Presentation on theme: "John Stark – Russelectric Inc.. Overview Recent changes to the National Electrical Code (NEC) require the selective coordination of overcurrent protective."— Presentation transcript:
John Stark – Russelectric Inc.
Overview Recent changes to the National Electrical Code (NEC) require the selective coordination of overcurrent protective devices at hospitals and other mission- critical facilities. Transfer switches with 30-cycle closing and withstand ratings dramatically simplify designing to that requirement.
Commercial Utility Power UPS UPS Batteries Air conditioning, Lighting, Mechanical, Building Loads,etc. Network Computer Loads Transfer Switchgear Generator Paralleling Control Switchgear Emergency Generators Transfer Equipment in a Common Scenario With regard to the emergency back-up and transfer scheme, it is incumbent upon engineers to select the proper equipment for the application. There are many considerations and they are becoming more with each decade.
What is Selective Coordination? Definition (Article 100 – NEC) Definition (Article 100 – NEC) Localization of an overcurrent condition to restrict outages to the circuit or equipment affected, accomplished by the choice of overcurrent protective devices and their ratings. For the full range of possible overcurrents, the act of isolating an overloaded or faulted circuit from the remainder of the electrical system, thereby eliminating unnecessary power outages. The circuit causing the overcurrent is isolated by the selective operation of only that overcurrent protective device which is closest upstream to the overcurrent condition. Article 100 provides the Code definition. Here is another way to describe it:
Selective coordination was first required by the NEC in 1993 for elevator circuits. Amendments to the Code in 2005 and 2008 strengthened the requirements and expanded them to include emergency and legally required standby systems, as well as critical operations power systems. Selective coordination, as defined in the 2008 NEC, is the (as in previous slide) localization of an overcurrent condition to restrict outages to the circuit or equipment affected, accomplished by the choice of overcurrent protective devices and their ratings or settings. It is a complicated process of coordinating the ratings and settings of overcurrent protective devices, such as circuit breakers, fuses, and ground fault protection relays, to limit overcurrent interruption (and the resultant power outages) to the affected circuit or equipment (the smallest possible section of a circuit). In other words, the only overcurrent protective device that should open is the device immediately upstream from the circuit/equipment experiencing an overcurrent condition. Selective Coordination, History & Requirements
Proper Selective Coordination is becoming more and more of an engineering consideration and is being enforced by inspectors more & more often… Refer to IAEI handout Selective coordination restricts outages to the circuit or equipment affected, ensuring reliability of electrical power.
NEC 2008 –Verbiage on Selective Coordination NEC(2008) Coordination: requires Emergency system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices. NEC(2008) Coordination: requires Emergency system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices. NEC(2008) Coordination: requires Legally required standby system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices. NEC(2008) Application of other articles: requires The essential electrical system shall meet the requirements of Article 700. NEC(2008) Application of other articles: requires The essential electrical system shall meet the requirements of Article 700. The overcurrent protective devices may include the following: The overcurrent protective devices may include the following: Molded Case Circuit Breakers Molded Case Circuit Breakers Fused devices Fused devices Insulated Case Circuit Breakers Insulated Case Circuit Breakers Air Power Circuit breakers Air Power Circuit breakers
More on Selective Coordination Requirements Selective coordination requirements for life safety are not a new concept for the Code. There has been a Code requirement to coordinate selectively the over-current protective devices for elevator circuits since Most engineers agree this is the simplest way to assure coordination, however….. Breakers Breakers Instantaneous circuit breakers will not coordinate properly because typically, they arent adjustable. Fuses
One-line G Utility 4000A APCB 1600A APCB 1600A APCB 800A ICCB 400A MCCB An overcurrent event (overload, short circuit, or ground fault) here should trip the 400A MCCB ATS MCCB's (Molded Case Circuit Breaker) typically instantaneous or Current Limiting Devices. ICCB's (Insulated Case Circuit Breaker) are 30 cycle withstand or up to 4 Cycle Instantaneous. APCB's (Air Power Circuit Breaker) are typically 30 cycle withstand devices.
Selective Coordination G Utility 4000A APCB 1600A APCB 1600A APCB 800A ICCB 400A MCCB Fault on load side of ATS could see up to 30 cycles of fault current -depending on the Air Power Circuit Breaker settings that is feeding it- and could travel through the ATS and the ATS contacts. ATS If the 400A MCCB does not trip/clear… ATS In the absence of other means to satisfy selective coordination, the ATS must withstand a fault or even close on potential fault to be properly coordinated.
Review of Code Requirements Review of Code Requirements Article 517 Health Care Facilities Application of Other Articles Application of Other Articles Article 620 Elevators, etc Article 620 Elevators, etc Selective Coordination (2008) Selective Coordination (2008) Article 700 Emergency Systems Article 700 Emergency Systems (B)(5)(b), Exception (B)(5)(b), Exception Article 701 Legally Required Standby Systems Article 701 Legally Required Standby Systems Coordination Coordination Article 708 Critical Operations Power Systems Article 708 Critical Operations Power Systems Selective Coordination Selective Coordination
2005 Code Adoption 2005 NEC 1999 NEC 2002 NEC Local Adoption
2008 Code Adoption 2005 NEC – 8 States WV WI MT ND SD WA OR NV ID UT AZ NM TX CO WY NB M I KY TN MN IA MO AR LA MS IL IN OH AL GA KS OK NH ME NY PA VA DE NJ MA RI FL NC SC VT CA Local Adoption – (10) MD 2008 NEC – 32 States M I Note: Some local adoption states have earlier than 2005 adoptions in some jurisdictions CT AK State Adopted Unincorporated Areas State Adopted S. Carolina Code Council adopted 2009 IRC with 2008 NEC 3/22/10 with implementation effective Expected July 10 Expected January 2011 Expected July 2010 AK HI, basically 2002 NEC but some islands back to 1993 NEC Revised April 19, 2010 HI
Code Rulings Panel 20 Statement:Panel 20 Statement: The overriding theme of Articles 585 (renumbered to 708) is to keep the power on for vital loads. Selective coordination is obviously essential for the continuity of service required in critical operations power systems. Selective coordination increases the reliability of the system. In the 2008 Code Cycle there were challenges to the selective coordination requirement. Proposal proposed the elimination of the selective coordination requirement for The proposal was to remove the selective coordination requirement from the mandatory text and places it in a non-mandatory in a FPN (fine print note). But Code Panel 13 rejected this proposal by a vote of 9-4. To follow is their statement: Panel 13 Statement:Panel 13 Statement: This proposal removes the selective coordination requirement from the mandatory text and places it in a non-mandatory FPN (fine print note). The requirement for selective coordination for emergency system over-current devices should remain in the mandatory text. Selective coordination increases the reliability of the emergency system. The current working of the NEC is adequate. The instantaneous portion of the time-current curve is no less important than the long time portion. Selective coordination is achievable with the equipment available now.This proposal removes the selective coordination requirement from the mandatory text and places it in a non-mandatory FPN (fine print note). The requirement for selective coordination for emergency system over-current devices should remain in the mandatory text. Selective coordination increases the reliability of the emergency system. The current working of the NEC is adequate. The instantaneous portion of the time-current curve is no less important than the long time portion. Selective coordination is achievable with the equipment available now. Then, Code Panel 20, which was responsible for the new Article 708, summed up the need for selective coordination in their statement to Comment 20-13, (which was another proposal for the deletion of the selective coordination requirement). This comment was rejected The actual panel statement to Comment 20-13:
Exceptions to Code Rulings Refer to IEEE handout Selective Coordination versus Arc Flash… page 12 There are numerous proposals being adopted by States and/or City or local governmental bodies which modify the selective coordination requirements. The most commonly heard proposals fall into two categories: 1. Allow the degree of selective coordination needed to be the responsibility of the qualified person responsible for the project. Exception No. 2: Where the system design is under the control of a licensed professional engineer engaged in the design or maintenance of electrical installations, the selection of overcurrent protective devices shall be permitted to coordinate to the extent practicable. The design shall be documented, stamped by the professional engineer, and made available for review by the authority having jurisdiction. (The Commonwealth of Massachusetts was the first State to adopt such a proposal as an exception to the Articles in , and , which require selective coordination as follows:
Exceptions to Code Rulings (cont.) 2. Proposals to modify the NEC requirement for selective to only be required for above a specific time. The leading proposal is 0.1 seconds (6 cycles) and above. The State of Oregon recently adopted a proposal submitted by the National Electrical Contractors Assoc., Oregon Pacific Cascade Chapter, as Statewide Alternate Method No. OESC applying to Articles in , and This states the following: The requirements in NEC , and for selective coordination may be demonstrated by providing a selective coordination study utilizing trip-curve data in the range of 0.1 seconds or more. Findings: By omitting the instantaneous range from the requirements for selective coordination, reasonable and affective safety can (still) be achieved. Signing supervisors and engineers can use readily available and published time current curves to determine if a system is selectively coordinated to a substantial degree without having to relay on unregulated manufacturer testing data and inconsistent engineering and design practices. Substantiation for this proposal included: 1). …selective coordination is not always possible or practical for all fault current levels when protection is provided by MCCBs. The requirement for total selective coordination means that over current protection devices must be coordinated for all faults, regardless of their magnitude or duration, including the most extreme case, the bolted fault. However, bolted three phase faults which rapidly generate extremely high current in the instantaneous range rarely occur in practice, except at start-up when interruption of power due to a lack of coordination is not likely to compromise safety... In order to achieve total short circuit selective coordination, the size of upstream overcurrent protective devices may need to be increased and/or time delay trip characteristics increased, thereby possibly increasing the arc flash hazard.
Arc Flash Considerations Refer to IEEE handout Selective Coordination versus Arc Flash… page 10 This is the other side of the argument regarding the subject of Selective Coordination VS Arc Flash Considerations. The presenter will not delve into this side of the argument, as he is in the business of providing emergency power to critical facilities and therefore is in the camp of having a non-sensitive, robust type system, selectively coordinated, that facility managers want to perform well when called upon. In cases of catastrophic outages, Arc flash considerations might take a back seat to keeping as much of the facility up and running as possible and only Tripping CBs closest to the fault. For more details on the ARC Flash concerns, and that whole side of the argument, please refer to your handout.
UL 1008 Withstand Test 34.1 When tested under the conditions described in 34.2 – 34.15, a transfer switch shall withstand the designated levels of current until the over-current protective devices open or for a time as designated in At the conclusion of the test: a)The switch shall be capable of being operated by its intended means; b)The fuse mentioned in shall not open, c)There shall be no breakage of the switch base to the extent that the integrity of the mounting of live parts is impaired, d)The door shall be prevented by its latch, without bolt or lock installed therein, from being blown open, and deformation of the door alone is not determined to be unacceptable; e)No conductor shall have pulled out of a terminal connector and there is no damage to the conductor insulation or the conductor (see 41.56); and f)For a plug in or draw out unit, the point of contact is to be the same both mechanically and electrically as before the test.
UL 1008 Closing Test 36.1 When tested in accordance with 36.2, a transfer switch shall comply with the requirements in 34.1(a) –(f) Revised September 18, The sample for this test is to be that used for the withstand test. Test procedures and conditions for the closing test are to be as described in 34.3 – The switch is to be closed on the circuit The test (for close on) current shall be the same as that used in the withstand test. test.
UL 1008 Short Circuit Test History Around 1989 UL introduced an optional 3 cycle test for any over- current protection device. Prior to this, manufactures could test with any over-current device. If a manufacturer didnt test to 3 cycles, they would be required provide a label that lists all breakers that the switch was coordinated with. This requirement did not take into consideration air power circuit breakers APCBs. Some of these breakers were 4-5 cycle devices (GE AKR and Westinghouse DS) January 9th, 2002 UL introduced an optional short time current rating test. A withstand and a close and withstand test is required to get a UL short time rating. This requirement did not take into consideration air power circuit breakers APCBs. Some of these breakers were 4-5 cycle devices (GE AKR and Westinghouse DS) This requirement did not take into consideration air power circuit breakers APCBs. Some of these breakers were 4-5 cycle devices (GE AKR and Westinghouse DS)
UL 1008 Short Time Current Test 36A.1 A switch marked with a short-time current rating in accordance with shall be tested under the conditions described in 36A.2 -36A.12 and shall withstand the short-time current for the period specified. At the conclusion of the test: a)The transfer switch shall be capable of being operated by its intended means, b)The fuse mentioned in 36A.7 shall not open, c)There shall not be any damage to the switch base to the extent that the integrity of the mounting of live parts is impaired, d)The door shall be restricted by its latch, without bolt or lock installed therein, from being blown open. Deformation of the door itself is not reason for rejection, e)No conductor shall have pulled out of a terminal connector and there shall not be any damage to the conductor insulation or the conductor (see 41.56), f)For a plug-in or draw-out unit, the point of contact shall be the same both mechanically and electrically as before the test, g)The Temperature Test, Section 29, shall be performed on the transfer switch at the completion of the tests described in 36A.8 and 36A.9, without maintenance, and the temperature rise shall not exceed the values given in Table 29.1, increased by 10° C or 18° F, and h)The Dielectric Voltage-Withstand Test (Repeated), Section 36B, shall be performed on the transfer switch at the completion of the tests described in 36A.8 and 36A.9.
UL 1008 Overload Test 28.1 Transfer switch equipment shall perform in an acceptable manner, as intended by the manufacturer, when subjected to an overload test consisting of the number of operations specified in Table 28.1, controlling a test current as described in Table Table 28.1 Overload Test Switch rating, amperesNumber of cycles of operationRate of Operation* and above per minute 1 per 2 minutes 1 per 3 minutes 1 per 4 minutes 1 per 5 minutes Device used forDevice rated in amperesPower test currentFactor Motor loads or total systema-c 6 times rated current Table 28.2 Method of determining test current for overload tests on transfer switches 28.4 A cycle is defined as making and breaking the required test current on both the normal and alternate contacts. During the test, the alternate source shall be displaced 120 electrical degrees from the normal source for a 3 phase supply or 180 electrical degrees for a single phase supply The minimum on time in each contact position is to be 1/6 second (ten electrical cycles based on a 60Hz source), unless automatic tripping of the over-current device occurs.
UL 1008 Endurance Test 30.1 A transfer switch shall perform as intended when subjected to an endurance test controlling a test current as described in Table 30.1 and at a rate and number of cycles described in Tables 30.2 and Table 30.1 Method of determining test current for endurance tests The test cycle is to be 1 second on and 59 seconds off. A controller may be operated at a rate of more than 1 cycle per minute if synthetic loads are used or if a sufficient number of banks of lamps controlled by a each bank will cool for at least 59 seconds between successive applications of current. Table 30.2 Endurance test cycles for emergency system switches including legally required stand-by systems.
UL 1008 Temperature Test 29.1 Transfer switches when tested under the conditions described in 29.2 – shall not attain a temperature at any point high enough to constitute a risk of fire or to damage any materials employed in the device, and shall not show temperature rises at specific points greater than those indicated in Table For the temperature test the transfer switch is to be operated under intended use conditions and is to carry its test current continuously at the test potential specified in Table The test current shall be 100 percent of the rated current.
Overcurrent Protective Devices Molded Case Circuit Breakers –MCCB (UL489) Molded Case Circuit Breakers –MCCB (UL489) May be Current Limiting to 200KA May be Current Limiting to 200KA Long Time Overcurrent Long Time Overcurrent Instantaneous Interruption is less than 3 cycles Instantaneous Interruption is less than 3 cycles Fuses and Fused Devices Fuses and Fused Devices Current Limiting Current Limiting Mostly used on 200KA circuits Mostly used on 200KA circuits Insulated Case Circuit Breakers -ICCB (UL489) Insulated Case Circuit Breakers -ICCB (UL489) May be Current Limiting to 200KA May be Current Limiting to 200KA Instantaneous Interruption is typically less than 4 cycles Instantaneous Interruption is typically less than 4 cycles Short Time delay available (30 cycles) with Instantaneous over-ride Short Time delay available (30 cycles) with Instantaneous over-ride Low Voltage Air Power Circuit Breakers -APCB (UL1066) Low Voltage Air Power Circuit Breakers -APCB (UL1066) May be Current Limiting to 200KA May be Current Limiting to 200KA Instantaneous Interruption is typically less than 4 cycles Instantaneous Interruption is typically less than 4 cycles Short Time delay available (30 cycles) without Instantaneous Short Time delay available (30 cycles) without Instantaneous
Low Voltage Air Power Circuit Breakers APCBs are ideal protective devices for the application of selective tripping. APCBs are ideal protective devices for the application of selective tripping. Short Circuit Duty Cycle: Oc,15 s – CO (applying fault current Short Circuit Duty Cycle: Oc,15 s – CO (applying fault current to a closed CB for ½ second [30 cycles] separated by 15 seconds to a closed CB for ½ second [30 cycles] separated by 15 seconds of zero current flow, then close on fault current for another ½ of zero current flow, then close on fault current for another ½ second [30 cycles] ). second [30 cycles] ). This test may be performed with or without an instantaneous override on the closing cycle. This test may be performed with or without an instantaneous override on the closing cycle. The GE AKR was tested without the instantaneous. Note some breakers now have a Trip Free feature in which the breaker will still clear a fault without instantaneous trip. Opinions vary on whether this is desirable or not in emergency power systems. The GE AKR was tested without the instantaneous. Note some breakers now have a Trip Free feature in which the breaker will still clear a fault without instantaneous trip. Opinions vary on whether this is desirable or not in emergency power systems. Short Time Current Short Time Current ANSI C (2)-1990 ANSI C (2)-1990 Short-Time Current Duty Cycle Application. The applicable short-time current duty cycle for unfused circuit breakers consists of two periods of 1/2s current flow, separated by a 15 s interval of zero current.
Selective Coordination - Good No overlapping fault current of individual devices. This is coordinated properly. In a perfect world this is great.
Selective Coordination - BAD In this case, since it takes 8 cycles for the upstream breaker to clear the fault, a 3 cycle rated transfer switch is inadequate. ATS Feeder Breaker8 cycles to clear
Complete Coordination A 30 cycle UL rated Transfer Switch truly gives you complete coordination with any over-current protective device.
What is our Competition Doing?
ASCO a a a a 4000a* * ATS only Short Time Close & Withstand 8. With fuses only Non UL 6
News regarding Cummins Power Generation 2009 News Releases June 12, 2009 Cummins Power Generation Transfer Switches First With UL-Listed 30Cycle Ratings MINNEAPOLIS, MINNESOTA – Series OHPC and CHPC PowerCommand® automatic transfer switches from Cummins Power Generation Inc. are the industry's first transfer switches to achieve UL-listed 10-cycle and 30-cycle withstand and closing (short-time) ratings. The OHPC open transition and CHPC closed transition switches demonstrated unprecedented short-time ratings of 25 kA at 10 cycles for 125 to 260-amp switches, 30 kA at 30 cycles for 300 to 600 amps, and 50 kA at 30 cycles for 800-amp switches in UL tests. The switches continued to operate safely at full load, even after testing. The UL listing provides consulting and specifying engineers independent assurance that the OHPC and CHPC transfer switches offer the industry's highest performance level, particularly for standby power systems requiring selective coordination. As defined by the 2008 edition of the National Electrical Code (NEC), selective coordination is mandatory for emergency and legally required electrical systems in buildings where life safety is paramount, including hospitals, health care facilities, emergency shelters and high-rise buildings with multiple elevators. NEC 2008 also requires selective coordination for critical operation power systems (COPS) in secure buildings such as banks, data centers, embassies and government offices. Selective coordination localizes an overcurrent condition to restrict outages to the circuit or equipment being affected. It is achieved by selecting circuit breakers and transfer switches with timing and withstand characteristics that delay or prevent faults from tripping upstream overcurrent protection devices. Selective coordination requirements are more easily satisfied by specifying OHPC or CHPC switches rather than products without UL-listed short-time ratings. The ability of CHPC and OHPC transfer switches to withstand fault current for up to 30 electric cycles (one-half second) gives the consultant the flexibility to adjust the instantaneous time delay on the ATS overcurrent protection device to prevent upstream 2breakers from tripping unnecessarily. Both transfer switches feature Cummins Power Generation's innovative High Endurance 8/12/2009 Page 2 Mechanism (HEM), designed to ride through a fault condition undamaged and retain its capability to carry 100 percent of the rated load. Magnetic forces developed during a fault cause a typical transfer switch's contacts to blow open, producing an electrical explosion that often results in extensive internal damage to the switch, requiring replacement of contacts, arc chutes and, in some cases, the controller. In contrast, the HEM uses that same magnetic energy to hold the contacts closed during a fault, virtually eliminating arcing, contact damage and performance degradation. It can survive multiple faults of the specified magnitude - listed on the nameplate as the withstand and closing current ratings (WCR) - and continue to carry the rated current without overheating. This proprietary Cummins Power Generation technology means that there will be no costly repairs or inconvenient downtime after a fault. "Cummins Power Generation is proud to be the first manufacturer of transfer switches proven to survive a fault condition and to continue to operate at full load without repair," said Rich Scroggins, ATS product manager of Cummins Power Generation. "This ability gives consulting engineers more design flexibility in addressing requirements, and potentially to lower costs by using fewer transfer switches. Underwriters Laboratories (UL) is a leading safety testing and certification organization that has conducted product safety testing for nearly 115 years. On electrical products, the UL mark designates products that have been certified for safety regarding foreseeable hazards that include electric shock, fire and mechanical hazards. Although Cummins Power was first to the market with some sizes, this is all theyve published so far.
Power Generation Switch Current Ratings Short Time Ratings Transfer Switches Bypass Switches DurationCycles a a 25 ka a a 30 ka a800a 50 ka a a The OHPC open transition and CHPC closed transition switches demonstrated unprecedented short-time ratings of 25 kA at 10 cycles for 125 to 260-amp switches, 30 kA at 30 cycles for 300 to 600 amps, and 50 kA at 30 cycles for 800-amp switches in UL tests. The switches continued to operate safely at full load, even after testing a a a a 4000a* * ATS only Short Time No Mention in the press release of bypass switches Only the 800a we dont match So weve distilled the info and put the values into a table.
EATON CUTLER HAMMER For which size ranges?
EATON CUTLER HAMMER Contactor based transfer switches. Same type we make No withstand values based on how many cycles?? While inconclusive as to whether these type switches carry a UL 30 cycle close and withstand rating, it doesnt seem as if they do.
EATON CUTLER HAMMER Circuit Breaker based transfer switches. First mention of 3 cycle rating but where is the 30 cycle listing ?? While inconclusive as to whether these type switches carry a UL 30 cycle close and withstand rating, it doesnt seem as if they do.
EATON CUTLER HAMMER Magnum Circuit Breaker based transfer switches. First mention of 30 cycle rating but only when used with upstream fuses ?? While inconclusive as to whether these type switches carry a UL 30 cycle close and withstand rating, it doesnt seem as if they do without the inclusion of upstream fuses.
G.E. Zenith To Our Knowledge, they presently publish nothing other than 3 cycle ratings.
New Russelectric 30 Cycle Automatic Transfer Switches and Bypass Isolation Switches
SIDE BARRIER: - -5/8 thk glass polyester - -Greater arc & track resistance - -Excellent flame resistance - -Movable contact support BACKPLATE: -increased thickness to added strength and stability Back Plate Assembly
Current Path Movable Main Contact Stationary Contact Movable Arcing Contact Blow Open Force Movable and Arcing Contact Springs Blow-Off Contact Design: - Used for Interrupting High Fault Currents - Magnetic forces push contacts open - Used for 3 cycle devices - Contact springs - only force to withstand fault Contact Design: Blow-off vs. Blow-on
- Used for withstanding High Fault Currents - Magnetic forces from fault increase pressure on contacts - - Offset hinge point allows for rotation toward contacts for blow on effect Current Path Contact Springs Hinge Point Stationary Contact Main Contact Force Contact Design: Blow-on
Contact Comparison: 3 Cycle vs. 30 Cycle Russelectric 3 Cycle Design Blow-Off Design Single Arcing Contact Multiple Contact Fingers depending on amperage Main Contact Pad material: AgWC50 – Silver Tungsten Carbide Tungsten to reduce erosion Arcing Pad Material: AgW73 – Silver Tungsten Stationary Contact Pad material: AgWC50 – Silver Tungsten Carbide Contacts Rotate on Copper Hinge Block and Pin Assembly Metal Contact Holder
30 Cycle Design Blow-On Design Blow-On Design Arcing Contact Designed into each Arcing Contact Designed into each main contact – Copper main contact – Copper Multiple Contact Fingers depending on Multiple Contact Fingers depending on amperage amperage Main Contact Pad material: Main Contact Pad material: AgWC40 – Higher Silver Contact to AgWC40 – Higher Silver Contact to prevent overheating prevent overheating Stationary Contact Pad material: Stationary Contact Pad material: AgC4 – 96% Silver, graphite to AgC4 – 96% Silver, graphite to prevent welding during withstand prevent welding during withstand Flexible Braided connectors – Flexible Braided connectors – prevents overheating and hot spots prevents overheating and hot spots Brush Movement in Main Contacts – Brush Movement in Main Contacts – Cleans contact pad every operation Cleans contact pad every operation Molded Contact Holder Molded Contact Holder - Contains arc - Contains arc - BMC thermoset material - BMC thermoset material - Withstands heat - Withstands heat - Great arc and track resistance - Great arc and track resistance
CROSSARM MECHANISM n Made from Square Steel Stock n Overcenter Spring Mechanism to Latch Contacts Closed and Open Utilizes same mechanics as the 3 cycle switch – Heavier spring Utilizes same mechanics as the 3 cycle switch – Heavier spring
OPERATORS Open Transition Switches with EMO Reliability of Motor Operators
30 CYCLE BYPASS SWITCHES Major Design Changes Elimination of Isolation Handle Elimination of Isolation Handle Gearbox, Rack-in Mechanism to engage switch Gearbox, Rack-in Mechanism to engage switch Bottom and Side Guiderails to align and Contain Switch Bottom and Side Guiderails to align and Contain Switch Secondary Disconnects accessible on Left side of cabinet Secondary Disconnects accessible on Left side of cabinet Optional Shutter Design Optional Shutter Design 800A Cradle is On the Ground Rollout Design 800A Cradle is On the Ground Rollout Design Complete Finger Cluster Redesign for all Sizes Complete Finger Cluster Redesign for all Sizes
Removal of Isolation Handle Single Handle is for Bypass Operation 800A Rollout Switch Cradle rolls out on Ground – not on rails
Gearbox Rack-in Mechanism Access Rack-in Shaft through door - only in Bypass Mode Position Indicator Window - Connected - Connected – Bypassed - Test - Isolated Gearbox needed for Increased Spring Pressure - Must Pass the Liz Test
Secondary Disconnect Located on left Side of Cubicle for accessibility Allows for Test Position Incorporated into Side Guide- Rail
Guide Plates Used for Left to Right Alignment Prevents Rollout Switch from jumping or shifting during fault
Shutter Design (Optional) Shutter Open (switch racked-in) Shutter Closed (switch in test position or isolated)
Finger Clusters 2500A Cluster800A Cluster Added Spring Pressure for Clamping Increased Contact Surface Area Withstood 100KA for 3 Cycles and 85KA for 30 Cycles - without a scratch