Tstuhl
Electrical
- Jun 1, 2018
- 3
Hello,
I am doing a study on transformer core magnetization and how it plays a role in the transients seen during energization. One of the things that I was tasked with looking into was why some of the transformers that we work with will demagnetize if isolated from the rest of the network (a short is created between all of the bushings and windings and connected to a common ground). The company I am with does not do actual demagnetization of the cores when we isolate them, but we will see that transformers that have been isolated for weeks will experience less severe inrush current upon energization while those that are isolated on the order of days will experience much more severe inrush. Since the peak of inrush current is closely linked to the residual flux of the transformer core, it has lead many of my superiors to conclude that the transformers are demagnetizing, over time, on their own. I am sure there is other, more empirical, evidence that suggests this as well since studies are not ordered for anything.
My question is:
Why would a transformer core demagnetize over the course of a month or more in this scenario?
With my understanding of how to magnetize/demagnetize a ferromagnetic material, you need some kind of energy input to the material, and I am not seeing where this energy would come from other than heat transfer into the core. This, however, seems to be an unlikely explanation. I also did see that there is a demagnetization method that utilizes a capacitor, but I could not find any kind of resource that explained the process or why it would work.
I am doing a study on transformer core magnetization and how it plays a role in the transients seen during energization. One of the things that I was tasked with looking into was why some of the transformers that we work with will demagnetize if isolated from the rest of the network (a short is created between all of the bushings and windings and connected to a common ground). The company I am with does not do actual demagnetization of the cores when we isolate them, but we will see that transformers that have been isolated for weeks will experience less severe inrush current upon energization while those that are isolated on the order of days will experience much more severe inrush. Since the peak of inrush current is closely linked to the residual flux of the transformer core, it has lead many of my superiors to conclude that the transformers are demagnetizing, over time, on their own. I am sure there is other, more empirical, evidence that suggests this as well since studies are not ordered for anything.
My question is:
Why would a transformer core demagnetize over the course of a month or more in this scenario?
With my understanding of how to magnetize/demagnetize a ferromagnetic material, you need some kind of energy input to the material, and I am not seeing where this energy would come from other than heat transfer into the core. This, however, seems to be an unlikely explanation. I also did see that there is a demagnetization method that utilizes a capacitor, but I could not find any kind of resource that explained the process or why it would work.