Bizarre partial power failure exprienced...

[Zorin the Lynx]

So at around 9PM, here in Miami, the power blinked for about three
seconds. No biggie, I have a UPS. Then I got some a report that a power
blink ocurred at work, but only certain circuits were affected. I
confirmed that both failures happened at the same time.

Is it possible for one phase feeding a substation to open up, resulting
in a power failure for only a certain fraction of the single-phase loads
fed from that substation? And yes, I'm certain that the loads that
remained powered at work are not on any sort of emergency generator or
battery backup system.

Either that or it was just a coincidence that both power failures
happened at once, and that there was a malfunction on the power grid at
work.

Any thoughts? My curiosity is getting the better of me...

-Z

 

[Charles Perry]

Yes it is possible for one phase to open up. As I understand it, if it
happens, it is supposed to be detected, and if not corrected, open the
other two phases to avoid problems.

In the US electric utililities generally provide no protection from
"single-phasing" and state so in the terms of service in the tariff. It is
the customers responsibility to protect their facility from a loss of one
phase. Most customers don't seem to realize this even though it is right
there in the service document.

Charles Perry P.E.

 

[Beachcomber]

In the US electric utililities generally provide no protection from
"single-phasing" and state so in the terms of service in the tariff. It is
the customers responsibility to protect their facility from a loss of one
phase. Most customers don't seem to realize this even though it is right
there in the service document.

Charles Perry P.E.

Why is it that the Electrical Codes do not normally require this
protection then? I know the standard answer is that the electrical
codes are concerned with safety and not convenience. But, this would
seem to be a safety issue...

Case in point. I was once vice-president of a condo association that
sustained $24,000 in damages when all the elevator motors burned out
due to a loss of one of the three phases when there was a problem at
the fire pump. (The utility fuse at the pole had blown for one phase
only).

These were critical life-safety elevators serving elderly people in
wheelchairs. Everyone assumed that the building developer and his
electrical contractor had done their job properly and, of course, by
bare minimum standards, they claim that they did. It seemed to be an
afterthought that a few inexpensive devices costing ($100 - $150)
could have fully protected us, yet they were not installed because
they were not required. It seems to me that if fuses or circuit
breakers are required to protect your wiring, an protection from
single phasing should be required to protect your motors.

Beachcomber

 

[Charles Perry]

Why is it that the Electrical Codes do not normally require this
protection then? I know the standard answer is that the electrical
codes are concerned with safety and not convenience. But, this would
seem to be a safety issue...

Case in point. I was once vice-president of a condo association that
sustained $24,000 in damages when all the elevator motors burned out
due to a loss of one of the three phases when there was a problem at
the fire pump. (The utility fuse at the pole had blown for one phase
only).

These were critical life-safety elevators serving elderly people in
wheelchairs. Everyone assumed that the building developer and his
electrical contractor had done their job properly and, of course, by
bare minimum standards, they claim that they did. It seemed to be an
afterthought that a few inexpensive devices costing ($100 - $150)
could have fully protected us, yet they were not installed because
they were not required. It seems to me that if fuses or circuit
breakers are required to protect your wiring, an protection from
single phasing should be required to protect your motors.

Beachcomber

Don't ask me. I once did a power quality investigation at a brand new, very
expensive, cash processing center. They had a gold plated electrical
system...it was all way over built. They had 4 times the onsite generation
that they needed and had 2.5 times the UPS capacity. But.....they tried to
save $15k and left of the loss of phase protection. It cost them about 3
times that is repairs to elevator equipment. The person responsible for
cutting out the protection (a VP) was "released" I believe.

Charles Perry P.E.

 

[Charles Perry]

|
| | <snip>
|>
|> Yes it is possible for one phase to open up. As I understand it, if it
|> happens, it is supposed to be detected, and if not corrected, open the
|> other two phases to avoid problems.
|>
|
| In the US electric utililities generally provide no protection from
| "single-phasing" and state so in the terms of service in the tariff. It is
| the customers responsibility to protect their facility from a loss of one
| phase. Most customers don't seem to realize this even though it is right
| there in the service document.

However, the problem exists with single phase customers getting half voltage.
That is not allowed by the tariffs, at least in this state, based on successful
lawsuits against the utilities. Running 120 volt applicances on 60 volts for
long periods of time can cause widespread damage.

I'm talking about this taking place on a city-wide basis, not about single
three phase customer where one transformer blows a fuse.

City-wide? Not a distribution problem then, has to be transmission.

Obviously the power company can be exempted when things are beyond their
control. But choosing to not open the remaining phases when one opens up
for some reason, is within their control, at least after some reasonable
period of time, short of substation damage.

Not sure what state you are in, but if the utility is using line to ground
connected transformers (high side connection) then a single phase of the
primary opening means you are either totally out or totally in power. This
is true if it is the high side fuse of the transformer or a main line fuse
or single phase recloser on the main line.

Charles Perry P.E.

 

[Chris Oates]

Not sure what state you are in, but if the utility is using line to ground
connected transformers (high side connection) then a single phase of the
primary opening means you are either totally out or totally in power. This
is true if it is the high side fuse of the transformer or a main line fuse
or single phase recloser on the main line.

Because of Starling migration we used to suffer with line
line shorting due to their weight suddenly landing on the lines
at 4 o'clock every day during the winter - we installed phase loss
detection which coped quite well except when the problem
wa reduced voltage as that caused chatter in the contactors
which burnt them out so we had to go to voltage sensing
with dropout & manual reset - luckily the Starlings have now moved on

 

[Zorin the Lynx]

Weirdest power problem that I've seen was one night I was awakened by an
AC-powered carbon monoxide detector going off. Except it sounded rather
sick. When I turned on the light it glowed a very dull orange. Checked
out everything to see if it was a problem on my end, found nothing.
AC voltmeter plugged into an outlet read something like 45 volts.
Unplugged the refrigerator, shut off the furnace emergency switch and went
back to bed.

Wow, that was pretty strange. Did you hear anything about it in the news
or from friends/coworkers the next morning? Like people complaining that
equipment was damaged? Or was it very localized and no one cared?

I had something similar happen once here; when hurricane Andrew hit us
back in 1992, the power flickered (little blinks) for the first 20
minutes or so of the storm, then suddenly all the lights got very dim,
much as you described, and the refrigerator sounded like it was
lurching... This condition lasted for about 10 seconds or so and then it
failed completely and didn't come back for six days... I didn't have
enough time to get a voltmeter; from the sound of it you did, so it must
have persisted longer (or you had the voltmeter very handy)

So apparently now I'm enlightened; it was probably a phase going out
somewhere.

-Z

 

[Charles Perry]

| City-wide? Not a distribution problem then, has to be transmission.

In one case where it occurred in a city of 60,000 near where I lived, I heard
that it was a fuse on the primary of the transformer feeding most of that
city. That in itself is not the issue. The issue is they left it that way
for nearly 3 hours before cutting power.

If it was a blown fuse, there is no way to automatically detect and open the
other three phases. Someone has to drive out and do it.

Single phase lost on a delta primary where the wye secondary feeds street
level distribution where lots of single phase line to ground transformers
feed residential areas. If the street primary was 12470/7200, then what
you'd have is 3600 on 2 of the 3 hot phases, and 120/60 coming out of those
transformers on those 2 low phases.

Wrong. The single phase transformer is connected line to ground. If the
voltage on the primary is 1/2 of normal then the secondary voltage will be
60-N-60 not 120-N-60. A single phase transformer connected line to ground
has no reference to the other two phases and is unaffected by the voltage on
them.

Charles Perry P.E.

 

[daestrom]

So at around 9PM, here in Miami, the power blinked for about three
seconds. No biggie, I have a UPS. Then I got some a report that a power
blink ocurred at work, but only certain circuits were affected. I
confirmed that both failures happened at the same time.

Is it possible for one phase feeding a substation to open up, resulting
in a power failure for only a certain fraction of the single-phase loads
fed from that substation? And yes, I'm certain that the loads that
remained powered at work are not on any sort of emergency generator or
battery backup system.

Either that or it was just a coincidence that both power failures
happened at once, and that there was a malfunction on the power grid at
work.

Any thoughts? My curiosity is getting the better of me...

One idea that I haven't seen mentioned yet in this thread is a single-phase
fault on a third feeder.

Imagine you and your work are fed from a three-phase substation. And
consider further another load, unrelated to you also fed from that
substation.

Now, the third load develops a large phase-ground or single phase-phase
fault. If it is severe, it can cause the substation secondary voltage to be
pulled down near zero. So you and work see a loss of one phase. Then the
fault is cleared by any number of protection schemes and the 'lost' phase
voltage restores to the remaining loads (you and work).

With a severe fault, this can happen in the blink of an eye. Medium faults
may take a second or two to be cleared depending on how they are protected
(fuse, inverse-time-delay relay, mho-relay, etc...). Or if primary
protection failed and a backup trip had to take place to clear an outgoing
line from the substation.

Just speculation.

daestrom

 

[Beachcomber]

Single phase lost on a delta primary where the wye secondary feeds street
level distribution where lots of single phase line to ground transformers
feed residential areas. If the street primary was 12470/7200, then what
you'd have is 3600 on 2 of the 3 hot phases, and 120/60 coming out of those
transformers on those 2 low phases.

I've seen this in Illinois, Ohio, and West Virginia. Many years ago my
grandfather successfully sued his electric company for losses due to the
low voltage persisting for half a day (he had to replace two freezers and
an air conditioning unit).

Did the managment of the utility company not have any common sense?

Assuming they were in control and could shut things down completely,
did they not realize that running perhaps hundreds or thousands of
their customers refrigerators at 60 volts for several hours was going
to create liability issues?

Beachcomber