Re: Using SSR to switch transformer


"Arlet Ottens" <usenet+5@xxxxxxxxxx> wrote in message
news:47e7e311$0$14354$e4fe514c@xxxxxxxxxxxxxxxxx
Jan Panteltje wrote:
On a sunny day (Mon, 24 Mar 2008 17:36:05 +0100) it happened Arlet
Ottens
<usenet+5@xxxxxxxxxx> wrote in
<47e7d876$0$14342$e4fe514c@xxxxxxxxxxxxxx>:

After reading the various bits of advice, I decided to order a big SSR
(50A continuous) to build a prototype.

Some solid state relais already have a zero crossing chip.
Does yours?

No, I picked one with random turn on (Crouzet 84 134 320), otherwise
there's no way to control the inrush currents.

The ones with zero crossing logic seem to be more prevalent, but there
are still plenty of choices for random turn on types.

I picked this big one for my prototype because it had a better chance of
surviving any timing errors. For production, I'll look for something
smaller and cheaper.

Your solution seems to be ideal. For my application, I cannot use a soft
start, because I must apply a full current waveform to a circuit breaker to
simulate a fault, and measure its response time accurately. The best I can
do is time the initial application of the test voltage to coincide
approximately to the expected zero crossing of current, based on the
impedance of the source and the load, which are both mostly inductive.

Also, in my case, the load itself opens while the test set has voltage
applied, and it may open at any point on the waveform. Thus arcing and
inductive spikes are inevitable, and the transformer may have some remanant
magnetism after the breaker trips, which will then cause a high inrush on
the next test.

But I have considered adding a demagnetizing sequence after the trip is
detected. I think a series of phase modulated pulses with gradually reduced
duty cycle might reduce the magnetization of the transformer to a minimal
level for the next test.

Any thoughts on that?

Thanks,

Paul


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Relevant Pages

  • Re: Using SSR to switch transformer
    ... to build a prototype. ... Some solid state relais already have a zero crossing chip. ... there's no way to control the inrush currents. ...
    (sci.electronics.design)
  • Re: Using SSR to switch transformer
    ... The ones with zero crossing logic seem to be more prevalent, but there are still plenty of choices for random turn on types. ... Thus arcing and inductive spikes are inevitable, and the transformer may have some remanant magnetism after the breaker trips, which will then cause a high inrush on the next test. ... I think a series of phase modulated pulses with gradually reduced duty cycle might reduce the magnetization of the transformer to a minimal level for the next test. ...
    (sci.electronics.design)