Re: SV: [CAD_CAM_EDM_DRO] Delta 3 Phase fault finding
Posted by
wanliker@a...
on 2000-03-10 09:36:52 UTC
In a message dated 3/10/00 7:51:08 AM Mountain Standard Time,
anders.blix@... writes:
<< If you ask for 3-phase you get earth allong as wel. But you are not
allowed to connect something betwen one phase and earth. I think this have
something to do wit why it is so easy to get 3-phase installed.
if one phase became grounded two things happened. The other two phases went
to very high voltages with reference to ground, electrical shock hazard, and
harder on insulation. But the bigger danger is one phase was shorted to
ground, at a given location, and another phase shorted to ground at another
location, fuses would blow, and equipment would go off line, and sometimes
damage equipment. One of the things we did was to monitor the phases to
ground with a series string of light bulbs, from each phase to ground, we
used three 120 volt lamps in series for a 220 volt circuit, per phase for a
total of 9 lamps. If all was well they would just glow dimly, if there was a
fault on a phase, one string would go out, and the other two would glow
brighter. This way we could turn off equipment to isolate the faulty
equipment, before the problem became a big one, shut off the faulty equipment
and the lamps would return to normal. Higher resistance and intermittent
faults would show clearly as the bulb strings would blink, and again show you
that there was a problem. I would highly recommend this kind of status board
for any 3 phase Delta equipped shop,
anders.blix@... writes:
<< If you ask for 3-phase you get earth allong as wel. But you are not
allowed to connect something betwen one phase and earth. I think this have
something to do wit why it is so easy to get 3-phase installed.
>>We used this system in the copper mines where we worked, the big danger was
if one phase became grounded two things happened. The other two phases went
to very high voltages with reference to ground, electrical shock hazard, and
harder on insulation. But the bigger danger is one phase was shorted to
ground, at a given location, and another phase shorted to ground at another
location, fuses would blow, and equipment would go off line, and sometimes
damage equipment. One of the things we did was to monitor the phases to
ground with a series string of light bulbs, from each phase to ground, we
used three 120 volt lamps in series for a 220 volt circuit, per phase for a
total of 9 lamps. If all was well they would just glow dimly, if there was a
fault on a phase, one string would go out, and the other two would glow
brighter. This way we could turn off equipment to isolate the faulty
equipment, before the problem became a big one, shut off the faulty equipment
and the lamps would return to normal. Higher resistance and intermittent
faults would show clearly as the bulb strings would blink, and again show you
that there was a problem. I would highly recommend this kind of status board
for any 3 phase Delta equipped shop,