Insulation
resistance is one of the core indicators for the safe operation of electrical equipment and electronic components. It refers to the ability of insulation materials to obstruct the passage of current when a direct current voltage is applied at both ends, usually measured in megaohms (M Ω). As a key parameter for evaluating insulation performance, the level of insulation resistance directly affects equipment reliability, system stability, and personal safety. Measurement and monitoring have become essential components of daily maintenance in fields such as power engineering, electronic manufacturing, and rail transit.
From a physical perspective, insulation resistance is determined by the inherent properties of insulation materials. High quality insulation materials such as polytetrafluoroethylene and alumina ceramics exhibit high resistance characteristics at room temperature and pressure due to their stable molecular structure and low free electrons. When materials become damp, aged, or contaminated, internal ion migration intensifies and conductive channels form on the surface, resulting in a significant decrease in resistance value. For example, if the insulation of a transformer winding absorbs moisture, its insulation resistance may decrease from several hundred megaohms to tens of megaohms, directly threatening equipment safety.
Measuring insulation resistance requires the use of a specialized instrument - a megohmmeter (commonly known as a shaker). The device generates a high DC voltage of 500V to 5000V through a built-in hand cranked generator or electronic circuit, forming an electric field at both ends of the insulator. According to Ohm's law, the measured leakage current can be converted to obtain the resistance value. Attention should be paid to environmental factors during operation: for every 10 ℃ increase in temperature, the insulation resistance decreases by about 15% -30%; When the humidity exceeds 80%, surface leakage current will interfere with the measurement results. Therefore, the standard requires that the equipment be fully discharged before measurement, and the average value should be taken by repeating the test in a stable environment.
The factors that affect insulation resistance are diverse and complex. In terms of materials, the purity, thickness, and curing process of insulating media such as mica tape and epoxy resin directly affect the resistance value; In terms of environment, high temperature accelerates molecular thermal motion, ultraviolet radiation breaks chemical bonds, and acidic and alkaline gases corrode insulation surfaces; In terms of craftsmanship, uneven coating of windings and poor terminal contact can result in local defects. Taking high-voltage cables as an example, their insulation resistance needs to meet the GB/T 12706 standard. If the insulation resistance is lower than 0.5M Ω/km during operation, the insulation layer damage or joint oxidation problem needs to be investigated.
The engineering application of insulation resistance runs through the entire life cycle of equipment. In the design phase, the creepage distance and electrical clearance are determined by calculating the insulation resistance; During the manufacturing phase, non-conforming products are screened through routine testing; During the operation and maintenance phase, regularly measuring the insulation resistance of equipment such as motors, capacitors, and lightning arresters can help detect insulation degradation trends in advance. In the field of new energy, the insulation resistance of photovoltaic modules directly affects the system's leakage protection; In rail transit, the insulators of high-speed rail pantographs need to pass insulation resistance tests in high humidity environments.
It is worth noting that the higher the insulation resistance, the better. Excessive resistance may indicate that the insulation system is too dry, which can lead to static electricity accumulation; A low resistance indicates a risk of leakage. Therefore, industry standards such as IEC 60243, GB/T 16927, etc. all specify the insulation resistance threshold for equipment of different voltage levels. For example, the insulation resistance of 10kV motor windings should not be lower than 10M Ω, while the insulation resistance of 500kV transformers should be greater than 1000M Ω.
With the advancement of technology, insulation resistance detection is developing towards intelligence. Infrared thermal imaging can locate insulation defects, spectrum analysis can identify partial discharge characteristics, and IoT sensors enable remote real-time monitoring. These innovations not only improve detection efficiency, but also expand the application scenarios of insulation resistance in condition based maintenance and predictive maintenance.
In summary, as the core barrier of electrical safety, the scientific measurement, precise analysis, and effective management of insulation resistance are of great significance for ensuring the stable operation of the power system. Through standardized operation, environmental control, and technological innovation, the warning and protection role of insulation resistance in the entire life cycle of equipment can be fully utilized, laying a solid safety defense line for industrial production and daily life.
