123 V dropped to 93 V for 2 hrs

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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
100525-0851 EST

A week ago about 7:10 AM EDT i was eating breakfast and watching TV. Voltage probably went to 0 for a second or so, came back to some level. Occurred once or twice more, then settled at about 93 V.

My normal line voltage is in the range of 121 to 125. Presently I am at 123.7 at the main panel on both sides and present load is 1.73 KW.

After discovering the 93 V level and it was fairly constant I disabled the refrigerators. I really do not know whether they can tolerate this low a voltage for a long time.

Most of my fluorescents were working. However, one group would not light. Virtually all are magnetic ballast.

My power company contact, first a dumb automated system, then an ignorant person that was most interested in not listening to me but most interested in informing me that I would be charged for a service call if they found no problem when there service truck arrived. It was very clearly my pole transformer or a system problem.

As an aside. Research has shown that a business that has a person that is knowledgeable that makes first contact with an incoming call provides the best customer relationship.

I had an appointment and could not stay at home to further investigate the problem.

Later in the morning I learned from neighbors that about 2 hours after the first incident power returned to normal. No service trucks were around. Obviously there was no real time monitoring information from the power system to the phone operators even if it exists at all.

At another point in town voltage was good. Thus, most likely a problem at our substation.

Other background. From my perspective our primary is a delta. I believe one or two adjacent neighbors are on a different phase than I am. One adjacent neighbor shares my transformer. A posteriori my neighbor that does not share my transformer also lost full voltage. No service truck and this neighbor's information confirmed that it was a primary system problem.

Now my question. What type of equipment failure at a substation would cause a sustained 2 hour 93 V condition? My guess is a voltage regulator. I have no knowledge relating to substations, or the range of voltage regulators.

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richxtlc

Senior Member
Location
Tampa Florida
If the voltage regulators in the substation are single-phase, one could have malfunctioned and went to the full buck position. These single-phase units have independent CMVMs (contact-making-voltmeters).

The fluorescent lamps that wouldn't go on probably had insufficient voltage to ignite, while those that stayed on had not reached the extinguish voltage for the lamps. Fluorescent lamps will stay lit at a lower voltage then it take to turn them on.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
100525-1236 EST

richxtlc:

Checking two Slimline fixtures I found initiation to be about 83 V. Depends upon the bulb. After off for a while and cooling down initiation was about 94 V.

Our sub-station is probably a Y source, however, our primary lines are effectively delta. Since I am fairly sure my adjacent neighbor that is not on my transformer is on a different phase this means at least two phases dropped in voltage. But if the sub-station is really a Y output, then it implies all three phases dropped. Are there likely to be three phase regulators vs three single phase units?

Since the problem lasted for about 2 hours, and probably more than one phase I assume it was not a transformer(s) secondary short at the sub-station. Is this a correct assumption?

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Varczar

Member
Location
Birmingham, AL
Ltc

Ltc

A good number of utility substations have an integrated Load Tap Changer (LTC) already in the substation transformer. So no matter how many distribution circuits are feed off of that substation transformer, the LTC gives them all the same voltage regulation.

The LTC's I have seen are generally using B phase as its reference voltage. There are a number of ways that this could have happened; but the most likely is equipment malfunction. There is an LTC control in the substation control house that most likely malfunctioned.

Another possiblity is that distribution line switching was going on in your area and the operater tied two different substations together without locking down the LTC's at the individual substations. Because of load flows, there is a possiblity of one of the substation LTC's boosting all the way to +16 and the other substation LTC bucking down to -16. Depending on the %voltage per step (generally 5/8V per step) on the LTC and voltage drop from the substation to your house ~ 93V is possible.

Hope this helps!:cool:
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
100525-1834 EST

richxtlc and Varczar:

Thanks. I conclude from your responses that the likely problem is a substation voltage regulator.


chris:

TED was not monitoring. And might not have functioned usefully during this event.

TED is an inexpensive instrument and moderately capable for its price. However, much is to be desired from a number of perspectives. I do use it for research purposes and get useful information.

I have never before experienced a situation like my above incident. However, I have always designed equipment to work from 95 to 135 V. This incident was clearly way out of norm for my supply. Typically 119 to 126 are the extreme excursions at the main panel.

Have you been able to see and play with the HP DMM that we talked about some time ago?

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hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
I'm presently having issues at a blue box that is similar, the voltage drop has not been as severe, at least while I was there (I'm putting a recorder on it tommorow) The problem surfaced when the store was complaining about the garden center lights tripping three seperate breakers after a couple of hours. The lights are Metal halide's, and the amperage would be almost inversely proportional to the voltage. 1 volt drop would result in 1 amp increase, at the time I was there it jumped as much as 5-6 amps, The tech I had there a couple of days earlier, recorded an almost doubling of amperage which would then trip the breaker. At first I thought we might have a ground fault somewhere (277 volt circuits) but the meters on the gear are not showing any amperage to ground. You can also "Hear" the voltage drop, all of the step down transformers change pitch in all of the electrical rooms when the voltage drops 4-5 volts, also I recorded the harmonic distortion going from around 70 % jump to 80% when the voltage dropped. I need to find out if this is the same store that was having severe voltage sags that I wrote about a month or so ago.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
100525-2024 EST

hillbilly1:

No problem. It is probably a good place for it.

I have no experience with a Metal Halide. Do you have a spare with which you could experiment? Running a plot of voltage vs current could produce a useful reference. I am surprised at the large change in current vs voltage.

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mivey

Senior Member
I conclude from your responses that the likely problem is a substation voltage regulator.
I agree. Sometimes the control board goes nuts and the regulators will peg out at either + or - 10%. You could have driven down to the station and looked through the fence at the indicator to see if the max/min needle had pegged (unless the POCO had already re-set it).

If you have any big industries on your feeder, a regulator problem would likely have been fixed much sooner as they have the phone numbers of key utility personnel and don't waste time with the answering service.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
100525-2153 EST

I do not know where the substation is for my home. This is all residential or commercial. I am certain we are not on the University's which is a little over a mile away. For our shop I know where the substation is location.

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jghrist

Senior Member
If the substation has a delta-wye transformer, as most do, and one phase is opened on the primary, you will get full voltage to neutral on one secondary phase and half voltage to neutral on the other phases. If the substation transformer has primary fuses, one fuse could have blown.

You say that you're primary is delta. I take from this that your distribution transformer is connected ?-?. Two of the ?-? voltages will be 0.866 times normal and one will be zero. So, you might get 0.866*120 = 104V. If you're transformer were connected ?-N (more common in USA) on one of the half voltage phases, then you would get 60V.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
100525-2322 EST

jghrist:

Yes we definitely have effectively a delta source. There are large areas in the DTE region that have this type of primary. Some parts of our neighborhood date to the early 1900s or before.

My former landlord, was a real estate developer of my neighborhood, and also sold me the lot where I live. His father bought a farm about 1870, and probably by about 1910 he was starting to subdivide the area around the farm. We are 8000 ft from the center of the University of Michigan central campus. So some of the residential property around the campus dates from the mid 1800s.

I can drive around many areas here and see that the primary distribution to subdivisions is effectively delta. But it is highly probably that the substation secondary is Y.

If a load is connected line to line on a Y supply and excitation is lost to one secondary, then is not the voltage about 0.57 times the original value, in my case 71 V, for two of the line to line connections, and full voltage on the third line to line?

.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
199526--0653 EST

jghrist:

I did not quite read your post correctly. So losing one line into the delta primary produces one output line to line phase of 0, and we get about 0.577 + 0.5*0.577 = 0.866 for the other two line to line phases. And the whole working secondary output is single phase and in phase.

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augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
informing me that I would be charged for a service call if they found no problem when there service truck arrived

Most interesting policy in that POCO folks almost never find a problem with THEIR system no matter.
So if they don't charge you then they are saying they had a problem and oppening themselves up for some liability....
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Most interesting policy in that POCO folks almost never find a problem with THEIR system no matter.
Really. I once had a customer with obvious over-voltage damage, found a gross voltage imbalance, called the POCO, they found the neutral broken in the pad-mount, and they blamed inadequate ground rods. :roll:
 

mivey

Senior Member
Really. I once had a customer with obvious over-voltage damage, found a gross voltage imbalance, called the POCO, they found the neutral broken in the pad-mount, and they blamed inadequate ground rods. :roll:
Everybody knows that if you drive enough ground rods then you won't need a neutral. :grin:
 

esobocinski

Member
Location
Ann Arbor, MI
gar, I can confirm that the University is unrelated with your situation. They own and operate an independent distribution system including their own substations, so their DTE feeds are HV. (They also generate a lot of their own power on the main campus some times of year). The outlying buildings that have traditional commercial power are too few to matter.

It's been a bad year for substations in this area. I wonder if there's some systemic problem that is damaging gear all over.
 

mxslick

Senior Member
Location
SE Idaho
gar, I can confirm that the University is unrelated with your situation. They own and operate an independent distribution system including their own substations, so their DTE feeds are HV. (They also generate a lot of their own power on the main campus some times of year). The outlying buildings that have traditional commercial power are too few to matter.

It's been a bad year for substations in this area. I wonder if there's some systemic problem that is damaging gear all over.

Yeah it's called lack of proper maintenance. :roll:

Way too many POCOs have deferred maintenance for far too long and now it's coming back to bite them.

Another possibility is an increase in sunspot activity which IIRC was expected to peak at worst-ever levels this year. But I would expect that to be a continent-wide issue at least, but doesn't seem to be the case so far.
 
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