What Are Electrically Insulated Bearings? Working Principle and Applications

Do your motor bearings fail prematurely due to shaft current erosion?

TFL’s electrically insulated bearings block shaft currents (insulation resistance ≥ 200 MΩ, withstand voltage ≥ 3000 V), preventing spark‐erosion, micro‑pitting, and lubricant degradation.

Advantages of TFL Electrically Insulated Bearings:

• Core Pain Point Solved: Completely block the shaft currents generated by PWM signals and common-mode voltage, preventing raceway fluting and pitting, which stops premature bearing failure.
• Key Performance Metrics: Utilizing a high-density aluminum oxide ceramic coating, the coating resistance is greater than 200 MΩ (measured at 500VDC) and can withstand voltages up to 3000V, meeting or exceeding international standards such as IEC 60349.
• Quantifiable Benefit: In high-voltage/VFD applications like wind power and rail transit, our insulated bearings can extend the Motor Mean Time Between Failures (MTBF) by over 30%, substantially reducing unplanned downtime and maintenance costs.

What Are Electrically Insulated Bearings?

Why Your Standard Bearings Fail? Shaft Current

Variable Frequency Drives (VFDs) are crucial for enhancing motor efficiency and flexibility, but their generated High-Frequency Pulse Width Modulation (PWM) signals bring a side effect: Shaft Current. When the shaft voltage exceeds the breakdown voltage of the lubricant film (typically 5-10V), current discharges across the roller and raceway, leading to:

1. Electrical Fluting: Dense, grayish-white pitting appears on the raceway, quickly expanding into distinct “washboard-like” patterns. This is the most direct evidence of electrical failure.
2. Lubricant Degradation: Electrical arcing generates high temperatures, rapidly aging and carbonizing the grease, which drastically reduces lubrication performance.
3. Premature Failure: Electrical erosion accelerates metal fatigue, shortening bearing life by 70% to 90% and causing unexpected motor stoppages.

TFL Bearing experts recommend: In all AC Motors utilizing VFDs, especially in systems with output power greater than 75kW or voltage exceeding 690V, insulated bearings must be considered to eliminate this risk.

TFL Electrically Insulated Bearings Working Principle

The primary function of Electrically Insulated Bearings is to establish a high-impedance barrier, electrically isolating the inner ring, rolling elements, and outer ring, thereby physically blocking the shaft current circuit.

The key to TFL insulated bearings lies in their high-quality Aluminum Oxide (Al2O3) ceramic coating. We utilize advanced Plasma Spraying Technology to ensure the coating possesses extremely high density and uniformity.

Unique Selling Proposition (USP): TFL employs a multi-layer spraying process and is subjected to strict High Voltage Dielectric Strength Testing to ensure insulation performance remains stable under long-term humid and high-temperature (up to 150∘C) operating conditions, with significantly higher impact resistance than thin single-layer coatings.

NOTE: Coating thickness must be optimized — too thick affects geometry and heat conduction, too thin compromises insulation. Therefore, there is no one-size-fits-all ideal thickness; it should be determined based on the actual operating conditions and environment of the bearing. TFL provides a coating thickness range of 50–500µm. If you have any questions regarding the selection of a specific thickness, please do not hesitate to contact our technical experts.

Common Types (Offered / Customizable by TFL)

1. Electrically Insulated Deep Groove Ball Bearings
   1. Series: 62xx,63xx Series.
   2. Application Focus: Most widely used, simple structure, suitable for small to medium-sized motors and general bearing arrangements.
2. Electrically Insulated Cylindrical Roller Bearings
   1. Series: NU,NUP Series.
   2. Application Focus: Suitable for large motors and generators requiring high radial load capacity and high-speed operation.
3. Electrically Insulated Tapered Roller Bearings
   1. Application Focus: Uniquely designed to handle combined radial and axial loads simultaneously, commonly used in heavy-duty gearboxes and high-power transmission equipment.
4. Electrically Insulated Spherical Roller Bearings
   1. Application Focus: Features self-aligning capability, suitable for applications where there is angular misalignment between the housing and the shaft, such as large vibrating screens or paper machinery.
5. Custom Insulated Bearings
   1. Service Scope: We offer tailored insulated bearing solutions based on your specific requirements, including inner/outer ring coating interchangeability, higher withstand voltage values (e.g., 5000 V), and a service for applying insulating coatings to existing bearings, greatly reducing replacement costs and lead times.

Typical Application Fields

TFL electrically insulated bearings are widely used in special industrial scenarios with high shaft current risks, characterized by high-voltage power supply or variable frequency speed regulation.

• Wind Power Generation: Main shaft bearings and generator bearings in wind turbines, operating voltages typically above 10kV. TFL insulated bearings ensure stable generator operation, preventing unexpected downtime due to electrical erosion. After implementing TFL electrically insulated bearings, a wind farm reported a 20% reduction in motor failure rates and a 30% extension in MTBF, saving hundreds of thousands annually in maintenance costs.
• Rail Transit: Traction motors for subways and high-speed trains, with voltage levels at 750V/1500V. Insulated bearings are crucial components for ensuring safe and reliable train operation.
• High-Voltage VFD Motors: 3kV/6kV/10kV VFD motors used in heavy industrial equipment for mining, metallurgy, and power generation. In these high-power, high-voltage environments, TFL insulated bearings significantly enhance equipment reliability.
• Other High-Voltage Equipment: Including high-voltage generators, large transformer cooling fans, electrostatic precipitators, etc., where bearing insulation performance is critically important.

TFL Electrically Insulated Bearings Selection and Maintenance Guide

Correct selection and maintenance are crucial to maximizing the benefit of insulated bearings.

Selection Checklist

1. Confirm Motor Type: Is it driven by a VFD? What is the output voltage?
2. Determine Insulation Need: Is outer ring insulation (VL0241) or inner ring insulation (VL2071) required? (TFL Expert Tip: Outer ring insulation is the most common and provides the largest insulation path.)
3. Match Bearing Model: Determine the required bearing type (deep groove ball, cylindrical roller, etc.) and size, for example: 6320M→6320M/C3VL0241.
4. Consider Environmental Factors: Humid, high-pollution, or ultra-high speed conditions may require considering Hybrid Ceramic Bearings for superior reliability.

Maintenance and Inspection of Insulated Bearings

Maintenance of insulated bearings should focus on the insulation layer status rather than just the mechanical condition.

• Regular Resistance Testing: We recommend using a 500V Megohmmeter to test the insulation resistance quarterly, ensuring it remains above 50 MΩ. Any reading below this value indicates potential cracks or contamination in the insulation layer.
• Avoid Mechanical Damage: During installation and removal, absolutely avoid striking the insulated coating surface, and prevent tool contact that could cause micro-cracks.
• Humidity Control: The insulation resistance of bearings stored or operated in humid environments may temporarily decrease, so ensure the storage and operating environment is dry.

Act Now: Protect Your Equipment, Extend Bearing Life!

Don’t let shaft currents erode your equipment’s performance and profits. Choose TFL electrically insulated bearings for a stable and reliable solution.

Visit our website now, browse our product catalog, or click the sidebar pop-up to connect with our expert team for customized quotes and technical support.

Frequently Asked Questions

How much voltage can TFL insulated bearings withstand?

The ceramic coating of TFL electrically insulated bearings can withstand voltage breakdown strengths of up to 3000V. This depends on the specific bearing model and coating specifications, and all products undergo rigorous testing before leaving the factory.

Can the insulation coating peel off? Does it affect the bearing’s load capacity and precision?

TFL uses advanced plasma spraying technology to ensure a strong bond between the coating and the substrate, making it highly resistant to peeling. The coating thickness is precisely controlled, having a negligible impact on the bearing’s load capacity and geometric precision, and complies with industry standards.

Can existing conventional bearings be converted into insulated bearings?

Yes, TFL offers customization services. If your existing equipment has conventional bearings installed, we can evaluate their condition and, under specific circumstances, apply an insulating coating to give them electrical insulation properties. Please contact our technical team for a detailed evaluation.

How do I determine if my equipment requires insulated bearings?

If your motor is driven by a variable frequency drive or operates in other high-voltage environments prone to shaft currents, the use of insulated bearings is strongly recommended. Persistent shaft currents can lead to premature bearing failure and increased maintenance costs. Measuring shaft voltage is a direct method to determine if insulated bearings are needed.