Residual magnetism in power relay electromagnetic systems can significantly prolong contact release time. This is essentially due to the residual magnetic field caused by the hysteresis properties of the core material. When the coil is de-energized, the residual magnetism remaining in the core continues to maintain the armature's closed state until the residual magnetic energy is gradually dissipated by mechanical friction, spring reaction force, or eddy current losses. This delayed release phenomenon is particularly prominent in DC-controlled power relays, potentially causing circuit switching lag, arcing of contacts, or control logic disruption.
Optimizing materials at the material level is fundamental to eliminating the effects of residual magnetism. Selecting soft magnetic materials with high permeability and low coercivity can significantly reduce residual magnetism. For example, the remanence of electrical pure iron DT4 is only one-third that of ordinary silicon steel sheets. Its grain structure rapidly reorganizes during the magnetization and demagnetization cycles, reducing the occurrence of fixed magnetic domains. For AC-powered power relays, using a laminated silicon steel core can accelerate the decay of residual magnetism by utilizing the eddy current effect. The insulating coating between the sheets effectively blocks the eddy current paths, allowing the magnetic field energy to be quickly dissipated through heat loss after power is removed.
Optimizing the electromagnetic system's structural design can fundamentally suppress residual magnetism. Adopting a hollow armature structure or adding a nonmagnetic air gap can significantly reduce the magnetic resistance of the magnetic circuit, allowing magnetic field energy to dissipate more easily after power is removed. For example, embedding a 0.1-0.3mm thick copper spacer at the interface between the armature and the core can reduce the release delay caused by residual magnetism by over 60%. For polarized magnetic system relays, optimizing the layout ratio of the permanent magnet and electromagnetic coil can reduce residual magnetism accumulation through the principle of flux cancellation, improving release time stability by 40%.
Reverse excitation technology is an effective method for actively eliminating residual magnetism. Applying a reverse pulse current at the moment the relay coil is de-energized generates a magnetic field in the opposite direction of the residual magnetism, accelerating the magnetic domain reorganization process. This technology is implemented by adding a reverse excitation circuit. Its core components include a MOSFET switch and a storage capacitor, and the reverse magnetic field can be applied within 1-2ms. Experiments have shown that the release time fluctuation range of power relays using this technology can be reduced from ±5ms to ±0.5ms, significantly improving control accuracy.
The short-circuit degaussing method uses the coil's self-inductance to eliminate residual magnetism. When the relay is de-energized, an electronic switch shorts the coil terminals, creating a closed loop for the induced electromotive force and accelerating the decay of the magnetic field energy. This method requires an RC snubber circuit to prevent excessive short-circuit current from damaging the coil. For a power relay rated at 24V, a combination of a 0.1Ω/10W shorting resistor and a 100μF/50V electrolytic capacitor can shorten the residual magnetism decay time by 70%.
Magnetic shielding technology reduces residual magnetism accumulation by isolating the relay core from external magnetic field interference. Wrapping the relay core with a high-permeability Permalloy shield effectively absorbs stray magnetic fields and prevents them from being captured by the core and forming residual magnetism. This technology is particularly effective in shielding AC magnetic fields, reducing the residual magnetism of the core by over 85% in a 50Hz power frequency magnetic field. The recommended shielding thickness is 0.5-1mm. Excessive thickness will increase eddy current losses, which will in turn affect the magnetic field decay rate.
Heat treatment can improve the magnetic stability of the core material. Vacuum annealing eliminates internal stress in the material, regularizing the magnetic domain alignment and reducing hysteresis losses. The process involves heating the core to 850-900°C in a hydrogen atmosphere for two hours, followed by slow cooling at a rate of 50°C/hour. This treatment reduces the remanence coefficient of the core material by 30% and improves magnetic stability by over 50%.
