Testing electric motors

How are electric motors tested?

Test benches for electric motors are used in research and development, for quality assurance, auditing and in production. A test bench for electric motors is a testing system for the reproducible testing of mechanical and electrical properties, the thermal design, overload capacity and other application-specific measurands on electrical drives. There are also special requirements on sound and reduction of that sound (NVH analysis and NVH optimization). A test bench for electric motors consists of a mechanical unit to which the electric motor or its components are connected and a measuring system that consists of sensors, application software and evaluation unit for the control and analysis of the test procedures. 

The determination of the power, efficiency, dynamics, stability and efficiency of an electric motor is based on the measurement of:

Electrical quantities

  • Current
  • Voltage
  • Power
  • Harmonic transients
  • Winding resistances
  • Insulation resistance
  • High-voltage test
  • Shield resistances

Mechanical quantities

  • Torque
  • Rotational speed
  • Angle of rotation

Temperature

Test specimen temperatures (engine/controller/storage area, etc.) during the heat run test measurements or during freely definable load cycles or in various test modules

Vibrations

For the detection of system errors, such as bearing damages, imbalances, etc., to prevent consequential damages that could occur during measurement

What are the different types of test benches for electric motors?

A distinction is made between the following types of electric-motor test benches:

  • Development test bench
  • Endurance test bench
  • Test bench for auditing electric drives
  • EOL test bench (End-of-Line test bench)
  • HiL test bench (Hardware-in-the-Loop)

What tests are performed on a test bench for electric motors?

  • Service life testing under maximum mechanical loading (full load)
  • Function and performance tests for monitoring and (predictive) maintenance
  • Testing in accordance with nominal operating modes S1-S10 from standard EN 60034-1
  • Testing with customer-specific load profile with specification of rotational speed and torque
  • Determination of the efficiency of the engine or drive system
  • Determination of characteristic curves of the engine or drive system
  • Type testing of electric motors
  • Routine testing of electric motors
  • Qualification of electric motors
  • Testing in accordance with standards EN 60034-2-1 and 60034-2-3

What requirements exist for a test bench for electric motors?

The development of drive systems for electromobility and highly efficient motors in the industrial sector places ever increased demands on electric-motor test benches with respect to flexibility and operability. It is necessary to cover various power, speed and torque ranges, even high speeds of up to, e.g., 50,000 rpm or torques in the range of several kilonewton meter (kNm). 

In addition to testing the power of electric motors, testing the energy and efficiency are becoming increasingly important. Because the drive technology consumes over two thirds of industrial power, a great deal of carbon dioxide can be avoided.
Test benches for electric motors must determine the energy efficiency of electric motors in accordance with the "Minimum Energy Performance Standards" (MEPS) for the energy efficiency of electric motors introduced worldwide and comply with the legal regulations regarding measurement accuracy. Standards IEC 60034-30-1, NEMA MG1 and others define the efficiency classes and minimum requirements on electric motors in power class 0.75 to 375 kW.

What are the application fields for test benches for electric motors in the area of electromobility? 

Electromobility includes a broad application field: from external starter and generator solutions for optimized automatic start/stop systems to purely electric drive systems.

Main drives of electric vehicles:

  • Synchronous, asynchronous and hybrid motors
  • Transmission-motor combinations

In addition to this is the added number of electric auxiliary drives

Automotive auxiliary drives:

  • Pump, fan, displacement, wiper motors
  • Electrically opening tailgate
  • Generators
  • Electric turbochargers

Due to the importance and various requirements placed on these auxiliary drives, demands on the auditing and testing of such auxiliary and ancillary units are also on the rise. For this purpose, the drives are frequently exposed to varying environmental conditions, such as the simulation of extremely low or extremely high temperatures. This is performed in specially modified temperature and climate chambers that can be connected to the test bench. 

But, depending on the function of the drive, axial and radial forces must also often be simulated as an endurance test.

What are the application fields for the test benches for electric motors?

Test benches for electric motors are used for:

  • Main drives of electric vehicles (cars, trucks, buses)
  • Main drives of hybrid vehicles
  • Auxiliary drives of electric vehicles
  • Powertools
  • Drives of machines and forklift trucks
  • Industrial robots
  • Industrial motors
  • Subways and commuter trains, high-speed trains
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