Hubei Xiangming Electric Technology Co

1. Overview
Most power grids in my country~
(including
) adopt an ungrounded operation mode with neutral points. When a single-phase metallic direct grounding occurs in this kind of power grid, the non-faulty phase-to-ground voltage will rise to the line voltage, and the three-phase line voltage will remain unchanged. The phase difference does not affect the operation of the three-phase electrical equipment, so it does not affect the normal transmission of electric energy. Therefore, national standards stipulate that this type of power grid is allowed to operate with faults for a short period of time after a single-phase ground fault occurs, which improves the reliability of the power supply of this type of power grid.
The current operating regulations stipulate that when a unit phase ground fault occurs in a neutral point non-effectively grounded system, it is allowed to operate for two hours, but the regulations do not clarify the concept of
single-phase ground fault
define. If the single-phase ground fault is a metallic ground fault, the voltage of the faulted phase drops to zero, and the ground voltage of the remaining two healthy phases rises to the line voltage. The electrical equipment of this type of power grid should be able to withstand this overvoltage under normal circumstances. Not damaged. However, if the single-phase ground fault is an intermittent arc ground fault, an overvoltage reaching twice the peak value of the phase voltage will be generated in the system. If such a high overvoltage acts on the power grid for several hours, it will inevitably cause damage to the electrical equipment. Accumulated damage to the insulation causes insulation to ground breakdown in the weak links of the insulation of the sound phase, which then develops into a phase-to-phase short circuit accident. During the intermittent arc grounding transient process, the actual system will form a multi-frequency oscillation loop, which will not only produce high-amplitude phase-to-ground overvoltage, but also may cause high-amplitude phase-to-phase overvoltage, causing the weak points of the phase-to-phase insulation to flashover. It develops into a phase-to-phase short circuit accident.
2. The arc-extinguishing effect of the resonant grounding method

The arc-extinguishing, harmonic-extinguishing small current line selection and over-voltage protection device are designed by our company to quickly eliminate the neutral point non-effective grounding arc grounding of the power grid. The latest technology product developed to eliminate the hazards caused by electrical equipment. It mainly consists of the following seven components
> Combined overvoltage protector composed of large-capacity nonlinear components ( )
Three-phase combined overvoltage protector Compared with various existing overvoltage protectors, the voltage protector has a lower protection value and a higher ability to withstand temporary overvoltage. It can ground high-amplitude arcs in the system before the subsequent protection device operates. It effectively limits the initial transient overvoltage and is the first device in this device to limit various types of overvoltage. It is mainly used to limit atmospheric voltage and operating overvoltage.
High-voltage vacuum contactor with split-phase control ( , , )
High-voltage vacuum contactor with split-phase control is composed of three single-phase vacuum AC contactors with mutually locked operating circuits, which are respectively connected to the three systems. Between phase bus and ground. When the system is normal, it is in the off state, which will not have any impact on the normal operation of the system. When a single-phase arc is grounded in the system, the vacuum contactor closes and opens according to the instructions of the microcomputer controller, and the faulty phase busbar is directly grounded, thus completing the Limitation on arc ground overvoltage.
Phase-separated resistance-capacitance absorber ( )
The phase-separation resistance-capacitance absorber is an absorption device composed of three sets of resistors and capacitors connected in series, and is connected to both ends of the phase-separated controlled high-voltage vacuum contactor, limiting Absorb high-frequency overvoltage that occurs in the system. When intermittent arc grounding occurs in the system, the arc grounding overvoltage is limited to a safe range before the arc-extinguishing contactor operates. When the arc-extinguishing contactor opens and exits, the recovery voltage amplitude and rising speed of the fault phase are limited so that the fault point does not Reignition will occur due to overvoltage caused by operating the vacuum contactor, thereby greatly increasing the success rate of the device in eliminating transient ground faults.
Multi-function microcomputer controller ( )
The multi-function microcomputer controller is the technical core component of this device. It adopts a new generation chip from an American company. It works stably and reliably. It is powered by an advanced switching power supply and has strong anti-interference ability. Measurement, display, calculation, communication and control functions. It determines the nature and grounding phase of the grounding based on the changes in the instantaneous values of the three-phase voltage, , and open triangle voltage provided by the voltage transformer, and issues corresponding instructions to control the turning on and off of the high-voltage vacuum contactor.
High-voltage current-limiting fuse ( )
High-voltage current-limiting fuse is a backup protection device for the entire device. It is used to prevent short-circuit accidents. It has the characteristics of rapid breaking and large breaking capacity.
Voltage transformer ( )
It is used to convert the primary high voltage of the system into a secondary low voltage that can be processed by the microcomputer controller for monitoring and sampling.
High-voltage isolation switch ( )
Used for switching during installation and maintenance of this device.
> Main features of the device
>> When a single-phase arc grounding occurs in the system, it not only immediately extinguishes the arc at the fault point, but also effectively limits the arc grounding overvoltage and limits various types of overvoltage to The lower voltage level greatly reduces insulation accidents and consecutive accidents caused by overvoltage.
Has a complete overvoltage protection function
It can protect atmospheric overvoltage, operating overvoltage and arc ground overvoltage. Its function of limiting arc ground overvoltage is better and more complete than installing an arc suppression coil. After installing this device, the system that originally required the arc coil to be installed according to the design specifications can no longer be installed. After the device is activated, the system capacitor current is allowed to pass continuously for hours so that the user can deal with the faulty line after completing the reverse operation of transferring the load
Improving the operating conditions of the power grid
Due to the elimination of long-lasting faults in this type of power grid Arc ground overvoltage greatly reduces the probability of accidents with metal zinc oxide arresters ( ). Overvoltages between various phases and phases in the system are limited to lower voltage levels, and the insulation breakdown and short circuit incidents caused by this are greatly reduced.
Simple selection and easy to use
The arc suppression and overvoltage protection mechanism of this device has nothing to do with the single-phase grounding capacitance current of the power grid, so its protection performance is not affected by changes in the power grid operating mode and expansion of the power grid. The impact can be used in both large and small networks.
Simple structure and easy installation
The entire device forms a high-voltage switch cabinet that can replace the original voltage transformer cabinet. It has a simple structure, small size, convenient installation and debugging, and does not require additional space. It is suitable for substations , is also suitable for high-voltage factory systems in power plants. It is suitable for both new stations and the renovation of old stations. The system originally equipped with arc suppression coils can be installed with this device for better protection.
Safe, reliable, and long-lasting, it can quickly and effectively limit various resonant overvoltages, prevent long-term resonant overvoltage from accelerating the aging of the system insulation structure, and prevent resonant voltage from causing damage to the closed gapless metal oxide arresters in the power grid and The influence of small inductive loads increases the safety and reliability of system operation and extends the service life of the system.