CN201576056U - A Grounding Resistance Online Detector Based on TMS320LF2407A - Google Patents

Abstract

The utility model discloses an online grounding resistance detector based on TMS320LF2407A, which comprises a current jaw, a preamplifier module, a program-controlled active filter, a voltage jaw, a power amplifier module, a low-frequency frequency conversion signal generator, a voltage divider module, Coupling voltage sampling module and TMS320LF2407A digital signal processor; current clamp, preamplifier module and program-controlled active filter are connected in sequence and then connected to an input port of TMS320LF2407A digital signal processor; voltage clamp, power amplifier module and low frequency The frequency conversion signal generator is connected in sequence and connected to an output port of the TMS320LF2407A digital signal processor; the voltage clamp, voltage divider module and coupling voltage sampling module are connected in sequence and connected to another input port of the TMS320LF2407A digital signal processor. The beneficial effects obtained by the utility model are: (1) through the TMS320LF2407A digital signal processor, the collected data can be accurately processed, so the measurement accuracy is high and the error is small; (2) the structure is simple and the price is low.

Description

A Grounding Resistance Online Detector Based on TMS320LF2407A

technical field

The utility model relates to an on-line grounding resistance detector, in particular to an on-line grounding resistance detector based on TMS320LF2407A.

Background technique

The grounding system of power plants and substations is an important measure to maintain the safe and reliable operation of the power system and ensure the safety of electrical equipment and operating personnel. In order to effectively prevent power equipment from being damaged by lightning strikes, DL/T 621-1997 "Grounding of AC Electrical Installations" puts forward very strict requirements for the daily maintenance of substation grounding and lightning protection facilities, such as before the arrival of the thunderstorm season every year Carry out a comprehensive inspection of all lightning protection facilities. The comprehensive grounding resistance of complex electrical equipment should not exceed 1Ω, and the grounding resistance of power plants and substations with 110kV and above should not exceed 0.5Ω. Large-scale 220-500kV power plants and substations Should not be greater than 0.25Ω, etc.

Reasonable selection of measuring instruments is the premise guarantee for accurate measurement of grounding resistance. As far as the current online ground resistance tester is concerned, there are mainly two types for users to choose from: the first is the traditional shaker digital ground resistance tester, and the second is the single-jaw ground resistance tester.

1. The traditional rocker digital ground resistance meter

Its measurement principle is to inject a low-frequency alternating current I between the current electrode and the grounding body under test. At this time, a voltage U can be obtained between the grounding body under test and the voltage electrode. By measuring the current and voltage values, according to Ohm's law R =U/I, the grounding resistance of the measured grounding body can be calculated. But it has the following disadvantages: (1) Two auxiliary ground poles must be used for each measurement, which not only increases the labor intensity of maintenance, but also cannot meet the needs of the ground network in many field situations. In the diagonal direction, the current auxiliary pole is about 40 meters away from the ground grid, and the voltage auxiliary pole is 20 meters away from the ground grid; (2) the measurement accuracy is very low, especially for the measurement of ground resistance below 0.5Ω; (3) due to The entire measurement process is manual operation from driving auxiliary ground piles to measurement, so the measurement results are greatly affected by human factors, such as the slow shaking speed of the handle during measurement, uneven frequency, etc. will have a great impact on the measurement results; (4) The grounding body needs to be disconnected from the equipment during measurement, so as to avoid the equipment's own grounding body from affecting the accuracy of the measurement, so that online measurement cannot be realized.

2. Single-jaw grounding resistance measuring instrument

The clamp-on ground resistance meter looks exactly like a clamp-on ammeter. It does not need auxiliary ground electrodes during measurement. It can measure the ground resistance of the equipment in use without cutting off the power supply of the equipment or disconnecting the ground wire. Once clamped, the measurement result can be obtained in a few seconds, which greatly facilitates the measurement of grounding resistance, but it has the following disadvantages: (1) Since the low-frequency AC voltage injected by the instrument into the grounding loop has a single frequency, when its frequency is the same as that of the electrical When the leakage current frequency of the equipment grounding network is close, the measurement accuracy is very low, and even cannot be measured in severe cases; (2) Since the voltage injection coil and the current measurement coil are combined in the same jaw, the mutual inductance effect between the coils has a significant impact on the measurement accuracy. Large impact; (3) The measurement error of the ground resistance below 0.7Ω is large, which cannot meet the measurement of the ground resistance below 0.5Ω; (4) The internal diameter of the jaw is small, generally 25mm, and the ground network with a lead width greater than 25mm Can not be measured.

Contents of the invention

The problem to be solved by the utility model is to provide a TMS320LF2407A-based on-line grounding resistance detector that can accurately measure the grounding resistance and is cheap.

In order to solve the above technical problems, the TMS320LF2407A-based grounding resistance online detector of the utility model includes a current jaw, a preamplifier module, a program-controlled active filter, a voltage jaw, a power amplifier module, a low-frequency variable-frequency signal generator, and a Voltage module, coupling voltage sampling module and TMS320LF2407A digital signal processor; The current clamp, preamplifier module and program-controlled active filter are connected in sequence and then connected to an input port of TMS320LF2407A digital signal processor; the voltage clamp port, power amplifier module and low-frequency frequency conversion signal generator are connected in sequence and then connected to an output port of TMS320LF2407A digital signal processor; the voltage clamp, voltage divider module and coupling voltage sampling module are connected in sequence and then connected to the TMS320LF2407A digital signal Another input port of the processor.

In the TMS320LF2407A-based grounding resistance online detector of the present invention, the TMS320LF2407A digital signal processor is also connected with an LCD display, a key input module and an RS232 communication interface.

The beneficial effects obtained by the utility model are: (1) through the TMS320LF2407A digital signal processor, the collected data can be accurately processed, so the measurement accuracy is high and the error is small; (2) the structure is simple, the price is relatively low, and the Very high performance-price ratio.

Description of drawings

Fig. 1 is a schematic diagram of the frame structure of the present utility model.

In the figure: 1. Current clamp, 2. Preamplifier module, 3. Voltage divider module, 4. Programmable active filter, 5. Coupling voltage sampling module, 6. TMS320LF2407A digital signal processor, 7. LCD display, 8 . Key input module, 9. Voltage jaw, 10. Power amplifier module, 11. Low frequency variable frequency signal generator, 12. RS232 communication interface.

Detailed ways

As shown in Figure 1, the ground resistance online detector based on TMS320LF2407A of the utility model includes a current jaw 1, a preamplifier module 2, a program-controlled active filter 4, a voltage jaw 9, a power amplifier module 10, and a low frequency conversion Signal generator 11, voltage divider module 3, coupling voltage sampling module 5 and TMS320LF2407A digital signal processor 6; said current clamp 1, preamplifier module 2 and program-controlled active filter 4 are connected in sequence and then connected to TMS320LF2407A digital An input port of the signal processor 6; the voltage clamp 9, the power amplification module 10 and the low-frequency frequency conversion signal generator 11 are connected in sequence and then connected to an output port of the TMS320LF2407A digital signal processor 6; the voltage clamp 9 , the voltage divider module 4 and the coupling voltage sampling module 5 are connected in sequence and then connected to another input port of the TMS320LF2407A digital signal processor 6; the TMS320LF2407A digital signal processor 6 is also respectively connected with an LCD display 7 and a key input module 8 And RS232 communication interface 12.

Description of TMS320LF2407A digital signal processor 6:

TMS320LF2407A digital signal processor 6 adopts TMS320LF2407A produced by TI Company as the detection core. In this measuring instrument, the on-chip programmable gain amplifier (PGA) is used to realize range switching; the on-chip ADC subsystem is used to measure the coupling voltage of the voltage clamp, the induced current of the current clamp and the interference current in the ground loop; The on-chip event manager module EV measures the frequency of interference current; the on-chip temperature sensor is used to realize temperature detection; the on-chip voltage comparator is used to realize battery undervoltage alarm; the on-chip serial port is used to upload the measurement data to the host computer. It can be seen that the measurement of grounding resistance can be completed by using a single chip of TMS320LF2407A digital signal processor 6, which simplifies the system hardware design, reduces system cost and power consumption, and prolongs the service life of the power supply battery.

Notes on the preamp circuit 2:

Since the induced current in the ground loop has a large variation range, generally tens of μA to tens of mA, the minimum amplitude of the induced current in the current jaw is only tens of μA, so the differential amplifier is used in this measuring instrument. The high-precision instrumentation amplifier AD620 has a three-op-amp circuit at its core, which has high common-mode rejection ratio CMRR, good temperature stability, and low noise figure. The gain can be set from 1 to 3000 as long as an external resistor is connected.

Due to the large dynamic range of the measurement instrument, in order to improve the measurement accuracy, the programmable gain amplifier in the TMS320LF2407A chip is used, and the gain can be adjusted through register settings.

Instructions for Programmable Active Filter 4:

Since the induced current in the ground loop is usually superimposed on the AC ripple and output noise of electrical equipment, the amplitude of these interference signals may be equivalent to the induced signal in the ground loop, and sometimes even greater, so the ground loop must be The measurement signal in the filter is well filtered to attenuate interfering signals. Here, the biquad general-purpose switched capacitor filter MAX260 is selected, and it interfaces with the TMS320LF2407A digital signal processor 6 through a parallel bus, which can be conveniently set to work modes such as band-pass, low-pass, high-pass, notch and all-pass, and its center frequency, Both corner frequency and Q value can be controlled by TMS320LF2407A digital signal processor 6 .

In this measuring instrument, according to the frequency of the interference current, the frequency of the low-frequency AC voltage generated by the voltage coil can be automatically selected among four frequencies: 94Hz, 105Hz, 111Hz, and 128Hz. Therefore, the center frequency of the active filter MAX260 must also be adjusted accordingly. change. When measuring the coupling voltage of the voltage clamp and the induced current of the current clamp, the filter works in the band-pass filtering mode; when measuring the interference current, it works in the low-pass filtering mode. These are all controlled by TMS320LF2407A digital signal processor 6 .

Explanation about the low-frequency frequency conversion signal generator 11:

The low-frequency variable frequency signal generator 11 generally has two implementation methods: analog and digital. The characteristic of the analog type is that the circuit is relatively simple, but when the output frequency is very low, a large electrolytic capacitor is required, which will cause a large frequency drift, and changing the output frequency requires changing the parameter values of resistors, capacitors and other components, which is troublesome to adjust ; While the digital circuit is relatively complex, but the generated frequency signal is very accurate, and it is relatively simple to change the frequency. For this reason, the utility model has adopted digital signal generator ML2036.

ML2036 is a programmable output frequency monolithic integrated zero-crossing sine wave generator launched by Fairchild (Fairchild Semiconductor Company), without external components. Through the serial SPI digital interface programming to output any frequency between DC ~ 50kHz, the full scale resolution is 1.5Hz, the resolution can be improved by reducing the output frequency range, and can provide ±VREF or ±VREF/2 voltage output range, which is low Ideal for frequency low cost sine wave applications.

About grounding resistance calculation:

The value of the grounding resistance can be calculated according to the value of the AC voltage and the induced current injected into the ground wire loop by the detector of the utility model.

Claims (2)

1. A grounding resistance online detector based on TMS320LF2407A is characterized in that: it includes a current clamp (1), a preamplifier module (2), a program-controlled active filter (4), a voltage clamp (9), a power Amplifying module (10), low frequency variable frequency signal generator (11), voltage dividing module (3), coupling voltage sampling module (5) and TMS320LF2407A digital signal processor (6); said current clamp (1), front The amplifying module (2) and the program-controlled active filter (4) are connected in turn to an input port of the TMS320LF2407A digital signal processor (6); the voltage clamp (9), the power amplifying module (10) and the low-frequency The frequency conversion signal generator (11) is connected successively and then connected to an output port of the TMS320LF2407A digital signal processor (6); the voltage clamp (9), the voltage divider module (4) and the coupling voltage sampling module (5) are sequentially Connect it to another input port of the TMS320LF2407A digital signal processor (6). 2. the grounding resistance online detector based on TMS320LF2407A according to claim 1, is characterized in that: on the described TMS320LF2407A digital signal processor (6), also be respectively connected with LCD display (7), key input module (8) and RS232 communication interface (12).

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