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Overvoltage on transformer secondary

Started by Unknown November 28, 2017
I his article about troubleshooting () Bob Pease writes:

: If the power line switch was turned off at exactly the wrong time of
: the cycle, the flux in the transformer steel core could be
: strored at high level.  Then, if the line power switch was
: reconnected at exactly the wrong time in the cycle, the flux
: in the transformer would ontinue to build up until the
: transformer saturated and produced a voltage spike of 70 to 90V
: on its secondary.

Possibility of saturation is well-known.  However, getting voltage
spike on secondary due to saturation looks strange:

1) saturation means that high current in primary gives only tiny
   increase of flux.  SEM is proportional to derivative of flux,
   so SEM is limited.  In fact, high current in primary is because
   SEM is to small to oppose line voltage.
2) Ignoring stray inductance SEM on the secondary is transformer
   constant times SEM on the primary.  Ohmic losses mean that
   SEM on primary is lower than voltage on the primary, SEM on
   secondary is higher than voltage on secondary.  I would expect
   similar effect from stray inductance.

So I do not see how saturation can lead to overvoltage on
secondary.  I can imagine getting overvoltage on secondary
for different reasons.  Pease wrote that overwoltage was releated
to having very small filtering capacitor and that bigger capacitor
solved the problem.  AFAIC bigger capacitor would solve problem
regardless of reason... Has anybody experienced such overvoltage?
Can you explain why saturation could lead to overvoltage on
secondary?

-- 
                              Waldek Hebisch
On Tuesday, November 28, 2017 at 9:51:15 AM UTC-5, anti...@math.uni.wroc.pl wrote:
> I his article about troubleshooting () Bob Pease writes: > > : If the power line switch was turned off at exactly the wrong time of > : the cycle, the flux in the transformer steel core could be > : strored at high level. Then, if the line power switch was > : reconnected at exactly the wrong time in the cycle, the flux > : in the transformer would ontinue to build up until the > : transformer saturated and produced a voltage spike of 70 to 90V > : on its secondary. > > Possibility of saturation is well-known. However, getting voltage > spike on secondary due to saturation looks strange: > > 1) saturation means that high current in primary gives only tiny > increase of flux. SEM is proportional to derivative of flux, > so SEM is limited. In fact, high current in primary is because > SEM is to small to oppose line voltage. > 2) Ignoring stray inductance SEM on the secondary is transformer > constant times SEM on the primary. Ohmic losses mean that > SEM on primary is lower than voltage on the primary, SEM on > secondary is higher than voltage on secondary. I would expect > similar effect from stray inductance. > > So I do not see how saturation can lead to overvoltage on > secondary. I can imagine getting overvoltage on secondary > for different reasons. Pease wrote that overwoltage was releated > to having very small filtering capacitor and that bigger capacitor > solved the problem. AFAIC bigger capacitor would solve problem > regardless of reason... Has anybody experienced such overvoltage? > Can you explain why saturation could lead to overvoltage on > secondary? > > -- > Waldek Hebisch
Do you have a link to article, or is it in his trouble shooting book? then give a page number. I'm not sure I can help.. or have seen saturation like this. But years ago I was playing with a home made flux gate magnetometer. Looking at the voltage waveform as I drove the coil in and out of saturation I realized that there are two terms to the voltage. V= d/dt(L*i) = i*dL/dt + L*di/dt Maybe it's the first term that is giving the spike? George H.
George Herold <gherold@teachspin.com> wrote:
> On Tuesday, November 28, 2017 at 9:51:15 AM UTC-5, anti...@math.uni.wroc.pl wrote: > > I his article about troubleshooting () Bob Pease writes: > > > > : If the power line switch was turned off at exactly the wrong time of > > : the cycle, the flux in the transformer steel core could be > > : strored at high level. Then, if the line power switch was > > : reconnected at exactly the wrong time in the cycle, the flux > > : in the transformer would ontinue to build up until the > > : transformer saturated and produced a voltage spike of 70 to 90V > > : on its secondary. > > > > Possibility of saturation is well-known. However, getting voltage > > spike on secondary due to saturation looks strange: > > > > 1) saturation means that high current in primary gives only tiny > > increase of flux. SEM is proportional to derivative of flux, > > so SEM is limited. In fact, high current in primary is because > > SEM is to small to oppose line voltage. > > 2) Ignoring stray inductance SEM on the secondary is transformer > > constant times SEM on the primary. Ohmic losses mean that > > SEM on primary is lower than voltage on the primary, SEM on > > secondary is higher than voltage on secondary. I would expect > > similar effect from stray inductance. > > > > So I do not see how saturation can lead to overvoltage on > > secondary. I can imagine getting overvoltage on secondary > > for different reasons. Pease wrote that overwoltage was releated > > to having very small filtering capacitor and that bigger capacitor > > solved the problem. AFAIC bigger capacitor would solve problem > > regardless of reason... Has anybody experienced such overvoltage? > > Can you explain why saturation could lead to overvoltage on > > secondary? > > > > -- > > Waldek Hebisch > > Do you have a link to article, or is it in his trouble shooting book? > then give a page number.
I followed links that Steve Wilson gave: http://www.introni.it/pdf/Bob%20Pease%20Lab%20Notes%20Part%208.pdf The specific text is in third paragraph on page 28 (using .pdf page numbers).
> > I'm not sure I can help.. or have seen saturation like this. > But years ago I was playing with a home made flux gate magnetometer. > Looking at the voltage waveform as I drove the coil in and out of > saturation I realized that there are two terms to the voltage. > V= d/dt(L*i) = i*dL/dt + L*di/dt Maybe it's the first term that > is giving the spike? > > George H.
-- Waldek Hebisch
antispam@math.uni.wroc.pl wrote:

> George Herold <gherold@teachspin.com> wrote: >> On Tuesday, November 28, 2017 at 9:51:15 AM UTC-5, >> anti...@math.uni.wroc.pl wrote: >> > I his article about troubleshooting () Bob Pease writes:
>> > : If the power line switch was turned off at exactly the wrong time >> > : of the cycle, the flux in the transformer steel core could be >> > : strored at high level. Then, if the line power switch was >> > : reconnected at exactly the wrong time in the cycle, the flux >> > : in the transformer would ontinue to build up until the >> > : transformer saturated and produced a voltage spike of 70 to 90V on >> > : its secondary.
>> > Possibility of saturation is well-known. However, getting voltage >> > spike on secondary due to saturation looks strange:
>> > 1) saturation means that high current in primary gives only tiny >> > increase of flux. SEM is proportional to derivative of flux, so >> > SEM is limited. In fact, high current in primary is because SEM >> > is to small to oppose line voltage. >> > 2) Ignoring stray inductance SEM on the secondary is transformer >> > constant times SEM on the primary. Ohmic losses mean that >> > SEM on primary is lower than voltage on the primary, SEM on >> > secondary is higher than voltage on secondary. I would expect >> > similar effect from stray inductance. >> > >> > So I do not see how saturation can lead to overvoltage on >> > secondary. I can imagine getting overvoltage on secondary >> > for different reasons. Pease wrote that overwoltage was releated >> > to having very small filtering capacitor and that bigger capacitor >> > solved the problem. AFAIC bigger capacitor would solve problem >> > regardless of reason... Has anybody experienced such overvoltage? >> > Can you explain why saturation could lead to overvoltage on >> > secondary?
>> > Waldek Hebisch
>> Do you have a link to article, or is it in his trouble shooting book? >> then give a page number.
> I followed links that Steve Wilson gave:
> http://www.introni.it/pdf/Bob%20Pease%20Lab%20Notes%20Part%208.pdf
> The specific text is in third paragraph on page 28 (using .pdf > page numbers).
Good catch! That took some good sleuthing. Like you, I find it hard to believe the failure occurred as described. I think it more likely happened on the previous shutdown. If the contacts opened at the wrong time, the flux in the transformer would collapse and generate a voltage spike, just like the ignition coil in your car or the flyback transformer in an old tube tv. This could charge the filter capacitor to high voltage and destroy the regulator. The failure would be noted on the next power on, and falsely attributed to a spike at turnon. Increasing the size of the capacitor is only a partial solution, as indicated by the residual failure rate. A better option may be to include a zener or similar protection at the input to the regulator, as well as increasing the size of the filter cap. Note if the supply can be disconnected from the regulator, there is a risk of destroying the regulator if the power supply is attached while it is powered on. The problem is a possible resonance in the power supply cable with the filter cap and the input cap of the regulator. This is described in one of the Linear Technology application notes. I forget what they used for a solution, but I will see if I can find the article.
He was bound to get something wrong.

At best, when saturation shorts out the core's EMF, the secondary voltage 
responds "delayed" -- and can thus overshoot or ring.  It's usually well 
damped, though.  This would be the RLC response of the secondary, a fairly 
high impedance, inconsequential to most any circuit.

Tim

-- 
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: https://www.seventransistorlabs.com/

<antispam@math.uni.wroc.pl> wrote in message 
news:ovjt4q$oth$1@z-news.wcss.wroc.pl...
>I his article about troubleshooting () Bob Pease writes: > > : If the power line switch was turned off at exactly the wrong time of > : the cycle, the flux in the transformer steel core could be > : strored at high level. Then, if the line power switch was > : reconnected at exactly the wrong time in the cycle, the flux > : in the transformer would ontinue to build up until the > : transformer saturated and produced a voltage spike of 70 to 90V > : on its secondary. > > Possibility of saturation is well-known. However, getting voltage > spike on secondary due to saturation looks strange: > > 1) saturation means that high current in primary gives only tiny > increase of flux. SEM is proportional to derivative of flux, > so SEM is limited. In fact, high current in primary is because > SEM is to small to oppose line voltage. > 2) Ignoring stray inductance SEM on the secondary is transformer > constant times SEM on the primary. Ohmic losses mean that > SEM on primary is lower than voltage on the primary, SEM on > secondary is higher than voltage on secondary. I would expect > similar effect from stray inductance. > > So I do not see how saturation can lead to overvoltage on > secondary. I can imagine getting overvoltage on secondary > for different reasons. Pease wrote that overwoltage was releated > to having very small filtering capacitor and that bigger capacitor > solved the problem. AFAIC bigger capacitor would solve problem > regardless of reason... Has anybody experienced such overvoltage? > Can you explain why saturation could lead to overvoltage on > secondary? > > -- > Waldek Hebisch
On Tue, 28 Nov 2017 14:51:06 +0000 (UTC), antispam@math.uni.wroc.pl
wrote:

>I his article about troubleshooting () Bob Pease writes: > >: If the power line switch was turned off at exactly the wrong time of >: the cycle, the flux in the transformer steel core could be >: strored at high level. Then, if the line power switch was >: reconnected at exactly the wrong time in the cycle, the flux >: in the transformer would ontinue to build up until the >: transformer saturated and produced a voltage spike of 70 to 90V >: on its secondary. > >Possibility of saturation is well-known. However, getting voltage >spike on secondary due to saturation looks strange: > >1) saturation means that high current in primary gives only tiny > increase of flux. SEM is proportional to derivative of flux, > so SEM is limited. In fact, high current in primary is because > SEM is to small to oppose line voltage. >2) Ignoring stray inductance SEM on the secondary is transformer > constant times SEM on the primary. Ohmic losses mean that > SEM on primary is lower than voltage on the primary, SEM on > secondary is higher than voltage on secondary. I would expect > similar effect from stray inductance. > >So I do not see how saturation can lead to overvoltage on >secondary.
Not on the half-cycle that saturates the core. But maybe on the next opposite-sign half cycle, the one that yanks the core out of saturation. That will happen when there is a lot of magnetizing (actually demagnetizing) current. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Tuesday, November 28, 2017 at 12:46:52 PM UTC-5, anti...@math.uni.wroc.pl wrote:
> George Herold <gherold@teachspin.com> wrote: > > On Tuesday, November 28, 2017 at 9:51:15 AM UTC-5, anti...@math.uni.wroc.pl wrote: > > > I his article about troubleshooting () Bob Pease writes: > > > > > > : If the power line switch was turned off at exactly the wrong time of > > > : the cycle, the flux in the transformer steel core could be > > > : strored at high level. Then, if the line power switch was > > > : reconnected at exactly the wrong time in the cycle, the flux > > > : in the transformer would ontinue to build up until the > > > : transformer saturated and produced a voltage spike of 70 to 90V > > > : on its secondary. > > > > > > Possibility of saturation is well-known. However, getting voltage > > > spike on secondary due to saturation looks strange: > > > > > > 1) saturation means that high current in primary gives only tiny > > > increase of flux. SEM is proportional to derivative of flux, > > > so SEM is limited. In fact, high current in primary is because > > > SEM is to small to oppose line voltage. > > > 2) Ignoring stray inductance SEM on the secondary is transformer > > > constant times SEM on the primary. Ohmic losses mean that > > > SEM on primary is lower than voltage on the primary, SEM on > > > secondary is higher than voltage on secondary. I would expect > > > similar effect from stray inductance. > > > > > > So I do not see how saturation can lead to overvoltage on > > > secondary. I can imagine getting overvoltage on secondary > > > for different reasons. Pease wrote that overwoltage was releated > > > to having very small filtering capacitor and that bigger capacitor > > > solved the problem. AFAIC bigger capacitor would solve problem > > > regardless of reason... Has anybody experienced such overvoltage? > > > Can you explain why saturation could lead to overvoltage on > > > secondary? > > > > > > -- > > > Waldek Hebisch > > > > Do you have a link to article, or is it in his trouble shooting book? > > then give a page number. > > I followed links that Steve Wilson gave: > > http://www.introni.it/pdf/Bob%20Pease%20Lab%20Notes%20Part%208.pdf > > The specific text is in third paragraph on page 28 (using .pdf > page numbers).
Thanks, maybe my Xmas gift can be some sort of e-reader. Otherwise, I've hardly read any of that... lucky me. :^) George H.
> > > > > I'm not sure I can help.. or have seen saturation like this. > > But years ago I was playing with a home made flux gate magnetometer. > > Looking at the voltage waveform as I drove the coil in and out of > > saturation I realized that there are two terms to the voltage. > > V= d/dt(L*i) = i*dL/dt + L*di/dt Maybe it's the first term that > > is giving the spike? > > > > George H. > > -- > Waldek Hebisch
Waldek wrote in message news:ovjt4q$oth$1@z-news.wcss.wroc.pl...

> I his article about troubleshooting () Bob Pease writes:
: If the power line switch was turned off at exactly the wrong time of : the cycle, the flux in the transformer steel core could be : strored at high level. Then, if the line power switch was : reconnected at exactly the wrong time in the cycle, the flux : in the transformer would ontinue to build up until the : transformer saturated and produced a voltage spike of 70 to 90V : on its secondary.
> Possibility of saturation is well-known. However, getting voltage spike > on secondary due to saturation looks strange:
> 1) saturation means that high current in primary gives only tiny
increase of flux. SEM is proportional to derivative of flux, so SEM is limited. In fact, high current in primary is because SEM is to small to oppose line voltage.
> 2) Ignoring stray inductance SEM on the secondary is transformer
constant times SEM on the primary. Ohmic losses mean that SEM on primary is lower than voltage on the primary, SEM on secondary is higher than voltage on secondary. I would expect similar effect from stray inductance.
> So I do not see how saturation can lead to overvoltage on secondary. I > can imagine getting overvoltage on secondary for different reasons. Pease > wrote that overwoltage was releated to having very small filtering > capacitor and that bigger capacitorsolved the problem. AFAIC bigger > capacitor would solve problem regardless of reason... Has anybody > experienced such overvoltage? Can you explain why saturation could lead to > overvoltage on secondary?
I have experienced the effects of remanent magnetism and DC offset in circuit breaker test sets, which use large step-down transformers to drive high currents (up to 100,000 amps) into circuit breakers. The load as seen by the mains power (usually 480 VAC) is mostly inductive, so the output is controlled by an SCR switch that fires close to the waveform peak, resulting in minimal DC offset. If the output is initiated at a zero crossing, the first half-cycle may have a peak as much as twice normal, and the waveform then decays until it is symmetrical about the zero voltage level. When an odd number of half-cycles is applied to the transformer, there is a net DC component that creates remanent magnetism in the core. If the next application of voltage is in the same phase, the core will saturate and cause a high current spike in the primary. Since under such circumstances, the core is already saturated, the output voltage on the secondary would be expected to be lower than usual, except perhaps for a very brief spike. However, if the phase is opposite to the magnetization, It might be possible for the output to see a higher-than-normal voltage, especially if the voltage is applied at or near a zero crossing to produce DC offset. At least, that's how I understand it and what I have observed. Paul
John Larkin <jjlarkin@highland_snip_technology.com> wrote:

> On Tue, 28 Nov 2017 14:51:06 +0000 (UTC), antispam@math.uni.wroc.pl > wrote:
>>I his article about troubleshooting () Bob Pease writes: >> >>: If the power line switch was turned off at exactly the wrong time of >>: the cycle, the flux in the transformer steel core could be >>: strored at high level. Then, if the line power switch was >>: reconnected at exactly the wrong time in the cycle, the flux >>: in the transformer would ontinue to build up until the >>: transformer saturated and produced a voltage spike of 70 to 90V on >>: its secondary.
>>Possibility of saturation is well-known. However, getting voltage >>spike on secondary due to saturation looks strange:
>>1) saturation means that high current in primary gives only tiny >> increase of flux. SEM is proportional to derivative of flux, so SEM >> is limited. In fact, high current in primary is because SEM is to >> small to oppose line voltage. >>2) Ignoring stray inductance SEM on the secondary is transformer >> constant times SEM on the primary. Ohmic losses mean that >> SEM on primary is lower than voltage on the primary, SEM on >> secondary is higher than voltage on secondary. I would expect >> similar effect from stray inductance.
>>So I do not see how saturation can lead to overvoltage on secondary.
> Not on the half-cycle that saturates the core. But maybe on the next > opposite-sign half cycle, the one that yanks the core out of > saturation.
> That will happen when there is a lot of magnetizing (actually > demagnetizing) current.
Instead of speculating, the correct procedure would have been to measure the pulse with a scope, something that Bob P. should have done in the first place. Guessing at the problem was very poor troubleshooting technique, as well as increasing the size of the capacitor by some arbitrary amount. Yhat was very poor engineering, as shown by the residual failure rate. Another problem was the cascading failure. If the cap failed, it would destroy the regulator. This could damage the following circuits which depended on the regulator output voltage. One of the tenets of good engineering is to prevent cascading failure, something that Bob P. should have emphasized. So in this case, Bob showed the worst possible examples of bad troublehooting technique and poor engineering. Not a very good result for a book on troubleshooting technique.
George Herold <gherold@teachspin.com> wrote:

> On Tuesday, November 28, 2017 at 12:46:52 PM UTC-5, > anti...@math.uni.wroc.pl wrote: >> > Do you have a link to article, or is it in his trouble shooting book? >> > then give a page number.
>> I followed links that Steve Wilson gave:
>> http://www.introni.it/pdf/Bob%20Pease%20Lab%20Notes%20Part%208.pdf
>> The specific text is in third paragraph on page 28 (using .pdf page >> numbers).
> Thanks, maybe my Xmas gift can be some sort of e-reader.
> Otherwise, I've hardly read any of that... lucky me. :^)
> George H.
Just curious, why do you need an e-reader to view a PDF file? How do you read datasheets that are usually in PDF format? What operating system do you run that doesn't have a pdf reader available? If it's Windows, have you tried PDF Xchange? It runs on XP and later: https://www.tracker-software.com/product/pdf-xchange-viewer If it's Linux, there should be a multitude of PDF readers available. I use the HP device manager for the HP 3050A Deskjet. This installs on Ubuntu 10.04, and has an excellent built-in PDF reader. I never use it to print anything, but it has an excellent scanner that can output PDF files. As usual for HP, it had a very low price and was further marked down for clearance. Irresistable. It was one of the more sane purchases I have ever made.