- Effect of low temperatures on different explosion-proof models
Ambient temperatures below -20°C may have an effect on the explosion-proof design of the equipment, and it is advisable to take this into account when evaluating and testing the equipment. If these low temperatures are not specifically provided for in the standards for the different explosion-protected versions, it is advisable to consider the critical issues that may arise. Explosion-proof enclosures “d” Fasteners to ensure the integrity of the enclosure should be made of materials that retain their strength at low temperatures. This is particularly important for temperatures below -40°C. For bonded joints, the use of cold-resistant adhesives is desirable. Explosion-protected bonding surfaces may require additional corrosion protection, especially for equipment used in maritime climates. For bonded joints of materials with different temperature coefficients, it is advisable to take into account the effect of temperature variations from the upper to the lower limit on the explosion-insulating gap. Intrinsically Safe “i” At low temperatures, components used in intrinsically safe equipment, such as safety barriers, as well as dynamic intrinsically safe components with a limited spark time limit power supply performance characteristics will change. It is appropriate to consider these changes in the selection of components, and it is appropriate to use the manufacturer’s specified operating temperature rating in accordance with the requirements of GB/T 3836.4. The rating should take into account the impact of intrinsic safety performance of semiconductor components operating changes to provide the required intrinsic safety features. The intrinsically safe performance of power supplies with dynamic intrinsically safe components used in such systems depends on the ambient temperature of the place of use. At low temperatures, the intrinsically safe power supply dynamic semiconductor components of the sensitivity decreases, switching time increases. GB/T3836.4 stipulates that the spark ignition test should be carried out in the most ignition-prone conditions of the circuit arrangement. However, in practice, the test is usually carried out at laboratory temperature. Therefore, where low temperatures are involved, systems with dynamic intrinsically safe protected power supplies need to be tested for intrinsic safety performance at temperatures within the application range, including the lowest temperature of the dynamic semiconductor components, and under conditions where the spark test device is connected to a suitable load at the maximum operating temperature. Semiconductor components providing intrinsic safety protection at ambient temperatures below -40°C may require special heating systems. For equipment used in cold marine climates, although the equipment meets GB/T 3836.4 creepage distances and insulation materials compared to the leakage trace index (CTI) regulations, may require higher than IP54 level of protection to ensure that the prevention of chlorine may be deposited on the surface of the printed circuit boards caused by traces. Positive Pressure Enclosures “p” Positive pressure systems operating at low temperatures may require additional measures to ensure reliable operation; fixed configurations of heaters, environmental purging devices, or other anti-condensation devices may be required. Liquid-immersed type “o” It is advisable to use liquids suitable for low temperatures or to preheat the equipment before starting. It is advisable to specify this in the manual.
- Effect of low temperature on explosion-proof electrical equipment
The following effects may occur at low temperatures and should be considered:
- Freezing and failure of electrochemical capacitors.
- discharge of battery packs
- Curing and cracking of waxes and protective compounds; 4.
- Loss of elasticity and failure of rubber materials.
- grease freezing affecting hinges and spindles; and
- Failure of relays
- Deterioration of amplification characteristics of transistors
- Loss of ductility or embrittlement of materials or weld surfaces; and
- Differences in material expansion or contraction affecting proper component fit; and
- Increase in oil viscosity, restriction or cessation of flow, resulting in lack of protection or mechanical system failure.
- In aged electrical equipment the oil used as dielectric insulation can contain more water, which can reduce the dielectric strength or even cause insulation failures.
- Selection, installation and use of equipment
1. limited function equipment explosion-proof certificate of compliance may allow the equipment to operate at low temperatures, but the function of the equipment at low temperatures is not specified. At low temperatures, some batteries should not be used as a backup power supply for emergency lights, can use the battery is located in a higher temperature place of uninterruptible power supply system, or other adequate measures (such as heating). At low temperatures, the light output of fluorescent tubes will be reduced and other light sources may be considered to provide the necessary light output. For other systems where batteries are typically used as a backup power source, simpler methods of backup power may be required.
2.Seals and sealing materials should be selected in accordance with their low-temperature characteristics and elastic seals should be selected to avoid freezing conditions. It is desirable that the seals are adequately treated to facilitate installation and maintenance, for example, lubrication of the seals.
3.cables and wires in addition to the requirements of GB / T 3836.15, the following circumstances should also be considered: low temperature cable sheath and cable introduction device sealing element hardness may change, in the installation, inspection and maintenance, it is appropriate to follow the manufacturer’s recommendations; low temperature cable may need to increase the minimum allowable bending radius; GB / T3836.15 due to the intrinsically safe equipment used in cable As GB/T3836.15 has no special requirements for intrinsically safe equipment cable introduction device, so for low-temperature applications, it is advisable to avoid the use of no “d”, “e”, “t” type explosion-proof certificate of conformity of the cable introduction device, because they may not have carried out low-temperature test.