CN114325468B - Method of grounding phase selection and line selection using 66kV active intervention arc suppression device - Google Patents

Abstract

The invention discloses a grounding phase and line selection method utilizing a 66kV active intervention arc extinction device, which can accurately and rapidly determine a fault line, thereby improving the power supply safety, reliability and economy of a 66kV system. The method comprises the following steps: and (3) sampling data, performing zero sequence increment starting, calculating and analyzing line and phase voltages, and S3, performing steady-state grounding phase selection, slope calculation and comparison and single-phase grounding phase selection based on a rapid switching type arc extinction and resonance elimination device by utilizing zero sequence voltage module angle comparison.

Description

Method of grounding phase selection and line selection using 66kV active intervention arc suppression device

Technical field

The present invention relates to the field of relay protection, in particular to a method of utilizing a 66kV active intervention arc suppression device for grounding phase selection and line selection.

Background technique

The 66kV voltage level power grid is an important part of the national power system and a bridge connecting the transmission system and power users. The safe and stable operation of the 66kV system is directly related to the interests of power users. According to statistics, more than 95% of power outage accidents suffered by power users are caused by the power distribution system, and more than 85% of 66kV system faults are single-phase ground faults. my country's 66kV system adopts a small current grounding method in which the neutral point is not directly grounded. The probability of a single-phase ground fault in a 66kV system is much greater than the probability of a two-phase short circuit fault. Due to the small current grounding method, when a single phase is grounded, the three line voltages It is still symmetrical and does not affect the power supply. According to the "Power System Safety Regulations", single-phase grounding can operate for 1 to 2 hours. However, with the continuous progress of social economy, the continuous growth of electricity load, the continuous expansion of city scale, the increase of cable outlets, the 66kV system network is becoming larger and larger, and the ground current of the 66kV substation is also increasing. According to regulations, if the single-phase grounding current exceeds 30A, single-phase grounding protection equipment must be installed. Because the 66kV system directly serves the masses and is close to people's residences, personal electric shock accidents in high-voltage power grids often occur. In order to ensure the safety of life and property, it is very important to quickly and accurately eliminate 66kV system faults and ensure the safety and reliable operation of the 66kV system.

At present, 66kV systems at home and abroad mainly adopt the methods of neutral point grounding through arc suppression coil and neutral point grounding through resistor. Among them, the arc suppression coil grounding method has the characteristics of operating with a single-phase fault point for a long time, which shows the good side of providing uninterrupted power supply to users, but it also leaves many problems that are difficult to solve for the safe operation of the system:

(1) If a single-phase ground fault occurs due to electric shock to humans and animals, since the line will not lose power quickly, humans and animals will not be effectively protected. The consequence is that the electric shock time will be prolonged and major injuries will occur.

(2) The neutral point ungrounded system does not have any arc extinguishing measures. The arc suppression coil in the neutral point grounded system through the arc suppression coil can only compensate for the power frequency reactive component in the ground current, but cannot compensate for the power frequency active component in the ground current. components and high-frequency components, the arc-extinguishing effect is limited. Once an arc occurs, it will cause arc overvoltage and cause cascading failure of the power grid. At the same time, arcs can cause fires and other accidents, causing heavy losses to the power grid and users.

(3) At present, with the increase in the length of overhead lines and the increase in cable lines, the system capacitor current is getting larger and larger. When the capacitor current increases to a certain level, the manufacturing of arc suppression coils will be very difficult and the cost will be too high. In order to solve this problem, some 66kV systems in my country have changed the grounding method of the neutral point to grounding through a small resistance, thus sacrificing the advantage of high reliability of power supply in the non-effective grounding method of the neutral point.

(4) At present, the problem of single-phase ground fault line selection and fault location in the 66kV system has not been well solved. Many substations use manual pulling methods for fault line selection and manual line inspection for fault location, which prolongs power outages. time, increasing the risk of faulty operation and reducing power supply reliability.

In addition, the neutral point grounding method through a resistor also has certain problems:

(1) After the neutral point is grounded with low resistance, we cannot rely on short-term fault operation to ensure power supply reliability. Instead, we rely on strengthening the power grid structure and improving the level of automation to improve power supply reliability;

(2) Due to the large current at the grounding point, if the zero-sequence protection does not operate in time, it will cause greater harm to the grounding point and the insulation nearby, resulting in permanent and non-permanent single-phase grounding line faults in the cable line. The number of trips increased significantly. Especially if the body is electrocuted, the ground current will increase, increasing the degree of injury.

Due to various reasons, the accuracy of line selection is not high. In addition, the fault phase is grounded through a low-impedance transformer, so that when the system is protectively grounded, the system's grounding current is completely transferred to the protective grounding point, which may further improve the line selection performance of grounding line selection devices made with different line selection principles. Decrease, or even lose its effect because it cannot meet multiple discrimination conditions.

In order to solve the above problems, 66kV active intervention arc suppression devices have appeared on the market, including primary grounding protection cabinets, secondary control panels, signal generators and handheld signal receiving devices. The primary grounding protection cabinets include single-phase circuit breakers, low impedance Transformer, zero-sequence current transformer; the secondary control panel includes a single-phase grounding phase selection control unit, a grounding line selection unit and a drive locking module; however, at present, this device still cannot guarantee the accuracy of fault phase selection, and the application effect is not good.

Contents of the invention

The present invention is to solve the above-mentioned problems existing in the prior art. Without changing the advantages of the neutral point non-effective grounding method, the present invention provides a grounding phase selection and line selection using a 66kV active intervention arc suppression device based on a low excitation impedance transformer. This method can accurately and quickly determine the fault line, thereby improving the safety, reliability and economy of the 66kV system power supply.

The technical solution of the present invention is: a method for fault line selection using a 66kV active intervention arc suppression device. Its special features are:

S1 samples data and performs zero-sequence incremental startup

Real-time collection of substation bus phase, line voltage, and zero-sequence voltage, and vector calculation of the zero-sequence voltage. When the change value exceeds the set limit, the grounding phase judgment is started;

S2 line and phase voltage calculation and analysis

Assume that phase A at point K is grounded through a transition resistor R _g . The positive sequence, negative sequence and zero sequence networks of phase A at point K are connected in series and then short-circuited to form a composite sequence network. The zero sequence voltage on bus M and the zero sequence voltage of fault point K/> Equal, that is, the zero-sequence voltage in the power grid is equal everywhere, regardless of the location of the fault point; from the composite sequence network, the /> on the bus M can be obtained for

Rewrite the above formula as

In the formula, θ—angle, θ=arctg(3ωR _g C _0∑ ), when R _g =0～∞ changes, θ=0°～90°, 2θ=0°～180°;

It can be seen from formula (2) The endpoint trajectory is /> The endpoint is the center of the circle, with/> As a clockwise half arc with a radius, establish a relationship diagram between the zero-sequence voltage and the transition resistance Rs vector when phase A is grounded through R _g . It can be seen in the figure: that is, when R _g =0~∞ changes,/> The endpoint changes along the semicircle in the figure in the direction of the arrow; when R _g =0, that is, metallic grounding, then So the three-phase voltages are

It can be seen that when a single phase is grounded, there is a high zero-sequence voltage in the power grid, and a zero-sequence voltage close to 100V can be detected on the open triangle side of the voltage transformer; at the same time, the non-faulty phase voltage increases times;

Respectively with the power supply electromotive force/> are equal, when the neutral point displacement is expressed by the electromotive force When expressed, the grid phase voltage/> Expressed as

It can be seen from the phase voltage phasor relationship diagram of the power grid that the three-phase voltage is in an asymmetric state, and the line voltage/> Still in a symmetrical state;

S3 uses zero-sequence voltage mode angle comparison for steady-state grounding phase selection

S3.1 Zero-sequence voltage angle comparison: Use the zero-sequence voltage phase angle comparison to predict the grounding phase. If the U0 phase is between 180° and 270°, phase A is grounded; if the U0 phase is between 60° and 150°, it is B. The phase is grounded; when the U0 phase is between 30° and 60°, phase C is grounded;

S3.2 Zero sequence voltage mode angle comparison:

It is the phase voltage before the grounding phase is grounded, and then the zero-sequence voltage amplitude and phase relationship is fitted to the semi-circular arc trajectory of the grounding phase zero-sequence voltage to determine the grounding phase and control the closing of the single-phase circuit breaker of the corresponding phase to realize single-phase circuit breaker closing. Phase ground protection function;

S4 slope calculation and comparison

When the mode angle comparison conditions are not met, the intermittent grounding phase is selected based on the slope change. From the wave recording chart, it can be seen that the faulty phase has a steep slope change, and the single-phase circuit breaker of the corresponding phase is controlled to close;

S5 single-phase grounding line selection based on fast switching arc suppression and harmonic suppression device

Analysis of grounding capacitor current distribution characteristics when S5.1 is unprotected grounding

When a single-phase grounding occurs in the system, the grounding current of the non-fault circuit is recorded as I _fo ', which is its own ground capacitance current I _oZ ', and the direction flows from the bus to the line, then there is the relationship: I _fo '=I _oZ '; fault The grounding current of the loop is recorded as I _go ', which is its own ground capacitance current I _oz '. The direction flows from the busbar to the line. There is also a whole network grounding capacitance current I _J ', which flows from the fault phase to the busbar, then I _go ' =I _oz '-I _J 'relationship;

S 5.2 Grounding capacitor current distribution and characteristic analysis during protective grounding

When the protection is grounded: the grounding current of the non-fault circuit is recorded as I _fo ”, which is still its own capacitance current to the ground. Since it becomes a steady-state metallic grounding, the amplitude changes accordingly, which is recorded as I _oz ”, and the grounding degree is recorded as U ₀ ”, then there is the relationship I _fo ”=I _oZ ”; the ground current of the fault circuit is recorded as I _go ”. Since the return current on the fault phase tends to 0, only its own capacitance current to the ground is left, which is recorded as I _oz ”, then I _go ”=I” _oz ;

S5.3 Zero-sequence current characteristic equation line selection

From the above analysis results, it can be seen that when the system is grounded and protected, the grounding current of the non-fault circuit is its own capacitance current to the ground. The size of the grounding current has nothing to do with the grounding position, but is only related to the degree of grounding. Relationship, derive the zero-sequence current characteristic equation:

Among them, UO’ and IO’ are the zero-sequence voltage and zero-sequence current of the line when grounding, UO” and IO” are the zero-sequence voltage and zero-sequence current of the line when grounding is transferred;

A grounding line selection unit is used to record waves before and after the split-phase circuit breaker operates. According to the changes in the zero-sequence current of each line before and after the split-phase circuit breaker is closed, the zero-sequence current characteristic equation is used to determine the ground fault line.

Furthermore, the grounding phase selection control unit includes a display communication module, an acquisition calculation module and a drive locking module. The acquisition calculation module uses the TMS320F2812DSP signal processor as the operation CPU, and the 14-bit A/D analog-to-digital conversion chip AD7865 performs analog-to-digital conversion. , complete the signal collection of zero sequence voltage and system phase-to-line voltage, analyze and calculate through DSP signal processor, realize the judgment of single-phase ground fault and identify the ground phase, and open the corresponding relay to control the action of single-phase circuit breaker, calculate the data and The action waveform is uploaded to the display communication module through the dual-port RAM7024.

Furthermore, the sampling speed of the DSP signal processor is 320-640 times/cycle, and the zero-sequence current of each circuit and the zero-sequence voltage of the system are synchronously sampled before and after the operation of the split-phase circuit breaker to ensure the synchronization of each signal.

Further, the drive locking module includes a MOSFET tube, a quick phase selection relay DZK-1, mutually locked relay contacts J2 and J3, and an A-phase relay, a quick phase selection relay DZK-2, and mutually locked relay contacts J3 and J1. and B-phase relay, fast phase selection relay DZK-3, mutually locked relay contacts J1 and J2 and C-phase relay. Only one phase selection relay is closed at any time, ensuring that only one channel is open at any time; single-phase circuit breaker nodes are mutually locked , one phase is closed, and the closing circuit of other single-phase circuit breakers is disconnected, ensuring that no two-phase closing occurs at any time.

This invention uses steady-state grounding technology to solve the problem of intermittent grounding overvoltage without protection; uses zero-sequence voltage and line voltage mode angle comparison technology to solve the grounding phase selection problem; uses the zero-sequence current characteristic equation method to solve the problem of grounding line selection accuracy, without Affected by factors such as system operation mode, line properties, geographical conditions, grounding degree, fault indicator measurement accuracy, installation interval distance and CT error, in order to develop a comprehensive single-phase grounding protection device for the distribution network, accurate line selection can be achieved to avoid intermittent It eliminates the hazards of system overvoltage caused by sexual grounding and phase-to-phase short circuit fault caused by single-phase grounding. At the same time, automatic identification of ground faults is realized, which facilitates maintenance personnel to quickly locate the ground fault point. It is important to ensure the safe production of power enterprises, reliable power supply and the life safety of the public. significance.

Description of drawings

Figure 1 is a phase A ground circuit diagram of the present invention;

Figure 2 is a schematic diagram of the zero sequence network when point K in the power grid is grounded;

Figure 3 is a schematic diagram of the composite sequence network when point K and phase A are grounded;

Figure 4 is a schematic diagram of the zero sequence voltage change when phase A is grounded through R _g ;

Figure 5 is a schematic diagram of the neutral point displacement when phase A is grounded through R _g ;

Figure 6 is the circuit schematic diagram of the 66kV active intervention arc suppression device;

Figure 7 is a circuit block diagram of the sampling calculation unit;

Figure 8 is the schematic diagram of the drive locking module circuit;

Figure 9 is a control flow chart of the present invention;

Figure 10 is a schematic diagram of intermittent grounding wave recording;

Figure 11 is a circuit block diagram of the grounding line selection unit.

Detailed ways

As shown in Figures 6, 7, 8 and 11, the fast switching arc suppression and harmonic elimination device involved in the present invention includes a primary grounding protection cabinet, a secondary control panel, a signal generator 4 and a handheld signal receiving device 7. The primary grounding protection cabinet includes a single-phase circuit breaker 2, a low-impedance transformer 3, and a zero-sequence current transformer 5; the secondary control panel 1 includes a single-phase grounding phase selection control unit, a grounding line selection unit and a drive locking module, which adopts high-speed Signal processor DSP, multi-channel synchronous sampling, its sampling speed can reach 640 times/cycle, and it can synchronously sample the zero-sequence current of each circuit and the zero-sequence voltage of the system before and after the operation of the split-phase circuit breaker to ensure the synchronization of each signal. Taking advantage of the unique characteristic of the automatic phase-divided grounding protection device that the zero-sequence current of the fault circuit will change before and after the action, we have innovated a characteristic equation method for line selection, which can accurately select the fault ground circuit.

The secondary control panel 1 is composed of a single-phase grounding phase selection control unit, a grounding line selection unit, and a drive locking module. It is the core part of the fast switching arc suppression and harmonic elimination device, and realizes grounding phase selection, line selection, and fault phase selection. Impedance measurement and other functions.

One end of the single-phase circuit breaker 2 (K1, K2, K3) is connected to the substation busbar, and the other end is connected to the ground grid 6 through the low impedance transformer 3. The system is in the open state during normal operation and is in the closed state during ground fault protection. The fault phase and the earth are forced to be at the same potential, and electrical and programmatic locking is achieved between each other by driving the locking module. Only one phase circuit breaker is allowed under any circumstances. Close.

Low impedance transformer 3 is composed of three coils, of which W1 is a primary coil, one end of the primary coil is connected to the split-phase circuit breaker, and the other end is connected to the ground grid 6; W2 is the secondary secondary coil of the reactive transformer, which is connected to the single-phase ground protection The control unit is connected for signal measurement; W3 is the main secondary coil of the reactance transformer, which is connected to the signal generator 4 as a high-frequency signal power supply for coupling high-frequency signals. The signal generator 4 injects a special frequency signal into the system according to the instructions of the single-phase grounding control unit for fault location and automatic fault recovery. This device is a specially designed device that can work with dual-frequency power. At power frequency, it is a reactor with an impedance of less than 1 ohm. It is mainly used for arc extinguishing and overvoltage protection. At high frequency, it is a transformer, mainly used to ensure that When the device effectively protects the faulty phase, it injects high-frequency voltage into the faulty phase.

The zero sequence current transformer 5 is installed on the connection line between the device and the grounding grid, and is used to measure the ground current flowing through the device.

The grounding grid 6 determines the effect of grounding protection. The device is required to be well connected to the grounding grid and reduce the grounding impedance as much as possible.

The handheld signal receiving device 7 can detect the special frequency signal injected into the system from the signal generator 4 through the low impedance transformer 3, and is used by the operator to inspect the line and locate the fault.

The grounding phase selection control unit adopts a 4u chassis and consists of three modules: display communication module, acquisition calculation module, and drive locking module. Each module exchanges data through dual-port RAM and adopts the rear plug-in board method to enhance the anti-interference performance.

The sampling calculation module uses the TMS320F2812DSP signal processor as the operation CPU, and the 14-bit A/D analog-to-digital conversion chip AD7865 performs analog-to-digital conversion to complete the signal acquisition of zero-sequence voltage and system phase-line voltage, and analyzes and calculates through the DSP signal processor to achieve Judgment of single-phase ground fault and identify the grounded phase, and open the corresponding relay to control the action of the single-phase circuit breaker. The calculation data and action waveform are uploaded to the display communication module through the dual-port RAM7024.

Main Specifications:

There are 8 sampling channels: zero sequence voltage, zero sequence current, three phase voltages Ua, Ub and Uc, and three line voltages Uab, Ubc and Uca;

Sampling frequency: 320 times per week;

Signal measurement range: voltage 0~100VAC, current 0~6A;

The drive blocking module completes the driving of the single-phase circuit breaker and blocks the drive circuit to avoid simultaneous closing of two phases at any time.

Since the single-phase circuit breaker selected for this device is a vacuum permanent magnet mechanism with an operating current of about 25A and an operating speed of only 40ms, a lower-power voltage-driven electronic switching device MOSFET is used to form the drive circuit. In order to ensure the accuracy of the action and avoid malfunction, the entire drive part implements triple lockout: 1) Only one MOSFET is designed on the drive lockout module to avoid driving output at the same time; 2) In the downstream stage of the drive circuit, a fast phase selection relay is used. And the relay contacts are locked with each other, and only one phase selection relay is closed at any time, ensuring that only one is open at any time; 3) The single-phase circuit breaker nodes are locked with each other, one phase is closed, and the other single-phase circuit breaker closing circuits are disconnected, ensuring that any There is no two-phase closing at any time. In Figure 8, DZK-1, DZK-2, and DZK-3 are phase selection relays for phases A, B, and C respectively, and J1, J2, and J3 are single-phase circuit breaker position relays.

work process:

The secondary control panel 1 collects the substation bus phase, line voltage, and zero-sequence voltage in real time, and determines whether there is a single-phase ground fault and grounding phase difference in the system based on the mode angle changes of the zero-sequence voltage and the line voltage. When a single-phase ground fault occurs At this time, the single-phase circuit breakers 2 (K1, K2, K3) of the corresponding phases are controlled to close quickly. After the circuit breakers of the corresponding phases are closed, the fault phases are forced to be at equal potential to the ground, thereby extinguishing the grounding arc and at the same time inducing electric shock to the human body. Provide effective protection to avoid personal injury accidents. When the nature of the grounding is intermittent grounding, this device can convert the unstable grounding into a stable metal grounding to avoid the generation of intermittent overvoltage.

The grounding line selection unit records waves before and after the split-phase circuit breaker operates. Based on the changes in the zero-sequence current of each line before and after the split-phase circuit breaker closes, the zero-sequence current characteristic equation is used to determine the ground fault line.

After the single-phase circuit breaker 2 is closed, after a set time delay, the signal generator 4 is started, and a special frequency voltage is injected into the system through the main secondary coil W3 of the low-impedance transformer connected to the signal generator 4 to generate a grounding current and grounding. The phase selection control unit collects the voltage and current signals fed back by the secondary secondary coil W2 of the low-impedance transformer, separates the special frequency signal injected into it, and calculates the change in the system grounding impedance. If the grounding impedance returns to the normal state of the system, it is judged that the grounding fault has disappeared and the grounding The phase selection control unit controls the opening of single-phase circuit breakers 2 (K1, K2, K3) to achieve automatic reset of single-phase ground faults. If the ground fault fails to recover for a long time, the operator holds the handheld signal receiving device to patrol along the fault circuit selected by the grounding line selection unit to find the fault point. When the handheld signal receiving device shows that the received signal changes from strong to weak, it is a fault. point to complete the single-phase ground fault location.

The grounding phase selection control unit collects zero sequence voltage, three-phase voltages of buses A, B, and C, three line voltages UAB, UBC, UCA, and zero-sequence current, and uses zero-sequence voltage angle comparison technology to complete the judgment of single-phase grounding faults and Identify the ground fault phase and control the closing of the single-phase circuit breaker of the corresponding phase to realize the single-phase grounding protection function.

The control flow of the present invention is shown in Figure 9, specifically as follows:

1) S1 samples data and performs zero-sequence incremental startup

The bus phases, line voltages, and zero-sequence voltages of the substation are collected in real time. In order to ensure the sensitivity of grounding phase selection and startup speed, the zero-sequence voltage incremental startup method is used to perform vector calculations on the zero-sequence voltage. When the change value exceeds the set limit value, start-up grounding phase judgment, improve start-up sensitivity, and avoid the possibility of malfunction caused by zero-sequence voltage due to system imbalance.

The hardware selection of the grounding line selection unit adopts the same model as the grounding phase selection control unit. The display communication module is constructed with a PC104 structure 486 host, and the sampling module is composed of a TMS320F2812DSP signal processor and an AD7865 analog-to-digital conversion chip. Multiple sampling modules use the same starting signal method, and the signal from the grounded phase selection control unit is used as the starting signal to ensure that each sampling module records waves simultaneously.

2. Calculation and analysis of line and phase voltages during steady grounding

Assume that phase A at point K in the middle line of Figure 1 is grounded through the transition resistor R _g . The positive sequence, negative sequence, and zero sequence networks of phase A at point K are connected in series and short-circuited to form a composite sequence network. Because the neutral point of the power grid is not grounded and the grounding current is not large, the positive sequence, negative sequence and zero sequence impedances of the transformer T and lines L1, L2... in Figure 2 can be ignored, so Z _∑1 at point K = 0 , Z _∑2 = 0, the zero-sequence network is shown in Figure 2, and the composite sequence network is shown in Figure 3.

As can be seen from Figure 3, the zero sequence voltage on bus M and the zero sequence voltage of fault point K/> Equal, that is, the zero-sequence voltage in the power grid is equal everywhere, regardless of the location of the fault point. From the composite sequence network, we can get the /> on the bus M for

Rewrite the above formula as

In the formula, θ—angle, θ=arctg(3ωR _g C _0∑ ), when R _g =0 to ∞ changes, θ=0°～90°, 2θ=0°～180°.

It can be seen from formula (2) The endpoint trajectory is /> The endpoint is the center of the circle, with/> is a clockwise half arc of radius, as shown in Figure 4. That is, when R _g =0～∞ changes,/> The endpoints change along the semicircle in the figure in the direction of the arrow. When R _g =0 (metallic grounding),

have So the three-phase voltages are

It can be seen that when a single phase is grounded, there is a high zero-sequence voltage in the power grid, and a zero-sequence voltage close to 100V can be detected on the open triangle side of the voltage transformer; at the same time, the non-faulty phase voltage increases times.

Respectively with the power supply electromotive force/> are equal, when the neutral point displacement is expressed by the electromotive force When expressed, the grid phase voltage/> Expressed as

The phasor relationship is made as shown in Figure 5. It can be seen that the three-phase voltage is in an asymmetric state, and the line voltage/> Still in a symmetrical state.

Steady-state grounding phase selection based on S3 zero-sequence voltage mode angle comparison

S3. When a single-phase grounding occurs, the grounded phase voltage decreases and the non-faulty phase voltage increases. As can be seen from Figure 5, when 2θ is larger, that is, when grounded through a larger transition resistance, the grounded phase voltage is not the lowest. It has also been proposed that the phase selection method is based on the positive phase sequence and the next phase with the highest voltage to ground is the ground phase. In extreme cases, such as when the metal is grounded, the two phase voltages are the same, and the distribution network is affected by other non-unitary voltages. The influence of phase grounding factors will also cause changes in zero sequence voltage and phase voltage, and there will be problems with selecting the wrong grounding phase.

By analyzing the change characteristics of the zero-sequence voltage during steady-state grounding, the zero-sequence voltage The endpoint trajectory is based on

The endpoint is the center of the circle, with/> is the clockwise half arc of radius. /> is the voltage before the ground phase is grounded. Determine the phase selection method for zero sequence voltage mode angle comparison.

1) Zero-sequence voltage angle comparison: Use zero-sequence voltage phase angle comparison to predict grounding phase differences

When the U0 phase is between 180 and 270, phase A is grounded; when the U0 phase is between 60 and 150, phase B is grounded; when the U0 phase is between 30 and 60, phase C is grounded.

S3.2) Zero-sequence voltage mode comparison: determine the grounding phase

is the ground phase voltage before grounding. Then, the grounding phase is determined by fitting the zero-sequence voltage amplitude and phase relationship with the semi-circular arc trajectory of the grounding phase zero-sequence voltage.

It has been proved through application that the accuracy of grounding phase selection is 100%. In the actual measurement, the zero sequence voltage change is 0.3v, and the grounding phase can be accurately selected.

S4 slope calculation and comparison

As can be seen from Figure 10, interstitial grounding is generally caused by insulation breakdown. When the voltage is low, the insulation does not break down and everything in the system is normal. When the voltage rises to a certain value, the insulation breaks down and the grounding phase voltage will be 0, a zero-sequence voltage appears. The zero-sequence change does not conform to the law of touch angle change, but the phase voltage changes suddenly, so a phase selection method for slope change is designed. When the mode angle comparison conditions are not met, the intermittent grounding phase is selected based on the slope change. From the wave recording chart, it can be seen that the faulty phase has a steep slope change, and the single-phase circuit breaker of the corresponding phase is controlled to close;

S5 single-phase grounding line selection based on fast switching arc suppression and harmonic suppression device

Analysis of grounding capacitor current distribution characteristics when S5.1 is unprotected grounding

When a single-phase grounding occurs in the system, it can be known from the grounding capacitor current distribution:

1) The grounding current of the non-fault circuit is recorded as I _fo ', which is its own ground capacitance current I _oZ ', and the direction flows from the bus to the line, then there is the relationship: I _fo '=I _oZ '.

2) The grounding current of the fault circuit is recorded as I _go ', which is its own ground capacitance current I _oz ', flowing from the bus to the line, and there is also a whole network grounding capacitance current I _J ', flowing from the fault phase to the bus, then there is The relationship between I _go '=I _oz '-I _J '.

S5.2 Grounding capacitor current distribution and characteristic analysis during protective grounding

When the protection is grounded:

1) The grounding current of the non-fault circuit is recorded as I _fo ”, which is still its capacitance current to the ground. Since it becomes a steady-state metallic grounding, the amplitude changes accordingly and is recorded as I _oz ”, and the grounding degree is recorded as U ₀ ”. Then there is the relationship I _fo ″=I _oZ ″.

2) The grounding current of the fault circuit is recorded as I _go ”. Since the return current on the fault phase tends to 0, only the capacitance current to the ground is left, which is recorded as I _oz ”, then I _go ”=I” _oz

S5.3 Zero-sequence current characteristic equation line selection

It is not difficult to see from the above analysis results that when the system is grounded and protected, the grounding current of the non-fault circuit is its own capacitance current to ground. The size of the grounding current has nothing to do with the grounding position, but is only related to the degree of grounding. The zero sequence current characteristics are derived. equation:

The established function expression is as follows:

(U0"/U0'×I0'-I0")→0 non-faulty line;

Among them, UO’ and IO’ are the zero-sequence voltage and zero-sequence current of the line when grounding, UO” and IO” are the zero-sequence voltage and zero-sequence current of the line when grounding is transferred;

This line selection method is not affected by factors such as system operation mode, grounding degree and CT error. It provides a major theoretical basis for the development of comprehensive single-phase grounding protection devices for distribution networks and accurate line selection.

Using high-speed signal processor DSP, multi-channel synchronous sampling, the sampling speed reaches 640 times/cycle, and the zero-sequence current of each circuit and the zero-sequence voltage of the system are synchronously sampled before and after the operation of the split-phase circuit breaker to ensure the synchronization of each signal. Taking advantage of the unique characteristic of the automatic phase-divided grounding protection device that the zero-sequence current of the fault circuit will change before and after the action, we have innovated a characteristic equation method for line selection, which can accurately select the fault ground circuit.

In the effective protection state, the zero-sequence voltage is the maximum value of the system. If the fault disappears at this time, the system cannot judge based on the changes in the zero-sequence voltage. At the same time, because the protection effect of the split-phase protection device is obvious, there is no obvious trace at the fault point. It is difficult for inspection personnel to determine the fault point. However, the current single-phase ground fault location technology is generally implemented in a power outage or without effective protection, and the fault location under single-phase ground protection is in a blank state.

The software function design of the grounding line selection unit adopts a mode in which the sampling calculation module is responsible for synchronous real-time sampling, and the display communication module is responsible for line selection calculation. The grounding line selection algorithm adopts the line selection method of the zero-sequence current transfer characteristic equation based on the action characteristics of the fast-switching arc-extinguishing and harmonic elimination device. That is, when a grounding fault occurs, the direction of the grounding loop zero-sequence current is from the line to the busbar, and the zero-sequence current The value is the sum of the zero-sequence currents of the system's non-ground loops; after the device operates and the grounding is transferred, the zero-sequence current of the ground loop will change significantly in direction and amplitude.

Since the grounding line selection algorithm compares the zero-sequence current before and after grounding protection, the accuracy of grounding moment judgment is very important. For the judgment of the grounding moment, the device zero-sequence current startup judgment method is used. When the device implements protection, the transfer system grounding current flows through the device. Based on the judgment of the device's zero-sequence CT measurement signal, the grounding transfer moment can be accurately judged. By comparing the changes in the zero-sequence current of each loop before and after the grounding transfer, it is found that the grounding loop has the largest change.

Claims (4)

1. A method for fault line selection by utilizing a 66kV active intervention arc extinction device is characterized by comprising the following steps:

s1, sampling data and performing zero sequence increment starting

The grounding phase selection control unit is utilized to collect bus phases, line voltages and zero sequence voltages of the transformer substation in real time, vector operation is carried out on the zero sequence voltages, and when the variation value exceeds a set limit value, grounding phase judgment is started;

s2 line and phase voltage calculation and analysis

Suppose K point A phase transition resistance R _g Positive sequence, negative sequence and zero sequence network of K point A phase are connected in series and then are short-circuited to form a composite sequence network, and zero sequence voltage on bus MZero sequence voltage to fault point K>Equality, i.e. zero sequence voltage throughout the networkEquality, independent of the location of the fault point; the +.>Is that

The above is rewritten as

In the formula, θ -angle, θ=arctg (3ωr _g C _0∑ ) When R is _g When =0 to infinity, θ=0° to 90 °,2θ=0° to 180 °;

as can be seen from the formula (2),the end point track is +.>The endpoints are the circle centers and +.>For the clockwise half arc of radius, a phase A warp R is established _g The vector relation diagram of the zero sequence voltage and the transition resistance Rs when the ground is grounded can be seen in the figure: i.e. R _g When =0 to infinity, the ratio of +.>The endpoints vary along the semicircle in the figure in the direction of the arrow; when R is _g When=0, i.e. metallic ground, then

The three-phase voltages are then respectively

It can be seen that the power grid has higher zero sequence voltage when the single phase is grounded, and the open triangle side of the voltage transformer can detect the zero sequence voltage close to 100V; at the same time, the non-faulty phase voltage increasesDoubling;

respectively with the electromotive force of the power supply>Equal, neutral point position electromotive forceWhen expressed, then the grid phase voltage +.>Represented as

As can be seen from the phase voltage phasor relationship diagram of the power grid, the three-phase voltageIn an asymmetric state, and line voltage +.>Still in a symmetrical state;

s3, steady-state grounding phase selection by utilizing zero sequence voltage module angle comparison

S3.1 zero sequence voltage angle comparison: the phase angles of the zero sequence voltages are compared and are prejudged to be grounded, and the phase of U0 is 180-270 DEG, namely the phase A is grounded; the phase of U0 is B phase between 60 and 150 degrees; the phase of U0 is C-phase grounding between 30 and 60 degrees;

s3.2 zero sequence voltage modular comparison:

the grounding phase is determined by fitting the zero sequence voltage amplitude and the phase relation with the zero sequence voltage semicircular arc track of the grounding phase, and the corresponding phase single-phase circuit breaker is controlled to be closed, so that the single-phase grounding protection function is realized;

s4 slope calculation and comparison

When the comparison condition of the mode angles is not met, the intermittent grounding is selected according to the slope change, the steep slope change is a fault phase through the wave recording diagram, and the corresponding phase single-phase circuit breaker is controlled to be switched on;

s5 single-phase grounding route selection based on rapid switching type arc extinction and resonance elimination device

S5.1 capacitor current distribution characteristic analysis at non-protection grounding

When the system is in single-phase grounding, the grounding current of the non-fault loop is recorded as I _fo ' is self capacitance current I to ground _oZ ' the direction from the bus to the line is: i _fo ’＝I _oZ ' relationship; the ground current of the fault loop is denoted as I _go ' is self capacitance current I to ground _oz ' the direction flows from the bus to the line, there is a whole network grounding capacitance current I _J ' if the direction from the fault phase to the bus is I _go ’＝I _oz ’-I _J ' relationship;

s5.2 capacitor current distribution and characteristic analysis at grounding protection

When the protection is grounded: the ground current of the non-faulty loop is denoted as I _fo The current is still self capacitance current to ground, and the amplitude value is correspondingly changed due to the change of the current to steady-state metallic ground, and is recorded as I _oz ” _， The grounding degree is recorded as U ₀ ", there is I _fo ”＝I _oZ "relationship; the ground current of the fault loop is denoted as I _go As the regression current on the fault phase tends to be 0, only the self capacitance to ground current remains and is recorded as I _oz ", there is I _go ”＝I” _oz；

S5.3 zero sequence current characteristic equation route selection

As shown by the analysis results, when the system is grounded and the protection is grounded, the grounding current of the non-fault loop is self-grounding capacitance current, the magnitude of the grounding current is irrelevant to the grounding position and is only relevant to the grounding degree, and the system has the following characteristics thatAnd (3) relation, deriving a zero sequence current characteristic equation: />A non-faulty line;

wherein UO 'and IO' are zero sequence voltage and zero sequence current of the circuit when grounded, and UO 'and IO' are zero sequence voltage and zero sequence current of the circuit when grounded and transferred;

the grounding line selection unit is adopted to record waves before and after the split-phase breaker acts, and the grounding fault line is determined by adopting the zero sequence current characteristic equation according to the change of the zero sequence current of each line before and after the split-phase breaker closes.

2. The method for fault line selection by using 66kV active intervention arc suppression device according to claim 1, wherein the method comprises the following steps: the grounding phase selection control unit comprises a display communication module, an acquisition calculation module and a driving locking module, wherein the acquisition calculation module adopts a TMS320F2812DSP signal processor as an operation CPU, a 14-bit A/D analog-to-digital conversion chip AD7865 carries out analog-to-digital conversion to complete signal acquisition of zero sequence voltage and system phase line voltage, the DSP signal processor carries out analysis and calculation to realize judgment of single-phase grounding faults and identify grounding phases, a corresponding relay is opened to control the action of the single-phase circuit breaker, and calculation data and action waveforms are uploaded to the display communication module through a double-port RAM 7024.

3. The method for fault line selection by using 66kV active intervention arc suppression device according to claim 1, wherein the method comprises the following steps: the sampling speed of the DSP signal processor is 320-640 times/cycle, and the zero sequence current and the system zero sequence voltage of each loop before and after the action of the phase-splitting circuit breaker are synchronously sampled, so that the synchronism of each signal is ensured.

4. The method for fault line selection by using 66kV active intervention arc suppression device according to claim 2, wherein the method is characterized in that: the driving locking module comprises a MOSFET tube, a quick-selection relay DZK-1, mutually locked relay contacts J2 and J3 and an A relay, a quick-selection relay DZK-2, mutually locked relay contacts J3 and J1 and B relay, a quick-selection relay DZK-3, mutually locked relay contacts J1 and J2 and C relay, and only one path of selection relay is closed at any moment, so that only one path of relay is opened at any moment; the single-phase circuit breaker nodes are mutually locked, one phase is switched on, other single-phase circuit breaker switching-on loops are disconnected, and two-phase switching-on is guaranteed not to occur at any moment.