bmaraldo@watdcsu.UUCP (08/19/87)
Are ferro-resonant transformers supposed to output a pseudo-square wave?
Brett L Maraldo
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-------- Unit 36 Research ---------
"Alien Technology Today"
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bmaraldo@watdcsuwtm@neoucom.UUCP (Bill Mayhew) (08/21/87)
bmaraldo@watdcsu.waterloo.edu (Commander Brett Maraldo) writes: > Are ferro-resonant transformers supposed to output a pseudo-square wave? Ferro resonant transformers put out a waveform that resembles a square wave due to the high 3rd harmonic content that their reguating action produces. Some sensitive equipment can be bothered by the presence of the harmonic content. Electronics that has power transformers that are designed strictly for 60 Hz can have problems. Sometimes the transformers get hot or the core laminations vibrate annoyingly. The vibration is particularly irritating, since it is 360 Hz due to the fact the laminations vibrate once per half cycle of the 180 Hz hamonic wave. Harmonic neutralized regulators are available but tend to be quite a bit more expensive than the standard models. Where the power problems are slow drifts rather than variations that occur over one or two cycles, I favor a tap switcher transformer. Basically, a tap switcher is usually an autotransformer that is equipped with a small voltage sensor circuit board. The output of the sensor goes to SCRs that select a tap on the autotransformer that will produce the desired output voltage. The advantage of such a transformer is that the output is relatively harmonic free, and the transformer itself is small, quiet and runs cool. I did have one nasty experience with a Topaz brand tap switcher at the last place I worked. The line input fuse on the sensor card blew, and somehow caused a commutation effect on the SCRs. The rapid switching of the SCRs turned the transformer into a big ringing choke and it fed 1800 volts into the output side!! Fortunately, nothing was plugged in when it blew. It was used in a test facility, and part of the morning ritual was to test the line voltage to the bench before plugging in the D.U.T. I sure did a double take when I saw my meter pin on the 250 vac scale on the 120 volt line. Bill (wtm@neoucom.UUCP)
rmrin@inuxh.UUCP (D Rickert) (08/21/87)
> > > Are ferro-resonant transformers supposed to output a pseudo-square wave? > > Brett L Maraldo > -- > -------- Unit 36 Research --------- > "Alien Technology Today" > ------------------------------------------- > bmaraldo@watdcsu Yes, it's how they work. The wave shape will change with input voltage and with load.