Enhancing Reliability of Legacy Systems with New Generation Low-Voltage Circuit Breaker Upgrades

Transcription

1 Enhancing Reliability of Legacy Systems with New Generation Low-Voltage Circuit Breaker Upgrades May 2012 / 1910DB1202 by Hal Theobald, Product Manager, Schneider Electric Services and Reza Tajali, P.E., Schneider Electric Engineering Services Make the most of your energy SM

2 Summary 1.0 Introduction Circuit Breaker Performance Upgrade Solutions Now Available Choosing the Right Solution Why Upgrade? Application Considerations Conclusion White paper for circuit breaker modernization

3 1.0 Introduction With increasing dependence on computers and automated processes, most modern facilities cannot afford downtime. In order to maximize the useful life of the electrical equipment and to mitigate the risk of unscheduled power outages, it is critical to properly maintain the switchgear and switchboards that distribute electricity throughout the power distribution system. Electrical switchgear is composed of passive and active components. The passive components include the horizontal and vertical bus structures while the active components are the power circuit breakers and fusible switching devices. The main function of the active components is to protect the electrical assets downstream and to disconnect the circuit and protect personnel in case of an arc flash event. Both the passive and active components require regular maintenance to ensure equipment integrity, proper mechanical and electrical functionality, and to extend the equipment s useful life. 2.0 Circuit Breaker Performance Unless maintenance testing has been utilized to track the performance of circuit breakers, degradation of insulation and the moving parts will not be noticed. Industry groups such as IEEE have analyzed the factors that affect the condition and performance of circuit breakers and published average failure rates for this equipment. However, these average failure rates do not account for the varying degrees of maintenance between different installations. Further, even the best maintained equipment is subject to two key phenomena: 1. Equipment ultimately degrades and reaches the end of its useful life, no matter how much maintenance is performed. 2. Advances in technology both in material sciences and microprocessor based controls facilitate the production of more modern circuit breakers with better performance, reduced maintenance requirements and on-board diagnostics, to name a few features. With the advancements in the design of the new circuit breakers, circuit breakers with older technology are no longer considered sustainable solutions. White paper for circuit breaker modernization 03

4 2.0 Circuit Breaker Performance (con t.) The oldest design power circuit breakers manufactured prior to 1980s employed dash-pot actuated trip units. In addition, their bearings, arc chutes, and contacts required regular maintenance. The introduction of solid state trip units and improved lubrication material produced significant advancement over these older circuit breakers. Modern composites, which combined the circuit breaker frame with the insulating material, provided further enhancement. Masterpact M frame circuit breakers are the product of this era of technological advancement. These circuit breakers quickly became the workhorse of the industry and appeared in large numbers in data centers, generating stations, industrial facilities and practically every other installation in the 1990s and 2000s. 3.0 Upgrade Solutions Now Available Masterpact MP is a UL 489 listed circuit breaker, Masterpact MC is an ANSI rated circuit breaker (UL1066), while Masterpact M is an IEC rated circuit breaker. Throughout the remainder of this document, we will refer to these three circuit breakers as the Masterpact M. Masterpact M circuit breakers have been discontinued since 2004 and are scheduled to become fully obsolete in At that time, it is anticipated that parts will no longer be available as inventories will quickly be depleted. A viable solution to consider is upgrading the existing equipment with the latest state of the art circuit breakers. Schneider Electric has developed methods for adapting the latest technology circuit breakers into a switchgear or switchboard cell that was originally designed for Masterpact M circuit breakers. ANSI standard C37.59 addresses this kind of upgrade and includes design and testing requirements for the adaptation. By following this standard, Schneider Electric provides a comfort level that the user will receive a reliable product. 04 White paper for circuit breaker modernization

5 4.0 Choosing the Right Solution There are two options available to replace the Masterpact M with today s current production Masterpact NW circuit breaker. Both options allow the Masterpact NW to fit into the existing cell and are engineered, fully tested and validated to ANSI C Choosing the right solution is dependent upon the existing circuit breaker ratings. Option 1: The Plug & Play approach is a fully-designed solution that is applicable only to 3-pole M-series circuit breakers that have a continuous current rating of 3000 amperes or less and an interrupting rating up to 85kA at 600V. With this option, only one electrical outage must be coordinated, with a total duration of approximately 4 hours. During this outage, the M-series circuit breaker is removed and modifications to the existing cradle rails and secondary contacts are made by an experienced field service representative to facilitate the installation of the new Masterpact NW circuit breaker. Option 2: A Retrofill solution, applicable to M-series circuit breakers of all ratings, is specifically designed for those with a continuous current rating greater than 3000 amperes or a short circuit rating greater than 85kA. This option requires two electrical outages. The first outage is brief and is utilized by a Schneider Electric engineer to measure bus connection locations. After this outage, Schneider Electric engineers will design a kit of components to facilitate the retrofill process. A second, and more extensive, outage is then coordinated to remove the old circuit breaker and the old cradle along with the bus run backs. Field service representatives will then install the new Masterpact NW cell adapters, cradle and circuit breaker. With either option, a system coordination study should be performed. After the upgrade, the end-user has a modern circuit breaker with enhanced features to help improve the reliability of their system. The original Masterpact M chassis is retained. (no intervention on the switchboard structure) Masterpact NW adapted for the "Plug and Play" solution Masterpact M White paper for circuit breaker modernization 05

6 5.0 Why Upgrade? With either of the two options referred to in section 4.0, Masterpact NW circuit breakers are provided. These circuit breakers feature enhancements that were not available with the Masterpact M circuit breakers. These consist of positive stops in the connected, test, and disconnected positions plus a visual position indicator. Also, the Masterpact NW circuit breaker maintains ground contact between its body and the draw-out cell when the cover is removed while the circuit breaker is in the connected, test, or disconnected positions. There is also a push-open crank interlock. Additional improved functionalities, some of which are optional, include: Power metering, monitoring and communication to building management systems Extended AIC rating when fault currents increase Finger clusters are on the circuit breaker instead of the cradle for the ANSI and UL versions, making them easier to maintain (Retrofill option only) Ring terminals are available for secondary connections (improved reliability) Electronic contact wear indicator provision (optimized maintenance) Additional keylock and padlock provisions Large LCD dot matrix display Field-replaceable trip unit and/or rating plugs Protective relaying functions built into the trip unit with up to six programmable contacts Internal shutter mechanism to isolate energized line side bus (Retrofill option only) 06 White paper for circuit breaker modernization

7 6.0 Application Considerations Taking on a project to upgrade the existing switchgear should involve an engineering evaluation of the system. Following are a few items that should be considered with either the Plug & Play or the Retrofill upgrade options. Schneider Electric Engineering Services is prepared to develop custom designs for any demanding application: Trip units The Masterpact NW circuit breaker uses a more sophisticated and function-rich trip unit as compared to the previous design (Masterpact M STR trip units). The new trip unit means different instantaneous and delay trip curves, therefore, a coordination study is recommended to appropriately set the new circuit breaker trip points. 4-wire system - Upgrading to the Masterpact NW will require a new neutral sensor and wiring. Zone Selective Interlocking (ZSI) - If a ZSI system is being utilized, upgrading from the Masterpact M to Masterpact NW will require a new ZSI module and interlocking scheme. Key Interlocking Scheme - The current key interlocking schemes on the existing Masterpact M circuit breakers will have to be incorporated into the new Masterpact NW upgrade solution. Modified Differential Ground Fault System - MDGF system is an arrangement of sensors (current transformers or CTs) to assure ground fault protection on systems that comprise multiple grounded power sources. As the old technology neutral current sensors are replaced to the new NW style external current sensors, some bussing modifications may be required in the switchgear. MDGF system complexity is facility-specific. The Schneider Electric Engineering Services team is available to address specific application requirements. 7.0 Conclusion The application of the circuit breaker and the operating environment come into consideration in choosing the upgrade method. Plug & Play or retrofill solutions upgrade the critical components that protect assets and personnel. They also provide enhanced system capabilities, such as communications, without the extended downtime of a full switchgear replacement. The existing structure remains intact, reducing the downtime required for the upgrade, and the active component is replaced to extend the useful life of the equipment. Upgrading existing equipment is a cost effective approach that does not compromise the reliability of the switchgear. Masterpact NW circuit breakers were designed and developed with an eye on retrofill applications. The new workhorse of the industry, Masterpact NW circuit breakers will provide many years of successful operation when properly installed by the original manufacturer s trained personnel. White paper for circuit breaker modernization 07

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