CN100442618C - A relay protection system capable of distinguishing short-circuit and harmonics and its working method - Google Patents

Abstract

A relay protection system capable of distinguishing short-circuit and harmonics is characterized in that it includes a digital signal processing unit, a data acquisition and data conversion module, a switch input/output module, a power supply module, an alarm module and a man-machine exchange module; The working method is data collection, detection and comparison, digital signal output, and relay protection action; its advantages are: ①Use digital signal processing chip to realize the control of relay protection action, which improves the reliability and rapidity of relay protection action ; ② Good adjustment performance and high reliability, reducing the probability of accidents such as production shutdown caused by relay protection malfunction or refusal to operate, thereby enhancing the stability of the power grid; ③ It can effectively prevent short-circuit faults in the system Distinguish from harmonics without affecting the original ability of relay protection to distinguish faults and normal operating states; ④Double signal control is performed on the action actuator of relay protection, the hardware circuit is simple, and the real-time control accuracy is high.

Description

A relay protection system capable of distinguishing short-circuit and harmonics and its working method

(1) Technical field:

The invention belongs to the technical field of electric power system relay protection, in particular to a relay protection system capable of distinguishing short circuit and harmonic and its working method.

(two) background technology:

The main task of power system relay protection is to selectively cut off the fault line in the shortest possible time when the power system fails. A general relay protection device is composed of three parts: a measurement comparison element, a logic judgment element and an execution output element. At present, in order to adapt to the rapid development of the electric power industry, so that the power grid can continuously, safely and reliably provide users with high-quality electric energy, digital relay protection control technology is more and more used in actual operations, thereby improving the relay protection. All aspects of performance of the protective device. At present, almost all relay protection devices, especially measuring relays, set the threshold value based on the analysis of the difference between the two different operating states of each electrical quantity in normal operation and fault operation of the system, without considering The operational characteristics of an abnormal operating state. However, with the development of power electronics technology, especially the application of thyristor technology, the system generates a large number of harmonics during operation, which poses a serious hazard to the power system, especially for relay protection and other automation devices. Normal operation has a large impact. As far as the relay protection itself is concerned, its ability to distinguish between fault conditions and abnormal operating conditions caused by harmonics is poor. It can be seen that how to quickly and effectively distinguish the power system fault operation state from the abnormal operation state, especially the short-circuit fault and harmonic state, so as to realize the correct and reliable operation of the relay protection device becomes very important.

(3) Contents of the invention

The purpose of the present invention is to invent a relay protection system capable of distinguishing short-circuit and harmonics and its working method. It uses the classical sequence current theory of the symmetrical component method, combined with a high-performance processor, and can better overcome the above-mentioned traditional The disadvantage of the control system is a fast, high-precision relay protection system that can effectively distinguish short circuits and harmonics.

The technical solution of the present invention: a relay protection system capable of distinguishing short circuit and harmonic, including a computer, characterized in that the system also includes a digital signal processing unit, a data acquisition and data conversion module, a switch input/output module, and a power supply module , alarm module and man-machine exchange module; the input end of said data acquisition and data conversion module is connected to external voltage transformer and current transformer, and its output end is connected to the input end of digital signal processing unit; said switch value input/ The input terminal of the output module is respectively connected to the output terminal of the digital signal processing unit and the protection unit, and its output terminal is connected to the input terminal of the protection unit; the output terminal of the said power supply module is connected to the input terminal of the digital signal processing unit; The exchange module is bidirectionally connected; the input end of the alarm module is connected to the output end of the digital signal processing unit.

The above-mentioned data acquisition and data conversion module is composed of voltage and current AC sampling front-end circuit, filter, amplification circuit and A/D conversion circuit; the AC sampling front-end circuit converts the current signal collected by the secondary current transformer into Small current, after filtering and amplifying circuit, the small current is transformed into the acceptable voltage range of A/D converter and stored in the digital signal processing unit RAM; the filtering circuit adopts a second-order low-pass active filter.

The above-mentioned voltage and current AC sampling front-end circuit uses D11, D12, D21, D22 to form the input limiter protection, and uses R24, R25, R26, R34, R35, R36, C11, C12, C16, C17 to form the transformer phase shift Compensation and resistance-capacitance filter circuit; said filtering and amplifying circuit are composed of R1, R2, R3, R4, R5, R6 and comparator; said A/D conversion circuit is composed of R6, R7, R8, R9, R10, R11, C3, comparators U3A, U4A and A/D conversion chip.

The above-mentioned digital signal processing unit is composed of a digital signal processing chip, a power management module, a crystal oscillator circuit and a data bus driver circuit; the output terminals of the said data bus driver circuit, power management module, and crystal oscillator circuit are respectively connected to the digital signal processing chip input terminal.

The digital signal processing chip mentioned above is a single-chip microcomputer or DSP chip; the power management module is composed of dual power supply devices and peripheral resistors R15, R16, C1, and C2 capacitors; the crystal oscillator circuit is composed of capacitors C3, C3, and C4 and crystal oscillator body U2; the data bus drive circuit is composed of a two-way data buffer; the output of the power management module and the crystal oscillator circuit is connected with the DSP chip, and the input is connected with the output of the AC sampling circuit.

The man-machine exchange module mentioned above is composed of a communication module, a keyboard and a display module; wherein the output of the keyboard is connected to the input of the digital signal processing unit, and the input of the display module is connected to the output of the digital signal processing unit terminal; said keyboard can be a determinant keyboard working in an interrupt mode, and the display module can be a color liquid crystal display.

A working method of a relay protection system capable of distinguishing short circuit and harmonic, characterized in that it comprises the following steps:

①When the system is put into operation, the current signal collected in real time by the voltage and current AC sampling front-end circuit in the data acquisition and data conversion module is converted into a small current after passing through the current transformer, and the small current is filtered and amplified. Transform it into a voltage range acceptable to the A/D converter and store it in the RAM of the digital signal processing unit, and the signal at this time is a digital signal acceptable to the digital signal processing unit;

② After receiving the digital signal, the computer will start the measurement and comparison step to judge the system operation mode corresponding to the current value collected at this time, the corresponding setting parameter value and equivalent impedance of the relay protection, and compare the collected current signal with the Setting parameter values for comparison;

③When an abnormal change in the current value in the system is detected, the computer will start the logical judgment step of distinguishing short circuit and harmonic state, decompose the current of the system into positive sequence, negative sequence and zero sequence current, and make further comparison and judgment , to distinguish between short circuit and harmonic;

④ Finally, the result of the judgment is notified in the form of a switch whether the executive device of the relay protection is active.

The logical judgment step of distinguishing the short circuit and the harmonic state in the above-mentioned step ③ is composed of the following steps:

(1) Decompose the collected current signal into positive sequence, negative sequence and zero sequence current forms;

(2) Judging whether the current flowing in the system line is greater than the setting value of the relay protection, if "yes", turn to (3), and if "no", turn to (11);

(3) Judging whether the zero-sequence current is zero, if "yes" then turn to (4), "no" then turn to (11);

(4) Judging whether the positive sequence current is zero, if "yes" then turn to (5), "no" then turn to (6);

(5) There are 3n-1 harmonics in the system, judge whether the harmonic current value accounts for more than 30% of the system current, "yes" then turn to (16), "no" then turn to (17);

(6) Judging whether the negative sequence current is zero, if "yes" then turn to (7), "no" then turn to (8);

(7) Judging whether the positive sequence current is equal to the current flowing in the system, if "yes" then turn to (9), "no" then turn to (10);

(8) If a two-phase short-circuit fault occurs in the system, judge the phase where the fault occurs, and trip the corresponding relay protection circuit breaker;

(9) When a three-phase short-circuit fault occurs in the system, judge the phase where the fault occurs, and trip the corresponding circuit breaker for relay protection;

(10) There are 3n+1 harmonics in the system, judge whether the harmonic current value accounts for more than 30% of the system current, "yes" then go to (16), "no" then go to (17);

(11) Judging whether the positive sequence current is equal to the negative sequence current, if "yes" then turn to (12), "no" then turn to (13);

(12) Judging whether the positive-sequence current and the negative-sequence current are equal and both are zero, if "yes" then turn to (14), "no" then turn to (15);

(13) If a two-phase grounding short-circuit fault occurs in the system, determine the phase where the fault occurs, and trip the corresponding circuit breaker for relay protection;

(14) There are 3n harmonics in the system, judge whether the harmonic current value accounts for more than 30% of the system current, "yes" then turn to (16), "no" then turn to (17);

(15) When a single-phase grounding short-circuit fault occurs in the system, judge the phase where the fault occurs, and trip the corresponding circuit breaker for relay protection;

(16) Send a trip signal to the executive device of relay protection, and disconnect the line with large harmonic content;

(17) Still maintain the original state of the relay protection without action;

n in the above-mentioned steps (5), (10) and (14) is a natural number.

The working principle of the present invention: the system mainly uses the control unit to monitor the current in the power system circuit. The signal shaping conversion processing circuit transforms the secondary side current of the current transformer of the transmission line into a lower amplitude AC voltage, and sends it to the central data processing circuit with DSP as the core after processing. Set the counter of the DSP as a time counter for regular sampling, and the data processing subroutine is concentrated in the interrupt service subroutine of the time counter, and its interrupt priority is given as the highest level in the system, which can prevent data processing from being interrupted by other interrupts. In order to ensure the real-time and accuracy of sampling data. In the data processing module, after collecting the discrete voltage and current, the most important step is to accurately calculate the instantaneous parameters of the power grid. During normal operation, the executive device of the relay protection (that is, the circuit breaker) is in the closed state, and the system is in the normal operating state. When the instantaneous sudden change of current is detected, the sudden change at this time may be caused by a fault, or it may be caused by switching of some devices or harmonics caused by normal manual operation. Using the sequence current theory in the classic symmetrical component method, according to the characteristics of the current value and harmonic components in the line, the central data processing circuit judges each sequence current and its relationship with each other according to a certain control law, and gives the circuit breaker control signal , only when there is a short circuit or a high content of harmonics in the system, the relay protection device will act.

The advantages and technical effects of the present invention are: 1. Utilize the high-performance digital signal processing chip to realize the control of the relay protection action, which greatly improves the reliability and rapidity of the relay protection action, and overcomes the PLC technology and single-chip microcomputer technology. Handle the defects of control lag and untimely action caused by speed limitation; ②The entire control system has good adjustment performance and reliability, which reduces the probability of accidents such as production stoppage caused by relay protection malfunction or refusal to operate, In turn, the stability of the power grid is enhanced; ③The sequence current theory of the classical symmetrical component method can effectively distinguish the short-circuit faults and harmonics existing in the system without affecting the original distinction between faults and normal operating states of relay protection ④Double-signal control of the action actuator of relay protection, the hardware circuit is simple, the real-time control precision is high, and it has broad technical application prospects.

(4) Description of drawings:

Fig. 1 is a structural schematic diagram of a relay protection system capable of distinguishing short-circuit and harmonics and its working method according to the present invention;

Fig. 2 is the functional block diagram of a kind of relay protection system and working method thereof that can distinguish short-circuit and harmonic according to the present invention (wherein I0 is zero-sequence current; I1 is positive-sequence current; I2 is negative-sequence current; I is system current flowing in);

Fig. 3 is the data acquisition and data processing circuit in a kind of relay protection system and working method thereof that can distinguish short circuit and harmonic according to the present invention (Fig. 3-a is voltage, current AC sampling circuit; Fig. 3-b is Filtering and amplifying circuits; Figure 3-c is an A/D conversion circuit diagram);

FIG. 4 is a structural schematic diagram of a central data processing circuit in a relay protection system capable of distinguishing short-circuit and harmonics and its working method according to the present invention.

(5) Specific implementation methods:

Embodiment: a kind of relay protection system (see Fig. 1) that can distinguish short-circuit and harmonic, comprises computer, it is characterized in that it comprises digital signal processing unit, data acquisition and data conversion module, digital input/output module, power supply Module, alarm module and man-machine exchange module; the input end of said data acquisition and data conversion module is connected to external voltage transformer and current transformer, and its output end is connected to the input end of digital signal processing unit; said switch value input The input end of the /output module is respectively connected to the output end of the digital signal processing unit and the protection unit, and its output end is connected to the input end of the protection unit; the output end of the said power supply module is connected to the input end of the digital signal processing unit; the central processing module and the human The machine exchange module is bidirectionally connected; the input end of the alarm module is connected to the output end of the digital signal processing unit.

The above-mentioned data acquisition and data conversion module (see Figure 3) is composed of voltage and current AC sampling front-end circuit, filter, amplification circuit and A/D conversion circuit; the current signal collected by the AC sampling front-end circuit passes through the secondary current After the transformer is converted into a small current, the small current is converted into a voltage range acceptable to the A/D converter after filtering and amplifying the circuit and stored in the digital signal processing unit RAM; the filter circuit adopts a second-order low-pass active filter.

The above-mentioned voltage and current AC sampling front-end circuit uses D11, D12, D21, D22 to form the input limiter protection, and uses R24, R25, R26, R34, R35, R36, C11, C12, C16, C17 to form the transformer phase shift Compensation and resistance-capacitance filter circuit; said filtering and amplifying circuit are composed of R1, R2, R3, R4, R5, R6 and comparator; said A/D conversion circuit is composed of R6, R7, R8, R9, R10, R11, C3, comparators U3A, U4A and A/D conversion chip ADS8364 form.

The above-mentioned digital signal processing unit (see Fig. 4) is made of DSP chip TMS320F2812, power management module, crystal oscillator circuit and data bus driver circuit; The input terminal of the digital signal processing chip; use the compiled software program to set various execution conditions to control the DSP chip TMS320F2812 to identify and process the input signal of the data bus drive circuit and issue relevant control instructions; the power management module The power management module consists of dual power supplies The power supply device TPS73HD301 is responsible for providing electric energy; the crystal oscillator circuit provides clock signals to the DSP chip TMS320F2812; the data bus driver circuit is mainly responsible for data buffering and level conversion.

The DSP chip mentioned above includes large-capacity fast flash memory, multiple 32-bit timers, 2 event managers, and various interfaces of SPI, SCI, and CAN, and provides 12 channels of PWM control pulse signals; the power management module is powered by dual power supply devices And peripheral resistors R15, R16, C1, C2 capacitors; the crystal oscillator circuit is composed of capacitors C3, C4 and crystal oscillator U2 that provide clock signals to the DSP chip; the data bus drive circuit is composed of a bidirectional data buffer 74LVC16245; the A/ The D conversion circuit receives the converted digital quantity to the DSP, compensates the data, and digitally filters the corresponding standard value to convert the corresponding standard value into the standard unit value, calculates the action setting value, and generates a total of 3 three-phase control Signal; wherein the output of the power management module and the crystal oscillator circuit is connected with the DSP chip, and the input is connected with the output of the AC sampling circuit.

The man-machine exchange module mentioned above is composed of a communication module, a keyboard and a display module; wherein the output of the keyboard is connected to the input of the digital signal processing unit, and the input of the display module is connected to the output of the digital signal processing unit terminal; said keyboard can be a determinant keyboard working in an interrupt mode, and the display module can be a color liquid crystal display.

A working method of a relay protection system capable of distinguishing short circuit and harmonic, characterized in that it comprises the following steps:

①When the system is put into operation, the current signal collected in real time by the voltage and current AC sampling front-end circuit in the data acquisition and data conversion module is converted into a small current after passing through the current transformer, and the small current is filtered and amplified. Transform it into a voltage range acceptable to the A/D converter and store it in the RAM of the digital signal processing unit, and the signal at this time is a digital signal acceptable to the digital signal processing unit;

② After receiving the digital signal, the computer will start the measurement and comparison step to judge the system operation mode corresponding to the current value collected at this time, the corresponding setting parameter value and equivalent impedance of the relay protection, and compare the collected current signal with the Setting parameter values for comparison;

③When an abnormal change in the current value in the system is detected, the computer will start the logical judgment step of distinguishing short circuit and harmonic state, decompose the current of the system into positive sequence, negative sequence and zero sequence current, and make further comparison and judgment , to distinguish between short circuit and harmonic;

④ Finally, the result of the judgment is notified in the form of a switch whether the executive device of the relay protection is active.

The logic judgment step of distinguishing the short circuit and the harmonic state in the above-mentioned step ③ is composed of the following steps (see Figure 2):

(1) Decompose the collected current signal into positive sequence, negative sequence and zero sequence current forms;

(2) Judging whether the current flowing in the system line is greater than the setting value of the relay protection, if "yes", turn to (3), and if "no", turn to (11);

(3) Judging whether the zero-sequence current is zero, if "yes" then turn to (4), "no" then turn to (11);

(4) Judging whether the positive sequence current is zero, if "yes" then turn to (5), "no" then turn to (6);

(5) There are 3n-1 harmonics in the system, judge whether the harmonic current value accounts for more than 30% of the system current, "yes" then turn to (16), "no" then turn to (17);

(6) Judging whether the negative sequence current is zero, if "yes" then turn to (7), "no" then turn to (8);

(7) Judging whether the positive sequence current is equal to the current flowing in the system, if "yes" then turn to (9), "no" then turn to (10);

(8) If a two-phase short-circuit fault occurs in the system, judge the phase where the fault occurs, and trip the corresponding relay protection circuit breaker;

(9) When a three-phase short-circuit fault occurs in the system, judge the phase where the fault occurs, and trip the corresponding circuit breaker for relay protection;

(10) There are 3n+1 harmonics in the system, judge whether the harmonic current value accounts for more than 30% of the system current, "yes" then go to (16), "no" then go to (17);

(11) Judging whether the positive sequence current is equal to the negative sequence current, if "yes" then turn to (12), "no" then turn to (13);

(12) Judging whether the positive-sequence current and the negative-sequence current are equal and both are zero, if "yes" then turn to (14), "no" then turn to (15);

(13) If a two-phase grounding short-circuit fault occurs in the system, determine the phase where the fault occurs, and trip the corresponding circuit breaker for relay protection;

(14) There are 3n harmonics in the system, judge whether the harmonic current value accounts for more than 30% of the system current, "yes" then turn to (16), "no" then turn to (17);

(15) When a single-phase grounding short-circuit fault occurs in the system, judge the phase where the fault occurs, and trip the corresponding circuit breaker for relay protection;

(16) Send a trip signal to the executive device of relay protection, and disconnect the line with large harmonic content;

(17) Still maintain the original state of the relay protection and do not act.

n in the above-mentioned steps (5), (10) and (14) is a natural number.

Each working module involved in the above technical solution adopts a conventional unit circuit.

Claims (1)

1, a kind of working method of the relay protection system that can distinguish short circuit and harmonic, it is characterized in that it comprises the following steps: ① When the relay protection system is put into operation, the voltage and current AC sampling front-end circuit in the data acquisition and data conversion module collects the three-phase current signal in the power system line in real time, and converts it into a small current after passing through the current transformer. After the flow is filtered and amplified, it is converted into a voltage range acceptable to the A/D converter, and is converted by the A/D converter and stored in the RAM of the digital signal processing unit. The signal at this time is the digital signal processing unit Acceptable digital signals; ②After receiving the above-mentioned digital signal, the computer will start the measurement and comparison step to judge the power system operation mode corresponding to the current value collected at this time, the corresponding setting parameter value of the relay protection and the equivalent impedance, and the collected current value The value is compared with the setting parameter value; ③ When abnormal changes in the current in the power system are detected, the computer will start the logical judgment steps for distinguishing short-circuit and harmonic states as follows: (1) Decompose the collected current value into positive sequence, negative sequence and zero sequence current forms; (2) Judging whether the current flowing in the power system is greater than the setting parameter value of the relay protection, if "yes", turn to (3), and if "no", turn to (11); (3) Judging whether the zero-sequence current is zero, if "yes" then turn to (4), "no" then turn to (11); (4) Judging whether the positive sequence current is zero, if "yes" then turn to (5), "no" then turn to (6); (5) There are 3n-1 harmonics in the power system, judge whether the harmonic current value accounts for more than 30% of the current flowing in the power system, if "Yes", go to (16), if "No", go to (17) ; (6) Judging whether the negative sequence current is zero, if "yes" then turn to (7), "no" then turn to (8); (7) Judging whether the positive sequence current is equal to the current flowing in the power system, if "yes" then turn to (9), "no" then turn to (10); (8) When a two-phase short-circuit fault occurs in the power system, determine the phase where the fault occurs, and trip the corresponding circuit breaker for relay protection; (9) When a three-phase short-circuit fault occurs in the power system, determine the phase where the fault occurs, and trip the corresponding circuit breaker for relay protection; (10) There are 3n+1 harmonics in the power system, judge whether the harmonic current value accounts for more than 30% of the current flowing in the power system, if "Yes", go to (16), if "No", go to (17) ; (11) Judging whether the positive sequence current is equal to the negative sequence current, if "yes" then turn to (12), "no" then turn to (13); (12) Judging whether the positive sequence current and the negative sequence current are equal and both are zero, if "yes" then turn to (14), "no" then turn to (15); (13) If a two-phase grounding short-circuit fault occurs in the power system, determine the phase where the fault occurs, and trip the corresponding circuit breaker for relay protection; (14) There are 3n harmonics in the power system, judge whether the harmonic current value accounts for more than 30% of the current flowing in the power system, "yes" then turn to (16), "no" then turn to (17); (15) When a single-phase grounding short-circuit fault occurs in the power system, determine the phase where the fault occurs, and trip the corresponding circuit breaker for relay protection; (16) Send a trip signal to the executive device of relay protection, and disconnect the line with large harmonic content; (17) Still maintain the original state of the relay protection without action; n in said steps (5), (10) and (14) is a natural number.

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