The principle of small current grounding line selection, small current grounding line selection devi

The device can find the fault situation of each circuit in a timely and effective manner, and provide functions such as alarm tripping, etc., the disadvantage is that the cost is increased, and the supporting cable increases.

The software is the opposite, although the cost is reduced, but the accuracy measurement is not as good as the line selection device.

Judging from the development direction of its application in intelligent stations, most of the devices are now selected, because relatively speaking, it is convenient for operation and maintenance, and the response state is intuitive and reliable.

With the strong support of Hubei Provincial Electric Power Company and Xiangyang Power Supply Company from scientific research funds, technical information and test equipment, Xiangyang Keneng Electromechanical Equipment has organized a group of engineers and technicians who have been engaged in power generation and distribution work for a long time in the power system from the end of the 80s of the last century. According to the principle of "fuzzy theory", various principles and methods such as "first half wave", "reactive power direction", "direction and magnitude of harmonic current" and "wavelet analysis" are comprehensively adopted. By combining a variety of data and operating experience when collecting the grounding state, fuzzy theory and computer technology are used, logical relationship and fuzzy weighting operation methods are adopted, and self-developed program software is adopted. In terms of hardware, large-scale integrated circuits and high-speed computer industrial computers imported from the United States are selected; The structure is a distributed network structure, and multiple processors work at the same time, which realizes real-time tracking, synchronous collection and calculation of a variety of data, and quickly obtains judgment results.

At the same time, it has also successfully developed a variety of products such as LXMZ-10 series bus type zero sequence current transformer, cable type zero sequence current transformer, open zero sequence current transformer and other products with high precision and high sensitivity matched with single-phase grounding protection device, which ensures the reliability of protection line selection from many aspects!

After 20 years of painstaking research and development, finally in 2008 successfully developed the first domestic DJDX-08 distributed single-phase grounding fault computer comprehensive line selection device, after two years of hundreds of sets of trials nationwide, from the customer's feedback effect and practice has proved that our "line selection accuracy" really reached more than 98%, which not only solves the need for neutral point completely ungrounded system protection line selection; It also solves the protection line selection needs of the neutral point through the arc suppression coil or resistance grounding system; It can also meet the protection line selection when multiple lines are grounded at the same time when multiple sections of the bus are combined in parallel or sectional operation mode. When the transition resistance at ground is high or the system has resonance, the accurate line selection can also be achieved.

It completely solves the worldwide problem that single-phase grounding fault has not been solved, which is of epoch-making significance! It has made an innovative contribution to the automation of power systems!

The company has obtained dozens of qualification certificates! A variety of products have won the Power Technology Progress Award; The busbar zero-sequence current transformer has been tested by the quality inspection and testing center of electrical equipment in the power industry; The scientific research achievements of the distributed single-phase grounding fault computer integrated line selection device have been supported by the Ministry of Science and Technology of the People's Republic of China, and have passed the testing and certification of various technical indicators of the State Grid Electric Power Research Institute.

It is generally based on the following principles.

1. The principle of zero sequence power direction.

The small current grounding device based on the principle of zero sequence power direction is to use the zero sequence current of the fault and the non-fault line to be reversed when a single-phase grounding fault occurs in the system, and the fault and non-fault current are determined by the zero sequence power relay.

Second, the principle of harmonic current direction.

When a single-phase ground fault occurs in a neutral ungrounded system, zero-sequence harmonic currents will occur in each line. Due to the increase of the number of harmonics, the corresponding inductive reactance increases, and the capacitive reactance decreases, so a m-harmonic can always be found, and the m-harmonic current of the fault line and the non-fault line is in the opposite direction, and all currents greater than the m-harmonic are satisfied with this relationship.

3. The principle of external high-frequency signal current.

When a single-phase grounding occurs in the neutral point non-grounding system, an external high-frequency signal current is injected into the bus grounding phase through the secondary winding of the voltage transformer, and the signal current is mainly grounded along the grounding point of the grounding phase of the faulty line, and part of the signal current is grounded through the ground-to-ground capacitance of other non-faulty lines. A signal current detector made of electromagnetic induction and harmonic principle is used to receive the signal current flowing through the fault phase of the line close to the line conductor (the signal current flowing through the ground phase of the fault line is large, and the signal current flowing through the ground phase of the non-fault line is small, and the ratio between them is greater than 10 times) to judge the fault line and the non-fault line.

The high-frequency signal current generator is started by the voltage of the open triangle of the voltage transformer. The frequency of the selected high-frequency signal current is different from the power frequency and the frequency of each harmonic, so the power frequency current and each harmonic current have no inductive signal for the signal detector.

In the case of a single-phase grounding fault, the signal current detector is used to trace the signal current injected into the grounding phase of the system, and the exact location of the grounding line and grounding point can also be found.

Fourth, the principle of the first half wave.

The first-half-wave principle is based on the assumption that the ground fault signal occurs at a moment when the phase voltage approaches the maximum. When the voltage is close to the maximum value, if a grounding fault occurs, the capacitance charge of the fault phase is discharged to the fault point through the fault line, and the distributed inductance and distributed capacitance of the fault line make the current have attenuation and oscillation characteristics, and the current does not pass through the arc suppression coil, so it is not affected by the arc suppression coil. However, the line selection device of this principle can not reflect the grounding fault when the phase voltage is low, and it is susceptible to the influence of the system operation mode and grounding resistance, and there is a working dead zone.

Small current grounding wire selection device:The small current grounding system refers to the neutral point is not grounded, the arc suppression coil is grounded or the power system is connected to the ground by high resistance, and most of the domestic power grids of 66kV and below adopt this grounding method.

It is commonly known as small current, small current line selection, small current grounding line selection, small current grounding line selection device.

TSH2007 series of small-current grounding power grid single-phase grounding fault line selection device is a more formal equipment product in the current domestic Nianshiye market.

At present, the small current grounding system refers to the neutral point is not grounded, grounded by arc suppression coil or grounded by high resistance local power system, most of the domestic 66kV and below power grids use this grounding method. Its main disadvantage is that it is not possible to quickly identify which line is the problem in the event of a single-phase ground fault.

Since the increase in phase voltage caused by such faults poses a great threat to the insulation performance of the system, it is necessary to quickly identify and eliminate faulty lines. In the late 80s, Professor Yang Yihan of North China Electric Power University first proposed the group ratio ratio phase selection technology, and developed the first line selection device in China.

The first generation of line selection products in the early 90s has been widely promoted and applied in China, but due to the early call of line selection theory and technical limitations, the sensitivity and accuracy of the first generation of products are not high, according to sampling statistics, to the late 90s more than 85% of the products have been withdrawn from operation.

At the end of the last century, the State Power Corporation, the State Economic and Trade Commission and the China Electricity Council jointly held a meeting and drafted the "Technical Standard for Small Current Grounding Line Selection Device", and unanimously confirmed the importance of further research on line selection technology in the future development of power grids.

1. In the power system, the neutral point is not grounded or the system is grounded by arc suppression coil and resistance is called small current grounding system, and the most common fault in the small current grounding system is single-phase grounding.

2. When a single grounding fault occurs in the small current grounding system, all lines with capacitance to the ground will have zero sequence current passing through, but due to the small buried traces of zero sequence current and great dispersion, it is difficult to select the grounding line; If there is an arc suppression coil in the system, the difficulty is even greater.

3. The grounding current is small when single-phase grounding, according to the provisions of the safety operation regulations of the rock rolling system of the power system, the single-phase grounding fault can continue to run for 1 to 2 hours, the crude liquid remains, but at this time, the system is not faulty relative to the ground voltage rises to the line voltage, if not dealt with in time, it is easy to develop into a two-phase short circuit to expand the fault, and the arc grounding will also cause the whole system overvoltage.

4. Through the small current grounding line selection device, the grounding line alarm can be accurately found.