MV designs are subjective and driven by the application. The protection relay setting must be calculated to give the plant the highest possible service continuity to avoid damage to network components. For emergency and legally required standby feeders, NEC Articles 700.26 and 701.26 require that the ground fault device shall be alarm only. Auxiliary power is used only for communication and high sensitivity earth fault protection. protection of machines and plants in medium voltage networks. 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. The biggest difference is that medium voltage fuses are not intended to provide overload protection. and Terminating Guide Quality Workmanship that Lasts. Selectivity comprises two major categories: a. Article 517.17(B) requires that both the main breaker and the first set of OPD downstream from the main have ground fault. Our protection relay gives you flexible control to maximize your motor’s output capabilities, and provides current, voltage and motor protection functions. CTs for protective relaying should be sized 150% to 200% of the full load amperage (FLA). All of these products have been designed to work together: electrical, mechanical and communication compatibility. When connecting to an existing utility, the utility typically directs the interconnection requirements including protective device requirements. NEC Article 240.21 (C)(1) and NEC Article 450.3(A) validate this statement is true. The choice of service voltage is limited by the voltages the serving utility provides. The purpose of the fuse is to allow for full use of the transformer and to protect the transformer and cables from faults. The overcurrent protection required for transformers is considered protection solely for the transformer. Bussmann is a world-leading supplier of medium voltage fuses. 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. protection of machines and plants in medium voltage networks. Our proprietary material formulations offer anywhere durability – even in HV-polluted environments. 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. 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. The biggest difference is that medium voltage fuses are not intended to provide overload protection. 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 Protection Guide completes the perfectly coordinated offer of products which meet all medium and low voltage electrical distribution requirements. Whether liquid filled or dry type transformers were correctly selected for the application. Article 450 is specific and limited to requirements for the transformer. In cases involving redundant protective devices, nonselective breaker operation is of little or no concern. The APS consists of electrodes nested within each other, which create the power to … The utility will include required setting parameters and limitations based on the manufacturer for the protective devices. Feeder and transformer protection is defined by the applicable equipment standards. 148. 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. 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. Medium voltage fuses are applied quite differently than fuses rated 600 volts and less. CE – European Directives for Safety and EMC 4. 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. There are three fundamental objectives to overcurrent protection to include ground fault protection: 1. High-voltage power fuses provide a reliable and economical means of protecting small to medium-sized 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 curve represents the ideal operation of the relay, and the manufacturing tolerances are not reflected in the curve. 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. 2 Innovative solutions, technology and reliability are ... conductor cables have additional protection in the form of an armor layer. Protective relay’s CTs are expected to deliver about 5 amps or less under healthy load conditions. Although the primary windings are rated for MV, the designer must choose either fuses or circuit breakers to protect the transformer. 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. To see the list of application documents for the product, go to the Specifiers Guide. Learn about code and standard “minimums” that must be considered in the coordination of MV protective devices. Increasing this setting may restrict feeder coverage or prevent a reasonable setting of upstream or source side fuses and protective relays. NEC Article 240-100 and 240-101 applies to MV overcurrent protection over 600 V for feeder and branch circuit. Furthermore, NEC Article 450.3(A) specifically covers transformers over 600 V to include MV transformers. 7.7 Protection of Distribution Transformers. Bulletin 857 Motor-Feeder Protection, Medium Voltage offers solutions for today’s motor and feeder protection requirements in one package. In some cases a protection relay is used with the aim of activating automatisms to manage the electric network. Many of these complexes also have high-rise components with MV risers servicing unit substations at strategic locations on multiple levels. Industry standard protection schemes for the transformer secondary include a circuit breaker equipped with long-time, short-time, instantaneous, and ground fault functions. As the power requirements increase, so too does the likelihood that the utility will require a higher service voltage. 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. NEC Section II (Article 300.31 through 300.50) covers MV wiring methods. 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. 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. 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. Learn about power engineering and HV/MV/LV substations. ANSI/IEEE Standard C37.20.2 – Standard for Metal-Clad Switchgear defines MV as 4.76 to 38 kV. Additionally, the ground fault protection shall be selectively coordinated per NEC Article 517.17(C). 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). Furthermore, NEC Art 215.2(B) requires a separate ground to handle short circuit currents. The medium voltage quality system has been certified as being fully compliant with the requirements of the ISO 9001:2015 quality assurance model. Protective relay curves cannot be used in the same way as low-voltage circuit breaker curves or fuse curves. Protection of a power system depends on its architecture and the operating mode. Safety requirements ensure equipment is of sufficient rating to withstand the maximum available energy of the worst-case scenario. Medium Voltage Motor & Feeder Protection. 13 Provide a full-size 600-volt insulated copper ground conductor in all conduits and 14 raceways with medium voltage cable. Understand overcurrent protection requirements for medium-voltage distribution transformers. If the 3-phase load is balanced, normal ground currents are near zero. ABB Surge Arresters — Buyer’s Guide Edition 5, 2003-10 1 High Voltage Surge Arresters Buyer´s Guide. 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. Medium- Voltage Switching Devices and Switchgear. Leslie Fernandez is senior project engineer, electrical at JBA Consulting Engineers. Short-circuit protection is still required. "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.". This booklet aims at illustrating the basic criteria needed for good protection of machines and plants in medium voltage networks. The content is copyrighted to EEP and may not be reproduced on other websites. The electrical installation is thus both optimised and has improved performance: The ground conductor is required to be sized per Table 205.122. ANYWHERE DURABILITY. For transformers greater than 5 MVA, protection schemes become more complex. Figure 4 Figure 5 Figure 6. Motor and generator curves are machine specific and are normally provided in the vendor data submittal packages. 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. Medium Voltage One Line Click here to switch to Low Voltage One Line The input for a distribution substation is typically at least two transmission or subtransmission lines. 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. Medium (M) 20 Heavy (H) 25 Very Heavy (V) 31 Typically, the fuse will cross the transformer damage curve in the long time region (overcurrent region). 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. Most solidly grounded MV distribution system short circuit currents can be well above 10,000 amps. As a general rule, 3000 kVA and smaller transformers installed as a stand-alone unit or as unit substations are usually protected by fuses. 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. 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. industrial substations. Typically, if the maximum demand approaches 30 MW, the utility typically may require an on-site substation. 3. The setting values must be selected above the transient conditions which can occur in the network without requiring disconnection. 14 3. 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. 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