AC Motor

DV GROUP: the solution for your asynchronous motors

By far the most widely used motor in the industry, the induction motor is considered reliable, with low maintenance costs while guaranteeing high efficiency. It consists of a fixed part – the stator that provides the winding – and a rotating part – the rotor, either in a squirrel cage or wound, which is supplied by AC power. Over 10 years, its overall cost is split between its purchase price (2%), its maintenance (3%) and its power consumption (95%).

DV GROUP offers a repair solution for all your motor types:

  • Aluminium and cast iron induction motors
  • DC motors
  • Medium-voltage motors
  • Rotor squirrel cages
  • Wound rotor
  • Explosive atmosphere (SAQR-ATEX certification)
  • Alternators from 0.02 kW to 2 MW.

AC motor repair at DV Group

Test solutions guaranteeing 100% functional products

A variety of tools adapted to your needs:

  • Winding equipment: megaohm meter, milliohm meter, probe into motor protection: CTP/PTC/PT100, Baker Index Control.
  • Mechanic’s equipment: ball bearing assembly using manufacturer’s specially designed tool, induction heating, machining equipment, etc.
  • Specific tools: shock wave analysis, impedance analysis, vibration measurements, balancing, etc.
  • Spare parts in stock (original equipment or adaptable)
  • Load bench: AC starter up to 1,000 A / load on impact 1,500 A.

Technical Procedures

  • Procedure before dismantling
  • Inspect motor connectors.
  • Metrological check of bearing seatings, joint surfaces, flanges, shaft, etc.  
  • Check lubrication and evacuation ducts
  • Electrical inspection (insulation, resistance, inductors, etc.) according to the data supplied by the manufacturer.
  • Cooling control: ventilation and water circuit.

Repair Procedure

  • Repair: chromium plating, ringing, molten metal cladding by spraying of the various joint surfaces, complete cladding of the drive shaft
  • Electrical inspection: ageing, pollution: BAKER index, state of winding
  • Repair: winding and dip impregnated Class H: High Temperature, turning the ring set (wound rotor motor)

Test/validation procedure

  • Tests: no-load tests in rotation on a platform up to 1,600 kW
  • Load tests up to 600 kW at 3/4 load – 50 / 60 Hz
  • Vibration measurement and signature

Traceability procedure

  • Diagnosis and testing history
  • Traceability produced by: machine number / customer number / DV GROUP number.
  • Test sheet and qualification/test certificate

Case study :


Need / Context

Glass producers must rebuild their furnaces every 15 years. The refractory brick component needs to be replaced to ensure its tightness of fit. During this shutdown, the OI Manufacturing site in Ardèche refurbishes the related equipment. Glass production has a reliability requirement, and must be able to ensure long periods without breakdown or maintenance stoppage.


To achieve these availability and efficiency goals, the glass producer entrusts us with the removal, overhaul and refitting of its fifteen 750 KW - 50 Hz medium-voltage fan and compressor motors. For one month (800 hours), our teams from the various electromechanical sites in Grigny, Cambrai and Lyon mobilised to process these products and meet the deadlines imposed by our customer. We added DV GROUP know-how to the flawless organisation demanded by this project. OI Manufacturing has atypical 750 KW - 50 Hz medium voltage motors with plain oil bearings instead of ball bearings. These bearings carry a higher radial load and have a longer life than bearings. However, they require a specific expertise.


- Deadlines met - Furnace restart with products 100% tested and 100% functional


Need / Context

The European Organization for Nuclear Research, commonly known as CERN, is the largest particle physics center in the world. CERN is located in Switzerland, near Geneva. On an ad hoc basis, CERN makes technical stops in order to recondition their equipment. Following the last stop, a lubrication problem on two cooling tower reducers is detected.


CERN wants a SIEMENS / FLENDER agreed repair partner which leads them to contact us. After many exchanges with the customer, particularly about the safety of this kind of repairs, CERN entrusts us with the project. Our customer asked us to overhaul these 2 FLENDER industrial reducers but also to supply and replace the lubrication pump within a period of 4 weeks. For a month, our teams were mobilized to treat these products and meet the deadlines our customer required.


- Deadlines respected - Preparation of a detailed report describing the different operations carried out - Convinced by the results of this first collaboration, CERN wishes to entrust us with the overhaul of 6 to 8 other reducers for the coming years.

Our other solutions

for Electromechanical maintenance