rlm escribi?:
>
> >...
> Tom Rauch:
> >> >As you learned, an open termination on a current transformer can produce
> >> >some large voltages!! But no more that the turns ratio of the transformer
> >> >and operating voltage would indicate.
> >>
> Me:
> >> ** it is my opinion that the counter-EMF spike can be many times the
> >> rated primary operating V.
> >
> >Yes, Rich, this has always been my understanding also. In fact, it's
> >difficult to define the extent of the CT primary, to determine the voltage.
> >The cable may connect from one phase of a power transformer to a bus feeder
> >breaker 300 ft away. It seems there's always more to things than first meets
> >the eye. I once listened to a man lecture on "motor stator insulation" for 2
> >solid days...and he kept my attention! It seemed he lived for motor stators!
> >A life like that is for people who don't know how to fish.
> >
> >Jeff
> >
> When DC current abruptly stops, the potential for reverse potential is
> impressive. I've measured 400v-pk with an o'scope across 24vdc relay
> coils. I would like to hear Mr. Rauch's explanation of why the operating
> voltage limits reverse potential.
>
In past lab practice tests at school we drove some relay coils on-off
frequently, and as Rich, have measured (...) pulses upto 800 V across
the coil, with nominal operating value; then came the explanation about
diode in parallel with relay's coil to absorb transient. The peak
voltage for the coil was tested also varying it a few volts below and
above of nominal one.
Best regards
Guillermo - LU8EYW.
|