CN108490248B - Voltage monitoring and protecting device - Google Patents

Abstract

A voltage monitoring and voltage protection device, comprising: a first transformer module, a second transformer rectifier module, an analog-to-digital converter, an analysis control unit, a digital communication interface module, an alarm module, and a voltage protection module; the first transformer module Connect with the analog-digital converter; the analysis control unit is connected with the analog-digital converter, the analog-digital converter converts the input voltage signal into a digital signal and outputs it to the analysis control unit, and the analysis control unit calculates the voltage deviation and voltage harmonic distortion rate; The analysis control unit is connected with the digital communication interface module, the alarm module and the voltage protection module; the second transformer and rectification module is used to convert the input AC voltage into a DC voltage, and is used for the analog-to-digital converter, the analysis control unit, the digital communication interface module and the The voltage protection module supplies power. The device of the invention realizes the monitoring of the deviation of the power supply voltage and the voltage harmonic distortion rate and realizes the voltage protection, and avoids the influence of large voltage deviation or excessive harmonic voltage on the normal operation and service life of user equipment.

Description

A voltage monitoring and voltage protection device

technical field

The invention relates to the field of low-voltage power distribution, in particular to a voltage monitoring and voltage protection device.

Background technique

The previous "Power Supply Business Rules" stipulated: "When the peak load of the power grid specified by the power supply company:

The user power factor of 100kVA and above high-voltage power supply is above 0.90, otherwise a reactive power compensation device should be added. Therefore, a large number of parallel capacitors and other reactive power compensation equipment are installed at the end of the distribution network. At the same time, because the power supply company implements the "two-part electricity fee system" for industrial users: (1) the basic electricity fee, the monthly payment is calculated according to the installed main transformer capacity (kVA); (kWh) to calculate the electricity bill, and multiply an adjustment factor according to the monthly average power factor. Where the monthly average power factor is higher than the specified value, a certain amount of electricity charges can be reduced. The document of the Ministry of Water Resources and Electric Power and the State Price Bureau - (83) Hydropower Caizi No. 215 "Power Factor Adjustment Electricity Tariff Measures" allows the monthly average power factor to be calculated according to the user's monthly utility active power and reactive power. Therefore, quite a lot of shunt capacitors configured by industrial and mining enterprises are usually put into operation for a long time. In addition, due to factors such as tight land use and safety and beauty, the urban power grid uses a large number of cable lines, and the cable lines have a large capacitance to the ground. In light loads such as late at night, it will cause excess reactive power and make the voltage level at the end of the distribution network On the high side.

On the other hand, due to the increasing attention to environmental and energy security issues in recent years, driven by national regulations and policies, the application of renewable energy power generation on the user side is gradually increasing rapidly. Since the original distribution network planning and operation did not take this situation into consideration, when a large amount of renewable energy is connected to the distribution network for power generation, the distribution network will change from the previous single-side power grid to a multi-power grid during operation. The large randomness of the output of renewable energy power generation and the need to use power electronic devices to be connected to the grid after rectification and inversion may have a series of impacts on the power quality of the distribution network, the reliability of power supply, and the configuration and setting of relay protection. , the original control measures for distribution network operation may not be able to exert their due effect.

At present, power quality monitoring and control is mainly concentrated on the power supply side of the power grid. If the current power quality monitoring solution is applied to the user side, the investment is too high. Also moot. For low-voltage users, the main factors affecting the quality of their power consumption are the deviation of the supply voltage and the harmonic voltage exceeding the allowable value. When the voltage deviation is large or the harmonic voltage exceeds the limit, it will affect the normal operation and service life of the user equipment. It is not uncommon for internal faults in the power supply system to increase the supply voltage and cause damage to a wide range of user electrical equipment. Miniature circuit breakers, which are widely used in the terminals of low-voltage power distribution systems, integrate short-circuit protection, overload protection, and leakage protection, but do not consider the situation of high or low voltage and excessive harmonic voltage.

Contents of the invention

The purpose of the present invention is to provide a voltage monitoring and voltage protection device. Therefore, the present invention adopts the following technical solutions.

A voltage monitoring and voltage protection device, said device comprising: a first transformer module, a second transformer rectifier module, an analog-to-digital converter, an analysis control unit, a digital communication interface module, an alarm module and a voltage protection module;

The first transformation module is connected to the analog-to-digital converter, and the first transformation module converts the input AC voltage into a voltage signal suitable for input to the analog-to-digital converter;

The analysis control unit is connected with the analog-to-digital converter, and the analog-to-digital converter converts the input voltage signal into a digital signal and outputs it to the analysis control unit, and the analysis control unit calculates voltage deviation and voltage harmonic Distortion rate;

The analysis control unit is connected with the digital communication interface module, the alarm module and the voltage protection module;

The second transformation and rectification module is used to convert the input AC voltage into a DC voltage to provide power for the analog-to-digital converter, the analysis control unit, the digital communication interface module and the voltage protection module.

Preferably, the first voltage transformation module includes a voltage transformer, a voltage amplitude attenuation circuit and a DC potential bias circuit.

Preferably, the second transformation and rectification module includes a transformer, a rectification circuit and a voltage stabilization circuit.

Preferably, the voltage protection module includes an output drive amplifier circuit, an intermediate relay, and an intermediate relay contact corresponding to the intermediate relay.

Preferably, the intermediate relay contacts are connected to the input AC power.

Preferably, the intermediate relay contacts are connected with an electromagnetic release.

Preferably, the digital communication interface module is an RS232 communication interface module or an RS485 communication interface module.

Preferably, the alarm module is an audible and visual alarm.

Preferably, the device further includes buttons and a display screen, and the buttons and display screen are connected with the analysis control unit.

The beneficial effects of the present invention are: the present invention provides a digital voltage monitoring and voltage protection device, which realizes the monitoring of power supply voltage deviation and voltage harmonic distortion rate and realizes voltage protection, avoiding large voltage deviation or harmonic The impact of voltage overrun on the normal operation and service life of user equipment. In addition, the device of the present invention adopts a set of transformers respectively in the rectification and stabilization input circuit and the voltage signal circuit to be measured, so as to avoid the interference of the rectification and stabilization input circuit to the voltage signal to be measured.

Description of drawings

Fig. 1 is a structural diagram of the voltage monitoring and voltage protection device of the present invention.

Fig. 2 is a schematic diagram of an 8-point DIT-FFT operation flow diagram of the present invention.

Fig. 3 is a calculation flow of voltage deviation and voltage harmonic distortion rate in the present invention.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

A voltage monitoring and voltage protection device, comprising: a first transformer module, a second transformer rectifier module, an analog-to-digital converter, an analysis control unit, a digital communication interface module, an alarm module and a voltage protection module. The first transformer module is connected with the analog-to-digital converter, and the first transformer module converts the input AC voltage into a voltage signal suitable for input to the analog-to-digital converter. The analysis control unit is connected with the analog-to-digital converter. The analysis control unit can be a single-chip microcomputer or an MCU. The analog-to-digital converter converts the input voltage signal into a digital signal and outputs it to the analysis control unit. The analysis control unit calculates the voltage deviation and voltage harmonic wave distortion. The analysis control unit is connected with the digital communication interface module, the alarm module and the voltage protection module. The second transformation and rectification module is used to convert the input AC voltage into a DC voltage to supply power for the analog-to-digital converter, the analysis control unit, the digital communication interface module and the voltage protection module.

The present invention will be described in detail below.

Voltage deviation is also called voltage deviation. For the power grid, the power supply voltage deviation refers to the relative value of the deviation between the actual operating voltage and the system nominal voltage, expressed in percentage; for electrical equipment, the voltage deviation refers to the deviation of the equipment at a given moment The percentage value of the difference between the terminal voltage U of the equipment and the rated voltage _U of the equipment to the rated voltage, that is:

According to GB/T 12325-2008 "Power Quality Supply Voltage Deviation", the three-phase power supply voltage deviation of 20kV and below is ±7% of the nominal voltage, and the 220V single-phase power supply voltage deviation is +7% and - of the nominal voltage 10%, users in special circumstances shall be determined by agreement between the power supplier and the power consumer.

Refer to the measurement method of the power supply voltage deviation of the power grid for statistics, that is, the basic measurement time window for obtaining the voltage effective value should be 10 cycles, and each measurement time window should not overlap with the adjacent measurement time window, and the voltage effective value should be continuously measured and calculated The average value is calculated to obtain the power supply voltage deviation value.

The voltage harmonic distortion rate is measured by the voltage total harmonic distortion rate THD _V and the voltage hth harmonic content rate HRV ^h index:

The superscript h in the formula indicates the harmonic order, and the superscript 1 indicates that the parameter is the fundamental wave quantity.

The indicators related to harmonic voltage in GB/T 14549-93 "Power Quality Harmonics of Public Power Grid" are shown in the following table:

Table 1 Voltage Harmonic Distortion Rate Limits

As shown in Figure 1, the power supply voltage is converted by a voltage transformer to obtain a 0-5V AC voltage signal (that is, the input AC circuit); the voltage is reduced by a passive attenuation circuit composed of R ₁ , R ₂ , and R ₃ , plus Based on the DC bias of the reference voltage source (TL431), to ensure that the voltage signal input to the A/D converter is between 0 and +5V, the A/D converter converts the analog voltage signal into a digital signal through sampling calculation (that is, A /D sampling conversion circuit) and output to the single-chip or MCU, the single-chip or MCU thus obtains discrete voltage data (the single-chip with its own A/D conversion function can also be used), and then based on the FFT algorithm to realize the power frequency and related sub-harmonics Extraction of voltage (2-25th harmonic voltage) and calculation of voltage deviation and voltage harmonic distortion rate. The FFT algorithm is realized by a single-chip microcomputer or MCU. When the calculated voltage deviation is greater than the preset value (such as ±20%) or the voltage harmonic distortion rate exceeds the limit, the single-chip microcomputer or MCU can change the state of the corresponding pin (set to 0) to start the connected alarm module or/ and the voltage protection module to issue audible and visual alarm prompts or/and perform corresponding tripping operations. The digital communication interface can use RS232 digital communication interface or RS485 digital communication interface, RS232 or RS485 digital communication interface can send digital control signals, upload data, etc. (also can be used as a reserved communication interface for intelligent control), and can upload the voltage monitoring situation. When the communication interface adopts MAX485 chip or MAX232 chip, it can form RS485 or RS232 communication interface respectively. The DC power of the device is obtained by full-wave rectification and 7805 voltage regulator circuit, which provides DC power for the A/D converter, MCU and digital communication interface. The power supply transformer (that is, the rectification and stabilization circuit of the power supply voltage).

Whether to allow voltage alarm and trip setting, setting of voltage alarm and trip threshold value, release of voltage alarm signal and trip control signal, whether to allow voltage alarm and trip control signal to be sent through RS232 or RS485 digital communication port, whether to allow It is allowed to upload data such as voltage pass rate, maximum/minimum voltage, voltage harmonic distortion rate, etc. through the RS232 or RS485 digital communication port; The highest/minimum voltage value and voltage harmonic distortion rate, whether to allow alarm, trip setting, voltage alarm, trip threshold setting value; when alarm setting is allowed, when the voltage deviation and/or voltage harmonic distortion rate exceeds the allowable value, through the sound Light alarm prompt; when the trip setting is allowed, the trip control threshold (such as 1.2U _N , etc.) can be set according to the allowable range of the working voltage of the electrical equipment and/or the voltage harmonic distortion rate.

The pin current driving capability of the microcontroller is insufficient, as shown in Figure 1, the pin of the microcontroller is connected to the resistor _R5 , and the resistor _R5 is connected to the PNP transistor, and the driving current is increased through a PNP transistor. The diode is connected in parallel with the intermediate relay KM. Resistor R ₅ , PNP triode and diode form an output drive amplifier circuit. When the power supply voltage exceeds the trip threshold and the trip setting is allowed, the pin level of the single-chip microcomputer connected to the intermediate relay KM changes from high level to low level, and the PNP triode is saturated and turned on at this time, thus connecting the circuit where the intermediate relay is located. The moving contact KM is closed, and the AC control circuit is connected, so that the action of the electromagnetic tripper drives the rotation of the built-in shaft to realize tripping. When the device comes with an electromagnetic release, it can be used with a low-voltage circuit breaker without an electromagnetic release to realize the tripping of the low-voltage circuit breaker. If the device only needs to provide a trip signal, the AC control circuit does not need the electromagnetic release shown in Figure 1, and the circuit is directly connected to the electromagnetic release of the matched low-voltage circuit breaker to achieve trip control. The device of the invention can be applied to the low-voltage circuit breaker at the terminal of the low-voltage power distribution system.

As mentioned above, the discrete voltage data is analyzed using the Fast Fourier algorithm (FFT), and its power frequency and harmonic components can be obtained by successively decomposing the time series x(n) where N is an integer power of 2.

For ease of explanation, take the 8-point DIT-FFT algorithm as an example, its operation flow diagram is shown in Figure 2, assuming that each cycle samples 8 points, then the number of points in the operation flow diagram (i.e. operation length) N=8, and N =2 ^M =2 ³ , where M is the number of operations of the algorithm. The sampling input sequence needs to be sorted in binary reverse order according to the serial number. For example, the binary code of the serial number of A(1) is 001, and after reverse sorting, it is 100. Therefore, the position of A(1) in Figure 3 corresponds to x(4), and A(0) The binary code of the serial number is 000, which remains unchanged after reverse order sorting, and the position of A(10) corresponds to x(0).

Each intersecting black dot in Figure 3 represents a butterfly operation, and each butterfly operation needs to be multiplied by the twiddle factor shown in formula (2), where a=cos(2π/N), a=-sin (2π/N).

According to the butterfly operation process shown in Figure 3, an example is as follows:

Level 1 first butterfly operation:

The second butterfly operation of the first level:

The first butterfly operation of the second level:

After completing the 3-level butterfly transformation, the effective value of the voltage is calculated according to the following formula:

(工频分量)，

where U(0)=A ₃ (0),

(power frequency component),

After calculating the voltage effective value and each harmonic voltage, the voltage deviation is calculated according to formula (1), and the voltage total harmonic distortion rate and each harmonic voltage content rate are calculated according to formulas (2) and (3).

The voltage monitoring and protection device is designed to sample 64 points per cycle, so there are 6 levels of butterfly operations, which can theoretically achieve up to 32 harmonic analysis. The calculation process of the voltage deviation is shown in Figure 3.

The simulation verification is based on the Proteus platform. Through the superposition of power frequency components and several harmonic components and according to the sampling frequency, analog voltage data is generated and stored in another single-chip microcomputer in advance, and the single-chip microcomputer sends data to the voltage monitoring module for simulation.

Harmonic components in the actual power grid are usually not large. For applications in low-voltage households, small and micro enterprises, and rural power grid users, harmonic analysis only needs to calculate the power frequency component and the 2nd to 25th harmonic components. The distribution transformer uses When Dyn is connected, the 3rd and its multiplier harmonic components are suppressed due to the formation of circulating current in the primary winding. Table 2 simulates the power frequency component and each harmonic component of the actual voltage, and the maximum error in the analysis results of power frequency and each harmonic is shown in Table 3.

Table 2 RMS value of each harmonic component of analog supply voltage

Table 3 Harmonic analysis maximum error

For the three-phase AC power supply system, there are three-phase three-wire system (each phase is represented by A, B, and C respectively, which has the difference between A phase, B phase, and C phase) and three-phase four-wire system (except for A phase, B phase, and B phase). There are three wires corresponding to phase and C, and a neutral wire, represented by N).

Figure 1 can represent the case where the power supply voltage is a single-phase voltage, which can be divided into the following two cases:

1. Single-phase case 1, with the phase voltage as the rated voltage (rated voltage 220V), then L1 and L2 in Figure 1 can be any one of A, N, B, N or C, N;

2. Single-phase case 2, with the line voltage as the rated voltage (rated voltage 380V), then L1 and L2 in Figure 1 can be any one of A, B, B, C or C, A.

In addition, it can also be extended from Figure 1 to the case where the power supply voltage is three-phase, which can be divided into the following two cases:

1. Three-phase situation 1, three-phase three-wire system, expand the first transformer module into three groups, namely the voltage transformer in Figure 1, resistors R ₁ , R ₂ , R ₃ , R ₄ , capacitor C ₃ and reference The voltage source is expanded into three groups, and L1 and L2 in Figure 1 become three-phase three-wire A, B, and C. A, B, B, C, C, and A respectively correspond to a group of first transformation modules, which respectively perform voltage conversion on the input three-phase voltage;

2. Three-phase case 2, three-phase four-wire system, expand the first transformer module into three groups, namely the voltage transformer in Figure 1, resistors R ₁ , R ₂ , R ₃ , R ₄ , capacitor C ₃ and The reference voltage source is expanded into three groups, and L1 and L2 in Fig. 1 become three-phase four-wire A, B, C and neutral wire N. A, N, B, N, C, and N respectively correspond to a group of first transformation modules, which respectively perform voltage conversion on the input three-phase voltage.

The present invention proposes a voltage monitoring and protection device based on single-chip microcomputer design, and develops an FFT-based analysis algorithm for voltage deviation and voltage harmonic distortion rate. Through simulation on the Proteus platform and device cost calculation, the results show that the device can Low-cost and convenient implementation of voltage monitoring and protection on the user side of low-voltage households, small and micro enterprises, and rural power grids.

The above-mentioned embodiments only illustrate the principles and effects of the present invention, but are not intended to limit the present invention. Anyone skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical ideas disclosed in the present invention should still be covered by the claims of the present invention.

Claims (5)

1. A low voltage home subscriber side voltage monitoring and protection apparatus, comprising: the device comprises a first voltage transformation module, a second voltage transformation and rectification module, an analog-to-digital converter, an analysis control unit, a digital communication interface module, an alarm module and a voltage protection module;

the first voltage transformation module is connected with the analog-to-digital converter and converts input alternating voltage into a voltage signal suitable for being input into the analog-to-digital converter;

the analysis control unit is connected with the analog-to-digital converter, the analog-to-digital converter converts an input voltage signal into a digital signal and outputs the digital signal to the analysis control unit, and the analysis control unit calculates a voltage deviation and a voltage harmonic distortion rate;

the analysis control unit is connected with the digital communication interface module, the alarm module and the voltage protection module;

the second voltage transformation and rectification module is used for converting input alternating-current voltage into direct-current voltage and supplying power to the analog-to-digital converter, the analysis control unit, the digital communication interface module and the voltage protection module;

the second voltage transformation rectifying module is independently arranged as a device power supply, so that the interference on the monitoring voltage waveform generated when the first voltage transformation module is used for rectifying and supplying power additionally can be effectively reduced;

the digital communication interface module adopts an RS232 digital communication interface module or an RS485 digital communication interface module, and the RS232 or RS485 digital communication interface can send digital control signals, upload data and upload voltage monitoring conditions; can also be used as a reserved communication interface for intelligent control;

the voltage protection module comprises an output drive amplifying circuit, an intermediate relay and an intermediate relay contact corresponding to the intermediate relay; the intermediate relay contact is connected with an input alternating current power supply; and the intermediate relay contact is connected with an electromagnetic trip of a low-voltage circuit breaker of a low-voltage distribution system terminal.

2. The low voltage household subscriber side voltage monitoring and protection apparatus of claim 1, wherein the first transforming module comprises a voltage transformer, a voltage amplitude attenuating circuit and a dc potential biasing circuit.

3. The low-voltage household-user-side voltage monitoring and protection device as claimed in claim 1, wherein said second transformer rectifier module comprises a transformer, a rectifier circuit and a regulator circuit.

4. The low-voltage household user side voltage monitoring and protection device as claimed in claim 1, wherein the alarm module is an audible and visual alarm.

5. The low voltage home subscriber side voltage monitoring and protection device of claim 1, further comprising a button and a display screen, said button and display screen being connected to said analysis and control unit.

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