medium voltage protection guide

The switchboards shall be equipped with two-level ground-fault detection in accordance with NEC Article 517.17(B). The problem of setting ground relay sensitivity to include all faults, yet not trip for heavy-load currents or inrush, is not as difficult as it is for phase relays. Article 517.17(B) requires that both the main breaker and the first set of OPD downstream from the main have ground fault. However, in the past 15 years, there has been an explosion of MV electrical distribution systems used in large commercial complexes. However, unless precautions are taken, this setting may be too low to prevent relay misoperation on inrush following an outage. A sample of a few of the protective function numbers that are used in this standard are shown in Table 1. For the coordination schemes presented in the examples, the breaker or fuse trip curves did not overlap. 148. Although the primary windings are rated for MV, the designer must choose either fuses or circuit breakers to protect the transformer. Our protection relay gives you flexible control to maximize your motor’s output capabilities, and provides current, voltage and motor protection functions. For example, Southwire Co. has published tape shields fault current capacity to be 1893 amps at 12.5% tape overlap, and 2045 amps at 25% tape overlap. The protection relay setting must be calculated to give the plant the highest possible service continuity to avoid damage to network components. Feeder and transformer protection is defined by the applicable equipment standards. Ampacity of MV conductors feeding to and extending from the transformer, as well as necessary overcurrent protection of the conductors and equipment, are covered under the following: Cold load pickup is defined as follows: Whenever a service has been interrupted to a distribution feeder for 20 minutes or more, it may be extremely difficult to re-energize the load without causing protective relays or fuses to operate. In practice, there may be overlapping non-selective protective schemes. NEC 310.60(C) and Tables 310.77 through 310 list ampacity of MV conductors 2001 to 35000 V. NEC Art 210.9(B) (1) requires the ampacity of the branch circuit conductors shall not be less than 125% of the design potential load. IEC – 61800-5 AC Drives Standard 6. NEC Article 240.21 (C)(1) and NEC Article 450.3(A) validate this statement is true. Furthermore, NEC Art 215.2(B) requires a separate ground to handle short circuit currents. ABB Surge Arresters — Buyer’s Guide Edition 5, 2003-10 1 High Voltage Surge Arresters Buyer´s Guide. Medium Voltage Distribution VIP Selection guide 01 (1) The protection is self-powered. The focus of this article is on overcurrent protection requirements for MV transformers, and connecting transformers to common MV distribution systems. Our proprietary material formulations offer anywhere durability – even in HV-polluted environments. 147. In some cases, the utility may provide options for the service voltage. a) 347 High Voltage Industrial Control Equipment b) 347A Medium Voltage Power Conversion Equipment Preliminary Standard 2. Article 701.27: Legally Required Standby Systems Coordination. Control of the network parameters to prevent false operations (for example, To activate network parameter recording to memorise the network disturbances (for example, the starting contacts of the overcurrent relay), To carry out protection of the interface with the external network (with contractual not protection settings). As a consequence, protective class CTs are accurate enough to drive a set of indication instruments, but will not be good enough for revenue class summation energy metering. 134. This paper covers general safe operations on Medium Voltage equipment and looks at the aspects of Switching, Isolating, Testing and Earthing, as well "For the use of this standard, high voltage (see IEV 601-01-27) is the rated voltage above 1000 V. However, the term medium voltage (see IEV 601-01-28) is commonly used for distribution systems with voltages above 1 kV and generally applied up to and including 52 kV.". The content is copyrighted to EEP and may not be reproduced on other websites. (3) standard on Premset cubicle PM100573 PM100576 VIP 40/45 VIP 400/410 industrial substations. The biggest difference is that medium voltage fuses are not intended to provide overload protection. Article 700.27: Emergency Systems Coordination, iii. A medium voltage fire resistant cable has been developed and tested exceeding existing fire performance requirements. Selectivity comprises two major categories: a. NEC Article 310.10 requires shield MV cable for distribution above 2000 V. NEC Article 490.46 MV circuit breaker shall be capable of being lock-out or if installed in a draw-out mechanism, the mechanism shall be capable of being locked. Selection of the protection system and relays depends on and is correlated with the plant characteristics, type of indus-trial process and its service continuity requirements, with the status of the neutral, characteristics of the machines, levels and duration of the fault currents, etc. These numbers are based on globally recognized IEEE standards as defined in IEEE Standard C37.2. Exception: NEC Article 240.4A and 695 allow conductors to be without overload protection where circuit interruption would create a hazard, such as fire pumps. Study specialized technical articles, papers, and electrical engineering video courses. Unlike low-voltage breakers and fuses, MV circuit breakers do not have fixed trip. 8. Medium voltage switchboard system from 1 to 36 kV Sepam Protection relays Masterpact Protection switchgear from 100 to 6300 A A consistent design of offers from Medium Voltage to Low Voltage Guiding tools for more efficient design and implementation of your installations The Guide Design office, consultant, contractor, 14 3. It is important to note that the overcurrent device on the primary side must be sized based on the transformer’s kVA rating and based on the secondary load to the transformer. Complete guide to protection of machines and plants in medium voltage networks (photo credit: ABB) Selection of the protection system and relays depends on and is correlated with the plant characteristics, type of industrial process and its service continuity requirements, with … Bussmann circuit protection solutions comply with major international standards: ANSI, BS, DIN, IEC and UL. Adequate capacity for the load to be served, Adequate temporary overload capacity (kVA size, or ratings), Primary and secondary voltages properly rated for the electrical distribution system. Unlike fuses and typical 600 V circuit breakers, MV circuit breakers rely on separate devices such as current transformers (CT), potential transformer (PT), and protective relays to provide the overcurrent protection. Medium-voltage surge arresters Surge arresters are used for protection of electrical equipment from all kind of overvoltages caused by lightening or switching operations. 15 • Outdoor medium voltage padmounted switchgear - … With protection for MV transformers addressed, the next step is to connect several transformers in a distribution system and to a utility system. United States Department of Agriculture Rural Utilities Service RUS Bulletin 1724E-300 Issued June 2001 Design Guide for Rural Substations Under a fault condition, the fault current can easily exceed the capacity of the cable tape shield or concentric neutral ground; hence, a separate ground wire is necessary. Device 51 or function long-time pick-up (LTPU): Recommend 100% to 125% of the transformer FLA and set below the transformer and cable damage curves. The PCM600 2.10 package includes the following files/documents: PCM600 2.10 Installation Package; PCM600 2.10 Hotfix 20201215; PCM600 2.10 Installation Guide Search Products And Discover New Innovations In Your Industry!! Device 50 or instantaneous: Set below cable damage curve and must be above the maximum fault current at the breaker total clear curve. To accommodate this inrush current, overcurrent protection is typically selected with time-current withstand values of at least 12 times the transformer primary rated current for 0.1 s and 25 times for 0.01 s. Engineers should ensure the protection scheme settings are below the transformer short-circuit damage curves as defined in. Selection of the protection system and relays depends on and is correlated with the plant characteristics, type of industrial process and its service continuity requirements, with the status of the neutral, characteristics of the machines, levels and duration of the fault currents, etc. 2 Innovative solutions, technology and reliability are ... conductor cables have additional protection in the form of an armor layer. ANYWHERE DURABILITY. Before determining the size or rating of the overcurrent devices, observe that Notes 1 and 2 of NEC Table 450-3(A) permit the rating or setting of primary and/or secondary OPD to be increased to the next higher standard or setting when the calculated value does not correspond to a standard rating or setting. Protection of a power system depends on its architecture and the operating mode. Medium Voltage One Line Click here to switch to Low Voltage One Line The RC-Snubber protects the primary windings of a medium voltage transformer from high Per ANSI C57.13, normal protective CT class secondary should withstand up to 20 times for a short period of times under fault conditions. The intent is to illustrate code and standard “minimums” that must be considered in the coordination of MV protective devices. Page 4 Medium Voltage Application Guide 710-12280-00A This reference guide is designed to help engineers in the field of medium voltage select and specify the right MV equipment for their application. High inrush current is caused by: Per NEC Art 240.101, the continuous ampere rating of a fuse shall not exceed three times the ampacity of the conductors, and the continuous ampere rating of a breaker shall not exceed six times the ampacity of the conductor. The latter is a special application although normal in plants, but in this case the relays cannot be considered as network and plant protections. Protective relay’s CTs are expected to deliver about 5 amps or less under healthy load conditions. In most cases, only one choice of electrical utility is available and typically there is limited choice of service voltage. This booklet aims at illustrating the basic criteria needed for good protection of machines and plants in medium voltage networks. Transformer MV breakers may include the following protective device numbers: In MV systems, current transformers (CTs) connect protective or metering devices. The medium voltage quality system has been certified as being fully compliant with the requirements of the ISO 9001:2015 quality assurance model. For balanced distribution systems, the ground relay can be set to pick up as little as 25% of load current. In distribution design, the three objectives still apply: For example, if the NEC requirements for transformer overcurrent protection are considered without reference to applicable standards and code requirements, the system may address protection of transformers, while other elements of the distribution system (such as the feeders connecting the transformer(s) to the distribution system) may not be protected in accordance with the code. NEC Articles 215.10, 230-95, and 240.13 require ground-fault protection for solidly grounded wye systems of more than 150 V to ground circuits, which includes 277/480 V “wye” connected systems. Settings do not correspond to those listed as standard in the NEC [NEC Article 240-6(a)]. Passive fire protection, fire resistant cable, hydrocarbon fire ... IEC 61892-4 does not provide a cable selection guide other than for a simple CF scenario. If the 3-phase load is balanced, normal ground currents are near zero. The rated secondary current is commonly 5 amp, though lower currents such as or 1 amp are not uncommon. All of these products have been designed to work together: electrical, mechanical and communication compatibility. Extremely inverse relay setting is superior in that substantially faster fault clearing time is achieved at the higher current levels. Maintenance and installation costs also increase with higher service voltages. The reason for this is the flow of abnormally high inrush current resulting from the loss of load diversity. Understand overcurrent requirements for medium-voltage distribution. The biggest difference is that medium voltage fuses are not intended to provide overload protection. To be clear, a properly sized and rated transformer includes the following features: The 2011 NEC requires that transformers be protected against overcurrent (NEC Article 450.3). The CTs provide isolation from the cable’s high voltage and current levels and translate the primary current to a signal level that can be handled by delicate relays/meters. To coordinate an overcurrent relay with other protective devices, a minimum time margin must be incorporated between the curves. 7.6 Protection of Low-Voltage Capacitors. The utility will include required setting parameters and limitations based on the manufacturer for the protective devices. In general, higher service voltage results in more equipment expense. NEC Article 215.2(B) (1) through (3) outlines the size of the circuit grounding conductors. paper is intended as a guide to aid engineers in selecting adequate grounding and ground fault protection schemes for medium voltage industrial and commercial generators for new installations, for evaluating existing systems, and for future expansion of facilities, to … Many of these complexes also have high-rise components with MV risers servicing unit substations at strategic locations on multiple levels. For the purpose of this guide, transformers having primary voltage ratings between 34.5 kV and 138 kV, with medium-voltage (4.16 kV through 34.5 kV) secondaries, will be covered. protection of machines and plants in medium voltage networks. Sizing MV components such as motors, generators, transformers, wiring systems, the architecture of MV systems, or design of complicated protection schemes such as reclosers, zone interlocks, differential protection, etc., are all beyond the scope of this article. ANSI/IEEE Standard C37.20.2 – Standard for Metal-Clad Switchgear defines MV as 4.76 to 38 kV. An excessive number of protections may also be harmful, since, even if they operate correctly in the case of a fault, they can operate, Get access to premium HV/MV/LV technical articles, advanced electrical engineering guides, papers, and much more! Time overcurrent protection is the predominant form of protective relaying in medium voltage industrial and commercial power systems. Instantaneous trip, 50 device, should be set below the transformer damage curves, below the cable damage curve at 0.1 set, and approximately 200% of inrush. Figure 4 Figure 5 Figure 6. Bussmann is a world-leading supplier of medium voltage fuses. For normal side circuits upstream from an automatic transfer switch (ATS), ground fault protection is required per NEC Article 230.95. The MV primary system voltage and current levels are dangerously high and cannot be connected directly to a relay or meter. MV is a term used by the electrical power distribution industry; however, various definitions exist. Understand overcurrent protection requirements for medium-voltage distribution transformers. Protective devices are redundant—no matter which device opens, the same outage occurs.

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