High-voltage switchgear

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800 kV high-voltage switchgear Switchgear HV.jpg
800 kV high-voltage switchgear

High-voltage switchgear is any switchgear used to connect or disconnect a part of a high-voltage power system. This equipment is essential for the protection and safe operation, without interruption, of a high voltage power system, and is important because it is directly linked to the quality of the electricity supply.

Contents

The term "high voltage" covers the former medium voltage (MV) and the former high voltage (HV), so refers to equipment with a rated voltage of over 1000 V in the case of alternating current, and over 1500 V in the case of direct current. The industrial applications of high voltage circuit breakers are for the moment limited to alternating current because they are more economical, there are however high voltage disconnectors for direct current connections.

High-voltage switchgear was invented at the end of the 19th century for operating motors and others electric machines. [1] The technology has been improved over time and can be used with voltages up to 1,100 kV. [2]

Classification

Functional classification

Disconnectors and earthing switches

Disconnectors and earthing switches are safety devices used to open or to close a circuit when there is no current through them. They are used to isolate a part of a circuit, a machine, a part of an overhead line or an underground line so that maintenance can be safely conducted.

The opening of the line isolator or busbar section isolator is necessary for safety, but not sufficient. Grounding must be conducted at both the upstream and downstream sections of the device under maintenance. This is accomplished by earthing switches.

In principle, disconnecting switches do not have to interrupt currents, as they are designed for use on de-energized circuits. In practice, some are capable of interrupting currents (as much as 1,600 ampere under 300 V but only if current is drawn via a same circuit half breaker bypass system), and some earthing switches must interrupt induced currents which are generated in a non-current-carrying line by inductive and capacitive coupling with nearby lines (up to 160 A under 20 kV). [3]

High-current switching mechanism

High-current switching mechanisms are used for energized circuits carrying a normal load. Some can be used as a disconnecting switch. But if they can create a short-circuit current, they can not interrupt it. [4] [5]

Contactor

Contactors are similar in function to high-current switching mechanisms, but can be used at higher rates. They have a high electrical endurance and a high mechanical endurance. [6]

Fuses

A fuse can automatically interrupt a circuit with an overcurrent flowing in it for a fixed time. This is accomplished by the fusion of an electrical conductor which is graded.

Fuses are mainly used to protect against short circuits. They limit the peak value of the fault current.

In three-phase electric power, they only eliminate the phases where the fault current is flowing, which can pose a risk for both the malfunctioning devices and the people. To alleviate this problem, fuses can be used in conjunction with high-current switches or contactors.

Like contactors, high-voltage fuses are used only in the band 30 kV to 100 kV.[ citation needed ]

Circuit breaker

A high voltage circuit breaker is capable of connecting, carrying and disconnecting currents under the rated voltage (the maximal voltage of the power system which it is protecting).

Under normal operational conditions, circuit breakers can be used to (dis)connect a line. Circuit breakers can also be used to interrupt current when anomalies are detected, such as a short-circuit.

Circuit breakers are essential elements of high-voltage power systems because they are the only means to safely interrupt a short circuit current. The international standard IEC 62271-100 defines the demands linked to the characteristics of a high voltage circuit breaker. [7]

The circuit breaker can be equipped with electronic devices to know at any moment their states, such as wear or gas pressure, and to detect faults from characteristic derivatives. It can also permit planned maintenance operations and to avoid failures. [8] [9]

To operate on long lines, circuit breakers are equipped with a closing resistor to limit overvoltages. [10] [11]

They can be equipped with devices to synchronize closing and/or opening, to limit the overvoltages and the inrush currents from the lines, the unloaded transformers, the shunt reactances and the capacitor banks. [12] [13]

Some devices are designed to have the characteristics of the circuit breaker and the disconnector, [14] but their use is not widespread.

Related Research Articles

<span class="mw-page-title-main">Circuit breaker</span> Automatic circuit protection device

A circuit breaker is an electrical safety device designed to protect an electrical circuit from damage caused by current in excess of that which the equipment can safely carry (overcurrent). Its basic function is to interrupt current flow to protect equipment and to prevent fire. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset to resume normal operation.

<span class="mw-page-title-main">Substation</span> Part of an electrical transmission, and distribution system

A substation is a part of an electrical generation, transmission, and distribution system. Substations transform voltage from high to low, or the reverse, or perform any of several other important functions. Between the generating station and consumer, electric power may flow through several substations at different voltage levels. A substation may include transformers to change voltage levels between high transmission voltages and lower distribution voltages, or at the interconnection of two different transmission voltages. They are a common component of the infrastructure. There are 55,000 substations in the United States.

<span class="mw-page-title-main">Fuse (electrical)</span> Electrical safety device that provides overcurrent protection

In electronics and electrical engineering, a fuse is an electrical safety device that operates to provide overcurrent protection of an electrical circuit. Its essential component is a metal wire or strip that melts when too much current flows through it, thereby stopping or interrupting the current. It is a sacrificial device; once a fuse has operated, it is an open circuit, and must be replaced or rewired, depending on its type.

<span class="mw-page-title-main">Recloser</span> Electricity distribution networks circuit breakers

In electric power distribution, automatic circuit reclosers (ACRs) are a class of switchgear designed for use on overhead electricity distribution networks to detect and interrupt transient faults. Also known as reclosers or autoreclosers, ACRs are essentially rated circuit breakers with integrated current and voltage sensors and a protection relay, optimized for use as a protection asset. Commercial ACRs are governed by the IEC 62271-111/IEEE Std C37.60 and IEC 62271-200 standards. The three major classes of operating maximum voltage are 15.5 kV, 27 kV and 38 kV.

<span class="mw-page-title-main">Switchgear</span> Control gear of an electric power system

In an electric power system, a switchgear is composed of electrical disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults downstream. This type of equipment is directly linked to the reliability of the electricity supply.

A crowbar circuit is an electrical circuit used for preventing an overvoltage or surge condition of a power supply unit from damaging the circuits attached to the power supply. It operates by putting a short circuit or low resistance path across the voltage output (Vo), like dropping a crowbar across the output terminals of the power supply. Crowbar circuits are frequently implemented using a thyristor, TRIAC, trisil or thyratron as the shorting device. Once triggered, they depend on the current-limiting circuitry of the power supply or, if that fails, the blowing of the line fuse or tripping the circuit breaker.

<span class="mw-page-title-main">Disconnector</span> Electromechanical switch

In electrical engineering, a disconnector, disconnect switch or isolator switch is a type of switching device with visible contacts, used to ensure that an electrical circuit is completely de-energized for service or maintenance. They are often found in electrical distribution and industrial applications, where machinery must have its source of driving power removed for adjustment or repair. Disconnectors can be operated manually or by a motor, and may be paired with an earthing switch to ground the portion that has been isolated from the system for ensuring the safety of equipment and the personnel working on it.

Power system protection is a branch of electrical power engineering that deals with the protection of electrical power systems from faults through the disconnection of faulted parts from the rest of the electrical network. The objective of a protection scheme is to keep the power system stable by isolating only the components that are under fault, whilst leaving as much of the network as possible in operation. The devices that are used to protect the power systems from faults are called protection devices.

<span class="mw-page-title-main">Arcing horns</span>

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In electric power systems and industrial automation, ANSI Device Numbers can be used to identify equipment and devices in a system such as relays, circuit breakers, or instruments. The device numbers are enumerated in ANSI/IEEE Standard C37.2 Standard for Electrical Power System Device Function Numbers, Acronyms, and Contact Designations.

Ferroresonance or nonlinear resonance is a rare type of resonance in electric circuits which occurs when a circuit containing a nonlinear inductance is fed from a source that has series capacitance, and the circuit is subjected to a disturbance such as opening of a switch. It can cause overvoltages and overcurrents in an electrical power system and can pose a risk to transmission and distribution equipment and to operational personnel.

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<span class="mw-page-title-main">Motor control center</span> Assembly to control a series of electric motors from one location

A motor control center (MCC) is an assembly to control some or all electric motors in a central location. It consists of multiple enclosed sections having a common power bus and with each section containing a combination starter, which in turn consists of motor starter, fuses or circuit breaker, and power disconnect. A motor control center can also include push buttons, indicator lights, variable-frequency drives, programmable logic controllers, and metering equipment. It may be combined with the electrical service entrance for the building.

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<span class="mw-page-title-main">Vacuum interrupter</span>

In electrical engineering, a vacuum interrupter is a switch which uses electrical contacts in a vacuum. It is the core component of medium-voltage circuit-breakers, generator circuit-breakers, and high-voltage circuit-breakers. Separation of the electrical contacts results in a metal vapour arc, which is quickly extinguished. Vacuum interrupters are widely used in utility power transmission systems, power generation unit, and power-distribution systems for railways, arc furnace applications, and industrial plants.

In an electrical power distribution system, a ring main unit (RMU) is a factory assembled, metal enclosed set of switchgear used at the load connection points of a ring-type distribution network. It includes in one unit two switches that can connect the load to either or both main conductors, and a fusible switch or circuit breaker and switch that feed a distribution transformer. The metal enclosed unit connects to the transformer either through a bus throat of standardized dimensions, or else through cables and is usually installed outdoors. Ring main cables enter and leave the cabinet. This type of switchgear is used for medium-voltage power distribution, from 7200 volts to about 36000 volts.

References

  1. ↑ British Pattern GB 20069 Improvements in Apparatus for Controlling the Application or Use of Electric Currents of High Tension and Great Quantity in 1893, on espacenet.com
  2. ↑ Lin Jiming et al., Transient characteristics of 1100 kV circuit-breakers, International Symposium on International Standards for Ultra High Voltage, Beijing, Juillet 2007.
  3. ↑ "IEC 62271-102 for A.C. disconnectors and earthing switches" (PDF). Archived from the original (PDF) on 2007-09-30. Retrieved 2008-04-21.
  4. ↑ "Norme CEI 60265-1 Interrupteurs pour tension assignée supérieure à 1 kV et inférieure à 52 kV" (PDF). Archived from the original (PDF) on 2007-09-30. Retrieved 2008-04-21.
  5. ↑ "Norme CEI 60265-2 Interrupteurs pour tension assignée supérieure à 52 kV" (PDF). Archived from the original (PDF) on 2007-09-30. Retrieved 2008-04-21.
  6. ↑ "Norme CEI 60470 Contacteurs pour courant alternatif haute tension et démarreurs de moteurs à contacteurs" (PDF). Archived from the original (PDF) on 2007-09-30. Retrieved 2008-04-21.
  7. ↑ "Norme CEI 62271-100 Disjoncteurs à haute tension" (PDF). Archived from the original (PDF) on 2007-09-27. Retrieved 2008-04-21.
  8. ↑ E.Thuries, G.Ebersohl, J.P.Dupraz, O.Chetay, J.P.Montcorgé, Introduction de l'électronique numérique dans les auxiliaires de l'appareillage et amélioration de la fiabilité, 1994, CIGRE session 1994, rapport 23/13-09
  9. ↑ Denis Dufournet, Disjoncteurs SF6 – Évolution de 1959 à 1994, 1994, Revue générale de l'électricité n° 5
  10. ↑ D.E. Heldman, I.B. Johnson, C.H. Titus, D.D. Wilson, Switching of Extra-High-Voltage Circuits, Surge reduction with circuit-breaker resistors, 1964, IEEE Transactions on Power Apparatus and Systems, Vol. 83 (1964–12)
  11. ↑ Eugène Maury, Problèmes apparaissant aux tensions les plus élevées lors de la manœuvre des disjoncteurs, 1964, CIGRE session 1964
  12. ↑ Eugène Maury, La fermeture synchronisée des disjoncteurs 525 kV et 765 kV, moyen de réduire les surtensions de manœuvre sur lignes à vide, 1966, CIGRE session 1966.
  13. ↑ Groupe de travail CIGRE 13.07, Controlled switching of HV AC circuit breakers, 1999, Electra N° 183
  14. ↑ Norme CEI 62271-108 Disjoncteur-sectionneurs
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