ABB Power T&D Company Inc.
Distribution Systems Division
Specification GuideTechnical Bulletin TB115
Low Voltage Metal-Enclosed Switchgear Page 1
This specification covers the basic design and functional requirements for low voltage metal-enclosed switchgear with drawout air circuit breakers. It is provided as a guide to assist in the specification of switchgear that combines the attributes of reliability, safety, maintainability, convenience and value for industrial and utility applications. The specification guide is intended as a supplement to single line diagrams and data sheets for switchgear projects. Requirements shown in (italics) are choices to be specified by the customer or his designated representative. This guide does not provide comprehensive recommendations for protective relaying, coordination or instrumentation.
The specification is arranged in the following sequence:
2.0Industry Standards and Ratings
3.0Switchgear Construction and Wiring
4.0Primary and Ground Bus Systems
6.0 Circuit Breaker Compartments
7.0Air Circuit Breakers
8.0Circuit Breaker Trip Units
9.0Internal Arc Detection Units
11.0Testing and Certification
The low voltage metal-enclosed switchgear shall consist of an (indoor, outdoor) assembly with drawout type air circuit breakers, rated at 600VAC and arranged for a _____ VAC, 3-phase (3, 4) -wire (grounded, ungrounded, high resistance grounded) system. The switchgear shall consist of a sufficient number of vertical frames to house the circuits specified on attached project drawings and data sheets, with a minimum of empty spaces remaining. Switchgear ratings shall be suitable for service conditions with ambient temperatures of -300C to +400C and an installation altitude which does not exceed 6600 ft (2000 m), without derating. The manufacturer of the switchgear shall have been in the business of manufacturing low voltage metal-enclosed switchgear and circuit breakers continuously for the last 5 years, and shall have adequate quality programs as evidenced by ISO 9001 certification.
2.0 Industry Standards and Ratings
The switchgear will be designed, factory-assembled and tested to meet or exceed the latest applicable versions of ANSI C37.13, C37.16, C37.17, C37.20.1 and C37.51. The switchgear shall comply with applicable requirements of NEMA and the National Electric Code. All required design tests shall have been satisfactorily completed and witnessed by a UL representative. (Optional - UL Listing shall be required). Ratings are specified on project drawings and data sheets in accordance with the following table. (Shaded lines are ANSI preferred Instantaneous Trip ratings. Other lines indicate extended ratings.)
3.0 Switchgear Construction and Wiring
3.1 General: Circuit breaker and auxiliary compartments will be of modular construction and fabricated primarily from 14 gauge pre-coated Galvalume material (zinc-aluminum over cold-rolled carbon steel). Hem-bends (rigid overlap bending) will be consistently used to enhance strength and to minimize potential exposures to sharp steel edges during installation and maintenance. Individual frames shall be divided into front breaker sections and rear bus sections isolated by steel panels. In addition, each breaker compartment shall be completely isolated from adjacent compartments by steel panels.
3.2 Loading: For maximum economy of floor space, a single vertical section of switchgear shall enable mounting of up to four feeder circuit breakers in any combination of continuous current ratings through 2000 amps, with loading requirements per ANSI C37.20.1, section 18.104.22.168, as referenced in Table 11.
3.3 Circuit breaker installation: For circuit breaker installation and removal, the indoor switchgear will be equipped with (a floor-rolling breaker lift truck) and/or (an overhead lift truck attached to the roof of the switchgear).
3.4 Cable supports and cover plates: (Cable supports are required to support incoming feeder cable connections to feeder lugs.) (Non-ferrous floor cover plates shall be provided with indoor equipment to prevent rodents from entering the enclosure and to provide provisions for customer entrance of conduit.)
3.5 Roof: (A drip proof roof shall be provided above indoor equipment to prevent overhead water leaks from getting to the main bus. This drip proof roof shall not interfere in any way with the overhead lift truck if specified.)
3.6 Space heaters: (The switchgear shall be supplied with appropriately located space heaters (120V-150W) (240V-300W to be operated at 120V) to reduce condensation. Heaters shall be [thermostatically, direct] controlled.)
3.7 Wireways: The switchgear shall have built-in steel wireways to shield communications cables passing into or throughout the switchgear.
3.8 Control wiring: Control wiring shall be 14 gauge minimum, extra-flexible 41-strand SIS type, CSA and UL VW-1 rated. Current transformer wires shall be properly sized for the relay burden. Control lugs shall be heavy duty (non-insulated/Insulated) equivalent to AMP Solistrand or PIDG. Crimping of control lugs shall be performed with ratchet style crimpers that are periodically calibrated. Calibration schedules shall be available for inspection. Terminal blocks shall be the heavy duty type rated at 600 volts and 30 amps, similar to Buchanan types B108 or 3B104P for shorting terminals. All breaker control circuits shall be protected with a pull-out fuse blocks rated at 250 volts and 30 amps, and suitable for rejection fuses. (White shrinkable wire markers with typed nomenclature shall be used to identify wiring. Wire markers shall be destination type.)
3.9 Finish: Indoor and outdoor switchgear shall be phosphate treated and painted with an oven-baked, corrosion-resistant enamel finish. Color shall be light gray, ANSI 61.
4.0 Primary and Ground Bus Systems
4.1 Main bus: A main bus shall extend through all frames of the switchgear, with connections to the circuit breakers in each individual compartment. All bus shall be made of solid copper. The main bus shall be rated at (______) amps, and shall not be tapered. It shall be of the same rating as the main circuit breaker or power source, and the minimum bus size shall be 1600 amps continuous. The bus shall be braced to withstand the stresses resulting from the maximum short circuit current available as specified on project data sheets, and the minimum bracing shall be 65,000 amps symmetrical. Riser bus shall be sized to meet individual breaker ratings.
4.2 Plating: The complete bus shall be plated with (tin - standard, silver - optional) over 100% of its surface. The use of ring plating, or plating only on contact services, is not permitted.
4.3 Connections: All primary bus connections must use 2 or more grade 5 bolts. All bus hardware shall be tightened to manufacturer recommendations with a calibrated torque wrench. Bus hardware shall be marked to indicate that torque was inspected.
4.4 Insulation: The primary bus system shall pass all applicable ANSI dielectric ratings without the use of bus insulation. (The switchgear shall be provided with an optional primary bus system consisting of insulated main and load bus, and isolated vertical riser bus.)
4.5 Barriers: (The switchgear shall use optional main bus barriers to segregate the main bus from the cable compartment. It shall be possible to remove sections of these barriers to inspect the main bus without the need to disconnect load cables.) (Line/load barriers shall be provided to segregate the (tie breaker only, main and tie breakers).
4.6 Ground bus: A continuous bare copper ground bus shall extend the length of the switchgear lineup.
5.0 Outdoor Switchgear Assemblies
Outdoor switchgear shall be of the (weatherproof, walk-in) type with gasketing. Sufficient filtered louvers and screened vents shall be used to provide adequate ventilation while preventing the ingress of rodents and vermin. Sufficient strip heaters shall also be provided. (Walk-in switchgear: Interior incandescent lighting and convenience outlets shall be furnished in the aisle space. A manually operated lifting device running the full length of the walk-in aisle shall be provided for easy handling of the breakers.) The roof of outdoor enclosures shall be sloped to prevent build-up of water or ice. (Outdoor switchgear must be coated with a mastic type undercoating material to reduce corrosion.) Space heaters (120V-150W or 240V-300W operated at 120V) shall be provided to reduce condensation. Heaters shall be (thermostatically, direct) controlled. Non-ferrous floor cover plates shall be provided to prevent rodents from entering outdoor enclosures and to provide provisions for customer conduit entrance.
6.0 Circuit Breaker Compartments
6.1 Cradles: Each circuit breaker compartment shall use a one-piece cradle frame for both standard and fused breakers, to provide structural rigidity and bracing, as well as to allow easy addition, removal or changing of compartments. Interference blocking shall be provided to allow only a circuit breaker with the correct rating to be inserted into the cradle. Drawout cradles for fused circuit breakers shall incorporate the features of the non-fused cradles, except that the cradles shall be extra deep to accommodate the fuses. These cradles shall also have interference blocking to prevent the insertion of non-fused breakers.
6.2 Shutters: The compartments shall have (primary contact shutters) (provisions for primary contact shutters) which automatically cover primary contacts upon withdrawal of the circuit breaker. The shutter provisions shall permit simple field installation of shutters without modification to the switchgear structure, if the buyer chooses to add the shutters at a later date.
6.3 Doors: Circuit breaker compartment doors shall be provided without ventilation louvers. All ventilation must be provided within the switchgear and through internal chimneys to the top of the switchgear.
6.4 Auxiliary (TOC) switches: Circuit breaker compartments shall be equipped with a (4-contact, 8-contact) truck-operated cell switch to indicate when the circuit breaker is in the fully-connected position, where shown on project drawings and data sheets.
6.5 Kirk key interlocks: The circuit breaker compartments shall have provisions for mounting Kirk Key interlocks where shown on project drawings and data sheets..
6.6 Current transformers: Each circuit breaker compartment shall be able to accommodate up to three, front accessible bushing-mounted current transformers per phase (2 relay types and 1 metering type) on primary stabs in front compartment. Current transformers shall meet the requirements of ANSI C57.13.
7.0 Air Circuit Breakers
7.1 General: The three-pole drawout circuit breaker shall be rated at (240, 480, 600) volts AC and shall have a continuous current rating of (800, 1600, 2000, 3200, 4000) amps as shown on project data sheets. The circuit breakers shall be (manually, electrically and manually) operated as shown on product data sheets, and shall be equipped with (manually, motor and manually) charged stored energy operating mechanism to provide quick-make, quick-break operation. The operating mechanism shall be designed so that the closing and opening speeds of the contacts are independent of both control voltage (within the range prescribed by ANSI standards) and of the operator. For electrically operated breakers, an indicator shall indicate the status of the closing spring. The circuit breaker shall be equipped with means for manually closing and manually opening the contacts, and for closing the contacts slowly for inspection and adjustment purposes. A manual trip button and automatic trip indicator shall be located on the front of the breaker and shall be easily accessible without opening the compartment door. On electrically operated models, a manual closing lever and (local electrical closing/local electrical tripping) push button(s) shall be provided on the front panel of the breaker.
7.2 Construction: The construction of the circuit breaker shall consist of plated or painted steel with a track resistant Class 130 polyester-glass insulation system. All plated steel parts shall use a yellow zinc chromate finish to retard corrosion. The main and arcing contacts of the breaker shall utilize refractory-type materials to resist the effects of arcing on contact parting. Arc chutes shall be asbestos free and removable for contact inspection and adjustment.
7.3 Racking: The circuit breaker shall have a means for racking in and out of the compartment in all positions without opening the compartment door. Interlocks shall be provided to prevent moving a circuit breaker from the fully-connected, test or fully-disconnected positions unless the breaker is open. Mechanical interlocks shall prevent closing the breaker between any of these positions. Racking positions shall be indicated on both the circuit breaker and in the drawout compartment. Provisions shall be provided for padlocking an open breaker with one or more padlocks, when the breaker is in the connected, test or disconnected position, to positively prevent unauthorized closing or racking of the breaker. An additional interlock shall be provided to assure automatic discharging of the closing springs upon removal of the breaker from the compartment.
7.4 Contacts: The drawout circuit breaker shall be equipped with self-aligning primary and secondary contacts. Primary contacts shall engage only when the circuit breaker is in the fully connected position. Primary contact fingers shall be mounted on the circuit breaker for easy inspection and maintenance. Secondary contacts shall engage in the connected and test positions to complete control circuits as required. In the disconnected position, all primary and secondary contacts shall be disengaged. The drawout mechanism shall hold the breaker rigidly in the compartment in all positions. The male side of the secondary disconnect shall be mounted on the circuit breaker, and the female side shall be mounted in the compartment, to prevent inadvertent contact with energized control circuits.
7.5 Controls: Each circuit breaker shall use a solid state control device that eliminates the need for electromechanical relays within the breaker. The control device shall be connected to circuit breaker wiring by a locking plug type connector. Each circuit breaker shall have at least (4, 8, 12) on-board auxiliary contacts available for customer use. All auxiliary contacts must be on-board the breaker and wired through the secondary disconnect. No MOC switches or external mechanical linkages shall be used for auxiliary contacts.
7.6 Fused breakers: The fused circuit breaker shall incorporate all of the features of the non-fused circuit breaker, but shall also incorporate the current limiting characteristics of UL Class L fuses. The current limiting fuse shall be integrally mounted on, and physically connected in series with, the circuit breaker. The fused breaker shall be equipped with an open fuse trip device which opens all three poles of the circuit breaker when one or more of the current limiting fuses opens, to prevent single phasing of the load. No external tripping power shall be required to open the trip device. Interlocking shall be provided so the circuit breaker cannot be reclosed until the fuse(s) have been replaced. An indicator and reset lever on the front of the circuit breaker shall indicate when the open fuse trip device has operated. Special interference shall be provided on the fused circuit breaker to prevent insertion of the fused breaker into a non-fused compartment.
8.0 Circuit Breaker Trip Units
Each circuit breaker shall be equipped with a microprocessor-based trip device to provide Long Time overcurrent protection, Short Time and Instantaneous short circuit protection, and three-wire Ground protection functions as standard capabilities of the device. True root mean square (RMS) sensing shall be used on the Long Time trip element. All power for trip sensing and operation of the flux shift trip device shall be derived from current sensors mounted on the circuit breaker. The trip device shall include (current) (current and voltage) protection and metering. The trip device shall include the full range of characteristic curves, set-points and time delay settings which can be programmed at the device or from a remote location. Password protection shall be used to prevent unauthorized access to protective settings.
All protection settings, trip data and metering information shall be accessible through an LCD display and keypad on-board the unit, or from a power control system at a remote location. Metering accuracy shall be 1% for current and voltage, and 2% for power indications. Historical information shall also be accessible from a remote location. The trip device shall be individually addressable and communications ready, so that it will not require modifications to the circuit breaker to communicate with switchgear-mounted network interface equipment at a future date.
The trip device shall include an integral self monitor light to indicate the condition of the trip system. A trip target shall be provided, and the cause of trip shall be indicated on the LCD display.
9.0 Internal Arc Detection System
The switchgear shall be supplied with an optional electronic system to detect the presence of an electric arc fault in any primary compartment, and to send a command without delay to trip the appropriate upstream breaker if an arc is detected.
Approval drawings shall be provided in the following standard scope and format. Standard Class I drawings shall consist of a system single line drawing; general arrangement; front view; floor plan; nameplate drawing; and bill of materials. Standard Class II drawings will consist of Class I drawings plus 3-phase elementary and schematic diagrams. Standard Class III drawings will consist of Class I and II drawings plus interconnection wiring diagrams. Standard “as built” Class III drawings will be submitted for record on all projects.
Drawings shall indicate all equipment, but only such equipment, as is actually in the switchgear scope of supply. All user connection and interface points shall be clearly marked, including primary and secondary cable entrances and connection points; installation details; and interframe assembly and connection details for shipping splits.
Drawings shall be professionally prepared on AutoCad release 12.0 or greater, to the maximum extent practical, and shall be provided to the customer (by electromagnetic disk) (as paper copies) in quantities as shown on project data sheets. The manufacturer shall have the ability to transmit drawings electronically over the Internet as file size permits.