Electrical motors are actuating devices used in all kind of industries. Which should be maintained and cared periodically to ensure the motor works properly.
Also, extreme care should be given if the electric motors are installed at location classified under hazardous locations. Some combustible materials that could easily ignite and create a fire hazard are a hazardous environment or location. To avoid posing an explosion threat to installation, the electric motors operated in such an environment need to be carefully specified and selected.
Arcs, sparks and high temperatures on the surfaces of electric motors are common sources of ignition of hazardous substances. Therefore it is necessary to specify and select the right motors otherwise the consequences of an explosion and eventual fire resulting from using the wrong type of motor could range from minor injuries, production downtime and destruction of valuable investment as well as death.
To define and select the right motor for use in a hazardous environment, four basic information is required:
- Class of materials in the hazardous environment
- Division classification of the hazardous environment
- Group classification of the hazardous environment
- The autoignition temperature (AIT) of the hazardous material in the environment
The motor should be dimensioned according to the standards so that it’s surface temperature with respect to the temperature class remains at a safe level.
The motor should be dimensioned according to the specifications so that it’s surface temperature remains at a reasonable temperature safe level. It includes either mixed form checks or direct temperature control in most cases.
Also PWM converter is important equipment comes with electrical motors, it should be subjected to test flame proof.
The following parameters must be shown on hazardous area motors intended for variable speed operation:
- speed range
- power range
- type of torque (constant or quadratic)
- converter type and required minimum switching
In order to be able to successfully apply an electric motor in a hazardous environment, these motors must have certain critical features that make them suitable for operation in this environment without creating problems.
These motors must be built and labelled as explosion-proof
An explosion-proof engine must withstand an internal explosion without splitting.
An explosion-proof motor must have flame paths during an explosion to exhaust hazardous gases and to cool the hazardous material as it leaves the motor to prevent further explosion.
The more severe the hazards of the explosion, the stronger the engine enclosures and the longer the paths of the flame. For example, group A environment engines with acetylene gas require the highest enclosure resistance and the longest flame paths compared to those used in group D environment with propane gas only.
A temperature code (T-Code) is assigned to engines for use in hazardous environments, an identification number that describes the maximum surface temperature in contact with hazardous materials. The T-code defined temperature value applies to all motor operating conditions including burnt-out, overload, and locked rotor current.
The T-code for a given engine must be lower than the hazardous gas or combination AIT in the area in which the engine works. This is to ensure that when it touches the motor surfaces and enclosure during operation, the hazardous materials do not flame spontaneously.
It is not an easy task to select the right type of engine that meets the requirements for use in a hazardous environment. Nevertheless, electric motor manufacturers for use in hazardous locations have standard nameplates containing the following information:
- Type of Enclosure of Motor
- Class of hazardous materials for which the motor is suitable
- Group of hazardous materials
- T-code of the electric motor