Arc protection

Arc protection is a special type of high-speed protection against short circuits , based on the recording of the light spectrum of an open electric arc.

Content

Consequences of arc faults

Dependence of the degree of damage to the switchgear elements from the arc time

A significant danger to complete distribution devices ( KRU ) with voltage of 6-10 kV is represented by internal short circuits (CC), accompanied by an electric arc (ED). The temperature of the electric arc can reach values of the order of 7000 ... 12000 ° C during less than one period of the industrial frequency.

An electric arc acts on the elements of the switchgear assembly, causing damage of varying severity, and in the absence of adequate and timely measures to eliminate it, it inevitably leads to their destruction. Experiments conducted in the research center for testing high-voltage equipment (SIC VVA) show that an open electric arc in isolated switchgear compartments leads to insulation damage (as a rule, these are bushing insulators). The degree of damage depends on the type of insulating material, the magnitude of the short-circuit current and the time it takes to flow.

Tire arc protection

Arc busbar protection (DUZSH) or protection against arc short circuits (ZDZ) is used to protect busbars and busbar elements of 6-10 kV distribution devices located in closed compartments (KRU or KRUN). The work of protection is based mainly on the physical principle. It can react to two factors: the flash of light in the switchgear compartments and the mechanical effect of the arc. In this regard, it can be used only in switchgears, where all current-carrying parts are located in closed compartments.

Valve-type ZDZ

To increase the air pressure in the limited compartment of the switchgear cell, ZDZ valve type responds. In the ZDZ of this type, as a sensor that reacts to an increase in air pressure, special unloading valves with limit switches mounted in a switchgear switchgear are used.

ZDZ with the membrane switch

It is a system of hoses, back pressure valves and a membrane switch. A hose is supplied to each protected compartment of the cell, the hoses are connected via back pressure valves, the combined section is connected to a membrane switch that reacts to pressure waves generated by an electric arc. ^[one]

Photo thyristor-type hdz

A photothyristor-type photocurrent protective device reacts to a light flash from an electric arc. A photo-thyristor is used as a sensor reacting to a light flash from an electric arc.

ZDZ fiber type

Device arc protection Ovod-MD. The conversion and monitoring unit is open. Visible connected fiber optic cables (blue) from optical fiber sensors

Like the photo thyristor type ZDZ, this type of ZDZ reacts to a flash of light from an electric arc. As a sensor that responds to a flash of light from an electric arc, a fiber optic sensor (VOD) is used. Two types of WATER are used:

loop type;
radial type.

WATER are placed one in each compartment of the switchgear cell:

in the input compartment;
in the withdrawable unit compartment;
in the cable compartment;
in the space of the bus bridge.

Economy options are also used for WATER placement - so, for example, one WATER can be simultaneously placed both in busbar compartments and in compartments of withdrawable elements in several cells of one section. With an arc short circuit, each EHL detects a light flash from an electric arc and generates a “Trigger” signal, which is transmitted via FOL to the MP ZDZ terminal. In turn, the MP ZDZ terminal, on the basis of the “Triggered” signals from the VOD, generates commands to turn off the corresponding switches in order to eliminate the arc short circuit.

In order to prevent a malfunction of the emergency protection system, a current control is provided - the signal for the shutdown is issued by the MP terminal of the emergency protection system only if there are 2 factors:

signal “Triggering” from VOD;
Start MTZ signal from the protection terminal (protection terminal of the switchgear switchgear or the terminal of the high-voltage side of the transformer).

If there is only the “Triggering” signal from the WATER without the “MTZ start-up” signal, the switches from the EELS do not open and the ZDZ terminal outputs the signal “Fault of the VOD”.

Building opto-electric arc protection

Optical-electric arc protection according to the type of sensors used can be divided into two groups: with semiconductor photo sensors and with fiber-optic sensors . The type of sensor determines not only information processing algorithms, but also the execution of protections that can be classified as individual and centralized.

Centralized protection is usually designed to protect a section or group of cells and does not provide for selective detection of the damage zone. Optical sensors, such as semiconductor photodevices, are connected in parallel, and the VOD is switched on in the form of a loop.

Individual protection design allows you to perform an impact on the switch of the damaged cell, to ensure the selectivity of the action of protection and to identify the damaged area.

Construction of optical - electric arc protection (EDCO)

The arc protection of a switchgear assembly should be based on its design features and types of switching devices. To do this, select as special elements of the switchgear, which include the input switch cells, section switch cells, special zones (compartments) of the switchgear cells: busbar compartment, high voltage switch compartments, voltage transformer, etc. optimally perform the effects on switching devices while minimizing damage volumes.

With short circuits in special elements, the section must be disconnected without time lag, and during short circuits in special zones, for example, in compartments of instrument current transformers, cable cuts and bushing insulators, only damaged cells can be disconnected, for example, using vacuum switches.

Burning an arc in a cell of an input switch requires an effect on switching off not only the section switch, but also the switch from the higher voltage side of the power transformer. Damage to the sectional switch requires the disconnection of the input switches. In view of the above, protection should provide for the selective detection of arc short circuits in cells and their compartments.

There is also another approach to building an arc protection switchgear, according to which any short-circuit in the switchgear should be turned off with an input switch, which leads to the “redemption” of the section. This approach simplifies the implementation of protection and allows for the integration of sensors, for example, allows you to perform an optical-electric sensor uniform, which occurs when using a fiber optic cable connected in a "loop". When implementing the protection in the first embodiment, it is possible to combine the DEEDS and devices acting on the same switches.

Regulatory Requirements

It should be noted that the requirements and test methods for arc resistance of elements of switchgear equipment, requirements for speed and type of arc protection, are not regulated today. The existing directives (Orders of RAO "UES of Russia" of 01.07.98 N 120 "On measures to improve the explosion and fire safety of power facilities" and from 29.03.2001 N 142 "On priority measures to improve the reliability of RAO" UES of Russia "and regulatory (" Rules of technical operation of power plants and networks ”, 15th edition, p. 5.4.19) documents, there are only requirements on the need for high-speed protection against arc short circuits inside switchgear cabinets.