Safe power for compressors

Complex requirements for explosion-proof motors

Safe power for compressors

Explosion-proof electric motors must meet the highest safety standards and operate absolutely reliably. Since plants generally run 24/7, energy efficient motors are a crucial factor when it comes to reducing operating costs in the petrochemical industry. Exactly which requirements modern, explosion-proof motors have to fulfil is demonstrated by the example of six W22X medium-voltage motors, which drive LMF piston compressors in a gas production project in the Middle East.

The risk of explosion in oil and gas production is especially high. When a certain level of distribution and concentration is achieved, the combustible gas only has to come into contact with oxygen and an ignition source (e.g. an electric spark) for a large quantity of uncontrolled energy to be released. The threat to people and plant in an emergency is immense. It is therefore crucial that explosion-proof motors such as the W22X series manufactured by WEG are built in such a way that if an ignitable mixture explodes inside the housing, sparks are prevented from spreading into the explosion-protected area at all costs.

In addition to this central aspect of basic protection against explosion, however, modern explosion-proof motors in the petrochemical industry must meet several supplementary requirements. Energy efficiency is an increasingly important issue in the oil and gas sectors. Drives combining explosion protection and high efficiency permit considerable cost savings in these energy intensive applications. Furthermore, the highest standards in terms of reliability and robustness are also a priority when it comes to the motors, in order to ensure maximum system availability and avoid expensive downtime. Against this background, WEG’s new W22X series of explosion-proof motors was designed in size 800; these motors are currently used by LMF, a high-pressure piston compressor specialist headquartered in Leobersdorf, Austria.

Explosion-proof electric motors have to comply with important international standards in order to meet the high safety requirements of equipment in potentially explosive atmosphere. WEG developed the W22X series according to the most demanding standards and meanwhile sells it worldwide. The W22X 800 already has Atex and IEC certification for the Ex d(e) IIB T4 Gb type of protection as well as for mining (Group I) and conductive dusts (Group III); additional certification for Ex d(e) IIC T4 Gb protection and regional certifications such as EAC, CCOE and INMETRO are in preparation.

The six motors which LMF purchased for use in its piston compressors are certified for the Ex d(e) IIB T4 Gb type of protection, meaning they have a completely flameproof enclosure (d) which eliminates the risk of explosion and prevents flames from spreading. They are also equipped with a terminal box which conforms to the requirements for increased safety (e) as well as gas group IIB (gas type: ethylene) and complies with temperature class T4 (surface temperatures up to +135 °C) – despite their high output of 1500 kW. Finally, the letters “Gb” stand for the equipment protection level: the motors can be used in potentially explosive (gas) atmosphere, in which there is no danger of ignition either during normal operation or in case of foreseeable faults and malfunctions.

The standard IM B3 version of the W22X 800 motors has a flex-resistant welded steel frame with IP 55 protection and integral feet. Owing to the robust housing, these explosion-proof motors can be used in even the most demanding applications, where they restrict vibration and noise to a minimum (less than 85 dB(A)). When it comes to sparking, the main terminal box provides even better resistance due to the supply voltage at the point of failure. Independent tests have proven its ability to withstand peak short-circuit currents up to 50 kA for 1 s. In addition to the very good protection against shocks and external impacts, the spacious terminal box of the W22X 800 allows easy attachment of all connectors.

Although motors of this size are typically tailor-made, WEG now offers them as a standard product with many optional modules in response to increased demand. They can therefore be customised easily and optimised for individual applications, for example with regard to ambient temperature (-55 to +60 °C), protective devices (surge arresters, capacitors, current transformers), terminal boxes (number, design), protection class (IP 56, IP 65, IP 66) or inverter operation.

This same flexibility is also evident in the LMF project. The robust W22X 800 motors used in the piston compressors, which weigh approximately 20 t, are customised for the installation site in the Middle East, where IP 56 protection, tropicalisation and suitability for ambient temperatures up to +48 °C are vital.

Petrochemical plants are particularly energy intensive, which is why the energy efficiency of the electric motors plays a crucial role. An efficiency increase of just 1 % adds up to significant savings when the output over the course of a year is as high as several megawatts. WEG designed the medium-voltage motors in the W22X series with optimal efficiency in mind. The 14-pole W22X 800 motors supplied to LMF have an output of 1500 kW and voltages up to 6 kV at 50 Hz at full load, giving an excellent efficiency value of 96 %.

The motors’ high efficiency is primarily attributable to their tubular cooling system (IC511 according to IEC 60034–6), which is made of stainless steel to optimise the air flow. The axial and radial air ducts ensure extremely efficient cooling of stators, rotors and critical components such as bearings. In addition, the aerodynamic fans and fan covers help ensure an effective air flow with the lowest possible noise level. Hot spots are avoided by the uniform temperature distribution throughout the entire frame.

With a maximum output of 5.6 MW and voltages up to 11 kV, the W22X 800 extends the W22X series at the high end of the range. Thanks to its comprehensive W22X portfolio with frame sizes from IEC 71 to IEC 800, WEG can provide optimised explosion-proof motors for practically any application, from gas pipelines in the Arctic to drilling rigs in the hottest regions of the Arabian desert.

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Andreas Schulte Mesum

Head of Energy Business, WEG