Case Study: How a Flywheel OEM Doubled Bearing Life and Cut Repair Costs with GMN Bearings

Flywheel Technology

Flywheel technology has proven itself to be very valuable and adaptable to many different industries.  These applications can range from emergency backups as an Uninterruptible Power Source (UPS), constant usage for power grid balancing, or combined with various forms of renewable energy including but not limited to Rail Energy Recovery systems, solar/wind energy storage systems, and hydrogen energy storage for quick/long usage systems.

UPS systems and quick usage grid systems like peak shaving or grid balancing are becoming quite common to increase the efficient use of energy.  Super precision ball bearings are vital to hold concentricity in these applications and maximize every last percentage of efficiency in the complete system. The bearings are essential to ensure the flywheel keeps its high rotational speed so that it can store kinetic energy and then release that energy as electricity during power disruptions.

GMN has worked with many customers around this type of flywheel technology.

The Challenge

In one particular instance, an OEM’s flywheel for a UPS system was experiencing very short bearing life with increased maintenance costs before reaching out to GMN.  This may be okay during the prototype stage, but not for long term field use.  Our team of expert engineers found multiple aspects that could be improved to support application life during initial analysis;

1. Rigidity within the bearing system
2. Duty Cycle analysis for speeds and loads to optimize bearing design
3. Better design to improve maintenance ease and speed

Initially, the customer had chosen radial ball bearings for their flywheel application.  While a quality radial bearing is often a good choice for many applications, in this circumstance the radial movement was wreaking havoc on the efficiency of the motor due to the concentricity movement and causing machine life issues due to the imbalance forces being extraordinarily higher than they should be.

Digging into the true Duty Cycle of the application, we found out that although the application was grid balancing, this particular grid area saw very large swings in voltage.  Therefore, field data showed the RPM duty cycle over a much larger band than was originally thought.

In addition to this, the design was not optimized for maintenance.  There were a multitude of parts and fastening hardware that could be moved to create a quick and easy maintenance cycle to save costs.

How GMN Helped

After a few more conversations, we landed where we thought was optimal for the longest bearing life; super precision angular contact bearings. 

Utilizing a pair of bearings at the top and bottom of the flywheel – vertical application – would solve more than one aspect found in the initial analysis. 

First, with any preload at all, angular contact bearings will hold the flywheel tightly to geometric center, improving motor efficiency and decreasing centrifugal loads from any orbit that radial ball bearings would allow. 

Because of our proper duty cycle analysis with the customer, the angular contacts were also sized appropriately to the speeds and loads.  The applicable bearing size was now designed with a proper custom preload from multiple iterations of bearing calculations done in-house by GMN Bearing USA engineers. 

At this point, the customer was already excited and happy to get started with testing to reduce field cost and double or triple MTBR (Meant Time Between Repair). 

We brought our experience to the table once more as design engineering partners to talk to the customer about ‘bearing cartridge’ concepts and how with minor component modifications, we could significantly reduce maintenance time.  When possible, one of the greatest gains with a bearing cartridge package design is that the same cartridge can be used top and bottom (i.e. manufacturing efficiency and scale gains).

The Results

Here’s what we changed through proper engineering, calculations, and analysis:

1. Pair of super precision angular contact bearings at the top and bottom: 

• Sized appropriately for the RPM and Load Duty Cycles
• Proper custom preload for the application

2. Supported system design change to a Bearing Cartridge design

Through initial testing, the customer was immediately happy with the results, and we were thrilled to hear the improved MTBR from the field.  A proud moment was the ‘thank you’ phone call we received after we doubled the previous maintenance cycle.  Not only are they still a great customer to this day, but also friends in some geeky high-level engineering.

Tech Tid-Bit

Permanent magnet bearings are also commonly used in flywheel technology for many types of applications.  Utilizing permanent magnets can greatly reduce the uni-direction axial load on the bearings due to rotor mass.  Reducing this load as much as possible will not only increase bearing life, but in many cases can save costs by reducing the required bearing size.  This type of technology combined with flywheel tech is also something GMN Bearing USA engineers have become increasingly familiar with over the years.

Talk to a GMN Engineer

We can help with your next project! Contact us to learn more about where we can provide support through design engineering, bearing inspections and troubleshooting, or application expertise.