What is arcing ground? What are the causes, consequences and cure?

Definition of arc grounding

Arc grounding is a kind of grounding fault phenomenon in power system. It mainly refers to the existence of grounding current in the form of arc when single-phase grounding fault occurs in the system where the neutral point is not grounded or the system is grounded through arc suppression coil.

Cause of arc grounding

Insulation damage

• Equipment aging: During the long-term operation of the power equipment, due to the effect of electrical, thermal, mechanical and other stresses, the insulating material will gradually age and reduce its insulation performance. For example, the insulation layer of the cable may be cracked or damaged, resulting in a grounding fault. When the grounding current is large, arc grounding may be formed.

• Overvoltage shock: Various overvoltages may occur in the power system, such as lightning overvoltage and operating overvoltage. These overvoltages may damage the insulation of the device and cause ground failures. For example, during a thunderstorm, an overhead line may be struck by lightning, causing the insulator to flashover, creating a single-phase ground fault.

External damage

• Construction damage: When carrying out activities such as road construction and building construction, underground cables or overhead lines may be accidentally damaged, resulting in ground faults. For example, when excavating, an excavator may accidentally injure underground cables, resulting in cable insulation damage and arc grounding.

• Tree contact: In some areas where overhead lines pass, if trees grow too high, they may touch the line, resulting in ground failure. Especially in severe weather conditions such as strong winds, tree shaking is more likely to cause ground failure. For example, in strong winds, tree branches may break off and land on overhead lines, creating a ground fault.

The consequences of arc grounding

Endangering equipment safety

• Damage to device insulation: The grounding of an arc generates high temperature and high energy arc, which may seriously damage the insulation of the device. For example, the arc may abate the insulation layer of the cable, the winding insulation of the transformer, etc., reduce the insulation performance of the equipment, and even cause the equipment to burn.

• Trigger overvoltage: Arc grounding may trigger intermittent arc overvoltage, which is usually of high amplitude and may cause further damage to the insulation of the equipment. For example, in a neutral ungrounded system, single-phase arc grounding may increase the voltage of the non-fault phase to up to times the line voltage, posing a serious threat to the insulation of the equipment.

The reliability of power supply is affected

• Tripping power outage: A severe arc ground fault may cause the protective device to operate, causing the circuit breaker to trip, thus interrupting power supply. This will bring inconvenience to users and affect the normal progress of production and life. For example, in the production process of a factory, if a sudden arc ground fault causes a power outage, it may cause production interruption and bring economic losses.

• Expand the fault range: If the arc grounding fault cannot be eliminated in time, it may develop into an interphase short-circuit fault, expand the fault range, and increase the difficulty and time of repair. For example, an electric arc may ablate surrounding equipment and conductors, triggering an interphase short circuit and extending the fault range.

The solution of arc grounding

Equipment maintenance and management

• Regular inspection: Regular inspection and maintenance of power equipment, timely discovery and treatment of equipment insulation defects. For example, regular cable insulation resistance test, partial discharge detection, oil chromatography analysis of the transformer, winding DC resistance test, etc., in order to find the potential failure of the equipment in time.

• Strengthen inspection: Strengthen the inspection of power lines and equipment, and timely discover and deal with hidden dangers such as external damage. For example, increase the number of inspections of overhead lines, timely clean up trees and debris near the line, and prevent trees from touching the line; Mark and protect the underground cables in the construction area to prevent construction damage.

Using arc suppression device

• Arc suppression coil: In the system where the neutral point is not grounded or the arc suppression coil is grounded, the parameters of the arc suppression coil can be adjusted reasonably, so that it can effectively compensate the grounding capacitance current and reduce the generation of arc. When the single-phase grounding fault occurs, the inductive current generated by the arc suppression coil can offset the grounding capacitance current, so that the grounding current is reduced to a lower level, thus reducing the harm of arc grounding.

• Grounding fault line selection device: The installation of a grounding fault line selection device can quickly and accurately detect the ground fault line and remove the fault line in time to prevent the expansion of the fault. For example, the grounding fault line selection device based on the principle of zero sequence current and zero sequence power direction can quickly determine the fault line when arc grounding fault occurs, and provide a basis for fault treatment.

Improve the insulation level of equipment

• Selection of high-quality insulation materials: In the manufacturing and installation process of power equipment, high-quality insulation materials are selected to improve the insulation performance of the equipment. For example, the use of insulation materials that are resistant to high temperature and aging can extend the service life of equipment and reduce the risk of insulation damage.

• Strengthen insulation treatment: Strengthen the insulation of the equipment to improve its insulation strength. For example, waterproof and moisture-proof treatment of cable joints and insulation wrapping of transformer windings can improve the insulation performance of equipment and reduce the occurrence of ground faults.