The use of variable frequency drives (VFDs) has led to improved efficiency and control in various industrial applications. However, their implementation in explosive atmospheres presents additional challenges that must be carefully managed to ensure the safety of operations.

Protection against explosive atmospheres: What do we need to know?

For an atmosphere to be considered hazardous, three factors must coincide: flammable material, oxygen, and an ignition source. Engines designed to operate in these conditions must be protected to prevent these three elements from combining, limiting the spread of a possible explosion.

Common Forms of Protection in Electric Motors

There are various forms of protection that are applied depending on the type of atmosphere and the level of risk:

• Ex nA (Non-Sparking): Prevents the generation of sparks or electric arcs during normal operation.
• Ex e (Additional Safety): Minimizes the risk of sparks and arcs, even under abnormal conditions.
• Ex p (Pressurized Appliance): The engine is placed inside a pressurized enclosure to avoid contact with flammable gases.
• Ex d (Flame Proof): Prevents the spread of an explosion inside the engine.
• DIP (Explosive Dust Protection): Prevents flammable dust from entering the engine and causing ignition.

The Impact of Variable Frequency Drives (VFDs) 

VFDs introduce a non-sinusoidal power supply that can lead to several problems. One of the main ones is the increase in temperature due to energy losses inside the engine.

How Do VFD-Generated Harmonics Affect Them?

VFDs produce harmonics that affect motor isolation and increase rotor losses. Not only does this generate additional heat, but it can also reduce the life of the motor by affecting the windings and creating potential ignition hazards.

Critical Factors That Cause Extra Heat in VFD Engines

The use of VFDs also generates several additional heat sources that can have a negative impact on motors:

• Electromagnetic losses: These are the main cause of extra heat, especially in rotor windings.
• Transient voltage spikes: These spikes press on the winding insulations, reducing the life of the motor.

Engine starting is another critical factor, as the initial current can be between 6 to 10 times higher than the rated current, generating considerable thermal stress.

Adaptation of Variable Frequency Drives in Hazardous Areas

One of the biggest challenges is the adaptation of drives and motors in hazardous areas. Not all motor manufacturers supply compatible drives, forcing users to combine products from different suppliers. Additional testing is critical to ensure that the motor and drive combination is safe for use in explosive atmospheres.

The Risk of Combining Products from Different Suppliers

Failure to properly test the motor and drive combination can lead to additional risks, as operating conditions change significantly when using a VFD instead of a direct power supply. In addition, installations of engines originally powered by in-line start require careful evaluation to avoid dangerous situations.

Ensuring Safe Use of VFDs in Explosive Zones

The use of variable frequency drives in explosive atmospheres requires meticulous planning and rigorous evaluation of all factors involved. Temperature, system compatibility and insulation safety are key aspects to avoid failures and ignition risks. By following regulations and performing the necessary tests, we can ensure the safe operation of engines in hazardous areas.