Ms. Can shared a story with her friend, Xiao J, who sells motors. Their company manufactures ordinary three-phase asynchronous motors , and during product promotion, even under normal operating conditions, customers still demanded a production license. Ms. Can suggested that Xiao J collect relevant regulations or materials regarding production license management to facilitate communication with customers.
Information on the management of industrial product production licenses
In June 2017, the State Council decided to further adjust the product catalog for which industrial product production licenses are required. Production licenses for 19 categories of industrial products were abolished, 3 categories of industrial products were transferred from production license management to mandatory product certification, and the authority to manage production licenses for 8 categories of industrial products was delegated from the General Administration of Quality Supervision, Inspection and Quarantine (AQSIQ) to the provincial-level quality and technical supervision departments. After the adjustment, a total of 38 categories of products continued to be subject to production license management, of which 19 categories were managed by AQSIQ and 19 categories by the provincial-level quality and technical supervision departments.
Today, Ms. Can will discuss with everyone the performance requirements and testing criteria for positive pressure explosion-proof motors, which differ from ordinary motors, based on the topic of Little J. Depending on the specific operating conditions of the motor, to obtain a production license, in addition to the requirements for ordinary motors, it must meet the relevant performance requirements and inspection specifications for positive pressure explosion-proof motors and obtain an explosion-proof certificate.
Positive pressure explosion-proof motor
Positive pressure motors are operated by supplying clean air or inert gas to the motor and maintaining a certain pressure. This prevents external explosive mixtures from entering the motor and coming into contact with sparks and heat-generating components inside, thus achieving explosion protection. Based on the gas supply method, they can be divided into two types: explosion-proof ventilated type and explosion-proof gas-filled type.
Seven Special Tests for Positive Pressure Explosion-proof Motors
●Shell strength test
The structural strength and sealing performance of the motor and its auxiliary pipelines are checked using air or inert gas. The casing strength must be able to withstand 1.5 to 2 times the maximum overpressure value specified during normal operation, but the minimum is 200 Pa. The test time is 1 minute, and the casing, pipelines and sealing rings are considered qualified if there is no damage.
●Spark ejection test
The air inlet and outlet of the motor ventilation duct should be located in a safe place without explosion hazards. If the exhaust outlet is located in an explosion hazard area, it should be equipped with a device to prevent sparks, electric arcs, and flammable materials from being blown out of the casing. If there is a risk of sparks being ejected from the gaps between the shafts and at the joints of the ducts, sparks can be artificially created, such as by igniting some flammable material, and then normal ventilation can be maintained to observe whether sparks can be blown out from the gaps.
●Minimum wind pressure test
Connect the fan and ventilation duct according to the design requirements, and connect the valves for adjusting air pressure and air volume at the air inlet. Determine the air pressure measurement point based on the motor structure, airflow path, and changes in air duct dimensions. The pressure measurement point should be set in places with low air pressure and in gaps where explosive gases may enter the casing. Generally, it should be set in the following locations: (1) air inlet and outlet. (2) the location where the pressure measuring instrument is to be installed. (3) places and gaps in the casing where leakage may occur, such as shaft extensions. (4) places where the airflow changes drastically.
U-tube manometers, micromanometers, and Pitot tubes are generally used to measure air pressure. Adjust the inlet flow rate and pressure to meet technical requirements, and then measure whether the positive pressure at each measuring point exceeds 50 Pa. Tests should be conducted with the motor stationary and at its rated speed.
● Ventilation dead zone inspection test
The motor casing is filled with hydrogen (nitrogen or carbon dioxide gas) at a concentration of 60% ± 1%. Ventilation and purging are performed with an airflow rate five times the total volume of the motor casing and associated ducts, or according to the airflow rate and time specified in the product instruction manual. Then, a gas analyzer is used to measure the gas concentration at 3-5 points in the expected ventilation dead zones. A gas concentration ≤ 1% is considered合格 (qualified).
● Reliability test of the interlocking device between the motor and the fan.
Before operating a positive pressure motor, both the motor and the ventilation duct must be ventilated and cleaned. The ventilation system must ensure that the motor is not powered on before air exchange in the motor and ductwork. The motor can only be powered on and put into operation after a measured amount of air (at least five times the volume of the motor and duct cavity) has been pumped into the motor and ductwork. When the motor stops, ventilation can only cease when the surface temperature of the internal components is below the permissible overheating temperature for explosive gases. This test verifies the accuracy and reliability of the system's control measures; failure to do so indicates a pass.
● Reliability test of wind pressure protection device
Positive pressure motors must maintain the air pressure specified by the product during normal operation. When the air pressure at the air outlet is artificially reduced to 100Pa or the minimum air pressure specified by the product, the air pressure protection device should activate.
This test must be performed 5 times. If the pressure relay cannot be installed at the air outlet, the operating value of the pressure relay is often increased to check and monitor the air pressure at the air outlet and ensure the air pressure at the motor outlet. This test should be performed not only when the motor leaves the factory, but also during the trial run at the installation location.
● Test on the temperature rise of the motor casing and the cooling time of internal heating elements after power failure
The temperature of the casing and internal heating elements of a positive-pressure motor must be measured under rated load. The air pressure and volume during measurement should be at minimum flow and pressure. It is also necessary to measure the maximum temperature of the motor casing when ventilation is stopped. A stopwatch should be used to measure the time required for the surface temperature of the internal heating elements to cool to the limit temperature (i.e., the maximum permissible surface temperature of the equipment) after power is cut off. This time is the shortest time that ventilation must continue after power is cut off when the motor has finished operating.
