Overview
Inside a conductive slip ring, there are multiple conductive rings, which are isolated from each other by insulating materials to prevent the mutual interference of electrical signals. Only a slip ring with sufficient insulation strength can prevent arcing and potential damage during the operation of the equipment. So, do you know what determines the insulation strength of a slip ring? Now, let's discuss it.
What is the Insulation Strength of a Slip Ring?
It refers to the voltage tolerance ability of the insulating parts and materials within the slip ring. Generally, the larger this value, the better, especially for applications with high voltage requirements. Because for insulators, the better the insulation performance, the stronger the withstand voltage ability.
Factors Affecting the Insulation Strength of a Slip Ring
(1) Insulation Property of Sealant
The insulation property of the sealant greatly affects the insulation strength of the slip ring. Currently, most slip rings use epoxy resin sealant. Its components mainly include bisphenol A epoxy resin as the main agent, various hydride curing agents, and fillers such as silicon micropowder or Al2O3 alumina powder. In addition, various toughening agents and accelerators are also added. After being cured at high temperature, these materials are not prone to cracks or damage when subjected to external forces, maintaining the sealed insulation of the slip ring.
(2) Insulating Materials
Insulating materials are installed between the conductive rings and have the following functions:
Insulation isolation between rings
Insulation isolation between the ring and the rotating shaft
Insulation between the brushes and between the brushes and the slip ring housing
They have differences in dielectric constant, breakdown electric field strength, volume resistivity, purity, water content, etc. Among them, the dielectric constant of ceramics is generally between 8 - 10, the breakdown electric field strength can be as high as 20 - 30 kV/mm, and the volume resistivity is greater than 10^12 Ω·m. It can withstand a relatively high voltage without being broken down. While the insulation performance of PTFE and POM is relatively low. In addition, the greater the thickness of the insulating material, the higher its insulation strength.
(3) Capacity of Insulating Elements
The capacity here can be understood as the electric field energy or charge accumulation ability that the insulating element can withstand. When the slip ring is working, a certain amount of charge will be distributed on the insulating element. If the capacity of the insulating element is insufficient, when the charge accumulates to a certain extent, it may cause local electric field distortion, resulting in a decrease in the breakdown voltage of the insulating material.
This capacity is also related to its geometric shape and size. Generally, increasing the surface area and thickness of the insulating element can increase its capacity.
(4) Spacing between Adjacent Circuits
When the spacing between adjacent circuits is small, the electric field coupling effect between them will be enhanced. This easily leads to an uneven and locally increased electric field strength, which can reach above 5000V/mm. This greatly increases the risk of insulation breakdown. Therefore, in high-voltage slip rings, we often increase the spacing between adjacent conductive rings to 5 - 10mm to improve the electric field distribution.
How to Test the Insulation Strength of a Slip Ring?
We use an 500V or 250V insulation withstand voltage tester to measure the withstand voltage strength of the specified insulator. When the voltage applied to the test object exceeds a certain limit, the insulator will be broken down and lose its insulation performance. The specific test steps are as follows:
Step 1
Use a multimeter to find the positive and negative poles of the conductive slip ring. Some conductive slip ring suppliers will mark them for customers when the product leaves the factory.
Step 2
Connect the insulation withstand voltage meter to the power supply and connect the positive and negative poles of the slip ring to the insulation withstand voltage meter respectively.
Step 3
Adjust the voltage on the insulation withstand voltage tester for testing, adjust the required withstand voltage, and check the withstand voltage strength of the conductive slip ring. If the slip ring cannot withstand it, the insulation withstand voltage meter will alarm.
Measures to Improve the Insulation Strength of a Slip Ring
(1) Optimize Insulating Materials
Select insulating materials with high dielectric strength, high resistivity, and good heat resistance according to the working environment and electrical parameters of the slip ring, such as ceramics or polyimide. They should also be well compatible with the conductive rings and brushes of the slip ring.
(2) Improve Manufacturing Processes
High-precision processing can ensure a tight and uniform fit between the insulating layer and the conductive ring, reducing the presence of air gaps and defects. We can also perform curing treatment and surface treatment on the insulating materials, such as coating with a moisture-proof, anti-fouling, and anti-corrosion silicone rubber coating or fluorocarbon coating. This can prevent the insulation resistance from decreasing due to water infiltration.
(3) Optimize the Slip Ring Structure
Increase the insulation distance between adjacent conductive rings and between the conductive ring and the housing of the slip ring. According to the electric field distribution theory, this reduces the occurrence of electric field concentration and improves the insulation strength. Alternatively, we can introduce a metal shielding layer into the slip ring structure and ground it. This helps to guide the external electromagnetic interference signals into the ground through the shielding layer, reducing the electric field strength on the insulating material.
(4) Strengthen the Maintenance of the Slip Ring
Keep the working environment of the slip ring clean and avoid the effects of high temperature, high humidity, strong electromagnetic fields, and chemical pollution. If a decrease in insulation resistance is detected, it may be due to surface contamination of the insulating material. At this time, it can be restored by drying treatment or cleaning the surface of the insulating layer.
Conclusion
In conclusion, the insulation strength of a slip ring is affected by multiple factors. Only by deeply understanding these factors and taking targeted measures during the design, manufacturing, and use of the slip ring can the stable operation of the entire rotating system be maintained. If you still have more doubts about this or want to customize high-insulation slip rings, please feel free to contact us!