Typically, service reliability tends to increase as service voltages increase. Made from non-tracking material, TE's Raychem Wildlife and Asset Protection portfolio is optimized to ensure tracking resistance, thermal endurance, and UV resistance for high performance protection of your assets throughout their service lifetime. The protective relay curve only represents the action of a calibrated relay and does not account for the actions of the associated circuit breaker or the accuracy of the current transformers that connect the relay to the monitored circuit. Most solidly grounded MV distribution system short circuit currents can be well above 10,000 amps. NEC Article 240.21 (C)(1) and NEC Article 450.3(A) validate this statement is true. Each product is backed by an efficient worldwide distribution network with unrivaled service and technical support. Additionally, the ground fault protection shall be selectively coordinated per NEC Article 517.17(C). Maintenance and installation costs also increase with higher service voltages. Article 700.27: Emergency Systems Coordination, iii. 14 3. The limits are clearly defined, however, in the IEC 60038 standard:  low voltage is up to 1000 V, medium voltage is from 1000 V to 35 kV, and high voltage is over 35 kV. ANSI/IEEE Standard C37.20.2 – Standard for Metal-Clad Switchgear defines MV as 4.76 to 38 kV. The cable damage curve must be above the maximum fault current at 0.01 s. For transformers 3 MVA and less, standard overcurrent protection schemes for MV switchgear breakers should include an instantaneous and overcurrent combination relay (device 50/51). 12 above and underground medium voltage applications and shall be contained in conduit. Search Products And Discover New Innovations In Your Industry!! Tell us what you're thinking... we care about your opinion! 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. High-voltage power fuses provide a reliable and economical means of protecting small to medium-sized NEC Article 215.2(B) (1) through (3) outlines the size of the circuit grounding conductors. For this article, a good working definition of MV is 1 to 38 kVac as any voltage level above 38 kV is a transmission level voltage versus a distribution level voltage. 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). The biggest difference is that medium voltage fuses are not intended to provide overload protection. The utility will include required setting parameters and limitations based on the manufacturer for the protective devices. The purpose of the fuse is to allow for full use of the transformer and to protect the transformer and cables from faults. NEC Article 490 covers equipment, over 600 V nominal. In industry practice, a feeder relay setting of 200% to 400% of full load is considered reasonable. 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. protection of machines and plants in medium voltage networks. Industry standard protection schemes for the transformer secondary include a circuit breaker equipped with long-time, short-time, instantaneous, and ground fault functions. Protective relay’s CTs are expected to deliver about 5 amps or less under healthy load conditions. Protection of a power system depends on its architecture and the operating mode. Medium- Voltage Switching Devices and Switchgear. Motor and generator curves are machine specific and are normally provided in the vendor data submittal packages. 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). In this case an analysis of options must be conducted to determine the best option for the project. Guide Form Specification RC-Snubber for Transformer Protection 1 General 1.1 This specification is for a _____ kV (line-line voltage) medium voltage three phase metal-enclosed RC-Snubber. Furthermore, NEC Art 215.2(B) requires a separate ground to handle short circuit currents. Fuse Types. 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. NEC Article 493.30 lists the requirement of metal-enclosed switchgear. The switchboards shall be equipped with two-level ground-fault detection in accordance with NEC Article 517.17(B). 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. This form of protection employs relays with inverse time-current characteristics; that is, operating time of these relays becomes less as the current magnitude increases. Learn about power engineering and HV/MV/LV substations. industrial substations. The current will go to a high value when a fault occurs. This booklet aims at illustrating the basic criteria needed for good protection of machines and plants in medium voltage networks. The secondary main device provides overcurrent protection for the circuit. The content is copyrighted to EEP and may not be reproduced on other websites. 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. 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. With protection for MV transformers addressed, the next step is to connect several transformers in a distribution system and to a utility system. Until recently, engineers didn’t work too frequently in the design of medium-voltage (MV) systems, mainly because anything over 600 V was primarily handled by the utilities. 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. and Terminating Guide Quality Workmanship that Lasts. Applying Medium Voltage Fuses 201 ittelfuse PW-A ® Products www.littelfuse.com Introduction Medium voltage fuses are applied quite differently than fuses rated 600 volts and less. The ground conductor is required to be sized per Table 205.122. MV is a term used by the electrical power distribution industry; however, various definitions exist. Furthermore, NEC Article 450.3(A) specifically covers transformers over 600 V to include MV transformers. Ideally suited for use in Eaton's coordinated primary and secondary unit substations , the transformers are explosion-resistant, fire-resistant, non-polluting to the environment. CTs for protective relaying should be sized 150% to 200% of the full load amperage (FLA). The medium voltage quality system has been certified as being fully compliant with the requirements of the ISO 9001:2015 quality assurance model. Bussmann circuit protection solutions comply with major international standards: ANSI, BS, DIN, IEC and UL. Article 517.17(C): Hospital Ground-Fault Selectivity. The electrical installation is thus both optimised and has improved performance: Unlike low-voltage breakers and fuses, MV circuit breakers do not have fixed trip. Medium-voltage dry type transformers. However, unless precautions are taken, this setting may be too low to prevent relay misoperation on inrush following an outage. 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. For normal side circuits upstream from an automatic transfer switch (ATS), ground fault protection is required per NEC Article 230.95. 2. This paper covers general safe operations on Medium Voltage equipment and looks at the aspects of Switching, Isolating, Testing and Earthing, as well Article 701.27: Legally Required Standby Systems Coordination. Understand overcurrent protection requirements for medium-voltage distribution transformers. A-1 Edition 5, 2004-10 ABB Surge Arresters — Buyer’s Guide ... specific solutions as regards protection levels and energy capability. The main objectives of protection relays are: Identification of the abnormal conditions mentioned is made by the protection relays, which operate to separate the faulty part of the network from the rest of the plant. This guide provides an overview of all the main components in … The biggest difference is that medium voltage fuses are not intended to provide overload protection. 3. Our protection relay gives you flexible control to maximize your motor’s output capabilities, and provides current, voltage and motor protection functions. “E” fuse ratings should always be greater than the transformer full load amps (FLA). 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 … There are three fundamental objectives to overcurrent protection to include ground fault protection: 1. For balanced distribution systems, the ground relay can be set to pick up as little as 25% of load current. Medium voltage fuses are applied quite differently than fuses rated 600 volts and less. 7.6 Protection of Low-Voltage Capacitors. In some cases, the utility may provide options for the service voltage. b. NFPA 70: National Electrical Code (NEC) requires selectivity for: ii. For emergency and legally required standby feeders, NEC Articles 700.26 and 701.26 require that the ground fault device shall be alarm only. For the coordination schemes presented in the examples, the breaker or fuse trip curves did not overlap. Article 450 is specific and limited to requirements for the transformer. As the power requirements increase, so too does the likelihood that the utility will require a higher service voltage. The APS consists of electrodes nested within each other, which create the power to … Long-time delay (LTD), STPU, and short-time delay (STD): Set to coordinate with downstream devices and below the transformer damage curve. The Protection Guide completes the perfectly coordinated offer of products which meet all medium and low voltage electrical distribution requirements. ANYWHERE DURABILITY. Voltages 600 V and below are referred to as “low voltage,” voltages of 600 V to 69 kV are referred to as “medium voltage,” voltages of 69 kV to 230 kV are referred to as “high voltage,” and voltages 230 kV to 1,100 kV are referred to as “extra high voltage” with 1,100 kV … 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 The setting values must be selected above the transient conditions which can occur in the network without requiring disconnection. (2) 14A with 630A CBs. Typically, if the maximum demand approaches 30 MW, the utility typically may require an on-site substation. For transformers greater than 5 MVA, protection schemes become more complex. 134. 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. The protection relays are normally provided for different objectives and aims! Medium (M) 20 Heavy (H) 25 Very Heavy (V) 31 Medium Voltage Arresters SSI's parallel connected medium voltage surge protective devices (1 kVRMS to 7.2 kVRMS) are engineered to protect mission critical systems during lightning strikes and transients that result from severe power system faults. (3) standard on Premset cubicle PM100573 PM100576 VIP 40/45 VIP 400/410 If the 3-phase load is balanced, normal ground currents are near zero. Safety: Personal safety requirements are met if protective devices are rated to carry and interrupt the maximum available load current as well as withstand the maximum available fault currents. Although the primary windings are rated for MV, the designer must choose either fuses or circuit breakers to protect the transformer. 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. Safety requirements ensure equipment is of sufficient rating to withstand the maximum available energy of the worst-case scenario. Magnetizing inrush currents to transformers. Medium Voltage Distribution VIP Selection guide 01 (1) The protection is self-powered. Increasing this setting may restrict feeder coverage or prevent a reasonable setting of upstream or source side fuses and protective relays. In cases involving redundant protective devices, nonselective breaker operation is of little or no concern. When voltage is switched on to energize a transformer, the transformer core normally saturates, which results in a large inrush current. In practice, there may be overlapping non-selective protective schemes. In general, higher service voltage results in more equipment expense. Article 517.17(B) requires that both the main breaker and the first set of OPD downstream from the main have ground fault. A medium voltage fire resistant cable has been developed and tested exceeding existing fire performance requirements. The installation on neutral grounding resistor should be considered to limit ground fault currents to a safe level for MV generation systems. United States Department of Agriculture Rural Utilities Service RUS Bulletin 1724E-300 Issued June 2001 Design Guide for Rural Substations To coordinate an overcurrent relay with other protective devices, a minimum time margin must be incorporated between the curves. 15 • Outdoor medium voltage padmounted switchgear - … "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.". 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. Equipment protection: Protection requirements are met if overcurrent devices are set above load operation levels and below equipment damage curves. NEC Article 240-100 and 240-101 applies to MV overcurrent protection over 600 V for feeder and branch circuit. He has more than 28 years of engineering and design and field experience that includes MV distribution systems for military, mining, tunneling, food manufacturing, power production facilities, high-rise facilities, and casino resort complexes. Leslie Fernandez is senior project engineer, electrical at JBA Consulting Engineers. Selectivity: Selectively requirements are intended to limit system fault or overload response to a specific area or zone of impact and limit disruption of service to the same. The MV primary system voltage and current levels are dangerously high and cannot be connected directly to a relay or meter. In addition, the engineer must ensure that the setting does not exceed the maximum available fault current or the instantaneous trip will be rendered worthless. Overcurrent, 51 device, should be set at 100% to 140% of FLA and set below the transformer cable ampacity. The reason for this is the flow of abnormally high inrush current resulting from the loss of load diversity. It is important to underline at once that trip selectivity must always be looked for, but must only be looked for after having ensured protection of the network component. 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 … The ground fault relay or sensor must be set to pick up ground faults that are 1200 amps or more and actuate the main switch or circuit breaker to disconnect all ungrounded conductors of the faulted circuit at a maximum of 1 s. For hospitals, the substation feeding the distribution system is typically liquid-filled MV primary to 480/277 V secondary transformers connected to service switchboards with both main and feeder breakers. Hitachi ABB Power Grids has more than 100 years of experience in designing and manufacturing surge arresters and protection devices. Many of these complexes also have high-rise components with MV risers servicing unit substations at strategic locations on multiple levels. They should only be applied in situations where 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. IEEE device numbers from IEEE C37.2 are used to outline the protection scheme. For emergency and legally required standby feeders, NEC Articles 700.26 and 701.26 require the ground fault device shall be an alarm only. The latter is a special application although normal in plants, but in this case the relays cannot be considered as network and plant protections. CSA – Industrial Control Equipment C22.2 No. Three-phase MV transformers are required to be provided with both primary and secondary overcurrent protective devices (OPD) mainly because the primary and secondary conductors are not considered protected by the primary overcurrent protection. Understand overcurrent requirements for medium-voltage distribution. 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. Time dial should be set below the transformer damage curve and above the secondary main breaker device. 8. Click on the desired product type in the Medium Voltage One-line Diagram below to access the detailed product page with product information and publication library links. NEMA – Medium Voltage Controllers Rated 1501 to 7200V AC ICS (formerly ICS2-324) 5. The rated secondary current is commonly 5 amp, though lower currents such as or 1 amp are not uncommon. Current to raise the temperature of lamps and heater elements. This is especially true for delta primary and wye secondary, where a secondary ground fault may not trip the primary protection. The overcurrent protection required for transformers is considered protection solely for the transformer. The choice of service voltage is limited by the voltages the serving utility provides. The motors in our new product series are thus all placed in the medium voltage category,” says Bjarne Nør. System Backup Protection (51V, 21) • For medium and small sized generators, voltage-restrained or voltage controlled time overcurrent relays (51V) are often applied • Control or restraining function used to prevent or desensitize the overcurrent relay from tripping until the generator voltage is reduced by a fault When connecting to an existing utility, the utility typically directs the interconnection requirements including protective device requirements. However, for large-scale developments, equipment such as large motors may require a service voltage of 4160 V or higher. The curve represents the ideal operation of the relay, and the manufacturing tolerances are not reflected in the curve. To improve overall system protection and coordination, redundant devices are intentionally set to overlap (i.e., non-selectivity coordinate with one another). Fla and set below the transformer full load is considered reasonable electrical engineering video.... 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