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.
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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 V in the case of alternating current, and over 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 other electric machines.[1] The technology has been improved over time and can be used with voltages up to 1,100 kV.[2]
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 cable 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 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]
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]
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]
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 -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.
High-voltage switchgear is any switch used to connect or disconnect a component of a high-voltage power system that operates at voltages more than 36 kV. This equipment is critical for the protection and uninterrupted functioning of a high voltage power system since it is directly related to the quality of the electrical supply.
The high voltage circuit breaker (CB), which is the most important component of HV switchgear, needs specific characteristics in order to operate safely and dependably. High-voltage circuit breakage and switching defects are quite rare. These circuit breakers can be utilized after a long period of time and are often kept in the ON state.
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CBS must therefore be trustworthy enough to guarantee safe functioning when required. The technology of high-voltage circuit breakers has advanced significantly during the past 15 years. Minimum oil circuit breakers (MOCB), air blast circuit breakers, and SF6 circuit breakers are often used for high-voltage switchgear.
There are three different classes of switchgear systems: low-voltage, medium-voltage, and high-voltage.
Understanding the operation of high-voltage switchgear requires familiarity with its basic elements. Although there are various components, we will concentrate on the essential ones. The basic components of high-voltage switchgear, present in both indoor and outdoor forms are:
The circuit breaker, a critical component in high-voltage switchgear systems, is an electrical switch that automatically protects a circuit from damage caused by overload or short circuits. Its innovative design enables it to function in milliseconds, rapidly reducing excessive and fault currents and therefore protecting the entire system.
Instrument transformers are critical measuring equipment that are built into high-voltage switchgear systems. The basic function of current transformers (CTs) and voltage transformers (VTs) is to reduce current and voltage levels. This decrease allows for the safe monitoring of electrical system flows, the activation of protection relays, and the transmission of fault signals to the control center.
The earthing switch, a safety-essential component in a power system, is important to the system's and operators' safety. When the isolator or breaker is opened, it establishes a ground connection. This operation dissipates any remaining electrical charges in the line that has been removed from the power source, preventing dangerous circumstances.
The largest and most expensive components of high-voltage switchgear are the step-up transformer, which increases the voltage of an electrical signal for efficient long-distance transport with minimal power loss, and the step-down transformer, which reduces the voltage before it reaches equipment that cannot handle high voltages.
Disconnectors are simple mechanical switches used in high-voltage switchgear systems to stop or restart electrical circuits. They are commonly used to connect or detach equipment from a power supply, primarily for maintenance or repair purposes. These components are also known as isolators.
A relay is a switch powered by electricity that may be used to activate or deactivate circuits. Protective relays are intended to detect problems in the electrical system and trip the circuit breaker. This breaker then disconnects the malfunctioning equipment from the power supply and helps to dissipate any ensuing electrical sparks.
Busbars are low-impedance cables that connect electrical devices. Busbars in high-voltage switchgear link high-voltage circuit breakers and other components, allowing electricity to be sent between places.
A surge arrester is a gadget that protects equipment from damage caused by unexpected high voltages, such as lightning strikes and switching surges. High-voltage switchgear arresters operate by collecting surge energy before it may damage the equipment.
An earthing grid, made up of metal rods or plates placed in the ground, is used to route electrical energy into the earth. This protects equipment from lightning strikes and abrupt voltage surges.
Simply described, a transformer is a device that employs alternating electromagnetic fields to convert various voltage levels (really electrical energy), with the voltage before and after the conversion being constant in frequency. It is classified into several types based on its application, including power transformers, rectifier transformers, voltage regulators, isolation transformers, and CT, PT, among others. A power transformer is something we frequently see on the project site.
A contactor is an electrical device that is used to routinely turn on and off AC and DC main circuits, as well as large-capacity control circuits over long distances. The major control objects are motors, lights, capacitor banks, and contactors, which are classified as AC or DC. Compared to the circuit breaker, the difference is that the frequency of action is extremely high (so the electrical and mechanical life must be long enough); it has a larger breaking and making capacity, but it is often utilized at voltage levels of 1kV and lower. It cannot be compared to circuit breakers that have tens or hundreds of kilovolts of voltage.
There are two primary categories of high voltage switchgear: gas-insulated switchgear (GIS) and air-insulated switchgear (AIS). Whereas gas-insulated switchgear employs gas'typically sulfur hexafluoride (SF6)'AIS switchgear uses air as its principal insulating medium. Here are some details on the two types of HV switchgear.
Air-insulated Switchgear (AIS) uses air as the primary insulation medium to isolate and control the electrical power system. AIS is typically used for lower voltage applications and is known for its simple design, low cost, and ease of maintenance.
Gas-insulated Switchgear (GIS) uses sulfur hexafluoride (SF6) gas as the primary insulation medium. GIS is designed for high-voltage applications and is known for its compact design, high reliability, and superior performance.
Troubleshooting a high voltage switchgear is dependent on the source of the issue. Common troubleshooting techniques for high-voltage switchgear include:
There are two primary categories of high-voltage switchgear: gas-insulated switchgear (GIS) and air-insulated switchgear (AIS). Whereas gas-insulated switchgear employs gas'typically sulfur hexafluoride (SF6)'AIS switchgear uses air as its principal insulating medium.
A switchgear in an electric power system consists of electrical disconnect switches, fuses, or circuit breakers that regulate, protect, and isolate electrical equipment. Switchgear is used to deenergize equipment so that work may be done and to remove problems downstream.
Transformers adjust the voltage level to enable power transmission and distribution. Switchgear protects and disconnects electrical circuits. UPSs safeguard equipment from voltage fluctuations and outages by supplying backup and conditioned power.