It's hard to believe, but the first electric vehicles were created almost 100 years ago. Electric trains were developed in Vermont and Scotland in the 1830s. The first electric autos and boats came in the 1880s, followed by electric submarines and dirigibles.
The early 20th century saw the rise of the internal combustion engine, and except for certain rail applications, electrical transportation fell out of fashion for several decades. e-transport's 21st-century resurgence was made possible by improvements in battery technology and the development of variable frequency drives (a.k.a. VFDs, inverters, converters, or simply 'drives').
Drives: A Boon to Electric Transport
VFDs convert DC power - supplied by a battery or a DC bus fed by an AC source - to AC at a wide range of frequencies. This is immensely useful in vehicles because it allows for easily-controlled, smooth, gradual acceleration. They are also more efficient than the all-DC forms of control used in 19th-century electric vehicles. Efficiency is paramount in battery-powered transport, since it can mean the difference between reaching your destination and being stranded.
The Drawbacks of Drives
Modern drives produce AC power by releasing a rapid series of positive or negative voltage pulses. Unfortunately, these rapid-fire pulses have damaging effects on the motors and systems they control. Among others, they produce stray currents in the motors they control, and without protection, this current can arc destructively through the motor bearings, gearbox, or other driven equipment. The resulting electrical damage can lead to premature bearing or gearbox failure.
Stray Current Mitigation
Fortunately, the risk of premature failure can be mitigated. AEGIS® Shaft Grounding Rings provide a "path of least resistance" to stray current, so rather than arcing through the bearings, gearbox, or other equipment, the current flows harmlessly through the AEGIS ring. AEGIS shaft grounding has been used extensively in both industry and transport to protect from the damaging effects of drives.
For just a few examples:
Electric Cars & Trucks
When most people hear "electric vehicle," they think of cars and trucks. Automotive manufacturers, both in the US and abroad, use AEGIS rings to protect their vehicles' motor bearings from stray current produced by inverter drive operation, and we are in talks with many more. For more information, see our white paper on the topic.
Rail
Electric trains, trams, and trolleys are an interesting case because they don't typically have batteries. Rather, they draw their power from a third rail. Regardless, they still use drives to control their electric motors, and thus have problems with electrical bearing damage. In this blog post, we go more into the specific aspects of shaft grounding in rail applications.
Marine
While e-cars typically have large batteries and trains draw line power through the third rail, ships tend to have their own generators. Some yachts may have wind turbines or solar arrays, but commercial ships usually have diesel generators to power their motors and other electrical systems. This case study tells how one ship suffered repeated failure due to "tiger-striping" electrical damage, caused by stray current from the generator shaft. The ship's owner eventually solved the problem with an AEGIS PRO Series ring in the problem ship - and also preemptively installed PRO Rings in their other ships as well.
Aviation
Although AEGIS Rings have been to space, as components in satellites and rovers, they have not yet been installed in commercial aircraft. But electric planes are subject to the same stray voltage as any other electric vehicle using drives in some capacity, and they, too, will have a problem with electrical bearing damage.
Summary
- Variable frequency drives are a critical component in 21st century electric vehicles
- Drives can cause electrical damage to motor bearings and other components
- AEGIS Shaft Grounding Rings divert drive-induced stray current around the bearings, by providing a path of lower resistance
AEGIS Rings also come with a 2-year extended warranty against bearing fluting damage. No other form of protection against VFD-caused bearing damage offers a warranty like this.
To learn more about AEGIS shaft grounding and best practices for electrical bearing protection, sign up for a training. We offer monthly live training webinars, and we can also visit your facility to review your exact application.
