North Dakota and Dickinson, Minnesota  

 

 

Power Company:    

              Cooperative Power (CP), Eden Prairie, MN United Power Association (UPA), Elk River, MN

 

 

Manufacturer:      ASEA, Sweden

 

 

Commissioned: August, 1979

 

 

Main Purpose:      Base load, bulk power transmission between Coal Creek lignite mine-mouth generation plant to Dickinson; reversal transmission is possible.

 

 

Main Data:    Bipole 1000 MW at ± 400 kV and 1250 A/pole. Overload capacity :

              1375 A continuously

              1500 A for 1 hour or continuously if the temperature is below 8°C

              max. 1820 A during damping control sequence

 

AC Networks: At both terminals, two 3-phase converter transformers (Wye-Delta and Wye-Wye) per pole, 1 for each 6-pulse group at each terminal

 

Coal Creek:

4 @ 308/339 MVA. 235 kV + 20 %/174.5 kV

                        - 10 %/174.5 kV

(+16 and -8 taps @ 1.25 %/tap)

connection to the 230 kV AC system

 

Dickinson:

4 @ 292/321 MVA. 350 kV + 21.25 %/165 kV

                        -  8.75 %/165 kV

(+17 and -7 taps @  1.25 %/tap)

connection to the 345 kV AC system

Minimum short circuit ratio of 3.5

 

 

 

 

 

HVDC System: Overhead lines : 701 km (435.8 miles)

Line towers: self supporting lattice steel 

structures

Conductors:  2 x 1150 mm2 ACSR/pole

             (d=1.504 in)

Shieldings:  2 x 130  mm2 steel wire

                (d=0.5 in)

Insulator leakage: 25 mm/kV.

 

 

Electrodes:   The Coal Creek Terminal is designed with 12 vertical electrodes, each approximately 60 meters deep and 0.3 meters in diameter ; coke backfill is used.

 

              The Dickinson Terminal is designed with 15 vertical  electrodes, each approximately 75 meters deep and 0.3 meters in diameter ; coke backfill is used.

 

Resistance/electrode: total less than 0.1 ohm

 

Electrode lines :  2 x 620 mm2 ACSR (d=1.108 in.)

Coal Creek: length ~ 10 km (6.6 miles);   ~ 0.38 ohm

Dickinson:  length ~ 20 km (12.5 miles); R ~ 0.72 ohm

On-line metallic return switching is available.

 

 

DC Filters:   Dickinson : third-order high pass, tuned to the 12th harmonic

Coal Creek : High pass type, tuned to the 12th harmonic

 

HVDC Valves: The thyristor valves are housed indoors, and they are designed as "Quadruple" valves. Three quadruple valves form a 12-pulse converter unit.

 

Each quadruple valve has 4 valve sections in series connection. Each valve section has 30 modules, each with 6 thyristors in series connection, giving the total of 180 thyristors in series connection/valve arm and none in parallel. This makes 720 thyristors in one quadruple valve or 2160 thyristors in one 12-pulse converter unit for 400 kV DC and 1250 A. The valve structure is air insulated and air cooled.

 

The smoothing reactor is placed on the neutral side and is designed for 0.4 Henry.

 

 

 

Filters and

Shunt Banks: Both terminals are provided with harmonic filters:

 

 

Coal Creek: 2 filters each for 11th and 13th harmonic and 2 high pass filters

 

 

Quan.

Harm.

MVAr *

C=µF

L=mH

R=ohm

2

 11th

  32.3

  1.55

  37.3

  1.6

2

 13th

  33.9

  1.63

  25.6

  1.5

2

  HP

  56.5

  2.72

   4.3

 78

 

 

Shunt

Banks

 

 

1

  SH

 102.8

  4.94

  --

  --

 

     * MVAR at 235 kV

 

 

Dickinson: 2 filters each for 11th and 13th harmonic and 2 high pass filters

 

 

Quan.

Harm.

MVAr *

C=µF

L=mH

R=ohm

2

 11th

  31.4

  .678

  85.5

   4.8

2

 13th

  33.4

  .72

  57.7

   4.4

2

  HP

  71.7

 1.55

   7.9 

 143

 

 

Shunt

Banks

 

 

3

  SH

 114.7

 2.48

   --

   --

           * MVAR at 350 kV  

 

 

References:   "Electra" No. 63 (1979)

 

"A.C. Harmonic filter and reactive compensation for HVDC"

A General survey by SC14-WG03

 

"The CPA/UPA ± 400 kV HVDC Project", Arnold E. Poppens, Robert J. Heiser, and John M. Nelson

Proceedings of the American Power Conference, 1976

 

"CU ± 400 kV HVDC Project, Converter Station Layout", D. J. Christofersen and J. C. Goerss. Panel Session, IEEE Power Engineering Society Tenth Conference and Exposition on Overhead and Underground Transmission and Distribution, September 14-19, 1986

 

 

 

 

 

 

 

System Correspondent :

 

Mr Karl N. MORTENSEN

United Power Association

ELK RIVER

55330 MINNESOTA

USA

 

Telephone : 1.612.241.2365

Fax :       1.612.241.2316


 

 Code

Redundancy

 Reserv System

 

 Spare parts

 

CU  

 

Yes/No

 Yes/No

Min. time needed

Yes/No

Min. time needed

 

 

 

 

 for change 

 

for install spares

 

 

1)

2)

over (hours)

3)

(hours)

 

 

 

 

 

 

 

  AC Filter and Shunt  Bank

 AC-E.F

    Yes

   

 

    Yes

         1

  AC Switchyard Equipment

 AC-E.SW

    No

    Yes

       0.5

    Yes

         4

  AC Control and Protection

 AC-E.CP

    No

    No

 

    Yes

         1

  Converter Transformer

 AC-E.TX

    No

    No

 

    Yes

        72

  Synchronous Compensator

 AC-E.SC

    Not used

    Not used

 

   

 

  AC and Auxilliary Equipment

 AC-E.AX

    Yes

    Yes

       0.5

    Yes

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  Valve Electrical

 V.E

    No

    No

 

    Yes

         2

  Valve Cooling (integral with valve)

 V.VC

    No

    No

 

    Yes

         2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  Local HVDC Control and Protection

 C-P.L

    No

    No

 

    Yes

         0.5

  Master HVDC Control and Protection

 C-P.M

    No

    No

 

    Yes

         0.5

  Telecommunication

 C-P.T

    Yes

 

 

    Yes

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  DC Filters

 DC-E.F

    No

    No

 

    Yes

         2

  DC Switching Equipment

 DC-E.SW

    No

    No

 

    Yes

         8

  DC Ground Electrode

 DC-E.GE

    No

    No

 

    No

 

  DC Ground Electrode line

 DC-E.EL

    No

    No

 

    Yes

         4

  Other DC Yard and Valve Hall Equipment

 DC-E.O

    No

    No

 

    Yes

         4

 

 

 

 

 

 

 

  DC Transmission Line

 TL

    No

    No

 

    Yes

 

1) 2) 3) Please give more detailed information on table 2


* C U *

 

 

 

1 * REDUNDANCY

 AC-E.F  2 AC filter sets per station. Rated power
         available with one filter out of service

 AC-E.AX - Redundant AC power sources with automatic
           transfer equipment.
         - Redundant cooling equipment including controls
         - Redundant batteries and battery chargers.

 C-P.T   Redundant microwave channels between stations
         with automatic transfer.


 2 * RESERV SYSTEM

 AC-E.SW Redundant AC breakers. About 0.5 hours to switch
         failed breaker out of service.

 AC-E.AX 0.5 hours for manual switching to isolate failed
         equipment.








 

 3 * SPARE PARTS
 AC-E.F  1 hour to replace capacitor unit
 AC-E.SW 4 hours to replace arrester unit
 AC-E.CP 1 hour to replace relay unit
 AC-E.TX 72 hours to replace converter transformer. One
         spare transformer of each type at each station
 V.E     2 hours to replace thyristor unit
 V.VC    2 hours to replace thyristor heat sink
 C.P.L   0.5 hours to replace printed circuit board
 C.P.M   0.5 hours to replace printed circuit board
 DC-E.LF 2 hours to replace capacitor unit
 DC-E.SW 8 hours to repair switching equipment
 DC-E.EL 4 hours to repair insulators on ground electode
         line
 DC-E.O  4 hours to replace arrester. Spare smoothing
         reactor and voltage divider at each station. One
         spare wall bushing, one spare transductor of each

         type common to both stations.