Re: phase angle convention
- From: JosephKK <joseph_barrett@xxxxxxxxxxxxx>
- Date: Tue, 13 Nov 2007 01:49:48 -0800
John Larkin jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx posted to
sci.electronics.design:
On Tue, 13 Nov 2007 01:33:00 GMT, JosephKK
<joseph_barrett@xxxxxxxxxxxxx> wrote:
John Larkin jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx posted to
sci.electronics.design:
On Sun, 11 Nov 2007 14:48:10 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@xxxxxxxxxxxxxxx> wrote:
On Sun, 11 Nov 2007 13:43:57 -0800, John Larkin
<jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
Suppose we have a 3-phase, Y-connected power system. Call the
phases A, B, and C. Assume A peaks at T=0, B peaks next (120
degrees, 5.6 msec later) and C peaks last. Call the phase angle
of A zero.
So, what's the convention for the sign of the phase of B? Is is
+120 degrees, or -120?
Similarly, if the current in an inductor lags the applied
voltage, is the current +90 or -90 degrees relative to the
voltage?
I used to know this stuff.
John
Does it matter what you call it ?:-) Or are you having to write a
specification ?:-)
...Jim Thompson
I'm (still) doing the firmware for a dds-based waveform generator.
If the user specifies a phase angle for a waveform, I'm adding a
value to the memory address pointer that aims into the 2048-point
sinewave lookup table. So if he says to set channel 3 to +45
degrees, I'm adding 256 to the ch 3 address pointer. That makes
the peak of the resulting sine wave come out 1/8 of a cycle
earlier in time.
I like that, but is it what electrical guys expect? By my
convention, to generate a textbook 3-phase set on channels 0, 1,
and 2, I'd have to send the serial commands
0Phase 0
1Phase -120
2Phase -240
which might be weird to power folk.
I did take two semisters of Electrical Machinery, but it's been a
while. Class average on exams was, as I recall, about 15. I ran in
the mid-40's, which was an A.
John
I am not really a power type. But as i understand the conventions
phases a, b, and c in your definition are called 0, 120, and 240
degrees. As stated, these will represent lag values. For normal
power engineers just use 3-phase, with phase rotation a, b, c which
will indicate the order of positive peaks. For other persons you
may
want a different interface (read modal interface). Some would call
this a suboptimal solution. My response to them is show me a better
one.
I'm getting the general impression that a positive angle represents
lag to the power people. But they rarely use signed angles... they
say "45 degrees lagging (or leading)." That makes math funny, but
maybe they don't do much math.
John
Unfortunately true, they would rather use tables.
.
- Follow-Ups:
- Re: phase angle convention
- From: Phil Hobbs
- Re: phase angle convention
- References:
- phase angle convention
- From: John Larkin
- Re: phase angle convention
- From: Jim Thompson
- Re: phase angle convention
- From: John Larkin
- Re: phase angle convention
- From: JosephKK
- Re: phase angle convention
- From: John Larkin
- phase angle convention
- Prev by Date: Re: phase angle convention
- Next by Date: Re: cool part
- Previous by thread: Re: phase angle convention
- Next by thread: Re: phase angle convention
- Index(es):
Relevant Pages
|
