Positive pressure type explosion-proof refers to the method of keeping the pressure of the protective gas inside the shell higher than the external atmospheric pressure to prevent the external explosive gas from entering the shell. The motor with the method of explosion-proof is called positive pressure type explosion-proof motor. With the progress of science and technology in our country, the positive pressure explosion-proof motor is gradually being produced in major domestic electric machine factories. As a kind of explosion-proof type, positive pressure explosion-proof motor has great advantages in the application of large explosion-proof motor structure, which is commonly used in the production of large explosion-proof motor explosion-proof structure.

Positive pressure type explosion-proof motor specific explosion-proof measures are: in the motor supplemented with clean air or inert gas and maintain a certain pressure, so that the external explosive mixture can not enter the motor and the spark and heating parts in the motor contact, so as to achieve the purpose of explosion-proof. According to the gas supply, it can be divided into explosion-proof ventilation type and explosion-proof inflation type.

To ensure explosion-proof performance, positive pressure explosion-proof motor must undergo a series of special tests, Ms. Take part in the analysis of these special test items one by one, and share with you the positive pressure explosion-proof technology and experience.

● Shell strength test

Air or inert gas to check the motor and the attached pipeline structural strength and sealing, its shell strength should be able to withstand the normal work of the maximum overpressure value of 1.5~2 times, but the minimum is 200Pa, the test time is lmin. It is qualified that there is no damage to the shell, pipe and sealing ring.

● Ventilation dead Angle inspection test

The motor housing is filled with hydrogen or nitrogen gas or carbon dioxide gas, and its concentration is 60% soil 1%. Air volume 5 times of the total volume of motor housing and auxiliary pipes or according to the air volume and time specified in the product instruction manual for ventilation and selection, and then, with the gas analyzer in the expected ventilation dead Angle 3-5 measurement. The above gas concentration ≤1% is qualified.

● Motor static and running minimum wind pressure test

According to the design requirements, connect the fan and ventilation duct, and connect the valve regulating the air pressure and air volume at the air inlet. According to the motor structure, airflow flow path, wind path size changes to determine the wind pressure measurement point.

The pressure measuring point should be set in the place where the wind is low and the gap where explosive gas may enter the shell, generally located in the following position:

(1) air inlet and outlet;

(2) the place where the pressure gauge is scheduled to be installed;

(3) the shell may leak places and gaps, such as shaft extension position;

(4) Where the airflow changes dramatically.

Measurement of wind pressure generally use u-tube manometer, micro manometer and complete trusteeship. Adjust the flow rate and pressure value of the air inlet, and measure whether the positive pressure value of each pressure measuring point exceeds 50Pa when meeting the requirements of technical conditions. The test should be carried out at rest and rated speed respectively.

● Action reliability test of interlocking device between motor and fan

The positive pressure motor should be ventilated and cleaned before working.

The working system of the ventilator should ensure that the motor can not be connected to the power supply before ventilation of the motor and air duct. Only when the air in the motor and air duct is flushed with a certain amount of air (at least 5 times the cavity volume of the motor and air duct) can the motor be connected to the power supply and put into operation. When the motor is shut down, the fan can stop ventilation only when the surface temperature of the parts inside the motor is lower than the overheating temperature allowed by explosive gas.

This test is to check the system to ensure the accuracy and reliability of positive pressure control test. The motor is qualified only when it can operate reliably or the positive pressure explosion-proof conditions are met.

● Operation reliability test of wind pressure protection device

Positive pressure type explosion-proof motor in normal operation to maintain the wind pressure specified by the product. When the air pressure at the air outlet is artificially lowered to 100Pa or the minimum air pressure specified by the product, the air pressure protection device shall operate.

The experiment was carried out five times. If the pressure relay cannot be installed at the air outlet, in order to check and supervise the air pressure at the air outlet, the action value of the pressure relay is often increased to ensure the air pressure at the motor outlet. This test should be repeated at the installation site in addition to the motor at the factory.

● Motor shell temperature and internal heating element after power failure cooling time test

The surface of the housing and internal heating elements of the positive pressure motor shall be measured at load rating of the motor. The wind pressure and volume are measured at the minimum flow and pressure. It is also necessary to measure the maximum temperature of the motor housing when the wind is stopped. Use a stopwatch to measure the time required by the heating parts inside the shell from the cooling of the surface temperature after power supply to the limit temperature (i.e. the maximum surface temperature allowed by the equipment). This time is the shortest time that the motor needs to continue ventilation after power supply is cut off at the end of operation.

● Prevent spark ejection test

The air inlet and outlet of the motor ventilation pipe should be located in a safe place without explosion risk. If the exhaust port is located in an explosion hazard, the exhaust port should be installed with fireproof flowers, electric arcs and inflammables blown out of the shell. If the gap between the rotating shaft and the joints of the pipeline may be in danger of ejecting sparks, artificial sparks can be manufactured, such as lighting some combustible materials, and then normal ventilation, observe whether sparks can be blown out of the gap.