Search

Safety has always been one of the most important topics of discussion within chemical, oil and gas industry organizations. Recent developments aiming to improve the safety of electrical machines used in hazardous areas include the adoption of risk assessment requirements for increased safety and non-sparking motors by the IEC 60079-7:2001/:2006 and IEC 60079-15:2005 standards. These requirements oblige manufacturers to prove their designs by testing, or to equip their products with special accessories if the risk levels exceed acceptable limits. As the risk assessment procedure requires input from both the manufacturer and end user, it also promotes collaboration in the interest of safety.

Asynchronous motors in conjunction with converters are being used more and more for the speed regulation of electric drives, even in the field of explosion protection. The speed regulation provides a suitable method for the control or regulation of chemical and petrochemical processes. Beside the advantages of asynchronous motors, compared to mains operation there are, however, some disadvantages involving planning and testing that affect the explosion protection. This paper provides an introduction to the particular problems of converter-fed asynchronous motors for use in potentially explosive atmospheres.

As a result of the increasing automation of process technology in the chemical and petrochemical industries, converter-fed drives are used to an ever increasing extent in the fields of explosion protection. In the paper, reference is made to some aspects which should be considered and which may be helpful for the approval of converter-fed explosion-protected motors. Compared with electrical machines connected to the conventional network, a number of additional criteria must be complied with for the approval of converter-fed drives. When the special features are taken into account, converter operation also offers considerable advantages. The absence of high short-circuit currents, for example, reduces the problem of sparks caused by loose rods in the rotor during acceleration. Voltage and current can be smoothed by the use of filters. This, however, increases the costs and reduces the dynamic response of the drive. Due to the filter losses, a lower voltage is to be expected at the motor. As converter-fed drives will in future be used to an ever increasing extent, it is of utmost importance that corresponding regulations are also included in the explosion protection standards.