A System Scheme of Leakage Protector Testing

introduction

According to incomplete statistics, my country’s annual electric shock accidents and fires caused by electric leakage cause thousands of deaths and billions of economic losses. Therefore, the performance of leakage protectors that can prevent leakage fires and personal electric shock protection is proposed to be higher. Claim. The automatic test system for the action characteristics of the leakage protector introduced in the article can measure the leakage action current value, the breaking time and the leakage non-operation current value of the leakage protector. It provides the main technical parameters for improving the reliability of the leakage protector. The detection process has With a higher level of automation, it can detect the leakage protector in online and off-line operation.

System hardware design

There are many parameters that characterize the leakage protector. Among them, the leakage operation performance is closely related to the personal safety of the electricity user. The main parameters describing the leakage operation performance are the rated leakage operation current (I△n) and the leakage operation time. The rated leakage current is the leakage current value that the leakage protector must operate under the specified conditions specified by the manufacturer, and it reflects the leakage operation sensitivity of the leakage protector. Leakage action time refers to the time from when the leakage action current is suddenly applied to the time the protection circuit is cut off. In order to prevent the malfunction of the leakage protector, the national standard specifies the leakage non-operation current (I△n0), which refers to the leakage current value (the priority value is 0.5I△n) that the leakage protector must not operate under the specified conditions. The technical parameters necessary for putting into operation on the power grid.



Figure 1 Block diagram of the leakage protector test system

The system is based on LPC2132, with extended test current generation and adjustment module, action execution unit, current detection circuit, keyboard and other peripheral equipment. LPC2132 is a microcontroller that supports real-time simulation and tracking of 32-bit ARM7TDMI-S core, 1 10-bit 8-channel A/D converter, 2 32-bit timer/counters, 6-channel PWM unit output, and 2 hardware I2C Interface and 47 GPIOs, 2 16C550 industry standard UARTs, and up to 9 edge or level triggered external interrupts. The 16kB on-chip static RAM and 64kB on-chip Flash program memory avoid the external expansion of the LPC2132 memory, simplify the circuit and increase the operating speed. The structural block diagram of the automatic test system for the action characteristics of the leakage protector is shown in Figure 1.



Figure 2 Test current generation and adjustment module

1 Test current generation and adjustment module

The test current generation and adjustment module is shown in Figure 2. The test current is generated by passing 50Hz, 220V sinusoidal alternating current through a 220:12 step-down transformer and electric voltage regulator, outputting 0-12V sinusoidal alternating current, and then passing the loop resistance to generate the required test current. The generation of test current is divided into 3 levels to meet different measuring ranges. Relay J1 is closed and can produce a test current of 0~1000mA; Relay J2 is closed and can produce a test current of 0~500mA; Relay J1 and J2 are not closed, and can produce a test current of 0~100mA. The adjustment of each test current is realized by LPC2132 controlling the electric voltage regulator. In order to make the test current change evenly, the electric voltage regulator adopts AC servo control. During the test, LPC2132 compares the collected test current value in the real-time loop with the set value, and calculates the control value, controls the rotation of the servo motor, and drives the brush of the electric voltage regulator to slide steadily on the secondary side. Change the voltage of the secondary side, thereby changing the current in the loop. The P0.2 pin of LPC2132 outputs a pulse signal to control the movement speed of the servo motor, and P0.3 pin outputs a high or low level signal to control the direction of rotation of the servo motor.

2 Current detection circuit

The current detection circuit is shown in Figure 3. The test current is sampled through a current transformer, and the secondary side output signal of the current transformer is filtered, amplified, and voltage boosted, and then transformed into a unipolar voltage signal (0~5V) that can be collected by the A/D module Sent into LPC2132.



Figure 3 Current detection circuit

When detecting the magnitude of the current, sampling is performed at 40 points per cycle according to the cycle (power frequency) of the test current. After sampling for one cycle, according to the attenuation multiple of the current transformer and the value of the boost voltage, the actual value is calculated by the software algorithm The effective value of the current. The circuit should meet the following conditions. When the instantaneous value of the AC current reaches the positive peak value, the amplifier outputs 5V; when the instantaneous value of the AC current reaches the negative peak value, the amplifier outputs 0V. 3 A/D conversion and control circuit current detection circuit output The signal VOUT is sent to the built-in 8-channel 10-bit high-speed A/D conversion input terminal of the LPC2132 to detect the magnitude of the leakage current.

Since the A/D conversion is 10 bits, when the input voltage is 5V, the output data value is 1024 (4FFH), so the resolution is 0.0049V (5V/1024). If the loop resistance that generates the test current is 12Ω, the resolution of the leakage current is 0.4mA (0.0049V/12Ω), which fully meets the test needs. The start signal generated by the leakage current of the leakage current and the disconnection signal of the moving and static contacts are respectively sent to the external interrupt input terminal of the LPC2132, and the breaking time of the moving and static contacts of the leakage protector is detected by means of interruption. Pins P0.5 and P0.6 control the closing and breaking of relays J1 and J2 respectively, and select three test currents with different measurement ranges. Serial communication is used between LPC2132 and the host computer. Since the system is a 3.3V system, SP3232E is used for RS-232 level conversion. SP3232E is a RS-232 converter chip with 3V working power supply. The A/D conversion and control circuit is shown in Figure 4.

  software design

The design of the LPC2132 software part is based on the embedded C language and adopts a modular program structure. Including the main program, system initialization subroutine, human-machine interface control function subroutine, current sampling subroutine, leakage action current detection subroutine, leakage action time subroutine, communication with upper computer subroutine, upper computer PC monitoring program.

The main program is the program for the leakage action characteristic detection test. After the test system starts to work, the program keeps cyclically running in the main program, and calls other function subprograms according to different needs. After the call is completed, the program returns to the main program to continue the cycle. The main program flow chart is shown as in Fig. 5.



Figure 5 Main program flow chart

The system initialization subroutine mainly completes the system initialization work, including pin configuration initialization, A/D conversion initialization, timer initialization, interrupt initialization, system parameter initialization, setting test items and parameters, etc. The man-machine interface control function subroutine is the communication between the control system and people, and mainly realizes the scanning of the key functions. The current sampling subroutine performs A/D conversion on the test current signal sent to the LPC2132 (after filtering, amplifying, and voltage boosting, it becomes a unipolar voltage signal of 0~5V), and the resulting digital quantity is restored to the actual circuit through calculation The current value. The leakage action current detection subroutine is used to detect the leakage current value (I△) at the moment when the leakage protector is disconnected. The leakage action time subroutine completes the detection of the leakage action time of the leakage protector. The communication subroutine with the upper computer mainly completes the communication between LPC2132 and the upper computer PC. The upper computer PC monitoring program mainly realizes the control of the upper computer PC to the LPC2132 and displays the measurement results.

The PC monitoring program of the upper computer of the test system is developed based on the LabVIEW8.6 platform. Through the graphical programming environment of LabVIEW, it is easier to use the serial communication operation function in the serial port sub-panel in LabVIEW8.6. It is easier to configure the serial port function. The programming interface of WYSIWYG is compiled, which simplifies the serial communication programming of Windows and realizes the receiving and sending of data.



Figure 6 Test system interface

The control interface is shown in Figure 6, which shows the measured data.

After the system starts the test, the test equipment is automatically initialized according to the set test parameters, and the software sets the control port control word to select the appropriate hardware circuit loop and sampling resistor. Start the test current from less than 0.2 I△n, and steadily increase to I△n within 30s, measure the leakage current value I△ at the moment when the leakage protector is disconnected, if it satisfies I△n0

  in conclusion

This test system overcomes the shortcomings of the traditional manual test method, the operation interface is simple, only need to enter the test conditions and parameters during the test to start the test. The test results are clear at a glance, and the measurement automation and intelligence are realized. It can detect both the non-online leakage protector and the online leakage protector. The test level of the leakage protector is improved, and an effective means is provided for the performance research, quality inspection and production of the leakage protector.