Testing of electric motors is one of the services of our organization, which allows us to make sure that the equipment is ready for safe and trouble-free operation after repairs. Testing of AC electric motors represents a wide range of different operations, the number and volume of which depends on what kind of repair was carried out (major, urgent, current).
Acceptance tests of electric motors after repair for synchronous and asynchronous machines must begin with an external inspection. The integrity of the housing, the condition of the insulating material, and winding terminals are assessed, which can be checked without disassembling the machine. The bearings, condition of the brushes, commutator, and brush holders are checked. The machine must be equipped with a suitable terminal box (especially important for explosion-proof models) and an appropriate nameplate.
Testing an AC electric motor with verification of mechanism components is an assessment of the following parameters:
- air gaps between the stator and rotor;
- condition of the fan assembly;
- condition of the bearings.
If, according to the measurement data, there are no deviations from the norms, further work is carried out, including testing the electric motor with a load (high voltage) and at idle to identify faults.
High-voltage testing of electric motors
The standard testing method used for electric motors up to 10 kV includes checking the condition of the insulating material of the windings, functional components of the motor, and direct testing. When testing an insulating material, its resistance is measured. If this indicator is normal, then the electric motors are tested with increased voltage (high voltage test).
Acceptance tests of electric motors are necessary to confirm the dielectric strength of insulating materials, as well as the ability of the windings to withstand increased network voltage. Testing of AC and DC electric motors is carried out with an increased direct, alternating voltage of 50 Hz. On a special stand, increased voltage is smoothly applied to the working stator windings. The currents in them are measured for 1 minute.
Electric motor testing: features
After a major overhaul of the electric motor (with rewinding of the stator windings), control (standard) electrical tests of the electric motors are carried out. If, as a result of repair work, the technical characteristics of the machine have been changed and they have become different from the passport data, then a standard test-check of the electric motor is performed. If the technical characteristics remain unchanged after repair (restoration), then control tests are carried out. Here the main technical characteristics include power, torque, rotor (armature, shaft) speed.
Typical post-repair tests of an electric motor include the following work (except for the main ones, mandatory for all types of testing):
- For AC machines - testing asynchronous electric motors with short-term increased voltage and current, checking heating, determining efficiency, power and maximum torque, assessing starting current, vibrations in operation.
- For DC machines: assessing the speed characteristics of the unit, efficiency, checking heating, determining the switching zone, checking its quality.
Testing AC electric motors (single-phase and three-phase) after current repair includes a smaller range of work.
In particular, using special equipment the following is carried out:
- checking the condition of the insulating material relative to the motor housing and between the turns of the winding;
- testing with increased voltage for 60 seconds (testing method for electric motors up to 10 kV);
- no-load operation.