Generally, the human body can feel the current value of the stimulation is about 1 mA. When the human body passes 5~20mA, the muscles will contract and twitch, so that the person cannot be separated from the wire. The product of electric shock current and time allowed by most countries is 30mA*S human body resistance Usually 1500 ohms~300000 ohms, typical value is 1000 ohms~5000 ohms, recommended value is 1500 ohms
The safe voltage value can be obtained from the reaction of the human body to the current and the resistance of the human body: the safe voltage value in our country is generally 12~50V
Withstand voltage, leakage current and safety of power EMI filter:
Pressure and safety
1. If the Cx capacitor in the filter is broken down, it is equivalent to a short circuit of the AC grid, at least causing the equipment to stop working; if the Cy capacitor is broken down,
It is equivalent to adding the voltage of the AC power grid to the casing of the equipment, which directly threatens personal safety and affects all the equipment with the metal casing as the reference ground.
Circuit or equipment safety, often lead to the burning of certain circuits or equipment.
2. Some international pressure-resistant safety standards are as follows:
Germany VDE0565.2 High Voltage Test (AC) P, N to E 1.5kV/50Hz 1 min
Switzerland SEV1055 High Voltage Test (AC) P, N to E 2*Un+1.5kV/50Hz 1 min
US UL1283 High Voltage Test (AC) P, N to E 1.0kV/60Hz 1 min
Germany VDE0565.2 High Voltage Test (DC) P to N 4.3*Un 1 min
Switzerland SEV1055 High Voltage Test (DC) P to N 4.3*Un 1 min
US UL1283 High Voltage Test (DC) P to N 1.414kV 1 minute
illustrate:
(1) The reason for using DC voltage in the P-N withstand voltage test is that the Cx capacity is large. If AC test is used, the current capacity required by the withstand voltage tester
It is very large, resulting in large volume and high cost; this problem does not exist when DC is used. But to convert the AC working voltage into the equivalent DC working voltage
For example, the maximum AC working voltage is 250V(AC)=250*2*1.414=707V(DC), so the UL1283 safety specification is
1414V(DC)=707*2.
(2) The withstand voltage test conditions in the manual of the internationally renowned filter professional factory:
Corcom Corporation (USA) P, N to E: 2250V(DC) for one minute P to N: 1450V(DC) for one minute
Schaffner (Switzerland) P, N to E: 2000V(DC) for one minute P to N: Except for
Domestic filter professional manufacturers generally refer to German VDE safety regulations or American UL safety regulations
Leakage current and safety
The common mode capacitor Cy of any typical filter circuit has one end terminated in a metal case. From the point of view of voltage division, the metal casing of the filter has
1/2 of the rated voltage, so from a safety point of view, the leakage current (leakage current) from the filter to the ground through Cy should be as small as possible.
will endanger personal safety.
The safety regulations for leakage current in some major industrial countries in the world are as follows:
Note: 1. The leakage current is directly proportional to the grid voltage and grid frequency. The leakage current of the 400Hz grid filter is 8 times that of the 50Hz grid (ie
Filters that meet safety regulations in power frequency power grids may not necessarily meet safety regulations in higher frequency power grids)
2. When checking the leakage current of the filter, a measurement circuit that conforms to international standards must be used (as shown in the figure below). When measuring, the metal case cannot
Grounded, must be suspended.
Block diagram of filter leakage current test circuit:
Applications
1: Household appliances - withstand voltage test of refrigerators:
Test the withstand voltage between the power supply part and the ground. Test conditions: AC1500V, 60s. Test results: no breakdown and flashover. Safety protection: The operator wears insulating gloves, the workbench is laid with insulating pads, and the instrument is properly grounded. Operator's quality: carry out pre-job training, proficient in operating instruments, and can basically identify and deal with instrument failures.
Optional instruments: RK2670/71/72/74 series, program-controlled RK7100/RK9910/20 series.
Testing purposes
Make the power supply of the instrument reliably grounded, and test the withstand voltage characteristics of the product.
Testing process
1.Connect the high voltage output of the instrument to the power input terminal of the refrigerator (L.N are connected together) to the grid power part. The ground terminal (return) of the instrument is connected to the ground terminal of the refrigerator.
2. The preset alarm current is set according to the user's standard. Set the time to 60s.
3. Start the instrument, adjust the voltage to display 1.5Kv, and read the current value. During the test process, the instrument does not have an over-leakage alarm, indicating that the withstand voltage has passed. If an alarm occurs, the product is judged to be unqualified.
Precautions
After the test is completed, the power of the instrument must be turned off before the product and the test line can be taken to avoid malfunctions and safety accidents.
2. Leakage current test of household appliances-washing machine
Test conditions: On the basis of 1.06 times of the working voltage, test the leakage current value between the power supply and the protective ground of the test network. Test purpose: Whether the exposed metal parts of the casing have unsafe currents when the electrical appliance under test is working.
Test results: read the leakage current value, whether it exceeds the safe value, the instrument will alarm with sound and light. Safety Note: During the test, the instrument and the DUT may be charged, and it is strictly forbidden to touch it with hands to prevent electric shock and safety accidents.
Optional models: RK2675 series, RK9950 series, according to the power of the tested product. The single-phase is optional from 500VA-5000VA, and the three-phase is RK2675WT, which has two functions of three-phase and single-phase.
Test steps:
1: The instrument is powered on, and the power supply is reliably grounded.
2: Turn on the power switch of the instrument, the instrument display window will light up. Press the test/preset button, select the current range of 2mA/20mA, adjust the PRE-ADJ potentiometer, and set the alarm current. Then pop up the preset/test button to test state.
3: Connect the electrical product under test with the instrument, start the instrument, the test light is on, adjust the voltage adjustment knob to make the voltage indication meet the test requirements, and after reading the leakage current value, reset the instrument and adjust the voltage to the minimum.
Note: During the test, do not touch the shell of the instrument and the DUT.
Three: ground resistance test
Test conditions: current 25A, resistance less than 100 milliohms. Test the on-resistance between the ground of the power input and the exposed metal parts of the case.
Optional instruments: RK2678XM series (current 30/32/70 ampere optional), RK7305 series program-controlled machine, RK9930 series (current 30/40/60 ampere optional), program-controlled series with PLC signal output, RS232, RS485 communication functions.
test steps
1: Plug in the power cord of the instrument to ensure that the instrument is reliably grounded.
2: Turn on the power and preset the upper limit of the alarm resistance.
3: Connect the test wire to the terminal of the instrument panel according to the color and thickness (the thick wire is connected to the large post, and the thin wire is connected to the small post).
4: The test clips are respectively connected to the ground of the device under test (the ground wire of the power input end) and the protective ground of the casing (bare metal parts) to ensure that the test point is turned on, otherwise the test current cannot be adjusted.
5: Start the instrument (click START to start), the instrument test light is on, adjust the current (program-controlled series needs to be set first) to the required value for the test, and read the resistance value.
6: If the test fails, the instrument will have a buzzer alarm (sound and light), and the program-controlled series of test results will have PASS, FAIL indicator lights and sound and light alarms.
Post time: Oct-19-2022
