How to define your power drive system for maximum Uptime? 

Your Power Drive System, in the heart of your critical machine, deserves a well-defined system approach for optimum reliability and quality.
You can go through the clarifications below or click straight through to your preferred subjects:

As shown in the simple diagram above you will need to work on different fronts to achieve sufficient profit.

Life cycle cost-based decision making is strongly supported by the need to maximize your uptime.

Your mission critical machine deserves a maximum fully productive time. Therefore, you will strive to reduce the losses as much as possible. Already in the early stage of the project you can have an important impact on the availabilty, performance and quality losses. It is worthwhile to invest enough research time in the definition phase of the project. Changes during execution along the road will always cost more and will endanger the planning of the project. About the losses:

• Availability losses include unplanned stops (such as equipment failures and material shortages) and planned stops. When it comes to process-critical equipment, downtime is always a major concern.
• Performance losses cover anything that causes the manufacturing process to run at less than the maximum possible speed.
• Quality losses relate to produced parts that do not meet quality standards.
  Both losses can be countered by ensuring compliance to the specifications and operating the equipment to the specifications.

So how can you reduce downtime?

• Avoid unscheduled downtime (by real time operating data helping you to predict failures).
• Avoid unnecessary preventive maintenance interventions (thanks to full visibility of the health of your assets).
• Maximize the uptime of your critical machine in a safe and efficient way.

Considering all the above, it is good practice to base the project scope requirements and purchase decisions on life cycle cost and not only on capital cost and/or schedule considerations. To obtain management support, you will need to collect at least following data to back this up:

• The cost of unavailability per unit of time (€ or $ per minute, hour or day).
• The daily revenue at stake.
• The possible savings over total life time of the machine.

The critical machine, with its typical machine specifications, should be considered as part of the production process. We should also factor in the power drive system, which is after all providing the energy to drive the machine (see diagram on top of this page).
For small power drive systems used in critical process equipment, the availability can often be enhanced by a redundant system. High power applications are often driven by Medium Voltage drives and a redundant Medium Voltage drive is often economically not viable. By consequence, the reliability and the availability of the MV-drive will be major priorities for our mission-critical machines.

RAMS and interactions of  the power drive system

For now, let’s not get into typical terms used in reliability such as MBTF, MTTR, availability percentage, yet.
The power drive system is part of the drive trains’ installation as shown on picture on top of this page. The reliability of the power drive system will be the result of multiple important interactions. Please find the mayor ones listed below with links to relevant insights:

• the environmental conditions (see also standard EC 60721-3-3), and
• the thermal balancing
• the quality of your in- and output power of your drive 
• the correct operation to specification of the combination of your power drive system and the driven machine
• the correct composition of your power drive system fit for your application
• the available support on-site in case of a breakdown

Some basic reliability definitions and what about your MV-drive?

Mean Time Between Failure (MTBF) is defined as the predicted elapsed time between inherent failures of a system during operation. The definition of MTBF depends on the definition of what is considered a “system failure.” We are interested in those failures that place the system out of service, into a state of repair.  Most critical machines expect to rely on drives for decades. So, a good target for your MTBF is a minimum of 100,000 hours which is more than 10 years before a predicted failure appears. It can generally be extended by following the manufacturer’s recommended preventive maintenance program. The MTBF is typically part of a model that assumes the failed system is immediately repaired (MTTR – Mean Time To Repair) as part of a continuous process.
The Mean Time to Repair (MTTR) is the amount of time the component is shut down in order to repair or replace a part. Considering the high cost of downtime, MTTR should usually be not more than 15 to 30 minutes for 7/24 operation.
Factors that influence a drive’s MTTR:

• The ease of replacing defect components without the need to disassemble the drive.
• The containment of the fault thanks to the inherent protection of the drive (one failure only).
• The available support:
  • Are your technicians with the right expertise to monitor, maintain and repair the drives present on-site?
  • Are the right spare-parts to repair the drive available on-site?
  • Can you rely on remote 7/24 expert support from your drive manufacturer?
  • What is the time required to get the drive manufacturers’ expert on-site in case of a severe breakdown? (to include into your service level agreements of your maintenance contract)

Availability is the percentage of time when system is operational.  Availability is determined by the reliability of the system and its recovery time when a failure occurs.  The formula for availability= MTBF/(MTBF +MTTR).
Availability is typically specified in nines notation. For example, 3-nines availability corresponds to 99.9% availability. A 5-nines availability corresponds to 99.999% availability.
Keep in mind that the Mean Time Between Maintenance Actions (MTBMA) will be shorter than the Mean Time Between Failure (MTBF). For a drive it makes sense to replace the fans after 5 to 10 years which is generally smaller than the MTBF. This preventive maintenance action can of course be scheduled in the planned maintenance shutdown of the machine, to avoid its impact on the availability during normal operation.
Downtime per year is a more intuitive way of understanding the availability. The table below compares the availability and the corresponding downtime.

We are ready to assist you as subject matter expert combined with the structured approach of decades of project management. 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 the following tasks:

• Setup of the project plan presentation.
• Definition and management of the requirements of the power drive system.
• Evaluation of the components of the power drive system.
• Internal and external pre-bid meetings.
• Set-up of invitation to bid.
• Screening of preferred vendors.
• Verification quotation and exceptions VS specs.
• Selection of the vendor.
• Order clarification.
• Factory acceptance tests requirements.
• Witnessed factory acceptance tests.
• Site acceptance tests requirements.
• Witnessed factory acceptance tests.