imagination at workg GE Confidential

Metal-EnclosedSwitchgear

LoadInterrupterSwitches

San Francisco IEEE / IAS Electrical Design and Applications Seminar

April 29,2011

Gary H. Fox, PEGE EnergySenior Specification Engineer

T 925 969 3608C 510 219 6868E gary.fox@ge.comwww.geindustrial.com/design

2120 Diamond Blvd., Suite 100Concord, CA 94520General Electric Company

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What is a Load Interrupter Switch?

Air insulated disconnect switch

Metal gear enclosure

Provides safe switching and circuit protection

Infrequent means of disconnecting is required.

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Fault current protection using various types of fuses.

On/off control of a transformer

Duplex switching

Selector switch

Grouped in a lineup configuration with other medium voltage distribution equipment.

What is a Load Interrupter Switch?

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How the Load Interrupter Switch Works

• Two-position (open/closed), three-pole switch.

• Quick make/quick break spring-charged mechanism for both opening and closing.

• Switch contact speed is independent of the speed at which the operator handle is moved.

• Operated externally from the front of the switch enclosure.

• Switch blades disengage and interrupt the flow of electricity.

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The Functions of a Load Interrupter Switch

Load Interrupter switch functions include:

•Safe interruption of power. •Fault protection with the use of fusing. •Can be used to select alternative power between two primary sources. •Can be used in line-ups of multiple sections.

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Key Components

Load Interrupter switches consists of the following components:

•Switch mechanism •Fuses •Viewing window •Ground bus •Bolted frame enclosure •Horizontal and interphase barriers

These components more fully on the following screens.

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Switch Mechanism

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How the Switch Mechanism OperatesThe switch interrupts the circuit by

opening in the following manner: 1. Closed position, both the main

moveable blades and the stationary contacts are engaged. Virtually all of the load current flows through the main moveable blades.

2. As the external operator handle moves, a helical spring in the stored energy mechanism becomes torqued, applying a separate force on the blades.

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How the Switch Mechanism Operates

1.The stored energy mechanism overcomes the friction force of the stationary contacts and the main moveable blades. 2. The quick-break blades maintain contact while the main blades separate with minimal arcing.3.The quick-break blades separate. While within the arc chambers, the distance between the blades and the stationary contacts is sufficient to maintain an arc. The arc chambers reduce the intensity of the arc by absorbing heat and by evolving a gas that quenches the arc.

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FusesTwo different power fuses are available to provide overcurrent protection. The can be coordinated to meet the overload and short circuit ratings specified.

Current Limiting Type

Expulsion Type

Equipped with blown fuse indicators on top of the fuse. Clear fault currents within their ratings without any expulsion of gases or debris.Interrupting capacity of 50kA RMS Symmetrical at both 5 and 15kV. They utilize a quartz sand filler to transfer heat away from the fuse element to the fuse body tube, which is made from either Pyrex glass or filament wound epoxy.

Boric acid expulsion type fuses are specified. Fuses are constructed of a holder, a refill, and a discharge filter.Fuse element melts and the spring in the holder pulls an arcing rod through the boric acid cylinder of the refill. Heat from the arc decomposes the boric acid and hydrides blast through the arc to de-ionize it. The steam and boric acid anhydrides then pass through into the discharge filter that absorbs the heat and muffles the noise of the interruption.

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Viewing Window

Safe means for inspecting the position and condition of the switch mechanism without opening the door.

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Ground Bus

An easily-accessible, front ground bus.

Silver-plated or tin-plated copper to match the main bus.

Constructed to carry the rated short time current of the switch assembly for two seconds.

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Switch Enclosure• Rigid, bolted frame construction enclosure. • 11-gauge sheet steel, including the doors,

back panels, and side panels.• All steel doors have concealed hinges and

captive screw or quarter-turn latches.• Foot operated doorstop.• Each switch compartment and the fuse

compartment are provided with individual or "split" doors.

• Typical indoor depth on the enclosure is 50 inches.

• Optional 60-inch deep enclosures for special applications or for mounting additional devices.

• Typical switch section is 35 inches wide.

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Horizontal and Interphase Barriers

• Glass polyester horizontal barriers are used to separate the switch mechanism compartment from the fuse compartment when fuses are provided to prevent access from either compartment to the other.

• Interphase barriers between switch poles

• Optional glass polyester vertical section barriers to segregate the rear compartment section from the switch and fuse sections.

• Rear compartments can contain arrestors, other equipment and used for the entry and exit of cables when required by the user.

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InterlocksMechanical switch and door interlocks are standard.

Prevent the opening of the doors when the switch is in the "ON" position.

Prevent switch from closing when the door is open.

Provisions for up to six optional key interlocks.

For example, Load Interrupter switches can be key interlocked with the main circuit breaker of a switchboard on the secondary side of a transformer.

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Terminology

•Rated Withstand Current

•Rated Fault Making Current

•Rated Continuous Current

•Basic Impulse Level (BIL) Withstand Rating

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Rated Momentary Withstand Current(Momentary Current Withstand Asymmetrical Rating)

Maximum rms total current including dc offset at the major peak of the maximum cycle during a 10 cycles period.

Standard available options are 40kA and 61kA.

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Rated Fault Making Current(Fault Close Asymmetrical Current Rating)

The rating is the maximum fault current the switch can close and latch into, then carry for 10 cycles.

The fault close rating shall be equal to the rated momentary current.

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Continuous Current Rating

Maximum current that the switch is able to carry continuously without exceeding specified temperature rise limitations.

Available options are 600 and 1200 amperes.

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Basic Impulse Level (BIL) Withstand Rating

This rating is a measurement of the surge voltage withstand capability of the switch assembly. The assembly can withstand a surge voltage impulse of the rated value without failing.

Standard BIL ratings60kV @ 5kV95kV @ 15kV

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Product Applications

•Transformer Disconnect •Duplex Switch •Selector Switch •Line-Ups

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Transformer DisconnectFeatures

Cable or bus close coupled transitionStandard orientation has load Interrupter switch on the left side of the transformer when facing the front of the transformer. Reverse orientation, switch on the right side.

Customer ApplicationsThe switch is used to isolate the transformer from the incoming supply or to isolate the load circuits from the transformer. Configurations• Single• Duplex• Selector switch

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Duplex SwitchFeatures• Provides on/off switching, utilizing two load

break switch sections connected via a common set of fuses to the load.

• Mechanical interlocks (key interlocks) prevent both switches from being closed at the same time.

Functions• Allow selection of one of two power sources,

such as a normal and alternate power source. • Load is isolated when both switches are off.• Application in primary selective systems but

not primary loop systems

Note that incoming cables are terminated in separate sections.

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Selector SwitchFeatures• Provides on/off switching• Utilizes a non-load break selector switch in

series with a fused load break switch. • Mechanical interlocks (key interlocks) prevent

operation of selector switch unless load break switch is open.

• Less width and more depth compared to duplex.

Functions• Allow selection of one of two power sources,

such as a normal and alternate power source. • Load is isolated when both switches are off.• Application in primary selective systems but

not primary loop systemsNote that both incoming cables are terminated in same section

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Line-UpsFeatures• 600, 1200, and 2000 ampere horizontal

through bus.• Incoming line sections• Main• Tie (non-fused)• Branch (feeder) switches• Auxiliary spaces (both bussed and un-bussed),• Transitions to other equipment• Front and rear aligned.• Main sections require a transition to branch

switches.• Low cost alternative to other types of

switchgear.