Get your motor matched in your power drive system.

In our clarification of the requirements of the power drive system, we work our way through the drive train, starting from your application towards the grid supply. After our zoom on your application, we need to make sure that your motor will be compatible to operate reliably in the drive train of your critical application. You can go through the clarifications below or click straight through to your preferred subjects:

Considerations when reusing your existing motor.

Solutions when reusing your existing motor.

Opting for a new motor.

Match your supply-drive-motor.

No time to read all this, contact-us for a free video call.

• Considerations when reusing your existing motor:

If you are retrofitting the drive train, you might want to consider reusing your existing motor. In this case, you should get a clear picture of your motors’ actual health (i.e. partial discharge tests, status of the bearings, repair history, …).

Let us consider the case where your existing motor will be powered by a variable frequency drive (voltage source inverter) instead of the mains supply.  This change of operation of the motor will set further requirements to the variable frequency drive. You should pass them on to the supplier in a smart way.
Let’s have a short closer look. While the diagram above shows the drive as a simple conversion from fixed voltage and frequency to variable voltage and frequency, the reality is quite different.

The AC-voltage from the power grid is rectified and via intelligent high frequency switching recombined to a nearly sinusoidal output voltage. Depending on the quality of this output voltage, the reliability of your motor might be endangered:

• Your motor will heat-up more and be noisier.
• Your motor needs to withstand the high voltage peaks and the high voltage steepness over time.
• Further investigation regarding mitigation of damaging bearing currents due to the high common mode voltages is highly recommended.
• The high frequency switching will also induce high frequency interference and leakage currents that will need to be dealt with as well.
• Torque pulsations or cogging can excite resonances with consequential damage to motor, gear and machine.

In our chapter “variable speed drive” you can find out more about the power quality delivered to the motor by the different types of variable frequency drives.
Driving your machine at variable speed creates some interesting advantages such as energy savings, flexibility for the production, gently ramping up to speed without mechanical shock nor high starting currents, … . But please always consult the manufacturer of the machine about the expected machine behaviour when operating at variable speed versus fixed speed.

• Solutions when reusing your existing motor:

We do not want to scare you away with all above possible issues.
We are confident that specifying the correct requirements along with their validation method and setting the right expectations towards your solution provider will mitigate these risks to an acceptable level.
You will need to require insights and reassurances from your variable frequency drive-manufacturer.
Some vfd-manufacturers might impose in their offer supplemental output filters. Please note that these supplemental output filters can be of a significant cost and might also introduce performance restrictions on the power drive system. Your vfd-manufacturer should also provide specifications on the preferred motor output cable, combined with clear installation instructions (EMC (*)). The measures to avoid damaging bearing currents in your motor and even in your machine might require thorough investigation.
Some types of variable frequency drives, such as medium-voltage multi-level cascaded output drives, on the other hand, do not impose any voltage stress nor supplementary heat losses to the motor thanks to their superior sine wave output.
Look for more useful data on this in the chapter MV-topologies.
Conclusion:
In order to gain confidence in the vfd-manufacturer, you will need to ask the right questions to your manufacturer candidates. Even more important is the evaluation of their answers. You can contact us to assist you as independent subject matter experts.

• Opting for a new motor

In general, the cost of a new motor versus the cost of the vfd is not really that high. This new motor will be defined for inverter duty according to current industry standards (withstand high voltage rise, insulated bearings, …). Manufacturers of both Medium Voltage motors and Medium Voltage drives might be in a better position to take full responsibility for the right match. To prevent issues with compatibility and reliability in the field, specifying the correct drive and motor for your application is paramount. We would be more than happy to provide you with specific advice on choosing the right Medium Voltage motor and drive combination for your machine.

•  Match your supply-drive-motor to your application.

You might also want to consider one manufacturer taking responsibility for the complete power drive system (match of supply-drive-motor). The correct engineering of the power drive system requires of course your application input data such as load torque versus speed and required transient over-torques if any present. The torque versus speed of your motor needs to be matched to your application data. The engineering proof should be made available by the manufacturer or solution provider preferably in graphic format presenting torque versus speed.
As there is no such thing as “one drive fits all applications”, your vendor should offer a multitude of drives tailor-made to different applications and specific requirements. The vendor should be able to provide you with references of successful power drive systems similar to your application. Give preference to reputable manufacturers with proven reliability record and with at least 10 years of drive-application experience and multiple similar field-installed units. A large installed base in your area often translates into a nearby robust service and support network.

This system approach, based on the engineering experience of the manufacturer, is an important advantage especially in critical applications. Integrating these key elements into your definition of requirements can prove to be extremely valuable. If you need any help on this, just contact us for a free consultation.

In all cases above we are ready to assist you. All it takes is that you contact us for a free consultation, no strings attached.
Further down the road, we can facilitate informed decision-making by offering you our independent advice and support for any of following tasks:

• Setup of the project plan presentation.
• Definition and management of the requirements of the power drive system PDS (transformer, inverter vfd and motor).
• Evaluation of the composition of the power drive system.
• Setting-up and coordinating internal and external pre-bid meetings.
• Set-up of invitation to bid with Engineering, Procurement and Contracting (EPC) companies and/or vendors.
• Screening of preferred manufacturers of transformer, inverter and motor.
• Verification of the offers and exceptions in regard to your specs of your PDS.
• Assist you to select the vendor.
• Support in order clarification.
• Develop witnessed and non-witnessed Factory Acceptance Tests (FAT) requirements.
• Define the Site Acceptance Tests (SAT) requirements.
• Valdiate On-site the site acceptance tests for your power drive system PDS.

(*) The term “ElectroMagnetic Compatibility” (EMC) according to the definition of the EMC Directive:
“the ability of a device to operate satisfactorily in an electromagnetic environment without itself causing
electromagnetic disturbances that would be unacceptable for devices operating in this environment”.