Electric motors are the heartbeat of many industries. From manufacturing plants to office buildings, these machines keep operations running smoothly. But motors face a hidden enemy: shaft voltage when powered by variable frequency drives (VFDs). This voltage damages motor bearings and can lead to premature failure, causing costly unplanned downtime.
Understanding Shaft Voltage in Electric Motors
When you run motors directly online, the input voltage is balanced - the voltage in each of the three phases cancels, so the net voltage is zero. But when you use a VFD to control a motor, the three phases do not cancel, so there is a net voltage. This voltage imbalance produces a voltage on the rotor, called shaft voltage. Shaft voltage seeks to discharge to ground. Without a proper path to ground, its voltage takes the path of least resistance — usually by arcing through the motor bearings.
Although each discharge arc is tiny, there can be tens of thousands of them per second, and each one creates a tiny pit in the smooth bearing surface. Over time, these microscopic pits can lead to more severe damage. You'll notice increased vibration, noise, and, eventually, bearing failure. In critical systems, this failure can halt entire production lines, leading to enormous losses.
The Purpose of Shaft Grounding Rings
The purpose of a shaft grounding ring is to provide a safe path to ground for shaft voltage, bypassing the bearings. Installing a shaft grounding ring protects the bearings from electrical damage. The ring encircles the motor shaft with conductive microfibers, offering 360-degree coverage. This design diverts the voltage directly to ground, preventing it from passing through the bearings.
Shaft grounding rings are virtually maintenance-free and designed to last for at least the L10 life of the bearings. Temperature, humidity, or other environmental factors do not significantly affect them. This makes them suitable for a wide range of industrial settings.
Preventing Bearing Failure
Bearing failure isn't just a mechanical issue; it's a financial one. Damaged bearings can halt production lines and disrupt services. By using shaft grounding rings, you reduce the risk of bearing failure.
Regular maintenance and monitoring can only go so far. Without addressing the root cause of shaft voltage, electrical bearing damage will continue to be a problem. Shaft grounding rings offer a proactive solution.
Applications That Benefit
Many applications, in many industries, can improve reliability by installing shaft grounding rings:
- HVAC Systems: Heating and cooling units in commercial buildings, hospitals, and universities rely on motors that need protection.
- Manufacturing Plants: Fans, pumps, grinders, mixers, and everything else electric motors drive can cause unplanned downtime if their motor bearings fail.
- Water Treatment Facilities: Continuous operation is critical, and motor failure can have serious consequences.
- Electric Vehicles: Motors in EVs also suffer from shaft voltage, which causes electromagnetic interference and bearing damage.
- Energy Sector: Both wind turbines and traditional generators are subject to electrical damage to bearings and gearboxes.
Shooting grounding rings contributes to more efficient and reliable operations by safeguarding motors across these industries.
Protect Your Motors with Shaft Grounding Rings
Shaft grounding rings play a crucial role in maintaining electric motor health. They offer a simple solution to a complex problem, protecting bearings from harmful shaft voltage. By understanding the shaft grounding ring's purpose and implementing best practices, you can protect motors from premature failure and keep your operations running smoothly. For a deeper dive into bearing protection, explore the AEGIS Bearing Protection Handbook, which provides comprehensive explanations and best practices.
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 - pandemic restrictions permitting - we can also visit your facility to review your exact application.
