deb5584@ultb.isc.rit.edu (D.E. Baker) (03/14/90)
Can someone tell me what happens when a transformer saturates ? Is it the primary,secondary,core...? How do you tell when this happens? Thanks Doug
whit@milton.acs.washington.edu (John Whitmore) (03/16/90)
In article <2437@ultb.isc.rit.edu> deb5584@ultb.isc.rit.edu (D.E. Baker ) writes: > > Can someone tell me what happens when a transformer saturates ? >Is it the primary,secondary,core...? How do you tell when this happens? > A transformer is a magnetic circuit. The magnetic flux is conducted by (usually) an iron transformer core, and the total flux this core can conduct is its saturation limit. When the limit is reached, the iron has no further effect on the circuit, so your transformer is now just two coils of wire. Typically, the resistance of the wire is low, and acts as a short-circuit; fuses pop. Saturation, then, occurs in the core. The primary is usually driving the current that causes saturation (as in operating a transformer at excessively high input voltage or excessively low input frequency), and the secondary is carrying OPPOSING current. Short-circuiting the secondary virtually guarantees the transformer will not saturate. Opening the secondary gets the transformer near to saturation. If you hear a transformer buzzing (generating acoustic energy far from 60 Hz), saturation and the associated distortion of the 60 Hz waveform should be suspected. If the lights in your vicinity dim, that is another clue. When the core ceases being a magnetic "conductor" at saturation, a large amount of magnetic field leaks out of the iron; this can be detected with a search coil or other magnetic field detector; it is not unusual to see a transformer with a copper wrap around it so that the leaking field encounters a short-circuited secondary winding when saturation occurs. Actually, some onset-of-saturation is normal for transformers; there is no sharp occurrence that can be identified as saturation, only a gradual lessening of permeability (think of this as magnetic conductance and you won't be far wrong). John Whitmore
ruck@sphere.UUCP (John R Ruckstuhl Jr) (03/18/90)
In article <2439@milton.acs.washington.edu>, whit@milton.acs.washington.edu (John Whitmore) writes: > In article <2437@ultb.isc.rit.edu> deb5584@ultb.isc.rit.edu (D.E. Baker ) writes: > > > > Can someone tell me what happens when a transformer saturates ? > >Is it the primary,secondary,core...? How do you tell when this happens? > > > If you hear a transformer buzzing (generating acoustic > energy far from 60 Hz), saturation and the associated distortion > of the 60 Hz waveform should be suspected. If the lights in I believe transformers operated at 60 Hz normally hum at 120 Hz. Iron core expansion (shrinkage?) is a function of !magnitude! of the magnetic flux density in the core. Flux (or flux density) is a function of the exciting current, i.e. it cycles at 60 Hz, but the !magnitude! is periodic at 120 Hz. Because this function (magnitude) is not sinusoidal (when the exciting current is sinusoidal), and because of core hysteresis (sp?) and any other nonlinearities, the 120 Hz hum is rich with harmonics. Saturating the core, i.e. operating the transformer at levels where the EMF/flux relationship is nonlinear, would introduce added distortion, but I do not believe my sense of hearing is sensitive enough to distinguish such a change of acoustic energy in the harmonics of the 120 Hz audio signal. -- John R Ruckstuhl, Jr ...!hplabs!hp-lsd!sphere!ruck