Any Power Engineers Lurking?
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Chris,
> The controller fires gates on SCR/Diode pairs on each leg of a three phase
> load. The zero-crossing timing is derived optically from the AC line, and
> the command input to the PIC sets the gate delay, or phase angle to fire
at.
> It was intended for resistive loads, where the relationship between
voltage
> and current is quite simple.
After much thought and numerous trips through to the RAC-EU manual. I
have come to a relitively stately conclusion that the leg angle stretch
rectumfier will pop under a warm load.
Best Regards,
Joe
Original Message
From: "Chris Loiacono (E-mail)" <chris01@t...>
To: "Basicstamps Group (E-mail)" <basicstamps@yahoogroups.com>
Sent: Monday, May 20, 2002 7:30 AM
Subject: [noparse][[/noparse]basicstamps] Any Power Engineers Lurking?
> I have an AC Phase-angle power controller design that I am trying to fit
to
> a customer's application.
> I mention it here because there are experts here in every field, it seems,
> although the part of it I'm working on is basically an AC Power EE
problem:
>
> The controller fires gates on SCR/Diode pairs on each leg of a three phase
> load. The zero-crossing timing is derived optically from the AC line, and
> the command input to the PIC sets the gate delay, or phase angle to fire
at.
> It was intended for resistive loads, where the relationship between
voltage
> and current is quite simple.
>
> I need to use it to gate the SCR's into a transformer primary, which is a
> simple 3-wire delta. The secondary is through a three-phase bridge
rectifier
> to a wye connected resistive load. You might envision it feeding the
> resistive equivalent of a 3-phase AC motor stator, but ignore the concept
of
> motion.
>
> I am trying to assess the net effect on the primary side of the coupling
> transformer, ie: as long as the rectifier is fairly well balanced, there
> should be no DC reflected back, right?
> Will the current at the transformer primary lag, and will that effect my
> zero-cross detect timing, since it is done by LED's? If so, the controller
> will fire past the zero-crossings and make some spectacular fireworks,
since
> it deals with hundreds of Volts at hundreds of Amps.
>
> Please let me know if anyone has experience with this sort of thing that
> would like to discuss it either on or off-list.
>
> Chris
>
>
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Body of the message will be ignored.
>
>
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>
>
>
> The controller fires gates on SCR/Diode pairs on each leg of a three phase
> load. The zero-crossing timing is derived optically from the AC line, and
> the command input to the PIC sets the gate delay, or phase angle to fire
at.
> It was intended for resistive loads, where the relationship between
voltage
> and current is quite simple.
After much thought and numerous trips through to the RAC-EU manual. I
have come to a relitively stately conclusion that the leg angle stretch
rectumfier will pop under a warm load.
Best Regards,
Joe
Original Message
From: "Chris Loiacono (E-mail)" <chris01@t...>
To: "Basicstamps Group (E-mail)" <basicstamps@yahoogroups.com>
Sent: Monday, May 20, 2002 7:30 AM
Subject: [noparse][[/noparse]basicstamps] Any Power Engineers Lurking?
> I have an AC Phase-angle power controller design that I am trying to fit
to
> a customer's application.
> I mention it here because there are experts here in every field, it seems,
> although the part of it I'm working on is basically an AC Power EE
problem:
>
> The controller fires gates on SCR/Diode pairs on each leg of a three phase
> load. The zero-crossing timing is derived optically from the AC line, and
> the command input to the PIC sets the gate delay, or phase angle to fire
at.
> It was intended for resistive loads, where the relationship between
voltage
> and current is quite simple.
>
> I need to use it to gate the SCR's into a transformer primary, which is a
> simple 3-wire delta. The secondary is through a three-phase bridge
rectifier
> to a wye connected resistive load. You might envision it feeding the
> resistive equivalent of a 3-phase AC motor stator, but ignore the concept
of
> motion.
>
> I am trying to assess the net effect on the primary side of the coupling
> transformer, ie: as long as the rectifier is fairly well balanced, there
> should be no DC reflected back, right?
> Will the current at the transformer primary lag, and will that effect my
> zero-cross detect timing, since it is done by LED's? If so, the controller
> will fire past the zero-crossings and make some spectacular fireworks,
since
> it deals with hundreds of Volts at hundreds of Amps.
>
> Please let me know if anyone has experience with this sort of thing that
> would like to discuss it either on or off-list.
>
> Chris
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>
Comments
a customer's application.
I mention it here because there are experts here in every field, it seems,
although the part of it I'm working on is basically an AC Power EE problem:
The controller fires gates on SCR/Diode pairs on each leg of a three phase
load. The zero-crossing timing is derived optically from the AC line, and
the command input to the PIC sets the gate delay, or phase angle to fire at.
It was intended for resistive loads, where the relationship between voltage
and current is quite simple.
I need to use it to gate the SCR's into a transformer primary, which is a
simple 3-wire delta. The secondary is through a three-phase bridge rectifier
to a wye connected resistive load. You might envision it feeding the
resistive equivalent of a 3-phase AC motor stator, but ignore the concept of
motion.
I am trying to assess the net effect on the primary side of the coupling
transformer, ie: as long as the rectifier is fairly well balanced, there
should be no DC reflected back, right?
Will the current at the transformer primary lag, and will that effect my
zero-cross detect timing, since it is done by LED's? If so, the controller
will fire past the zero-crossings and make some spectacular fireworks, since
it deals with hundreds of Volts at hundreds of Amps.
Please let me know if anyone has experience with this sort of thing that
would like to discuss it either on or off-list.
Chris
equipment? Snubbers across the transformers primary might help. What
size? What rating? A power & control engineer with a professional
ticket would need to answer this, if you want a real answer.
HTH,
Leroy
"Chris Loiacono (E-mail)" wrote:
>
> I have an AC Phase-angle power controller design that I am trying to fit to
> a customer's application.
> I mention it here because there are experts here in every field, it seems,
> although the part of it I'm working on is basically an AC Power EE problem:
>
> The controller fires gates on SCR/Diode pairs on each leg of a three phase
> load. The zero-crossing timing is derived optically from the AC line, and
> the command input to the PIC sets the gate delay, or phase angle to fire at.
> It was intended for resistive loads, where the relationship between voltage
> and current is quite simple.
>
> I need to use it to gate the SCR's into a transformer primary, which is a
> simple 3-wire delta. The secondary is through a three-phase bridge rectifier
> to a wye connected resistive load. You might envision it feeding the
> resistive equivalent of a 3-phase AC motor stator, but ignore the concept of
> motion.
>
> I am trying to assess the net effect on the primary side of the coupling
> transformer, ie: as long as the rectifier is fairly well balanced, there
> should be no DC reflected back, right?
> Will the current at the transformer primary lag, and will that effect my
> zero-cross detect timing, since it is done by LED's? If so, the controller
> will fire past the zero-crossings and make some spectacular fireworks, since
> it deals with hundreds of Volts at hundreds of Amps.
>
> Please let me know if anyone has experience with this sort of thing that
> would like to discuss it either on or off-list.
>
> Chris
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and Body
of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
Continuing BTL:
> Could you ask some questions of the company's engineers who made the
> equipment?
There is no existing equipment, just a concept.
> Snubbers across the transformers primary might help. What
> size? What rating?
I already have snubbers and MOV's across the SCR's, which will in effect be
across the primary. These serve to ensure that dv/dt & line noise don't
detonate the SCR's; they prevent improper latching and turn-on. They are now
sized according to the load rating of each board.
Too much capacitance will cause greater noise suceptibility and will lag
current further in the wrong direction, will it not?
> A power & control engineer with a professional
> ticket would need to answer this, if you want a real answer.
While I'll appreciate input such as yours, I'm willing to go the route -
hence my thought in the original post about off-line replies. This usually
generates business offers....As a Consulting Engineer, I appreciate the
value of hiring a good specialist from time to time. On the other hand, my
gut is telling me that this is a fairly simple one that I have simply not
yet grasped yet.
I am returning from a vacation today, and I have a heap of project problems
in front of me, so getting help sounds like a good idea at the moment
Chris
before. I assumed you were using commercial equipment, a mistake on my
part. Your statement, "I am trying to assess the net effect on the
primary side of the coupling transformer, i.e.: as long as the rectifier
is fairly well balanced, there should be no DC reflected back, right?"
is new to me. I have heard of power reflected in an RF radio type
situation, we call it SWR. But I have not heard of DC being reflected
back across the winding of a x-former. MAybe we could discuss the
situation off list. if you like. Sounds interesting at the very
least.. I consider myself more a controls engineer, in that I have
expertise in PLC.s but power control is also very interesting although
my experience there is limited more to the theoretical rather than the
practical side. Good luck..
Leroy
"Chris Loiacono (E-mail)" wrote:
>
> I have an AC Phase-angle power controller design that I am trying to fit to
> a customer's application.
> I mention it here because there are experts here in every field, it seems,
> although the part of it I'm working on is basically an AC Power EE problem:
>
> The controller fires gates on SCR/Diode pairs on each leg of a three phase
> load. The zero-crossing timing is derived optically from the AC line, and
> the command input to the PIC sets the gate delay, or phase angle to fire at.
> It was intended for resistive loads, where the relationship between voltage
> and current is quite simple.
>
> I need to use it to gate the SCR's into a transformer primary, which is a
> simple 3-wire delta. The secondary is through a three-phase bridge rectifier
> to a wye connected resistive load. You might envision it feeding the
> resistive equivalent of a 3-phase AC motor stator, but ignore the concept of
> motion.
>
> I am trying to assess the net effect on the primary side of the coupling
> transformer, ie: as long as the rectifier is fairly well balanced, there
> should be no DC reflected back, right?
> Will the current at the transformer primary lag, and will that effect my
> zero-cross detect timing, since it is done by LED's? If so, the controller
> will fire past the zero-crossings and make some spectacular fireworks, since
> it deals with hundreds of Volts at hundreds of Amps.
>
> Please let me know if anyone has experience with this sort of thing that
> would like to discuss it either on or off-list.
>
> Chris
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and Body
of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
Why not control the secondary rectifier using a SCR/diode bridge, you
then have no Voltage/current phasing problems caused the inductance of
the transformer to worry about. I'm assuming this is at 60Hz and as you
state the load is mostly resistive, dv/dt should not be a problem.
Rob
Original Message
From: Chris Loiacono [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=DzXIURV1cDQnhd9qwLED84nSAiRzk5IDKRNLfxCEeohFZPsUyhhx74Q5pM0ESbwQZZHoCnsIWgIHNI4]chris@m...[/url On Behalf Of Chris
Loiacono (E-mail)
Sent: 20 May 2002 16:30
To: Basicstamps Group (E-mail)
Subject: [noparse][[/noparse]basicstamps] Any Power Engineers Lurking?
I have an AC Phase-angle power controller design that I am trying to fit
to
a customer's application.
I mention it here because there are experts here in every field, it
seems,
although the part of it I'm working on is basically an AC Power EE
problem:
The controller fires gates on SCR/Diode pairs on each leg of a three
phase
load. The zero-crossing timing is derived optically from the AC line,
and
the command input to the PIC sets the gate delay, or phase angle to fire
at.
It was intended for resistive loads, where the relationship between
voltage
and current is quite simple.
I need to use it to gate the SCR's into a transformer primary, which is
a
simple 3-wire delta. The secondary is through a three-phase bridge
rectifier
to a wye connected resistive load. You might envision it feeding the
resistive equivalent of a 3-phase AC motor stator, but ignore the
concept of
motion.
I am trying to assess the net effect on the primary side of the coupling
transformer, ie: as long as the rectifier is fairly well balanced, there
should be no DC reflected back, right?
Will the current at the transformer primary lag, and will that effect my
zero-cross detect timing, since it is done by LED's? If so, the
controller
will fire past the zero-crossings and make some spectacular fireworks,
since
it deals with hundreds of Volts at hundreds of Amps.
Please let me know if anyone has experience with this sort of thing that
would like to discuss it either on or off-list.
Chris
To UNSUBSCRIBE, just send mail to:
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> the rectifier
> is fairly well balanced, there should be no DC reflected back, right?"
This refers to an effect that can be demonstrated by placing a single
rectifier diode in one side of a transformer secondary in a single-phase AC
circuit. A DC component will appear in the primary that opposes the effect
in the secondary. This is shown on the scope as a sine wave that is no
longer centered around 0V. Since current can't flow in one direction through
the secondary, the voltage rises during that 1/2 cycle in the primary...
This is just one good reason why the time-proportioning method of power
control isn't often used with inductive loads.
C
fact, I like it so much that a short while ago I sent an Email to the
original author of this project. Interestingly, and by no coincidence (great
minds think alike [noparse]:)[/noparse] ), I asked for the primary purpose of the transformer
(I am only contracted to contribute to the power control segment of the
project, not the entire system). I suggested that if it is used only for
isolation, it can go away, and this method you are suggesting should work.
If on the other hand, it is needed to step the line voltage up or down on
it's way to the load, the idea of eliminating the large, costly transformer
is not likely to fly. I'll inform you of the reply.
Chris
> Hi
>
> Why not control the secondary rectifier using a SCR/diode bridge, you
> then have no Voltage/current phasing problems caused the inductance of
> the transformer to worry about. I'm assuming this is at 60Hz
> and as you
> state the load is mostly resistive, dv/dt should not be a problem.
>
> Rob
Original Message
From: Chris Loiacono [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=ZxuAc2mD1QPwuwgMl5eC5m2RBo5zTlm0Gml1nBKekkYoRCw47Bl9WG9Vfqr0XJ6TPoK75g8M6CfYfK0]chris@m...[/url
Sent: Tuesday, May 21, 2002 12:39 PM
To: 'basicstamps@yahoogroups.com'
Subject: RE: [noparse][[/noparse]basicstamps] Any Power Engineers Lurking?
I said I would share the info on the transformer. It is a step-down
transformer, and is a necessary part of the overall process. Oh well....
C
>
> If on the other hand, it is needed to step the line voltage
> up or down on
> it's way to the load, the idea of eliminating the large,
> costly transformer
> is not likely to fly. I'll inform you of the reply.
>
> Chris
> > Hi
> >
> > Why not control the secondary rectifier using a SCR/diode
> bridge, you
> > then have no Voltage/current phasing problems caused the
> inductance of
> > the transformer to worry about. I'm assuming this is at 60Hz
> > and as you
> > state the load is mostly resistive, dv/dt should not be a problem.
> >