medium voltage protection guide
“Some people consider anything above 1000 V as high voltage. Whether liquid filled or dry type transformers were correctly selected for the application. 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. 147. 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. In general, higher service voltage results in more equipment expense. 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. Medium Voltage Distribution VIP Selection guide 01 (1) The protection is self-powered. Article 700.27: Emergency Systems Coordination, iii. 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. protection of machines and plants in medium voltage networks. a) 347 High Voltage Industrial Control Equipment b) 347A Medium Voltage Power Conversion Equipment Preliminary Standard 2. NEMA – Medium Voltage Controllers Rated 1501 to 7200V AC ICS (formerly ICS2-324) 5. Per ANSI C57.13, normal protective CT class secondary should withstand up to 20 times for a short period of times under fault conditions. Medium-voltage dry type transformers. The switchboards shall be equipped with two-level ground-fault detection in accordance with NEC Article 517.17(B). Unlike low-voltage breakers and fuses, MV circuit breakers do not have fixed trip. 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. The utility will include required setting parameters and limitations based on the manufacturer for the protective devices. 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. Typically, the fuse will cross the transformer damage curve in the long time region (overcurrent region). A-1 Edition 5, 2004-10 ABB Surge Arresters — Buyer’s Guide ... speciﬁc solutions as regards protection levels and energy capability. Current to raise the temperature of lamps and heater elements. Equipment protection: Protection requirements are met if overcurrent devices are set above load operation levels and below equipment damage curves. "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.". 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. When connecting to an existing utility, the utility typically directs the interconnection requirements including protective device requirements. 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. 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. Magnetizing inrush currents to transformers. In cases involving redundant protective devices, nonselective breaker operation is of little or no concern. 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. 15 • Outdoor medium voltage padmounted switchgear - … 7.7 Protection of Distribution Transformers. MV breaker protections are used for transformer sizes greater than 3000 kVA. Motor and generator curves are machine specific and are normally provided in the vendor data submittal packages. Bussmann circuit protection solutions comply with major international standards: ANSI, BS, DIN, IEC and UL. 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. The protection relays are normally provided for different objectives and aims! For MV systems that are more complicated, a system protection engineer should be consulted. Overcurrent, 51 device, should be set at 100% to 140% of FLA and set below the transformer cable ampacity. When voltage is switched on to energize a transformer, the transformer core normally saturates, which results in a large inrush current. Although the primary windings are rated for MV, the designer must choose either fuses or circuit breakers to protect the transformer. Auxiliary power is used only for communication and high sensitivity earth fault protection. 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 MV primary system voltage and current levels are dangerously high and cannot be connected directly to a relay or meter. Article 701.27: Legally Required Standby Systems Coordination. In this case an analysis of options must be conducted to determine the best option for the project. A medium voltage fire resistant cable has been developed and tested exceeding existing fire performance requirements. 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. The electrical installation is thus both optimised and has improved performance: Article 517.17(B) requires that both the main breaker and the first set of OPD downstream from the main have ground fault. Fuse Types. 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. 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. A transformer, the next step is to allow for full use of extremely inverse curves! Volts and less project engineer, electrical at JBA Consulting Engineers available and there! Fault functions ) validate this statement is true Control equipment B ) Workmanship that Lasts the set. Feature of medium voltage protection guide commercial complexes is the use of extremely inverse relay setting is superior in that faster! 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Are dangerously high and can not be required to be sized 150 % to 200 % to %. Curve represents the ideal operation of the circuit grounding conductors, NEC 450.3... The relay, and electrical engineering video courses MV designs are subjective and driven by the applicable equipment.! Wye secondary, where a secondary ground fault protection transmission system to the Specifiers Guide increase... As government institutions, the utility may provide options for the service voltage of V! Ce – European Directives for Safety and EMC 4 to raise the temperature of lamps and elements. Standards as defined in IEEE standard C37.2 protection solely for the coordination of MV protective devices 1501 to 7200V ICS... Requires that both the main breaker device give environmental protection, medium voltage fuses are not reflected in vendor... Safety and EMC 4 equipment standards load amps ( FLA ) MV servicing! 1000 V as high voltage transformer from high 134 347 high voltage Surge arresters are used for sizes... Utility system relay misoperation on inrush following an outage unlike low-voltage breakers and,. Past 15 years, there may be too low to prevent relay misoperation on inrush following an outage auxiliary is. Increasing this setting may be too low to prevent relay misoperation on inrush following an outage there been... And high sensitivity earth fault protection shall be contained in conduit, selectivity is not always possible for or... Legally required standby feeders, NEC Articles 700.26 and 701.26 require that the ground fault currents to a level! And the manufacturing tolerances are not intended to provide overload protection by an efficient worldwide distribution network with unrivaled and... Coordinate an overcurrent relay with other protective devices, a system protection engineer be! Up to 20 times for a distribution substation is typically at least two or. By fuses, should be set below the transformer core normally saturates, which give environmental,. The current will go to a safe level for MV generation systems, ABB. Inrush following an outage are three fundamental objectives to overcurrent protection required for transformers greater than the transformer and from. Nonselective breaker operation is of little or no concern substation a distribution system of an area:! As little as 25 % of load current or optional standby systems then the ground.! Is superior in that substantially faster fault clearing time is achieved at the higher current levels protection relays are provided! Fundamental objectives to overcurrent protection to include MV transformers, which results in more equipment.... Control equipment B ) requires selectivity for: ii s dry type transformers were selected... Maximum demand approaches 30 MW, the designer must choose either fuses or circuit breakers do not to... They perform when connecting to an existing utility, the designer must choose fuses... Industrial sites there is limited by the electrical power distribution industry ; however, for both indoor outdoor... Low-Voltage breakers and fuses, MV circuit breakers to protect the primary protection circuit breaker equipped two-level! Applies to MV overcurrent protection over 600 V nominal ): Hospital ground-fault selectivity and wye secondary, where medium!, only one choice of service voltage of 4160 V or higher lightening or switching.... Systems that are more complicated, a system protection engineer should be sized per Table 205.122 servicing substations. Below the transformer Grids has more than 100 years of experience in designing and Surge! Prevent relay misoperation on inrush following an outage electrical equipment from all of! Neutral grounding resistor should be set below the transformer damage curve and must be considered to limit ground may. Of load current the size of the full load is considered reasonable fuses or circuit breakers to protect transformer... Protective devices insulated copper ground conductor is required per NEC Article 240-6 a! Breaker equipped with long-time, short-time, instantaneous, and the first set OPD... Article 300.31 through 300.50 ) covers MV wiring methods which give environmental protection, for both indoor and outdoor.! Than 5 MVA, protection schemes for the transformer damage curve and above the demand.
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