Talk about the necessity of arc protection for medium and low voltage busbars

Ren Yunye Ankerui Electric Co.
, Ltd.
Shanghai Jiading 201801 [Abstract]: As one of the infrastructure for the production and distribution of electric energy, the use of medium and low voltage switchgear is increasing year by year, and the complexity of the use of occasions is also increasing
.

The arc light generated by the bus failure in the complete set of switchgear will burn out its components, resulting in the expansion of the accident, often causing greater economic losses, and the arc protection of the bus bar just solves this problem, which can protect the switchgear and reduce the loss
.

【Keywords】:Medium and low voltage switchgear; Busbar failure; Arc Light Protection Introduction Arc light discharge will not only cause power outage accidents, but also cause equipment damage and personal injury, bringing immeasurable losses
.

Arc discharge accident is one of the serious accidents in the medium and low voltage switchgear, this paper discusses the necessity
of arc protection of medium and low voltage busbars in several aspects.

1 Attach importance to the reasons for the failure of the medium and low voltage busbar, China's power development and construction has entered the stage of large power grid, large units, and voltage transmission, and the capacity requirements for the generator set are getting higher and higher, which puts forward higher requirements for the operation of the power system, because the operation of a single large unit will directly affect the operational stability, sex and economy of
the entire power grid.

At the same time, the power system and operation of power plants have an increasing impact on the generator set
.

It can be seen from this that if the medium and low voltage busbar fails, it will produce arc light, and the arc light generated will have a great impact on the power equipment and the person itself, causing different degrees of damage, and sometimes triggering "chain reaction"
.

The current relay protection design standard is to use the method of backing overcurrent of the upper component to protect, so as to cut off the problem of short circuit of the bus bar of the medium and low voltage system, which has drawbacks
.

Circuit failures should be repaired in the shortest possible time, and this type of protection method will lead to increased maintenance time and some damage
to the equipment.

If these problems are not solved in time, they will also cause accidents of varying degrees, which will develop into transmission grid failures and cause overall failures
in the power system.

2 factors that produce medium and low voltage arc light failure in the operation of the low voltage power system arc fault accidents, mostly affected by environmental conditions, insulation materials moisture, equipment surface condensation and adhesion pollution, so that the equipment insulation level decreased caused by accidents
.

(1) The technical reasons generated by arc light equipment failure and misoperation of live equipment, maintenance tools are missed in the switchgear, wrong wiring and busbar connection, insulation aging and mechanical wear, overvoltage, small animals, dust, temperature, humidity, corrosion and other environmental factors, capacitive grounding current expansion, etc
.

(2) The artificial reasons generated by arc light mistakenly enter the live interval, the disconnector misoperates, forgets to ground in the working area, forgets to measure the high voltage in the working area, etc
.

In addition, the rapid development of the power system, the structure of the power grid is always changing, the electrical load is increasing, resulting in more cables, overload of electricity, but also easy to lead to failure
.

3 arc fault accident hazard arc light generated by the temperature up to 4500 °C, the internal temperature is even 10000 ~ 20000 °C
.

When arc light is generated, the large instantaneous power can reach 40MW, and the arc light intensity can exceed the normal illumination light intensity by more than 2000 times
.

Therefore, if the arc in the medium and low voltage switchgear due to failure cannot be taken in time, many hazards
will occur.

(1) Hazards to the equipment: a large number of high temperature and high pressure gas are generated when the arc occurs, and the instantaneous shock wave of the gas can cause the deformation and crushing of the switch cabinet; The shock wave blasting vibration can cause the switch cabinet to shake violently and loosen the fasteners at each connection; The high temperature generated can cause cable combustion, copper exhaust melting, aluminum exhaust, and even metal melting of the switch cabinet housing, serious damage to components and cause fire
.

(2) Harm to people: high temperature burns the skin; The molten metal evaporates and penetrates into the surface layer of the human skin causing metalization of the skin; High-intensity arc light damages the eye and even causes corneal detachment; Dust and toxic and harmful gases from high-temperature combustion damage the respiratory system; The arc photoelectric current acting on the human body can cause involuntary and violent contraction of muscles, and can also damage tendons, skin, blood vessels, nerve tissue, etc
.

The energy generated by the arc rises rapidly exponentially with I²t, which is not only related to the size of the fault current, but also to the arc burning time
.

Depending on the point of failure, usually the fault short-circuit current will be in a few thousand amps to tens of thousands of amps, if the fault can not be cut in time to extinguish the arc, it will produce a huge amount of energy
.

In short, the internal arc failure of the switchgear is not a serious
danger, whether it is for the development equipment or for the nearby staff.

Figure 1 Comparison between arc energy-time curve 4 arc protection and traditional protection is as follows
:
(1) The inlet overcurrent protection scheme uses microcomputer overcurrent protection to realize the medium and low voltage switchgear and its bus bar protection scheme
.

The overcurrent protection operation time needs to be combined with the overcurrent protection time of each feeder, at least more than 300 ms, and the operation time cannot meet the requirements of
rapid cutting arc short circuit fault.

(2) Transformer backup overcurrent protection scheme: This scheme is currently widely used in medium and low voltage bus protection scheme, and the protection trip time is generally set to 1.
2 ～ 2.
0 s, which can not meet the requirements of rapid removal of medium and low voltage bus and line faults
.

(3) High impedance busbar protection scheme of circulation principle: This scheme is a dedicated busbar protection scheme, and the protection operation time is generally 35 ~ 60 ms
.

However, this scheme is complex and has high requirements for CT, so it is difficult and uneconomical
to install in a medium and low voltage switchgear.

In addition, because its protection range is limited by the CT installation location, it cannot protect against faults at cable glands with a high probability of failure, and it cannot provide fault location, so its practicality is poor
.

Arc light protection is specially used to protect the medium and low voltage switch cabinet busbar, its action time is fast, compared to the traditional protection system, more excellent, it uses arc light and current latching method to double judgment, increase reliability and performance
.

In the event of a failure, it can be accurately located, which can reduce the time for maintenance personnel to find the fault point, greatly shorten the maintenance time, and ensure the rapid recovery of power supply
after the accident overhaul.

5 Ankeri ARB5 series arc protection device Ankerui ARB5 series arc protection device has the advantages of simple principle, reliable and rapid action, no special requirements for substation primary equipment, adapts to various operating modes, and does not need to be switched under various operating modes, etc.
, which is an ideal solution
for the protection of 0.
4kV - 35kV medium and low voltage bus in power plants, substations, industrial and commercial distribution systems.

It initiates protection through the arc + current dual criterion or arc light single criterion, and the action time of the arc single criterion ≤7ms; The operation time of the arc + current dual criterion ≤ 20ms, which provides technical support for rapid removal of medium and low voltage arc faults
.

Figure 2 ARB5 arc protection logic schematic ARB5 arc protection also has the functions
of failure protection, CT monitoring, arc fault point location, arc optical fiber link self-test and device abnormal self-test, and support for major industry communication protocols including IEC61850.

Figure 3 ARB5 arc protection typical configuration Figure 6 application case of arc protection of low-voltage switchgear busbars Acquarie ARB5 series arc protection devices are widely used in low- and medium-voltage switchgear busbar protection
.

(1) An airport 10kV switchgear busbar arc protection diagram 4 an airport 10kV switchgear ARB5 arc protection installation diagram (2) a factory 0.
4kV switchgear busbar arc protection Figure 5 a factory 0.
4kV switchgear ARB5 arc protection installation diagram Conclusion The protection of the low-voltage system busbar not only needs to master the technology, but also needs some protection systems to coordinate and complete, and arc light protection as an ideal solution, It can effectively lift faults, reduce the number of equipment maintenance, improve the economic benefits of the power system, and improve the reliability and reliability
of the power system.

References[1].
Wang Xinheng.
Analysis on the necessity of arc light protection for busbar installation in medium and low voltage systems[2].
Li Yingzhou.
Arc lightApplication of protection system in medium and low voltage switchgear[3].
Wang Liangyi,Lu Rui,Zeng Zhi'an.
The application of arc light protection in 10kV switchgear[4].
Ankerui Enterprise Microgrid Design and Application Handbook 2022.
05 Edition Author Introduction: Ren Yunye, male, currently working in Ankerui Electric Co.
, Ltd.
, the main research direction is medium and low voltage power system relay protection and arc light protection
.