RU140217U1 - DEVICE FOR MEASURING EARTH RESISTANCE - Google Patents

Abstract

The device allows to increase the accuracy, reliability, speed of measurements, as well as to provide measurement on alternating current of industrial frequency in real time without interfering with the grounding circuit of the electrical installation. The specified technical result is achieved by the fact that the device contains a power source, rectifier devices (VU), a remote electrode, a grounding device for electrical installation (ZEE), a measurement unit (BI) and a measuring device (IP). As a power source, the transformer supplying the electrical installation is used, connected via the phase bus L and the zero PEN bus. A test current generation unit (BF) and a control unit (CU) have been introduced. L and PEN bus connected to the BF. The PEN bus, connected to the grounding bus to the memory device, is also connected to the inputs of the VU through quick connectors. BI is made of a voltage measurement channel (CIN), a current measurement channel (CIT) and a divider (D). The outputs of the WU are respectively connected to the input of the KIN and to the input of the KIT BI. The remote electrode is connected to the reference input of the slave connected to the input of the CIN. The input of the VU connected to the input of the KIT is connected via a current transformer to the ground bus. CIN and CIT are made providing compensation of background voltage and background current, respectively. The output of the KIN is connected to the first input D, the output of the KIT is connected to the second input D, the output of which serves as the output of the BI. The control outputs of the control unit are respectively connected to the control inputs of the BF, BI and IP. 8 s.p. f-ly, 1 drawing

Description

The utility model relates to electrical engineering, namely, devices for ensuring electrical safety, and can be used to measure the resistance of grounding devices of electrical installations of buildings and structures.

A known method of measuring voltages on the grounding device is that the points of the grounding device between which voltage is to be measured are connected by an insulated wire made of resistive material, the current in this wire is measured, and the voltage is calculated from the previously measured value of the wire resistance and the measured current value (RU, No. 2452968, C1, G01R 19/00, publ. 10.06.2012).

A device that implements this method contains an energy object (building), a grounding device, a lightning rod, an electric power generator, a power transformer with a grounded neutral, a power line, a measuring and recording device (for example, a processor), insulated wires made of resistive material, worn on They are current transformers, and a grounding conductor.

However, the known device and method has certain disadvantages: for measurements it is necessary to accumulate information indefinitely and there is no method for calculating the resistance value of the grounding device.

The closest is a device for measuring grounding resistance, containing a power source, rectifier devices, a remote electrode, which is used to connect consumer equipment to the grounding device, a measuring unit and a measuring device, the input of which is connected to the output of the measuring unit. (RU, No. 201775, U1, G01R 27/20, publ. 20.10.2001).

The device is designed to measure the grounding resistance of quarry electrical installations. This device uses a tunable measuring current generator with a frequency of 90-170 Hz and a voltage of up to 500 V as a power source, as well as rectifier devices and voltage stabilizers. The measurement unit is made of an amplifier, a synchronous detector and an integrator. The measuring device is made of variable resistance and indicator. Two remote electrodes are used - potential and current.

The limitations of the known device are the insufficiently high measurement speed due to the need to take measurements twice with a change at the terminals of the wires of the potential and current electrodes with repeated adjustment of the measuring device; the need to incorporate potential and current electrodes and a resistor into the consumer's grounding device, which reduces the reliability and accuracy of measurements; there is no accounting for background voltages and current, which also reduces the accuracy and reliability of measurements; the measurements are carried out at a test current different from the alternating current of industrial frequency, which leads to the inconvenience of using the known device for monitoring the state of grounding devices of various industrial electrical installations of the consumer.

The task solved by the utility model is the improvement of technical and operational characteristics.

The technical result that was obtained by performing the claimed utility model is to increase the speed, reliability and accuracy of measurements, to ensure the measurement of grounding resistance at alternating current of industrial frequency in real time without interfering with the grounding circuit of the electrical installation.

To solve the problem with the achievement of the specified technical result in a known device for measuring grounding resistance, containing a power source, rectifier devices, a remote electrode, a grounding device, a measurement unit and a measuring device, the input of which is connected to the output of the measurement unit, according to the claimed device as the power source used phase and zero bus network, introduced the block forming the test current and the control unit, phase and zero bus and connected to the test current generation unit, while the grounding bus connected to the grounding device of the electrical installation is also connected to the inputs of the rectifier devices via their quick disconnect connectors, the measurement unit is made of a voltage measurement channel, a current measurement channel and a divider, the outputs of the rectifier devices are individually connected to the input of the voltage measurement channel and to the input of the current measurement channel of the measurement unit, the remote electrode is connected to the reference input of the rectifier of the imaging device connected to the input of the voltage measurement channel, the voltage measurement channel and the current measurement channel are designed to compensate for the background voltage and background current, respectively, the output of the voltage measurement channel is connected to the first input of the divider, the output of the current measurement channel to the second input of the divider, the output of which serves as the output of the measurement unit, the control output of the control unit is respectively connected to the control inputs of the test current generation unit, the measurement unit and will measure ceiling elements of the device.

Additional embodiments of the device are possible, in which it is advisable that:

- as a quick disconnect connector of the rectifier device, the output of which is connected to the input of the voltage change channel, the Crocodile electric clamp was used, and as a quick disconnect connector of the rectifier device, the output of which is connected to the input of the current change channel, the current transformer - clamps;

- the control unit was made of a timer and a start key connected to it;

- the test current generation unit was made of the first key and a ballast resistor connected in series to the phase and zero bus, and the control input of the first key serves as the control input of the test current generation unit;

- rectifier devices for the voltage measurement channel and the current measurement channel of the measurement unit were identical, and each of them is made of a normalizing amplifier, a bandpass filter, a rectifier connected in series, and the outputs of the rectifiers serve as the outputs of the rectifier devices;

- the plus (+) input of the normalizing amplifier of the rectifier device, the output of which is connected to the input of the voltage channel of the measurement unit is connected by the Crocodile electric clamp to the ground bus, and the minus (-) reference input is connected to the remote electrode;

- the plus (+) input and the minus (-) input of the normalizing amplifier serves as the input of the rectifier device, the output of which is connected to the input of the current measurement channel of the measuring unit, and is connected to the ground bus by means of a current transformer - clamps;

- the voltage measurement channel and the current measurement channel of the measurement unit were identical, and each of them is made of a second key, a storage device, an inverting amplifier and an adder connected in series, the input of the second key serves as the input of the corresponding measurement channel, the output of the inverting amplifier is connected to the first input of the adder , the input of the second key is with the second input of the adder, and the control input of the second key serves as the control input of the measurement unit for each of the measurement channels;

- the measuring device was made of a series-connected indicator and a third key, the input of which serves as the input of the measuring device, and the control input of the third key serves as the control input of the measuring device.

The indicated advantages of the utility model, as well as its features are explained with the help of a variant of its implementation with reference to the attached drawing.

Figure 1 depicts a functional diagram of the device.

A device for measuring grounding resistance (Fig. 1) contains a power source 1, rectifier devices 2, 3 (VU), a remote electrode 4, a grounding device 5 of an electrical installation (ZUE), a measurement unit 6 (BI) and a measuring device 7 (IP), the input of which is connected to the output of BI 6. As a power source 1, the phase bus L and the zero bus PEN of the power transformer of the tested electrical installation are used. A test current generation unit (BF) 8 and a control unit 9 (CU) have been introduced. Phase L and zero REK bus are connected to BF 8. The zero PEN bus connected to the grounding bus to ZUE 5 is also connected to the input of VU 2, 3 by means of their quick disconnect connectors. BI 6 is made of a voltage measuring channel (CIN) 10, a current measuring channel (CIT) 11, and a divider 12 (D). The outputs of the WU 2, 3, respectively, are separately connected to the input of the KIN 10 and to the input of the KIT 11 of the measurement unit 6. The remote electrode 4 is connected to the reference input "minus" VU 2 connected to the input of the KIN 10. KIN 10 and KIT 11 are made providing compensation for the background voltage and background current, respectively. The output of the KIN 10 is connected to the first input of the divider 12, the output of the KIT 11 is connected to the second input of the divider 12, the output of which serves as the output of the BI 5. The control output of the BU 9 is respectively connected to the control inputs of the BF 8, BI 6 and IP 7.

As a quick connector VU 2, the output of which is connected to the input of KIN 10, the Crocodile electric clamp can be used, and as a quick connector VU 3, the output of which is connected to the input of KIT 11, a current transformer 13 can be used - pincers.

BU 9 is made of a timer 14 and a start key 15 connected to it.

BF 8 is made of the first key 16 (electronic, normally open) and a ballast resistor 17 connected in series to the phase L and zero PEN bus, and the control input of the first key 16 serves as the control input of the BF 8.

WU 2, 3 for KIN 10 and KIT 11 of the measuring unit 6 are identical, and each of them is made of a normalizing amplifier 18 (NU), a band-pass filter 19 (PF), and a rectifier 20 (V) connected in series. Outputs 20 serve as outputs WU 2, 3.

The plus input of NU 18 (+) VU 2 for KIN 10 of the measuring unit 6 is electrically clamped to the ground bus at the point of its connection to the PEN bus. The reference input "minus" NU 18 (-) is connected to the remote electrode 4 to set the reference voltage level.

The input of NU 18 VU 3 for KIT 11 of the measurement unit 5 is connected to the ground bus by means of a current transformer 13 with a split core - pincers.

KIN 10 and KIT 11 of the measurement unit 6 are identical. Each of them is made of a second key 21 (electronic), a storage device 22 (memory), an inverting amplifier 23 (DUT) and an adder 24 (C) connected in series. The input of the second key 12 serves as the input of the corresponding measurement channel KIN 10 and KIT 11. The output of the DUT 23 is connected to the first input C 24, the input of the second key 21 to the second input C 24. The control input of the second key 21 serves as the control input of BI 6 for each of the channels KIN 10 and KIT 11 measurements.

The measuring device 7 is made up of a third key 25 (electronic) connected in series and an indicator 26. The input of the third key 25 serves as the input of IP 7, and the control input of the third key 26 serves as the control input of IP 7.

A device for measuring grounding resistance (Fig. 1) works as follows.

To connect the claimed device BF 8 is connected to the phase bus L and the zero PEN bus at the point of connection with the ground bus, the plus (+) input of NU 18 VU 2 is connected to the same point using the Crocodile type electric clamp. The input "minus" (-) NU 18 VU 2 is connected to a remote electrode 4, located at a distance many times greater than the typical size of the ZUE 5. Current transformer 13 (clamps) is installed on the ground bus, the output of which is connected to the input of the normalizing amplifier 18 VU 3 .

The choice of the location of the remote electrode 4 depends on the actual technical conditions on the ground, but the distance from it to the ZUE 5 should obviously exceed the characteristic geometric dimensions of this grounding device, preferably more than 10 times, because the resistance of the grounding device is determined by the spreading resistance of the current in the soil, the influence of which can affect the measurement accuracy.

The sequence of measurements is determined by the timer 14 BU 8 according to the program installed in it. BU 8 is used to control the first key 17, the second keys 21 KIN 10 and KIT 11, the third key 25 IP 7 and generates a control signal of duration Δt at the moment of operation of PC 15. The choice of the length of time Δt during which the measurement depends from the response time of electronic keys and the time constant of the measuring circuits. The control output of the BU 9 only works for connecting electronic keys, and when removing the control signal from the output of the BU 9 electronic keys: the first key 17, the second keys 21 KIN 10 and KIT 11, the third key 25 IP 7 automatically go to the initial state, and the keys 17 and 25 are normally open, and keys 21 of KIN 10 and KIT 11 are normally closed.

The normalizing amplifier 18 VU 2 and VU 3 serves to ensure a given level of signals and to coordinate the input and output elements of the blocks. Its main technical indicators include input and output resistances, gain, overload capacity, linear and non-linear distortions, signal-to-noise ratio, dynamic range, and stability of indicators. Since it is the first cascade in the path, its noise properties significantly affect the attainable dynamic range of the entire device.

In the claimed device, the normalizing amplifier can be made on the basis of the AD 623 chip manufactured by Analog Devices.

The bandpass filter 19 of the VU 2 and VU 3 is tuned to the center frequency of 50 Hz and can be performed on the basis of the OP196 chip manufactured by Analog Devices. The band-pass filter is used to eliminate spurious frequency components of the signals.

As rectifiers 20 VU 2 and VU 3, for example, a half-wave detector based on the OP296 chip manufactured by Analog Devices can be used.

At the output of rectifier devices 2 and 3, DC signals are proportional to the level of variable signals at their inputs, voltage or current, respectively.

The operation of the device is based on the use of two measuring channels KIN 10 and KIT 11, which serve to measure the voltage on the ZUE 5 relative to the reference remote electrode 4, and the current flowing through the ground bus to the grounding device 5.

For at least 10 seconds before turning on the test current generated by BU 9, the background voltage U _background and background current I _background are measured _. . The signals U _background and I _background are fed to the VU 2 and VU 3 and stored through the closed second key 21 in the memory 22 when the first key 16 BF 8 and the third key 25 IP 7 are turned off. Background values of voltage and current are very important parameters, depending on very many factors: specific electrical devices, their power, type UZE 5, the condition of rooms and soils, etc. In this case, the U _background and I _background vary widely even for the same grounding devices. The gain of the inverting amplifier 23 is selected corresponding to a decrease in the signal levels in the second key 21 and the memory 22. The memory 22 and the memory 23 can be based on the chip OP196 manufactured by Analog Devices, and the key 21 can be made on the chip 74HC4066 of Pilips Semiconductors. After the PC 15 closes with the timer 14 of the control unit 8, the control signal is supplied to the control input of the BF 8, which connects the ballast to the phase bus L and the zero PEN bus using the first key 17 and disconnects the second keys 21 KIN 10 and KIT 11 for the time interval Δt . As a result, a test current flows through the network.

The current is distributed between the power line, the grounding device 5 and the grounding device of the supply transformer in accordance with their resistances.

As a result of this, an overvoltage ΔU occurs on the PEN, the ground bus and, accordingly, the ZEE 5, generating a current ΔI through the ground bus.

The voltage ΔU + U _background passes through VU 2 and enters the input of KIN 10, and the current ΔI + I _background through VU 3 passes to the input of KIT 11. Since the second keys 21 KIN 10 and KIT 11 are turned off, the rectified signals go to the second input C 24, and the inverted signals U _background and I _background respectively for KIN 10 and KIT 11 are received at the first input C 24 from the output of IU 23, therefore, ΔU is received at the output of 24 KIN 10 and ΔI is received at the output of 24 KIT 11 (pure not polluted by background parameters). From the output C 24 KIN 10, the signal ΔU goes to the first input D 12, from the output C 24 the signal ΔI goes to the second input D 12 of the measurement unit 6. From the output D 12 receive a signal proportional to the resistance R _s ground. The third key 25 is also closed for a time ΔI and the value of the resistance R _z grounding is displayed by indicator 26.

Thus, KIN 10 and KIT 11 are made providing compensation of the background voltage and background current, which increases the reliability and accuracy of measurements of grounding resistance. The input of the VU 3 is connected via a current transformer 13 (clamps) directly to the ground bus, therefore, the reliability and accuracy of the measurement are also increased, and, in addition, by introducing the BF 8, it is possible to measure the ground resistance on an alternating current of industrial frequency in real time without intervention in electrical grounding circuit. The increase in the measurement speed compared to the closest analogue is achieved by eliminating the second remote electrode, and the concomitant measurement of voltage and current twice with a change at the terminals of the wires of the potential and current electrodes with repeated adjustment of the measuring device.

In FIG. 1, the functional diagram of the device is shown in analog form, however, the measurement control algorithm can be implemented in digital form using analog-to-digital converters (ADCs) and a microprocessor.

The most successfully claimed device can be industrially applicable for measuring with high accuracy and speed the resistance of the grounding devices of buildings and structures with alternating current of industrial frequency in real time without interfering with the electrical installation.

Claims (9)

1. A device for measuring grounding resistance, comprising a power source, rectifying devices, a remote electrode, an electrical grounding device, a measuring unit and a measuring device, the input of which is connected to the output of the measuring unit, characterized in that the phase and zero mains buses are used as the power source , the test current generation unit and the control unit are introduced, the phase and zero buses are connected to the test current generation unit, while the ground bus connected to the ground the electrical installation device is also connected to the inputs of the rectifier devices by means of their quick disconnect connectors, the measurement unit is made from a voltage measurement channel, a current measurement channel and a divider, the outputs of the voltage recovery devices are individually connected to the input of the voltage measurement channel and to the input of the current measurement channel of the measurement unit, the remote electrode is connected to the reference input of the rectifier device connected to the input of the voltage measurement channel, the voltage measurement channel and the current measuring channel is designed to compensate for the background voltage and background current, respectively, the output of the voltage measuring channel is connected to the first input of the divider, the output of the current measuring channel to the second input of the divider, the output of which serves as the output of the measuring unit, the control output of the control unit is respectively connected to the control inputs a test current generation unit, a measurement unit, and a measuring device. 2. The device according to claim 1, characterized in that the Crocodile electric clamp is used as a quick disconnect connector of the rectifier device, the output of which is connected to the input of the voltage change channel, and as a quick disconnect connector of the rectifier device, the output of which is connected to the input of the current change channel , used current transformer - pincers. 3. The device according to claim 1, characterized in that the control unit is made of a timer and a start key connected to it. 4. The device according to claim 1, characterized in that the test current generating unit is made of a first key and a ballast resistor connected in series to the phase and zero buses, and the control input of the first key serves as the control input of the test current generating unit. 5. The device according to claim 1, characterized in that the rectifier devices for the voltage measurement channel and the current measurement channel of the measurement unit are identical, and each of them is made of a normalizing amplifier, a bandpass filter, a rectifier connected in series, and the outputs of the rectifiers serve as outputs of the rectifier devices . 6. The device according to claim 5, characterized in that the plus (+) input of the normalizing amplifier of the rectifier device, the output of which is connected to the input of the voltage measurement channel of the measurement unit, is connected by the Crocodile electric clamp to the ground bus, and the reference input is minus (-) connected to the remote electrode. 7. The device according to claim 5, characterized in that the plus (+) input and the minus (-) input of the normalizing amplifier serve as the input of the rectifier device, the output of which is connected to the input of the current measurement channel of the measurement unit and is connected to the ground bus by current transformer - ticks. 8. The device according to claim 1, characterized in that the voltage measurement channel and the current measurement channel of the measurement unit are identical and each of them is made of a second key, a storage device, an inverting amplifier and an adder connected in series, the input of the second key serves as the input of the corresponding measurement channel , the output of the inverting amplifier is connected to the first input of the adder, the input of the second key is connected to the second input of the adder, and the control input of the second key serves as the control input of the measurement unit for each of the measurement channels rhenium. 9. The device according to claim 1, characterized in that the measuring device is made up of an indicator and a third key connected in series, the input of which serves as the input of the measuring device, and the control input of the third key serves as the control input of the measuring device.

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