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S&C ELECTRIC COMPANY

CASE STUDY 621-1003June 10, 2002

New Publication 2002

S&C Metal-Enclosed Switchgear Connects Wind TurbineGenerators to Utility Grid

METMETAL-ENCLOSEDAL-ENCLOSED

SWITCHGEARSWITCHGEAR

BackgroundLoad growth in one western state has been two to three times

the national average for the past eight years. Additional

power is clearly needed. But public demand dictates that the

new power be generated in a non-polluting manner. Wind

power seems to be a good prospect.

But the states major

utility was initially

concerned about the

economics of wind

generation. The cost per

kilowatt would be

considerably higher thanfor coal-fired generation,

although this gap would

narrow significantly with

the installation of more

wind turbine generators.

To make the project

feasible, the utility

commission agreed to

higher rates for customers

who voluntarily choose green power.

The utility then proceeded with plans for a pilot wind farm

producing a guaranteed output of 20 MW. If successful, theplant will be expanded to 60 megawatts. Metal-enclosed

switchgear will be utilized to feed the power to the utility

grid.

What did they do?The pilot farm was designed somewhat oversized to offse

variations in wind velocity (which affect the output of th

wind turbine generators) and to allow a few generators to b

taken out of service at a given time for maintenance.

Forty-three 700-kW wind turbine generators were specified

providing a total desig

output of 30 MW. Eac

generator includes a 690

volt to 25-kV step-u

transformer.

Two new six-bay lineupof S&C Metal-Enclose

Switchgear were als

specified. The utility wa

very satisfied with othe

S&C equipment they ha

purchased and knew o

S&Cs experience in co

generation applications.

As shown in the single

line diagram below, the system has six wind-turbin

generator groups, each consisting of six to eight generators

Power from each group is metered and fed to one of th

feeder bays in the switchgear lineups. From the switchgea

power is fed to a 25-kV to 115-kV step-up transforme

connected to the transmission line.

(3)(3) (3)

S

O

S

O

S

O

(7) (6)

To substationand grid

Station servicepower

(3)

(8)

(3)(3) (3)

S

O

S

O

SO

Meters

Windturbinegeneratorgroups

(7) (7)

Number of wind turbine generators in group

To substationand grid

Station servicepower

(3)

(8)

Relay bay

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Switching for each wind-turbine generator group is

provided by a 400-ampere Mini-Rupter Switch, power-

operated by a Type MS-2 Switch Operator. S&C SM-4

Power Fuses clear cable faults between the switchgear and

generator groups, isolating them from the utility grid.

Fused voltage transformers provide control power for the

switch operators as well as voltage monitoring.

Current transformers provide sensing for a directional

overcurrent protection arrangement, which utilizes

Schweitzer 351 Relays. Power in this system normally

flows from the wind turbine generators to the utility grid.

In the event of power flow from the utility grid to the wind

turbine generators, the 351 Relay will send a trip signal to

the switch operator of the affected Mini-Rupter Switch,

for current below 400 amperes. For current above 400

amperes, no trip signal will be sent; such current is likely

the result of a cable fault and, as discussed above, will be

cleared by the SM-4 Power Fuses.

Station service power is provided through another

manually operated fused Mini-Rupter Switch in each

lineup.

Results

The pilot wind farm has performed very

well, meeting all expectations.

S&C has also provided other equip-

ment for the application, including

115-kV Line-Rupters, Series 2000

Circuit-Switchers, and SMD-2B Power

Fuses, as well as numerous Loadbuster

Disconnects.

Another wind farm project is now under

construction, employing S&C Vista

Underground Distribution Switchgear. An

S&C FVR Circuit Breaker, Line-Rupters,

and Series 2000 Circuit Switchers will be

used in this project.