Not to boast, as you will see, but here in the good ol'USA, SE corner, I
thought we had about the WORST electrical supply in the world. This region's
portion of man's largest machine (as the US electrical grid has been labeled
by the MIT Tech. journal) is a hodge-podge of generators and wiring methods
that changes every 50 to 100 miles or so. Some of the overhead wiring goes
through quite inhospitable terrain and is outdated, most of it done before
there was much standardization of methods or materials. Much is buried in
wet swamp land and some is new, state of the art. I get calls from customers
often telling of weird voltages, Neutral connections coming and going, and
old oil-filled transformers being swapped out on poles nearby as they fail-
for new ones with different configurations (as in: the N connection is moved
from one point to another, or a 'wye' becomes a 'delta') from one day to the
next without notice.
One day some weeks ago, I lost a PC (was on a transformer isolated UPS) a
nuke box and a water softener in one episode that occurred at the stroke of
midnight when a series of surges went through the lines (BTW, the PC's on
APC back up pro's did fare well). I have installed hundreds upon hundreds of
phase angle power controllers with 7500V optical isolation in US, Japan and
Europe (guess I'm spoiled), and have never had one fail due to opto
isolators crashing. I suppose part selection has much to do with this....But
I have to admit, I don't think any of mine are in India or Romania. That
situation sounds pretty scary.....

How could the series resistor scheme protect a circuit from fast spikes
better than optos? Are we saying that they do, or that since they pass more
transients, they don't fail as often? I suppose that would be OK if a motor
winding was on the other side of the spike, but a micro I/O pin?
Hmmm....unless those tiny protection diodes really do work well....
It seems I learn something every day....
Chris

-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Vasile Surducan
Sent: Thursday, January 31, 2002 11:06 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [EE]: Phase failiure Detection in 3 Phase


If the distortion regime on indian supply lines are the same like in
Romania, any semiconductor devices ( ie optocouplers ) will crash after a
while. I suggest you a much simple detection mechanism: three relays
connected from phase to neutral. Al closed contacts in series to your MCLR
pin used as IO input. Resistor to vcc, series end to gnd.
If one of the phase fails the io pin see high level.
Take care about the incomplete failure of a phase ( ie: 30% voltage or
less can be still active, because of inductive 3-phase loads, also the
phase can be differet from 120 degree in malfunction regim )

Vasile



On Thu, 31 Jan 2002, Jeethu Rao wrote:

> I have designed a 16f628 based timer for 3 phase loads (using a
contactor).
> Now, here in India, its quite a common occurance that 1 or 2 phases in the
> 3 phase supply fail. And it could quite easily kill the 3 Phase Motors.
> I want to design a system for detecting phase failiure and to signal the
PIC
> about this. I've got only one Input pin left on the PIC (MCLR!). Any
> suggestions
> or Ideas ?
>
> I thought of using a 3 input AND gate fed by each of the phase via a 1 meg
> resistor and
> a 1N4007 diode. and connecting the output of the AND gate to the PIC. Is
> this ok, or do
> I need to use 3 opto couplers for isolation?
>
> TIA,
>
> Jeethu Rao
>
> --
> http://www.piclist.com hint: To leave the PICList
> mailto:piclist-unsubscribe-request@mitvma.mit.edu
>
>

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads