CE certification of electronic appliances

LVD and EMC directives are involved in CE certification of electronic appliances

General inspection

Including visual inspection;Check the overall dimension and installation dimension of electrical appliances;Electrical clearance and creepage distance inspection;Contact opening distance, overtravel and pressure inspection;Electrical operation force inspection, etc.The gap of an electrical appliance refers to the minimum air insulation distance between different poles or between two conductive circuits after one pole is disconnected.Creepage distance refers to the leakage distance along the surface of insulating parts supporting and fixing different poles or between two conductive circuits after one pole is disconnected.When the surface of electrical insulation is adsorbed with water, heated or polluted, the surface resistance decreases sharply.In order to ensure a certain insulation performance of electrical insulation parts, the minimum electrical clearance and surface leakage (creepage) distance are specified according to voltage level and place of use.Contact opening distance refers to the shortest distance between contacts when the electrical contact is in the breaking position.The over travel of the contact is to ensure the reliable closing of the contact after a certain wear during the operation of the electrical contact.For manually operated electrical appliances, the operating force shall be checked to check whether the operating force meets the specified requirements of manual operation.

Voltage drop measurement

Measure the voltage drop at both ends of the measured part after DC current is applied to the contact or conductive circuit.The purpose of measurement is to evaluate the resistance value at both ends of the measured part, and use the resistance value to indirectly judge the assembly quality and heating temperature rise of electrical appliances.For example, for the contact of small relay, the temperature of the contact cannot be measured by thermoelectric couple, but by measuring the voltage drop at both ends of the contact.

Temperature rise test

It is used to verify whether all parts and components are within the allowable temperature rise range after the electrical appliance is powered on and heated until stable.The temperature rise of contacts, wires, copper bar terminals and coils of different electrical appliances are specified in standards or technical conditions.If the temperature rise at the terminals of electrical contacts and conductive copper bars is too high, it will lead to oxidation of the contact surface. The oxidized contact surface will increase the contact resistance, which will further increase the temperature rise.If the temperature rise of the coil is too high, the outer insulation material will age rapidly, shorten the service life or burn out the coil.

Insulation resistance and withstand voltage test

The insulation quality of electrical products is usually evaluated by insulation resistance and withstand voltage test.Insulation resistance refers to the resistance of the insulation structure between two electrodes of electrical products.After DC voltage is applied to the two electrodes, there is leakage current in the insulation volume and along the insulation surface, that is, the insulation material has insulation resistance.The insulation resistance of electrical appliances is related to many factors. When the working temperature of electrical appliances increases, the insulation resistance of insulating materials will decrease;When the insulating material is damp, the surface adsorbs water or is polluted, the insulation resistance will also decrease;After the on-off capacity test of the switching apparatus, the insulation structure of the tested apparatus is burned by the arc, and the insulation resistance will also decrease.In order to ensure the safety of electrical appliances, there are certain requirements for the resistance of insulation resistance.The insulation resistance of general electrical appliances shall be greater than 1.5 megohm.The insulation part of the electrical appliance shall not only bear the rated voltage for a long time, but also bear overvoltage several times higher than the rated voltage in a short time.Overvoltage is caused by lightning in the atmosphere or the operation of switches in the line.When the overvoltage exceeds a certain value, the insulating material will have surface discharge (called surface flashover), or insulation breakdown and become a conductive path.The voltage withstand test of low-voltage apparatus is divided into power frequency voltage withstand test and impulse voltage withstand test.

Rated making and breaking capacity test

A test to verify that the switchgear has the specified on and off capacity under the specified service conditions.During the test, connect the resistor and reactor to the load end of the tested switch to simulate the actual load (such as motor load).Short circuit making and breaking capacity test is a test to verify the making and breaking capacity of low-voltage apparatus under load short circuit.

hort time withstand current capability test

Test to verify the ability of low-voltage apparatus to withstand short-circuit current thermal effect and electrodynamic effect in closed state.The electrodynamic force between conductive circuits is directly proportional to the square of the current passing through the circuit. Therefore, the greater the short-circuit current, the stronger the electrodynamic force.If the mechanical strength of the insulation support of the electrical conductive circuit is not enough, it will produce mechanical deformation or even be damaged.Through a large short-circuit current in a short time, the temperature of the conductive circuit will rise rapidly, but the maximum temperature rise shall be within the allowable value.

Action characteristic test

Action characteristic is the main technical performance of low-voltage apparatus.The action characteristic test includes the measurement of the closing and releasing action value of the electric appliance and the measurement of the protection characteristics.For example, the electromagnetic mechanism of low-voltage apparatus has certain requirements for the pull-in voltage and release voltage of the voltage coil.

life test

The allowable operation times of low-voltage apparatus are the service life of low-voltage apparatus.For frequently operated electrical appliances, this is an important technical index.For example, the service life of contactor is the main basis for evaluating quality.There are two life indicators of electrical appliances. One is mechanical life, which refers to the number of no-load operations that electrical appliances can withstand without repairing or replacing parts;The other is the electrical life, which refers to the number of operations that the electrical appliance can withstand the load without repairing or replacing parts under the specified working conditions.The former mainly depends on the firmness of electrical mechanical structure and the mechanical strength of parts;The latter mainly depends on the wear resistance of the contact.Generally, the electrical wear of the contact is serious, so the electrical life of the low-voltage apparatus is only a fraction of the mechanical life.Immunity test some low voltage apparatus are made of electronic devices, such as AC electronic release, transistor time relay, etc.In use, these electronic devices are required to withstand certain external high-frequency and low-frequency interference signals, and their action value and error shall not exceed the provisions of product technical conditions.The interference signal is high frequency in the range of 0.15 ~ 300 MHz and low frequency in the range of 150 ~ 15000 Hz.The radiated electromagnetic wave of high-frequency interference signal can act on the tested appliance from space, or it can be added to the tested appliance from the power lead of the tested appliance.The low-frequency interference signal is mainly added to the tested electrical appliance from the power lead.Immunity test is to simulate high and low frequency interference signals with a certain strength, add them to the tested appliance from space and from the power line, and detect the repetition error and action value error of the tested product.

Special test

Special test items for low-voltage electrical appliances for special purposes.For example, conduct explosion-proof performance test on mining explosion-proof electrical appliances;Carry out vibration, impact and centrifugal acceleration tests on aviation low-voltage electrical appliances;Conduct damp, salt spray, vibration and impact tests on marine low-voltage electrical appliances;Carry out chemical corrosion resistance test on low-voltage electrical appliances for chemical industry.