CN105356441B - The method and apparatus of intelligent PT harmonic eliminations phase selection - Google Patents

Abstract

A method and device for intelligent PT harmonic elimination and phase selection, using three-phase five-column voltage transformer PT to collect voltage data in the power grid, when zero-sequence voltage occurs, the voltage sampling module samples the three-phase bus voltage and zero-sequence voltage ;The current sampling module samples the zero-sequence current of each feeder, and all the sampled values are input to the single-chip microcomputer. The duration of ground fault is classified as transient fault or permanent fault. For transient single-phase ground fault, the protection only acts on alarm to ensure the reliability of power supply; for permanent single-phase ground fault, the protection also acts on trip in addition to alarm Ensure power supply security.

Description

Method and device for intelligent PT harmonic elimination and phase selection

technical field

The invention relates to the field of power grid safety, especially a method and device for phase selection of harmonic elimination, in particular to a method and device for intelligently identifying and protecting single-phase grounding faults by eliminating resonance in a neutral point non-effectively grounded power grid.

Background technique

In the neutral point non-effectively grounded power grid, resonance and single-phase grounding are the main fault forms in the operation of the power grid, which affect the safe operation of the power grid.

There are many energy storage components in the power system. When the system is in operation or fails, the series connection of nonlinear inductive components containing iron core components such as transformers and transformers with the capacitance in the system may cause ferromagnetic resonance, which poses a threat to the safe operation of the power system. harm. In the indirect grounding system where the neutral point is not grounded, the ferromagnetic resonance overvoltage caused by the ferromagnetic voltage transformer is common, and it is an internal overvoltage that causes more accidents. This kind of overvoltage may cause the primary fuse of the voltage transformer to blow, or burn the voltage transformer, or even blow up the porcelain insulator and lightning arrester, causing the system to stop operating. Under the action of a certain power supply, a series resonance phenomenon will occur, resulting in serious resonance overvoltage in the system.

With the continuous expansion of the grid scale and the cableization of urban power grids, the single-phase ground fault current of the system has increased sharply. The neutral point ungrounded method has long been unable to meet the requirements of arc extinguishing and limiting arc overvoltage, and the capacity of arc suppression coils is also required to be larger and larger. In some heavy-duty substations, a single large-capacity arc suppression coil compensation device can no longer meet the requirements. , it is necessary to install two or more automatic tracking compensation arc suppression coils on the same bus to meet the compensation requirements. This not only increases the installation cost of the arc suppression coil, but also increases the installation space, which brings many inconveniences. And the role of the arc suppression coil in single-phase ground fault is also limited: 1) The arc suppression coil can reduce the probability of single-phase ground overvoltage occurrence but cannot eliminate the intermittent arc overvoltage; 2) It can reduce the number of arc restrikes, It cannot eradicate the generation of grounding arc; 3) It can only compensate the power frequency component in the grounding capacitance current, but not the harmonic component; 4) It can only compensate the reactive component (capacitance current) in the grounding current, and cannot compensate Among them, the active component; 5) It cannot judge and protect the high-resistance grounding fault.

In the distribution network where the neutral point is grounded by resistance, since the neutral point resistance limits the neutral point voltage, no high overvoltage will be generated. At the same time, a large resistive current flows through the grounding line to ensure accurate judgment of the zero-sequence protection and quickly cut off the faulty line. However, the operation mode of resistive grounding also has certain disadvantages: 1) When a single-phase grounding occurs, a large grounding current may generate high contact voltage and step voltage, which poses threats to equipment and people, and damages the surrounding communication lines. 2) The single-phase grounding protection action trips, which increases the number of fault trips and power outage time, and reduces the reliability of power supply; The power supply capacity makes the operation more complicated; 4) It cannot judge and protect the high-resistance ground fault.

Contents of the invention

The purpose of the present invention is to propose an intelligent single-phase grounding protection scheme for the disadvantages of the neutral point grounding mode of the existing medium-voltage power grid. The scheme is classified into transient faults or For permanent faults, for instantaneous single-phase ground faults, the protection only acts on alarm to ensure the reliability of power supply; for permanent single-phase ground fault protection, in addition to alarming, it also acts on tripping to ensure power supply safety.

Technical scheme of the present invention is:

An intelligent PT harmonic elimination and phase selection device is characterized in that it includes a three-phase five-column voltage transformer PT, a microcomputer measurement and control device WJCK and a trip box TZX, and the three-phase five-column voltage transformer PT is used to collect The three-phase bus voltage and zero-sequence voltage in the power grid in the power grid, its secondary voltage output terminal is connected to the input terminal of the voltage sampling module of the microcomputer measurement and control device WJCK, and the current sampling signal input terminal of the microcomputer measurement and control device WJCK is connected to the zero sequence of each feeder The secondary terminals of the CT are connected to collect the feeder zero-sequence current signal. The K1...Kn output terminals of the microcomputer measurement and control device WJCK are connected to the trip box TZX, and the output terminals L1...Ln of the trip box TZX are correspondingly connected to each feeder. The microcomputer measurement and control device WJCK controls the trip box TZX acts to cut off the ground fault feeder; the other control output terminal of the microcomputer measurement and control device WJCK is connected to the driving end of the resonance elimination solid state relay XJ, and the resonance elimination circuit is controlled by the resonance elimination solid state relay XJ to realize resonance elimination.

Microcomputer measurement and control device WJCK of the present invention comprises: voltage sampling module, current sampling module, single-chip microcomputer and relay output control module, the signal output end of described voltage sampling module and current sampling module connects the signal input end of single-chip microcomputer after sampling filter module, The control output terminal of the single-chip microcomputer is connected with the input terminal of the relay output control module. The single-chip microcomputer calculates, processes and judges each voltage sampling and current sampling, and controls the single-phase ground fault line selection tripping protection action and eliminates resonance through the relay output.

A method for intelligent PT harmonic elimination and phase selection, which uses an intelligent PT phase selection device, which includes the following steps: using a three-phase five-column voltage transformer PT to collect voltage data in the power grid, and when zero-sequence voltage occurs, the voltage sampling The module samples the three-phase bus voltage and zero-sequence voltage; the current sampling module samples the zero-sequence current of each feeder, and all sampled values are input to the single-chip microcomputer, which calculates and judges the amplitude and phase of each phase voltage and zero-sequence voltage , if in the three-phase voltage: the voltage of two phases rises and the voltage of one phase decreases; or the voltage of one phase rises and the voltage of two phases decreases, and the phase of any one of the reduced phase voltages lags behind the phase of the zero-sequence voltage by 90°, then the sampling time is judged When a single-phase ground fault occurs, the voltage drop phase lagging behind the zero-sequence voltage phase by 90° is the fault phase.

The method of the present invention also includes a determination step of the ground fault line: the single-chip computer calculates the amplitude and phase of the zero-sequence current of each feeder, and compares the phase of the feeder current with the first four ranks in the order of amplitude with the phase of the zero-sequence voltage, and determines that the phase lags the zero-sequence The line whose voltage phase is 90° is the ground fault line.

The method of the present invention also includes a step of protecting the single-phase ground fault after phase selection and line selection: when it is judged that a single-phase ground fault occurs in the power grid, and the time interval between the occurrence of the last single-phase ground fault is greater than or equal to the set value, query the current fault Whether it is in the same phase and line as the last fault;

If there is any difference between the current fault and the last fault phase and fault line, it is determined that the last fault is an instantaneous ground fault, and the alarm for the phase selection and line selection of the last fault is maintained, and this fault is a new ground fault, and the record Fault time, phase, line and alarm;

If the current fault is in the same phase and line as the previous fault, it is determined that the fault is a permanent ground fault, an alarm is issued and the selected ground line is tripped to cut off the faulty line.

Beneficial effects of the present invention:

The present invention adopts different protection strategies for different properties (instantaneous or permanent) of single-phase grounding faults, which is not only beneficial to power supply reliability, but also beneficial to power supply security. It makes up for the disadvantages of the neutral point grounding mode of the existing medium-voltage power grid.

The invention combines a conventional three-phase five-column voltage transformer with a microcomputer measurement and control device and a trip box, has strong practicability, simple and reliable measurement and control, can provide intelligent single-phase grounding protection and can reliably eliminate ferromagnetic resonance.

The invention classifies faults as transient or permanent according to the duration of the fault occurrence, and only selects a line for an alarm for a transient fault, and performs a line selection trip to cut off a faulty line in addition to an alarm for a permanent fault.

Description of drawings

Fig. 1 is a flow chart of the discrimination and protection method of the present invention.

Fig. 2 is a schematic diagram of the electrical structure of the device of the present invention.

Fig. 3 is a functional block diagram of the microcomputer measurement and control device of the present invention.

In the figure: QS: isolation trolley (or isolation switch); FU: high voltage fuse; PT: voltage transformer;

XJ: harmonic elimination solid state relay; WJCK: microcomputer measurement and control device; TZX: trip box;

Io1...Ion: feeder zero-sequence current input terminal; K1...Kn: output terminal of microcomputer measurement and control device;

L1...Ln: trip box outlet

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

An intelligent PT harmonic elimination and phase selection device is characterized in that it includes a three-phase five-column voltage transformer PT, a microcomputer measurement and control device WJCK and a trip box TZX, and the three-phase five-column voltage transformer PT is used to collect The three-phase bus voltage and zero-sequence voltage in the power grid in the power grid, its secondary voltage output terminal is connected to the input terminal of the voltage sampling module of the microcomputer measurement and control device WJCK, and the current sampling signal input terminal of the microcomputer measurement and control device WJCK is connected to the zero sequence of each feeder The secondary terminals of the CT are connected to collect the feeder zero-sequence current signal. The K1...Kn output terminals of the microcomputer measurement and control device WJCK are connected to the trip box TZX, and the output terminals L1...Ln of the trip box TZX are correspondingly connected to each feeder. The microcomputer measurement and control device WJCK controls the trip box TZX acts to cut off the ground fault feeder; the other control output terminal of the microcomputer measurement and control device WJCK is connected to the driving end of the resonance elimination solid state relay XJ, and the resonance elimination circuit is controlled by the resonance elimination solid state relay XJ to realize resonance elimination.

The electrical structure principle of the comprehensive protection system of the present invention is shown in FIG. 2 , and the microcomputer measurement and control system is shown in FIG. 3 . The microcomputer measurement and control device detects the three-phase voltage and zero-sequence voltage of the voltage transformer, as well as the zero-sequence current of the feeder connected to the bus in this section. Once it is judged that a single-phase-to-ground fault occurs in the system, firstly select the faulty phase and faulty line, and then judge whether it is the same faulty phase and the same faulty line as the last single-phase-to-ground fault record, if one of the conditions is not met, it is a For a new fault, record the fault phase, fault line and fault occurrence time of the fault, and return the alarm; if both are satisfied, it is the same fault, calculate the fault duration, and return the alarm if the fault duration is less than the set time; If it is longer than the set time, it will be judged as a permanent ground fault, and the microcomputer measurement and control device will drive the trip box to act and cut off the ground fault line.

The microcomputer measurement and control device can accurately judge whether the resonance occurs in the system by detecting the three-phase voltage and zero-sequence voltage of the voltage transformer. Once it is judged that resonance occurs, the solid-state relay connected to the open triangle of the voltage transformer is immediately driven and closed instantaneously to consume resonance energy. achieve harmonic elimination.

Specific examples are as follows:

example 1.

When a feeder instantaneous single-phase ground fault occurs on the busbar where the device is located, the microcomputer measurement and control device immediately selects the single-phase ground fault phase and fault line from the changes of three-phase voltage, zero-sequence voltage and feeder current, and checks whether there is a continuous fault If there is no record, it is a new fault. The program records the fault phase, fault line and fault occurrence time, gives an alarm and returns to re-judgment; after returning to re-judgment several times, the fault disappears, and its duration is shorter than the permanent fault If the value is set, the device will determine that the fault is an instantaneous ground fault, and the protection will only be used as an alarm for phase selection and line selection.

Example 2.

When a feeder permanent single-phase ground fault occurs on the busbar where the device is located, the microcomputer measurement and control device immediately selects the single-phase ground fault phase and fault line from the changes of three-phase voltage, zero-sequence voltage and feeder current, and checks whether there is a continuous fault. If there is no fault record, it is a new fault. The program records the fault phase, fault line and fault occurrence time, gives an alarm and returns to re-judgment; after returning to re-judgment several times, the fault still exists, and its duration is longer than permanent If the fault setting value is set, the device determines that the fault is a permanent ground fault. The protection not only performs phase selection and line selection alarm, but also drives the trip box corresponding to the output terminal of the selected fault line to cut off the ground fault line.

Example 3.

Due to voltage disturbances such as single-phase grounding faults on the busbar where the device is located, the ferromagnetic resonance of the voltage transformer is excited. The microcomputer measurement and control device immediately judges the occurrence of resonance from the changes in the three-phase voltage, zero-sequence voltage and frequency, and drives and connects to the opening of the voltage transformer. The solid-state relay of the triangle is closed instantaneously, consuming resonance energy to achieve harmonic elimination.

The parts not involved in the present invention are the same as the prior art or can be realized by adopting the prior art.

Claims (1)

1. A method for intelligent PT harmonic elimination and phase selection is characterized in that it uses a device for intelligent PT phase selection, which includes three-phase five-column voltage transformer PT, microcomputer measurement and control device WJCK and trip box TZX, said The three-phase five-column voltage transformer PT is used to collect the three-phase bus voltage and zero-sequence voltage in the power grid. Its secondary voltage output terminal is connected to the input terminal of the voltage sampling module of the microcomputer measurement and control device WJCK. The microcomputer measurement and control device The current sampling signal input terminal of WJCK is connected with the secondary terminal of the zero-sequence CT of each feeder line to collect the zero-sequence current signal of the feeder line. The K1...Kn output terminal of the microcomputer measurement and control device WJCK is connected to the trip box TZX, and the trip box TZX output terminal L1...Ln Corresponding to the connection of each feeder, the microcomputer measurement and control device WJCK controls the action of the trip box TZX, and cuts off the ground fault feeder; the other control output terminal of the microcomputer measurement and control device WJCK is connected to the driving end of the harmonic elimination solid state relay XJ, and the harmonic elimination is controlled by the harmonic elimination solid state relay XJ The on-off of the loop realizes the elimination of resonance; the microcomputer measurement and control device WJCK includes: a voltage sampling module, a current sampling module, a single-chip microcomputer and a relay output control module, and the signal output terminals of the voltage sampling module and the current sampling module are connected after the sampling filter module The signal input terminal of the single-chip microcomputer, the control output terminal of the single-chip microcomputer are connected with the input terminal of the relay output control module, and the single-chip microcomputer performs calculation, processing and judgment on each voltage sampling and current sampling, and controls the single-phase grounding fault line selection tripping protection action and Eliminate resonance; It includes the following steps: using three-phase five-column voltage transformer PT to collect voltage data in the power grid, when zero-sequence voltage occurs, the voltage sampling module samples the three-phase bus voltage and zero-sequence voltage; the current sampling module samples each feeder The zero-sequence current is sampled, and all sampled values are input to the single-chip microcomputer. The single-chip computer calculates and judges the amplitude and phase of each phase voltage and the zero-sequence voltage. If the three-phase voltage: two-phase voltage increases, one-phase voltage decreases; or One-phase voltage increases and two-phase voltage decreases, and the phase of any one of the decreased phase voltages lags behind the zero-sequence voltage phase by 90°, then it is judged that a single-phase ground fault has occurred at the sampling time, and the voltage decrease phase lagging behind the zero-sequence voltage phase by 90° is fault phase; It also includes the judgment step of the ground fault line: the single-chip computer calculates the amplitude and phase of the zero-sequence current of each feeder, and compares the phase of the feeder current with the first four digits in the order of magnitude with the zero-sequence voltage phase, and determines that the phase lags behind the zero-sequence voltage phase by 90 ° is a ground fault line; It also includes the protection steps for single-phase ground fault after phase selection and line selection: when it is judged that a single-phase ground fault occurs in the power grid, and the time interval between the last single-phase ground fault is greater than or equal to the set value, check whether the current fault is consistent with the previous fault. In-phase and same-line for minor faults; If there is any difference between the current fault and the last fault phase and fault line, it is determined that the last fault is an instantaneous ground fault, and the alarm for the phase selection and line selection of the last fault is maintained, and this fault is a new ground fault, and the record Fault time, phase, line and alarm; If the current fault is in the same phase and line as the previous fault, it is determined that the fault is a permanent ground fault, an alarm is issued and the selected ground line is tripped to cut off the faulty line.