Electric motors in the oil and gas industry

Electric motors for the oil industry are a special class of machines that are subject to the most stringent requirements in the industry for explosion protection, reliability and maintainability. Any mistake in selecting or restoring such an engine can result not only in a production stop, but also in an accident with casualties. In this article, Elektromotors engineers analyze what motors are used at oil and gas production facilities in Uzbekistan, what regulatory requirements the PUE and GOST impose on them, and what are the specifics of their repair in the conditions of the Bukhara and Fergana regions.

Hazard zones and types of explosion protection

The main difference between electrical equipment for the oil and gas industry is the mandatory explosion-proof design. According to the classification of PUE (Chapter 7.3) and GOST IEC 60079, objects are divided into zones: B-I, B-Ia, B-Ib (gas) and B-II, B-IIa (dust). For each zone, certain types of protection are allowed, indicated by markings.

• Ex d - explosion-proof enclosure. The housing withstands an internal explosion and does not allow flames to escape. The most common type for oil industry engines.
• Ex e - increased protection. The design eliminates the formation of sparks and dangerous heating in normal mode. Used in less hazardous areas.
• Ex de - combined version: Ex e stator, Ex d terminal box.
• Ex n - for zones B-Ib (without gas evolution in normal mode).
• Ex p - overpressure protection, used for large machines from 250 kW.

The engine marking looks like 1Ex d IIB T4 Gb, where IIB is the mixture category, T4 is the temperature class (up to 135 °C on the surface), Gb is the explosion protection level. Before purchasing or repair of industrial electric motors for the oil industry, this marking must be checked with the design documentation.

Where are explosion-proof engines used in the fields of Uzbekistan

Gas fields of the Bukhara-Khiva region, Shurtan, Kokdumalak, Mubarek, oil fields of the Fergana Valley and compressor stations of main gas pipelines are all objects where hundreds of explosion-proof electric motors operate. Main areas of application:

1. Pumping stations - drives of main and booster pumps for pumping oil and condensate, power from 55 to 800 kW.
2. Booster compressor stations (BCS) - drives of piston and screw compressors 250-2500 kW, often with frequency regulation.
3. Gas treatment units (GTU) - air cooling fans, methanol, amine, glycol pumps, power 15-90 kW.
4. Tank farms and drainage racks - pumping pumps, shut-off valve motors.
5. Flare systems and separation - fans and booster pumps.

At the facilities of Uzbekneftegaz and joint ventures, engines of the VAO2, AIM, 2EDKOF series, as well as imported ABB M3JP, Siemens 1MJ7, WEG W22Xd, predominate. They are operated around the clock in conditions where the air temperature in summer reaches +50 °C, and in winter drops to -25 °C.

PUE requirements and regulatory framework

For the operation of explosion-proof electric motors in Uzbekistan, there is a set of regulatory documents that every chief power engineer of an oil company must know.

The most important practical requirement: repair of explosion-proof motors can only be performed by an organization licensed and certified according to GOST IEC 60079-19. After the repair, a report must be drawn up indicating all the restored explosion protection parameters - gaps of explosion-proof connections, condition of seals, winding insulation.

Features of Ex-engine repair

Repairing an explosion-proof electric motor is fundamentally different from repairing a conventional asynchronous motor. Here you cannot “just rewind” - each action must preserve or restore the explosion protection parameters set by the manufacturer.

• Control of explosion-proof gaps. The gap between the shaft and the bearing shield, between the terminal box covers and the housing should not exceed the values ​​​​specified in the passport (usually 0.15-0.30 mm for a certain gap length).
• Maintenance of roughness of the mating surfaces of the body - no more than Ra 6.3.
• Rewinding with exact repetition of the number of turns, wire cross-section and connection diagram. Changing the parameters is unacceptable - this changes the thermal regime and temperature class. Therefore, rewinding of the winding of an explosion-proof electric motor is carried out only according to the manufacturer’s technological map.
• Use of original seals and hardwarewith certificates. Replacement of bolts with “similar” ones is prohibited.
• Post-repair tests: insulation resistance measurement, high voltage test, clearance check, housing crimp testing for Ex d.

For each repaired engine, a passport with a test report is drawn up. Without this document, approval of the motor for operation at the facility of Uzbekneftegaz or Lukoil Uzbekistan is impossible.

Typical engine failures at oil and gas facilities

Over the years of working with industry enterprises, we have accumulated statistics on failures of explosion-proof asynchronous motors.

• Wear of bearing units and violation of explosion protection gaps - about 40% of requests. It is not just necessary to replacement of bearings, but also to control the geometry of the seats.
• Breakdown of interturn insulationdue to frequent starts and overvoltages - 25%. Can only be restored by complete rewinding with class H impregnation.
• Rotor damage - breakage of cage rods, shaft deflection. Elimination requires rewinding the rotor or restoring the shaft.
• Destruction of the Ex d terminal box from vibration and shock loads is 15%.
• Contamination of cooling channels with sand and dust is a common problem in the Kyzylkum fields.