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Necessity of safety upgrade of standard increased safety mot
source：未知 time：2024-09-05 13:56nbsp; click：
1. Increased safety explosion-proof motors are widely used in flammable and explosive hazardous places, and their explosion-proof performance is closely related to safe production. At present, a large number of increased safety explosion-proof motors in service are manufactured in accordance with the requirements of the old national standard GB3836.3-2000, and only some increased safety motors meet the requirements of the new national standard GB3836.3-2010. Therefore, it is very necessary to analyze the differences between the new and old standards, evaluate the explosion-proof performance of motors, and explore strategies to improve motor safety.
2. Standards related to purge of increased safety motors
Currently, the explosion-proof motors commonly used in the domestic petrochemical industry are mainly: (1) flameproof type (Exd); (2) increased safety type (Exe); (3) positive pressure enclosure type (Exp), and the applicable standards are GB∕T 3836.2-2021 "Explosive atmospheres Part 2: Equipment protected by flameproof enclosure "d""; GB∕T 3836.3-2021 "Explosive atmospheres Part 3: Equipment protected by increased safety type "e""; GB∕T 3836.5-2021 "Electrical apparatus for explosive gas atmospheres Part 5: Positive pressure enclosure type "p"". There is no requirement for pre-purging before starting the flameproof motor. Before the release of the national standard GB 3836.3-2010, there was no mandatory requirement for the evaluation of the stator/rotor ignition hazard factor for increased safety motors. Positive pressure housing type motors need to be pre-purged before starting and pressure maintained during operation. The pre-purging and pressure maintaining system of the motor requires the use of a clean and safe gas source, which increases the operating cost. Traditionally, from the perspective of economy and convenience of operation and maintenance, and due to factors such as equipment manufacturing, the explosion-proof motors in petrochemical plants are mainly flameproof motors and increased safety motors that do not require pre-purging, and positive pressure housing type motors are rarely used. With the release of GB∕T 3836.3-2021, the situation has changed. According to the national standard GB∕T 3836.3-2021, for increased safety motors with excessive ignition hazard factors/coefficients, certain special measures must be taken to ensure safety, generally by setting up a pre-purging system and using it before starting. The vast majority of motors in petrochemical plants are squirrel cage motors, and some are synchronous motors.
3. Purge requirements for increased safety motors
GB/T 3836.3-2021 Explosive atmospheres Part 3: Equipment protected by increased safety "e" requires the following: 5.2.7.3 Assessment of possible air gap sparks Rotating motors shall be assessed for possible air gap sparks as follows. For the "ec" protection level, this assessment is only performed for motors with duty S3, S4, S5, S7, S8 or S10 and rated power exceeding 100 kw. If the total factor determined in accordance with Table 5 is greater than 6, one of the following protection methods shall be adopted. a) The motor or representative sample shall be tested in accordance with the provisions of 6.2.3.2. b) The motor shall be designed to allow special measures to ensure that there is no explosive gas environment in its housing during startup. In this case, the explosion-proof certificate number shall include the "X" suffix in accordance with the marking requirements of GB/T 3836.1, and the special method adopted shall be detailed in the special conditions of use of the explosion-proof certificate. c) The starting current of the motor is limited to 300% of the rated current (In). If external current limitation is required, the explosion-proof certificate number shall include the "X" suffix in accordance with the marking requirements of GB/T 3836.1, and specify in the special conditions of use of the explosion-proof certificate that the motor is only suitable for reduced voltage starting and the starting current is limited to 300% of the rated current. Note 1: Special methods include ventilation before starting to remove accumulated flammable gases (for example, using purge, but different from GB/T 3836.5 positive pressure protection "pzc" level) or fixed gas detectors in the motor housing (see GB/T 20936.2) to determine that the motor does not have ignitable concentrations of flammable gases. Other methods are carefully negotiated between the manufacturer and the user. Note 2: For motors driving high inertia loads or motors used for automatic restart, these tests can only be carried out under representative operating conditions, away from the torsional resonance of the entire transmission mechanism series, and phase loss restart is not included here. Special uses are carefully negotiated between the manufacturer and the user. Note 3: Using a frequency converter to control the motor to provide current limitation is usually an acceptable solution. For other reduced voltage starting methods, careful adjustments must be made to the motor and reduced voltage starter.
electric motor price, Ex motor, Motor manufacturers in China, three phase induction motor, Wolong Nanyang Explosion Protection
Currently, the explosion-proof motors commonly used in the domestic petrochemical industry are mainly: (1) flameproof type (Exd); (2) increased safety type (Exe); (3) positive pressure enclosure type (Exp), and the applicable standards are GB∕T 3836.2-2021 "Explosive atmospheres Part 2: Equipment protected by flameproof enclosure "d""; GB∕T 3836.3-2021 "Explosive atmospheres Part 3: Equipment protected by increased safety type "e""; GB∕T 3836.5-2021 "Electrical apparatus for explosive gas atmospheres Part 5: Positive pressure enclosure type "p"". There is no requirement for pre-purging before starting the flameproof motor. Before the release of the national standard GB 3836.3-2010, there was no mandatory requirement for the evaluation of the stator/rotor ignition hazard factor for increased safety motors. Positive pressure housing type motors need to be pre-purged before starting and pressure maintained during operation. The pre-purging and pressure maintaining system of the motor requires the use of a clean and safe gas source, which increases the operating cost. Traditionally, from the perspective of economy and convenience of operation and maintenance, and due to factors such as equipment manufacturing, the explosion-proof motors in petrochemical plants are mainly flameproof motors and increased safety motors that do not require pre-purging, and positive pressure housing type motors are rarely used. With the release of GB∕T 3836.3-2021, the situation has changed. According to the national standard GB∕T 3836.3-2021, for increased safety motors with excessive ignition hazard factors/coefficients, certain special measures must be taken to ensure safety, generally by setting up a pre-purging system and using it before starting. The vast majority of motors in petrochemical plants are squirrel cage motors, and some are synchronous motors.
3. Purge requirements for increased safety motors
GB/T 3836.3-2021 Explosive atmospheres Part 3: Equipment protected by increased safety "e" requires the following: 5.2.7.3 Assessment of possible air gap sparks Rotating motors shall be assessed for possible air gap sparks as follows. For the "ec" protection level, this assessment is only performed for motors with duty S3, S4, S5, S7, S8 or S10 and rated power exceeding 100 kw. If the total factor determined in accordance with Table 5 is greater than 6, one of the following protection methods shall be adopted. a) The motor or representative sample shall be tested in accordance with the provisions of 6.2.3.2. b) The motor shall be designed to allow special measures to ensure that there is no explosive gas environment in its housing during startup. In this case, the explosion-proof certificate number shall include the "X" suffix in accordance with the marking requirements of GB/T 3836.1, and the special method adopted shall be detailed in the special conditions of use of the explosion-proof certificate. c) The starting current of the motor is limited to 300% of the rated current (In). If external current limitation is required, the explosion-proof certificate number shall include the "X" suffix in accordance with the marking requirements of GB/T 3836.1, and specify in the special conditions of use of the explosion-proof certificate that the motor is only suitable for reduced voltage starting and the starting current is limited to 300% of the rated current. Note 1: Special methods include ventilation before starting to remove accumulated flammable gases (for example, using purge, but different from GB/T 3836.5 positive pressure protection "pzc" level) or fixed gas detectors in the motor housing (see GB/T 20936.2) to determine that the motor does not have ignitable concentrations of flammable gases. Other methods are carefully negotiated between the manufacturer and the user. Note 2: For motors driving high inertia loads or motors used for automatic restart, these tests can only be carried out under representative operating conditions, away from the torsional resonance of the entire transmission mechanism series, and phase loss restart is not included here. Special uses are carefully negotiated between the manufacturer and the user. Note 3: Using a frequency converter to control the motor to provide current limitation is usually an acceptable solution. For other reduced voltage starting methods, careful adjustments must be made to the motor and reduced voltage starter.
electric motor price, Ex motor, Motor manufacturers in China, three phase induction motor, Wolong Nanyang Explosion Protection
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