Tree falls on utility line causing downstream breaker in building to trip?

[RobbieR]

Had an interesting occurance today.

Utility had a tree fall on thier transmission line. A building being served by this utility caused an input breaker for a UPS to trip downstream from the Main distribution board. The settings and coordination curves are set to have this breaker trip first before the upstream breaker. So it did its job. However, I'm trying to determine why no other breakers tripped in the overall system.

With a line to ground or a line to line fault from the utility happens, does a "surge" occur on the line for a few cycles once the fault clears?

I don't belieive the facility has surge protection. Has anyone seen this before?

Thanks!

 

[broadgage]

Might have been overvoltage.
The breaking of one phase conductor, or of the neutral could result in overvoltage on another phase.
A MV conductor might have briefly touched a conductor at utilisation voltage, resulting in overvoltage.
The sudden opening of fuses or breakers on the MV system can cause surges due to suddenly breaking the circuit to inductive loads such as transformers or motors.

 

[steve66]

It could of been a lot of things. The UPS might have input surge suppression that clamped on a surge, tripping the breaker. Or it could have been a three phase unbalance. Or if the UPS has an input transformer, maybe it tripped the breaker due to undervoltage or underfrequency.

Also possible- a surge could of caused some of the UPS SCR's to fire at the wrong time, creating a short in the input of the UPS.

 

[kwired]

Couple of years ago in a local town a conductor from a transmission line fell down and contacted a conductor of the local MV distribution system. It left the entire town without power for an hour or two. When power was restored I started getting service calls from all over town about different items not working. I think anyone that happened to be on the phase that was elevated to a higher voltage was at risk of having problems. I noticed some of my service call customers were likely on the same primary phase. One guy had a fried controller in a fairly new range as well as a surge arrestor for his computer got fried - but the computer was fine. Another customer had GFCI receptacles all over the house that tripped and would not reset.

Elevate the voltage on the MV distribution and the secondary voltage is going to go up also. Even though it was very short duration it was destructive.

I don't know what the voltage of the transmission line was - maybe anywhere from 34 - 69KV. It dropped onto a 2.4Kv line. Only a slight change in voltage there.

 

[Speedskater]

.....When power was restored I started getting service calls from all over town about different items not working. ....... I noticed some of my service call customers were likely on the same primary phase. ......

How do you tell what primary phase different areas are on?

 

[kwired]

How do you tell what primary phase different areas are on?

I don't know for sure. Some POCO may have some standards such as east is always same phase or north is always same phase. If an area only has one phase serving it then all customers are supplied by same. Town I was in is small enough it does not take much effort to trace the line to find out. If it goes underground they usually mark cables but you would need access to inside their equipment to see the markings on the cables, they could have markings on exterior but you may need to understand how it is coded.

 

[zog]

Had an interesting occurance today.

Utility had a tree fall on thier transmission line. A building being served by this utility caused an input breaker for a UPS to trip downstream from the Main distribution board. The settings and coordination curves are set to have this breaker trip first before the upstream breaker. So it did its job. However, I'm trying to determine why no other breakers tripped in the overall system.

With a line to ground or a line to line fault from the utility happens, does a "surge" occur on the line for a few cycles once the fault clears?

I don't belieive the facility has surge protection. Has anyone seen this before?

Thanks!

What type of trip did the breaker in question see?

 

[RobbieR]

More info....

This breaker has tripped twice. Both times that this has happened, commercial power was lost, and then restored within 30 seconds. I've confirmed this with the serving utility. The first time was a "material failure" and the second was the tree falling across the line.

The downstream UPS is an Eaton Powerware 9395. Had an Eaton tech go out yesterday to download all trending data.

According to the data power was lost once before, but the breaker did not trip. So we have had three instances where power was lost: twice the UPS input breaker has tripped.

My only hunch at this point are two possible options:
1) The UPS is backfeeding into the UPS input breaker during a utility outage causing it to trip...or...
2) There is no surge protection in the Main Distribution Board causing transients to run wild during a utility blip.

I don't know what the upstream breakers are set at in regards to instantaneous time delay, but if this is a utility issue I'm assuming they are set high.

I guess the next logical thing to do is to put an ammeter on the line and load side of the UPS input breaker in question, and then switch the upstream breaker off and then on to see what kind of amperage the breaker is seeing.

 

[kwired]

I guess the next logical thing to do is to put an ammeter on the line and load side of the UPS input breaker in question, and then switch the upstream breaker off and then on to see what kind of amperage the breaker is seeing.

Or drop another tree branch on the transmission line while taking measurements

Switching upstream breaker is not likely going to produce same transients as when the transmission line failure happened. If the only problem from this event was a tripped breaker then you may be lucky. Is also possible unit did what it was supposed to do. Some specifications on the unit may help determine this.

 

[Open Neutral]

When power was restored I started getting service calls from all over town about different items not working. I think anyone that happened to be on the phase that was elevated to a higher voltage was at risk of having problems.

Who paid? I recall reading of 2-3 incidents of HV->LV cross where the POCO paid out. Worse was a FIOS contractor in Northern VA who {as far as I could guess from the newspaper article} while ramming a feed in from the backyard had somehow shorted the pad xfmr primary and secondary. Every outlet in the house had blown from the wall spitting fire, and of course everything plugged in was toasted. Impressive pictures in the Washington Post. Repair was to replace all wiring in the 2-3 y.o. house.

(Verizontal said it was not their responsibility, it was their contractors' nut; and refused to help...Maybe correct legally but a really bad PR move.)

 

[kwired]

Who paid? I recall reading of 2-3 incidents of HV->LV cross where the POCO paid out. Worse was a FIOS contractor in Northern VA who {as far as I could guess from the newspaper article} while ramming a feed in from the backyard had somehow shorted the pad xfmr primary and secondary. Every outlet in the house had blown from the wall spitting fire, and of course everything plugged in was toasted. Impressive pictures in the Washington Post. Repair was to replace all wiring in the 2-3 y.o. house.

(Verizontal said it was not their responsibility, it was their contractors' nut; and refused to help...Maybe correct legally but a really bad PR move.)

Customers paid me - whether or not any other action was taken - I was not a part of it. This incident was likely easily seen by POCO or their representatives as an 'Act of nature' and they would have likely pursued that approach aggressively. The line that fell down was taken down by a falling tree being washed out at the base by a flooding river. Although they probably could have had the tree trimmed or removed long before it became a threat to the line - I'm sure they have the right to do so since they have easements for the areas where their lines are located.

 

[robbietan]

More info....

This breaker has tripped twice. Both times that this has happened, commercial power was lost, and then restored within 30 seconds. I've confirmed this with the serving utility. The first time was a "material failure" and the second was the tree falling across the line.

The downstream UPS is an Eaton Powerware 9395. Had an Eaton tech go out yesterday to download all trending data.

According to the data power was lost once before, but the breaker did not trip. So we have had three instances where power was lost: twice the UPS input breaker has tripped.

My only hunch at this point are two possible options:
1) The UPS is backfeeding into the UPS input breaker during a utility outage causing it to trip...or...
2) There is no surge protection in the Main Distribution Board causing transients to run wild during a utility blip.

I don't know what the upstream breakers are set at in regards to instantaneous time delay, but if this is a utility issue I'm assuming they are set high.

I guess the next logical thing to do is to put an ammeter on the line and load side of the UPS input breaker in question, and then switch the upstream breaker off and then on to see what kind of amperage the breaker is seeing.

there may be a simpler explanation. my take would be the facility does not have other 3 phase loads other than the loads the UPS is supplying. or that the UPS has the only phase-out protection.

 

[steve66]

More info....

This breaker has tripped twice. Both times that this has happened, commercial power was lost, and then restored within 30 seconds. I've confirmed this with the serving utility. The first time was a "material failure" and the second was the tree falling across the line.

The downstream UPS is an Eaton Powerware 9395. Had an Eaton tech go out yesterday to download all trending data.

According to the data power was lost once before, but the breaker did not trip. So we have had three instances where power was lost: twice the UPS input breaker has tripped.

My only hunch at this point are two possible options:
1) The UPS is backfeeding into the UPS input breaker during a utility outage causing it to trip...or...
2) There is no surge protection in the Main Distribution Board causing transients to run wild during a utility blip.

I don't know what the upstream breakers are set at in regards to instantaneous time delay, but if this is a utility issue I'm assuming they are set high.

I guess the next logical thing to do is to put an ammeter on the line and load side of the UPS input breaker in question, and then switch the upstream breaker off and then on to see what kind of amperage the breaker is seeing.

Maybe the UPS breaker is sized too small so that the breaker trips on overcurrent when the UPS starts recharging the battery??