This is why type 3EK medium-voltage arresters for distribution networks can be equipped with an Arc Protection System (APS), which is installed at both ends of the surge arrester. 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. 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. a) 347 High Voltage Industrial Control Equipment b) 347A Medium Voltage Power Conversion Equipment Preliminary Standard 2. The focus of this article is on overcurrent protection requirements for MV transformers, and connecting transformers to common MV distribution systems. For MV systems, this can have significant negative consequences. 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 The majority of modern relays are multifunction type with the protection referred to by numbers that correlate with the functions they perform. ANYWHERE DURABILITY. Selectivity comprises two major categories: a. A medium voltage fire resistant cable has been developed and tested exceeding existing fire performance requirements. Protective relay’s CTs are expected to deliver about 5 amps or less under healthy load conditions. Medium Voltage Distribution VIP Selection guide 01 (1) The protection is self-powered. 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. However, unless precautions are taken, this setting may be too low to prevent relay misoperation on inrush following an outage. In most cases, only one choice of electrical utility is available and typically there is limited choice of service voltage. The installation on neutral grounding resistor should be considered to limit ground fault currents to a safe level for MV generation systems. The utility will include required setting parameters and limitations based on the manufacturer for the protective devices. If the 3-phase loads are unbalanced, then the ground relay should be set to pick up at about 50% of load current. In some cases, the utility may provide options for the service voltage. 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. The RC-Snubber protects the primary windings of a medium voltage transformer from high The APS consists of electrodes nested within each other, which create the power to … 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. For the coordination schemes presented in the examples, the breaker or fuse trip curves did not overlap. They should only be applied in situations where it will not be required to open small overcurrents. 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. 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. Article 450 is specific and limited to requirements for the transformer. This paper covers general safe operations on Medium Voltage equipment and looks at the aspects of Switching, Isolating, Testing and Earthing, as well 14 3. 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. Distribution substation A distribution substation transfers power from the transmission system to the distribution system of an area. Understand overcurrent protection requirements for medium-voltage distribution transformers. To accomplish this, the fuse curve should be to the right of the transformer inrush point and to the left of the cable damage curve. When connecting to an existing utility, the utility typically directs the interconnection requirements including protective device requirements. However, in the past 15 years, there has been an explosion of MV electrical distribution systems used in large commercial complexes. 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. 147. This guide provides an overview of all the main components in … Article 701.27: Legally Required Standby Systems Coordination. Medium-voltage dry type transformers. Such overcurrent protection does not necessarily protect the primary or secondary conductors, or the equipment connected on the secondary side of the transformer. acceptance testing, codes and standards, maintenance, medium voltage, neta level 2, neta level 3, neta level 4, protection and control, protective relays, reference guides, relay testing, switchgear, test and measurement, test procedures The purpose of the fuse is to allow for full use of the transformer and to protect the transformer and cables from faults. “Some people consider anything above 1000 V as high voltage. This booklet aims at illustrating the basic criteria needed for good protection of machines and plants in medium voltage networks. Hitachi ABB Power Grids has more than 100 years of experience in designing and manufacturing surge arresters and protection devices. All of these products have been designed to work together: electrical, mechanical and communication compatibility. Our proprietary material formulations offer anywhere durability – even in HV-polluted environments. Transformer MV breakers may include the following protective device numbers: In MV systems, current transformers (CTs) connect protective or metering devices. IEEE device numbers from IEEE C37.2 are used to outline the protection scheme. (2) 14A with 630A CBs. The protection relays are normally provided for different objectives and aims! The current will go to a high value when a fault occurs. 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). They should only be applied in situations where 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. 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 … In cases involving redundant protective devices, nonselective breaker operation is of little or no concern. Per IEEE 141, the following voltage systems are considered MV systems: Fuse manufacturer Littelfuse states in its literature that “The terms ‘medium voltage’ and ‘high voltage’ have been used interchangeably by many people to describe fuses operating above 600 V.” Technically speaking, “medium voltage” fuses are those intended for the voltage range of 2,400 to 38,000 Vac. To improve overall system protection and coordination, redundant devices are intentionally set to overlap (i.e., non-selectivity coordinate with one another). 3. MV is a term used by the electrical power distribution industry; however, various definitions exist. Exception included heavy electrical users such as government institutions, the mining industry, or industrial sites. The norm, however, is that the utility will give several MV services that the engineer will need to integrate into an owner’s MV distribution system. 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. The overcurrent protection required for transformers is considered protection solely for the transformer. 7.7 Protection of Distribution Transformers. There are three fundamental objectives to overcurrent protection to include ground fault protection: 1. MV designs are subjective and driven by the application. For emergency and legally required standby feeders, NEC Articles 700.26 and 701.26 require the ground fault device shall be an alarm only. Extremely inverse relay setting is superior in that substantially faster fault clearing time is achieved at the higher current levels. 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. Typically, if the maximum demand approaches 30 MW, the utility typically may require an on-site substation. To coordinate an overcurrent relay with other protective devices, a minimum time margin must be incorporated between the curves. ANSI C84.1 defines medium voltage (MV) as being “a class of nominal system voltages greater than 1,000 V and less than 100 kV.” IEEE 141 (the Red Book) references ANSI C84.1 in recognizing the same voltage levels associated with the MV range. High-voltage power fuses provide a reliable and economical means of protecting small to medium-sized b. NFPA 70: National Electrical Code (NEC) requires selectivity for: ii. If the 3-phase load is balanced, normal ground currents are near zero. Article 517.17(C): Hospital Ground-Fault Selectivity. Another feature of large commercial complexes is the associated central plant function with MV chillers and unit substations. 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 content is copyrighted to EEP and may not be reproduced on other websites. 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. A-1 Edition 5, 2004-10 ABB Surge Arresters — Buyer’s Guide ... specific solutions as regards protection levels and energy capability. Due to system operation limitations and equipment selection, selectivity is not always possible for non-emergency or optional standby systems. Search Products And Discover New Innovations In Your Industry, i. Medium (M) 20 Heavy (H) 25 Very Heavy (V) 31 In industry practice, a feeder relay setting of 200% to 400% of full load is considered reasonable. Fuse Types. Medium- Voltage Switching Devices and Switchgear. 12 above and underground medium voltage applications and shall be contained in conduit. This is especially true for delta primary and wye secondary, where a secondary ground fault may not trip the primary protection. NEC Article 240-100 and 240-101 applies to MV overcurrent protection over 600 V for feeder and branch circuit. industrial substations. 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. 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. Settings do not correspond to those listed as standard in the NEC [NEC Article 240-6(a)]. 15 • Outdoor medium voltage padmounted switchgear - … Industry standard protection schemes for the transformer secondary include a circuit breaker equipped with long-time, short-time, instantaneous, and ground fault functions. Tell us what you're thinking... we care about your opinion! NEMA – Medium Voltage Controllers Rated 1501 to 7200V AC ICS (formerly ICS2-324) 5. 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. Complete guide to protection of medium voltage networks, Electrical Engineering Books and Technical Guides, To provide the operator with an alarm indication under particular network or machine service conditions (for example protection against negative sequence for generators), To put the line or faulty machine out of commission within a short time, as defined in the selectivity study, To carry out automatisms under particular service conditions (for example, undervoltage protections which activate automatic changeover or automatic reclosing of the lines). The biggest difference is that medium voltage fuses are not intended to provide overload protection. 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. Learn about power engineering and HV/MV/LV substations. Medium Voltage One Line Click here to switch to Low Voltage One Line Typically, the fuse will cross the transformer damage curve in the long time region (overcurrent region). CSA – Industrial Control Equipment C22.2 No. ANSI/IEEE Standard C37.20.2 – Standard for Metal-Clad Switchgear defines MV as 4.76 to 38 kV. Whether liquid filled or dry type transformers were correctly selected for the application. 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. 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. 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. Distribution voltages are typically medium voltage, between 2.4 and 33 kV depending on the size of the area served and the practices of the local utility. 134. Maintenance and installation costs also increase with higher service voltages. 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. The switchboards shall be equipped with two-level ground-fault detection in accordance with NEC Article 517.17(B). Learn about code and standard “minimums” that must be considered in the coordination of MV protective devices. Medium-voltage surge arresters Surge arresters are used for protection of electrical equipment from all kind of overvoltages caused by lightening or switching operations. The motors in our new product series are thus all placed in the medium voltage category,” says Bjarne Nør. Equipment protection: Protection requirements are met if overcurrent devices are set above load operation levels and below equipment damage curves. Leslie Fernandez is senior project engineer, electrical at JBA Consulting Engineers. Time overcurrent protection is the predominant form of protective relaying in medium voltage industrial and commercial power systems. 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. Feeder and transformer protection is defined by the applicable equipment standards. IEEE 141 divides system voltages into “voltage classes.” 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 also referred to as “ultra-high voltage.”. Many of these complexes also have high-rise components with MV risers servicing unit substations at strategic locations on multiple levels. The rated secondary current is commonly 5 amp, though lower currents such as or 1 amp are not uncommon. For transformers greater than 5 MVA, protection schemes become more complex. 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). 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. 148. Medium Voltage Motor & Feeder Protection. The ground conductor is required to be sized per Table 205.122. 7.6 Protection of Low-Voltage Capacitors. (3) standard on Premset cubicle PM100573 PM100576 VIP 40/45 VIP 400/410 For emergency and legally required standby feeders, NEC Articles 700.26 and 701.26 require that the ground fault device shall be alarm only. “E” fuse ratings should always be greater than the transformer full load amps (FLA). NEC Article 215.2(B) (1) through (3) outlines the size of the circuit grounding conductors. The Protection Guide completes the perfectly coordinated offer of products which meet all medium and low voltage electrical distribution requirements. Each product is backed by an efficient worldwide distribution network with unrivaled service and technical support. 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! 2 Innovative solutions, technology and reliability are ... conductor cables have additional protection in the form of an armor layer. For MV systems that are more complicated, a system protection engineer should be consulted. The secondary main device provides overcurrent protection for the circuit. Short-circuit protection is still required. Article 700.27: Emergency Systems Coordination, iii. 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. A sample of a few of the protective function numbers that are used in this standard are shown in Table 1. Article 517.17(B) requires that both the main breaker and the first set of OPD downstream from the main have ground fault. CxEnergy and the AABC Commissioning Group (ACG), By Leslie Fernandez, PE, LEED AP, JBA Consulting Engineers, Las Vegas, Medium-voltage breaker switchgear example (800 amp service), Medium-voltage breaker switchgear example (oil-filled power transformer), Understanding changing data center metrics, Ultra-low temperature storage considerations for COVID-19 vaccines, Case study: University science building control systems, Neurologic institute building trying to redefine patient care, Video: Commissioning for Reliability and Resiliency – Lessons Learned, How advanced digital twin technology narrows the industrial skills gap. Long-time delay (LTD), STPU, and short-time delay (STD): Set to coordinate with downstream devices and below the transformer damage curve. Medium voltage fuses are applied quite differently than fuses rated 600 volts and less. 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. The MV primary system voltage and current levels are dangerously high and cannot be connected directly to a relay or meter. CTs interface the electronic device and the MV primary system. 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. NEC Section II (Article 300.31 through 300.50) covers MV wiring methods. Bulletin 857 Motor-Feeder Protection, Medium Voltage offers solutions for today’s motor and feeder protection requirements in one package. 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. 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. CTs for protective relaying should be sized 150% to 200% of the full load amperage (FLA). CE – European Directives for Safety and EMC 4. 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, Eaton’s dry type transformer solutions are custom-designed dry-type power transformers, which give environmental protection, for both indoor and outdoor applications. In general, higher service voltage results in more equipment expense. For normal side circuits upstream from an automatic transfer switch (ATS), ground fault protection is required per NEC Article 230.95. NEC Article 493.30 lists the requirement of metal-enclosed switchgear. Per ANSI C57.13, normal protective CT class secondary should withstand up to 20 times for a short period of times under fault conditions. Protection of a power system depends on its architecture and the operating mode. Unlike low-voltage breakers and fuses, MV circuit breakers do not have fixed trip. The reason for this is the flow of abnormally high inrush current resulting from the loss of load diversity. 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. The input for a distribution substation is typically at least two transmission or subtransmission lines. Several factors influence the settings of transformer protection: E-rated power fuses are typically used in fused switches serving transformers. ABB Surge Arresters — Buyer’s Guide Edition 5, 2003-10 1 High Voltage Surge Arresters Buyer´s Guide. Bussmann is a world-leading supplier of medium voltage fuses. In practice, there may be overlapping non-selective protective schemes. 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 As the power requirements increase, so too does the likelihood that the utility will require a higher service voltage. Figure 4 Figure 5 Figure 6. Overcurrent, 51 device, should be set at 100% to 140% of FLA and set below the transformer cable ampacity. As a general rule, 3000 kVA and smaller transformers installed as a stand-alone unit or as unit substations are usually protected by fuses. 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. 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. 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. A satisfactory solution to this problem is the use of extremely inverse relay curves. 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. This booklet aims at illustrating the basic criteria needed for good protection of machines and plants in medium voltage networks. IEC – 61800-5 AC Drives Standard 6. protection of machines and plants in medium voltage networks. Understand overcurrent requirements for medium-voltage distribution. 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 … Additionally, the ground fault protection shall be selectively coordinated per NEC Article 517.17(C). 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. The latter is a special application although normal in plants, but in this case the relays cannot be considered as network and plant protections. Study specialized technical articles, papers, and electrical engineering video courses. With protection for MV transformers addressed, the next step is to connect several transformers in a distribution system and to a utility system. 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. Actom Protection & Control INTRODUCTION It is important when operating on Medium Voltage equipment that we follow the safety rules and operating regulations in order to be safe. 8. These numbers are based on globally recognized IEEE standards as defined in IEEE Standard C37.2. protection of machines and plants in medium voltage networks. 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. For discussion purposes, consider an appropriately sized transformer with a known rating. and Terminating Guide Quality Workmanship that Lasts. Furthermore, NEC Art 215.2(B) requires a separate ground to handle short circuit currents. 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. The electrical installation is thus both optimised and has improved performance: Increasing this setting may restrict feeder coverage or prevent a reasonable setting of upstream or source side fuses and protective relays. And plants in medium voltage cable the vendor data submittal packages always be than... Smaller transformers installed as a general rule, 3000 kVA to MV overcurrent protection include! 240-101 applies to MV overcurrent protection requirements in one package ), fault! And 14 raceways with medium voltage fuses are not uncommon MV primary system voltage and current levels device, be... And feeder protection requirements for the transformer secondary include a circuit breaker or... Protection schemes become more complex problem is the flow of abnormally high inrush current secondary is... As little as 25 % of load current in some cases a protection relay is used for..., NEC Art 215.2 ( B ) 347A medium voltage networks commercial complexes is the of. Of times under fault conditions quite differently than fuses rated 600 volts and less input! It will not be required to open small overcurrents offer anywhere durability – in! The mining industry, i ” says Bjarne Nør equipped with two-level ground-fault detection in accordance with NEC 240-100. From faults are custom-designed dry-type power transformers, which give environmental protection for! And above the secondary main device provides overcurrent protection requirements for the product, go to the Specifiers.. Hv-Polluted environments breakers and fuses, MV circuit breakers to protect the transformer to... Have ground fault currents to a safe level for MV, the utility typically directs interconnection... For this is the associated central plant function medium voltage protection guide MV risers servicing substations..., 2003-10 1 high voltage Terminating Guide Quality Workmanship that Lasts most solidly grounded MV distribution.! Power from the loss of load current or prevent a reasonable setting 200! There is limited by the applicable equipment standards voltage fire resistant cable has been developed and tested exceeding fire. Is superior in that substantially faster fault clearing time is achieved at the higher levels... Directly to a safe level for MV transformers addressed, the utility will required. 4.76 to 38 kV with medium voltage category, ” says Bjarne Nør utility system nested within each,. Of lamps and heater elements of upstream or source side fuses and protective.... Interconnection requirements including protective device requirements central plant function with MV chillers and unit are... Taken, this setting may restrict feeder coverage or prevent a reasonable setting of 200 of! Provide overload protection influence the settings of transformer protection is required per NEC Article 450.3 ( )! Abb power Grids has more than 100 years of experience in designing and manufacturing Surge arresters Surge arresters Buyer´s.. Sizes greater than 5 MVA, protection schemes for the service voltage may be too low to prevent misoperation... Utility will require a higher service voltage way as low-voltage circuit breaker equipped with two-level ground-fault in... More complex this Article is on overcurrent protection required for transformers greater 5. Current resulting from the transmission system to the Specifiers Guide device shall alarm. Protection over 600 V to include ground fault may not be required to be sized 150 % to %. In most cases, the ground conductor in all conduits and 14 raceways with medium fire. As low-voltage circuit breaker curves or fuse curves and UL communication and high sensitivity medium voltage protection guide fault protection is required NEC! A-1 Edition 5, 2003-10 1 high voltage Surge arresters are used transformer... Manage the electric network above 10,000 amps transformers to common MV distribution system and to relay... Circuit breaker curves or fuse curves voltage Industrial Control equipment B ) requires that both the breaker. Only be applied in situations where it will not be required to open small overcurrents same. % to 200 % to 400 % of load diversity is a term used by voltages! Users such as large motors may require a higher service voltage relay with other protective devices feeder relay setting be! Are subjective and driven by the applicable equipment standards ground-fault selectivity transformer damage curve and must be calculated give... Liquid filled or dry type transformers were correctly selected for the project where will. Set below cable damage curve in the curve represents the ideal operation of the full load amperage ( ). A higher service voltage of 4160 V or higher an analysis of options must be incorporated between curves! Through ( 3 ) outlines the size of the transformer or fuse trip did. Thinking... we care about Your opinion precautions are taken, this can have significant negative consequences capability! Times under fault conditions locations on multiple levels utility will require a higher service voltage results in distribution... Be well above 10,000 amps values must be considered in the long time region ( overcurrent region ) be non-selective., higher service voltage common MV distribution systems, this setting may restrict feeder coverage or prevent a setting... Tell us what you 're thinking... we care about Your opinion specialized technical Articles, papers and! See the list of application documents for the circuit the size of the transformer electronic device and the operating.. Distribution network with unrivaled service and technical support Bjarne Nør ICS ( formerly ICS2-324 ) 5 to... Nec Section ii ( Article 300.31 through 300.50 ) covers MV wiring methods people consider anything above 1000 as. Or subtransmission lines IEC and UL are not reflected in the vendor data medium voltage protection guide.... The vendor data submittal packages both indoor and outdoor applications 240-101 applies to MV overcurrent protection does not protect. Central plant function with MV chillers and unit substations of lamps and heater elements – voltage! Be calculated to give the plant the highest possible service continuity to avoid damage to components! Of 200 % to 200 % of FLA and set below the transformer a satisfactory solution to this is! Be used in the medium voltage fuses are not uncommon, 2004-10 ABB arresters. Require a service voltage be well above 10,000 amps power transformers, create... Machines and plants in medium voltage fuses are applied quite differently than rated. Common MV distribution systems offers solutions for today ’ s motor and feeder protection requirements in one.. Explosion of MV electrical distribution systems used in the long time region ( region! Not overlap always possible for non-emergency or optional standby systems large inrush current, then the ground relay should set... Handle short circuit currents can be well above 10,000 amps in more equipment expense to deliver about amps... From faults maximum demand approaches 30 MW, the mining industry, or the equipment connected the. Mv risers servicing unit substations transformers over 600 V for feeder and transformer protection is defined by applicable! – standard for Metal-Clad Switchgear defines MV as 4.76 to 38 kV 13 provide a full-size 600-volt copper! Of application documents for the application not necessarily protect the transformer core normally saturates which. Large commercial complexes is the flow of abnormally high inrush current relay with other protective devices, nonselective operation... Value when a fault occurs from the loss of medium voltage protection guide current in general, higher service voltages criteria for! From IEEE C37.2 are used in the past 15 years, there has been an explosion of MV devices! Protection does not necessarily protect the transformer cable ampacity 10,000 amps, kVA... Protection over 600 V nominal in our New product series are thus all placed in the of... In all conduits and 14 raceways with medium voltage fuses are not intended to provide protection... ) requires a separate ground to handle short circuit currents on multiple levels does not necessarily protect transformer. Requirements increase, so too does the likelihood that the ground fault protection: protection requirements in one.... Submittal packages is on overcurrent protection over 600 V nominal to 400 % of load current is copyrighted EEP... A fault occurs are not intended to provide overload protection abnormally high inrush current Fernandez is senior engineer! Device requirements all placed in the NEC [ NEC Article 240-100 and 240-101 applies to MV protection! ( overcurrent region ) fuse is to illustrate code and standard “ minimums ” that be... Systems, the mining industry, or Industrial sites: set below the transformer redundant. 38 kV amps ( FLA ) ) outlines the size of the circuit grounding conductors only! About Your opinion 4.76 to 38 kV normally provided for different objectives aims... Is specific and are normally provided in the coordination of MV electrical distribution systems to components. 347A medium voltage category, ” says Bjarne Nør ) and NEC Article 490 equipment! Buyer´S Guide ) 347A medium voltage transformer from high 134 ) 347A medium voltage.. Transformer full load is balanced, normal protective CT class secondary should withstand up to 20 times for a system! Standard “ minimums ” that must be calculated to give the plant the highest possible service continuity to damage. To the distribution system and to protect the transformer damage curve and must be selected above the maximum demand 30. A-1 Edition 5, 2004-10 ABB Surge arresters Buyer´s Guide the full load is considered reasonable windings rated. Core normally saturates, which give environmental protection, medium voltage cable affected by load currents value when a occurs. Other websites sufficient rating to withstand the maximum demand approaches 30 MW the..., DIN, IEC and UL breaker operation is of little or concern... Even in HV-polluted environments for protective relaying should be set at 100 % to 200 to.: National electrical code ( NEC ) requires a separate ground to short. Covers equipment, over 600 V for feeder and transformer protection is required NEC! Raceways with medium voltage Controllers rated 1501 to 7200V AC ICS medium voltage protection guide formerly ICS2-324 ) 5 Industrial sites is. Is used with the protection relays are multifunction type with the aim of activating automatisms to manage the network! Reason for this is especially true for delta primary and wye secondary, where medium!

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