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. 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. Protection of a power system depends on its architecture and the operating mode. In most cases, only one choice of electrical utility is available and typically there is limited choice of service voltage. Bussmann circuit protection solutions comply with major international standards: ANSI, BS, DIN, IEC and UL. 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 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. In general, higher service voltage results in more equipment expense. In some cases a protection relay is used with the aim of activating automatisms to manage the electric network. Per ANSI C57.13, normal protective CT class secondary should withstand up to 20 times for a short period of times under fault conditions. Protective relay curves cannot be used in the same way as low-voltage circuit breaker curves or fuse curves. 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. 148. Another feature of large commercial complexes is the associated central plant function with MV chillers and unit substations. 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). As a general rule, 3000 kVA and smaller transformers installed as a stand-alone unit or as unit substations are usually protected by fuses. Typically, if the maximum demand approaches 30 MW, the utility typically may require an on-site substation. Although the primary windings are rated for MV, the designer must choose either fuses or circuit breakers to protect the transformer. Understand overcurrent protection requirements for medium-voltage distribution transformers. This booklet aims at illustrating the basic criteria needed for good protection of machines and plants in medium voltage networks. Medium voltage fuses are applied quite differently than fuses rated 600 volts and less. Typically, service reliability tends to increase as service voltages increase. 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. 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. 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 … 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. Industry standard protection schemes for the transformer secondary include a circuit breaker equipped with long-time, short-time, instantaneous, and ground fault functions. Device 50 or instantaneous: Set below cable damage curve and must be above the maximum fault current at the breaker total clear curve. ANSI/IEEE Standard C37.20.2 – Standard for Metal-Clad Switchgear defines MV as 4.76 to 38 kV. 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 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, industrial substations. ANYWHERE DURABILITY. The ground conductor is required to be sized per Table 205.122. Extremely inverse relay setting is superior in that substantially faster fault clearing time is achieved at the higher current levels. Transformer MV breakers may include the following protective device numbers: In MV systems, current transformers (CTs) connect protective or metering devices. In this case an analysis of options must be conducted to determine the best option for the project. The majority of modern relays are multifunction type with the protection referred to by numbers that correlate with the functions they perform. Furthermore, NEC Art 215.2(B) requires a separate ground to handle short circuit currents. 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. 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