electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
I don't folow you. Why would the SEC or MDP need to be upgraded based on the utilty transformer size?
Transformer Overload
- Thread starter That Man
- Start date
- Status
I don't folow you. Why would the SEC or MDP need to be upgraded based on the utilty transformer size?
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
There remains the point that the NEC sets a performance requirement on the fire pump. If POCO configuration is somehow preventing the OP from meeting those requirements, then either the OP persuades POCO to make the needed changes or he figures out some way (even if it ends up being a generator) to meet the requirements without POCO's cooperation.
I don't think it has been demonstrated to have progressed to this point in the OP's case, but that is a possible extreme.
- Location
- Massachusetts
It sets a performance standard to the equipment it applies to and nothing more.
Just like the NEC has no input at all about the voltage and it's tolerance the utility supplies a building.
- Location
- Massachusetts
I suspect this is not the first time a utility service would not support the fire pump starting needs.
There are some solutions offered on this page.
http://www.emersonnetworkpower.com/...lectricFirePumpControllers/Pages/Default.aspx
There are some solutions offered on this page.
http://www.emersonnetworkpower.com/...lectricFirePumpControllers/Pages/Default.aspx
Julius Right
Senior Member
- Occupation
- Electrical Engineer Power Station Physical Design Retired
For the record, I have to apologize for my mistake.
In my post of 11-19-16 #31 the last sentence I said:
“any transformer could withstand
2 minute 6*Irated , 10 minute 3*Irated and 24*Irated for up to 10 seconds”
It is wrong. Both standards IEEE 57.96 and IEC 600076-12 recommend as maximum overload not
more than 150%.In this case a 600 kVA –instead of 300-it is required.:ashamed1:
In my post of 11-19-16 #31 the last sentence I said:
“any transformer could withstand
2 minute 6*Irated , 10 minute 3*Irated and 24*Irated for up to 10 seconds”
It is wrong. Both standards IEEE 57.96 and IEC 600076-12 recommend as maximum overload not
more than 150%.In this case a 600 kVA –instead of 300-it is required.:ashamed1:
Fnewman
Senior Member
- Location
- Dublin, GA
- Occupation
- Sr. Electrical Engineering Manager at Larson Engineering
I'm not going to jump into the middle of all the 'calculations' but I find it strange that the party who will ultimately have to approve the installation (the client's property/fire insurer) has not been mentioned. For sure this sort of issue has been resolved many times before, so great wisdom can likely be obtained from either the insurance carrier and/or the fire pump vendor. JMHO.
kwired
Electron manager
- Location
- NE Nebraska
I agree, but they may also rely on codes and inspections by the local AHJ to approve it. An area that has history of poor code or inspections may not get as favorable of a premium as same property located in a place that has better codes and inspections.
NewtonLaw
Senior Member
- Location
- Honesdale, PA USA
Missing Something Here?
Missing Something Here?
I am not sure we have all the information necessary to help you answer this question but from what I have seen so far is that the utility company is supplying power from a 300 kVA transformer. I'll assume a three phase pad-mounted oil filled transformer. "That Man" has stated the fire pump motor is 150 HP supplied by a 300 kVA transformer. Also not given is the operating voltage. Most utility company's allow for 130% to 150% overload capacity for pad-mounted transformers for load duty cycles of 10% or less. Meaning that the total load at 130% last for no more than about 2 to 3 hours with the remaining time at a load level less than 100% over the next 21 to 22 hours. It comes down to the hot spot temperature expected in the transformer windings under various loading conditions. Usually the limit is about 190°C which is where possible bubbles may be created in the oil at the hot spot. This in turn causes winding to winding shorts and leads to failure of the transformer.
Based on this, the transformers primary side will be protected by a 20K fuse if operated at 208 volts on the secondary side and a 15K fuse if operated at 480 Volts. Next, assuming the motor is at locked rotor condition and using the 962 secondary amps "That Man" used and assuming the primary voltage is 12470, the primary amps would be about 31 amps. At this current level the primary fuses would melt open at about 16 minutes on the 15K and about 50 minutes on the 20K fuse link. This supposes the fuses were not already preloaded. In that amount of time, there is a possibility that the transformer windings would be damaged causing an internal that may increase the primary current and blow the fuse. It is more likely the internal Eutectic fuse links would open to save the transformer from this type of overload. There for nothing would happen to the transformer as far as an external visual is concerned. The overall mass of the transformer core and oil will have enough thermal inertia that it is likely to show little or no overall temperature rise.
Last, isn't the fire pump motor protected by a motor overload and/or thermal device? At locked rotor these devices should clear the motor within a minute.
Hope this helps
Missing Something Here?
I am not sure we have all the information necessary to help you answer this question but from what I have seen so far is that the utility company is supplying power from a 300 kVA transformer. I'll assume a three phase pad-mounted oil filled transformer. "That Man" has stated the fire pump motor is 150 HP supplied by a 300 kVA transformer. Also not given is the operating voltage. Most utility company's allow for 130% to 150% overload capacity for pad-mounted transformers for load duty cycles of 10% or less. Meaning that the total load at 130% last for no more than about 2 to 3 hours with the remaining time at a load level less than 100% over the next 21 to 22 hours. It comes down to the hot spot temperature expected in the transformer windings under various loading conditions. Usually the limit is about 190°C which is where possible bubbles may be created in the oil at the hot spot. This in turn causes winding to winding shorts and leads to failure of the transformer.
Based on this, the transformers primary side will be protected by a 20K fuse if operated at 208 volts on the secondary side and a 15K fuse if operated at 480 Volts. Next, assuming the motor is at locked rotor condition and using the 962 secondary amps "That Man" used and assuming the primary voltage is 12470, the primary amps would be about 31 amps. At this current level the primary fuses would melt open at about 16 minutes on the 15K and about 50 minutes on the 20K fuse link. This supposes the fuses were not already preloaded. In that amount of time, there is a possibility that the transformer windings would be damaged causing an internal that may increase the primary current and blow the fuse. It is more likely the internal Eutectic fuse links would open to save the transformer from this type of overload. There for nothing would happen to the transformer as far as an external visual is concerned. The overall mass of the transformer core and oil will have enough thermal inertia that it is likely to show little or no overall temperature rise.
Last, isn't the fire pump motor protected by a motor overload and/or thermal device? At locked rotor these devices should clear the motor within a minute.
Hope this helps
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
A fire pump motor is deliberately not protected by normal overloads since it is considered more important that it try to deliver water under abnormal circumstances than it is to protect itself.
The branch breakers must be specified to allow Locked Rotor Amps indefinitely. A standard overload would be much more restrictive.
Sent from my XT1585 using Tapatalk
The branch breakers must be specified to allow Locked Rotor Amps indefinitely. A standard overload would be much more restrictive.
Sent from my XT1585 using Tapatalk
Knightryder12
Senior Member
- Location
- Clearwater, FL - USA
- Occupation
- Sr. Electrical Designer/Project Manager
I don't know where you are located, but here in Florida, the County Fire Marshall will have to deem the utility company as a reliable source for the fire pump. If the utility is not deemed as a reliable source you can not use the utility as the power source for the fire pump and you will need to provide another source, typically a generator. If the utility company is deemed a reliable source, than you need to coordinate the requirements of the fire pump with the utility company and here in Florida they have the final say as to the size of the transformer. I feel as many on here do, that the NEC has no say as to the sizing the utility transformer.
As far as statements from others on here about the existing service gear having to be switched out due to the transformer upgrade, that would only be required if the existing gear is not rated for the AFC from the transformer. If the AIC in the existing gear is correctly sized than the existing service would not have to be upgraded as you would provide a new service lateral from the utility transformer to the new fire pump controller.
As far as the owner not wanting to pay for the transformer upgrade, it seems at this point he has no choice as he is being told he has to put in a fire pump. Which, by the way, is a bigger question to me. Who is telling him that he has to install fire pump? Is he expanding the existing building? Is he changing the use of the building?
Good point! Utilities have performance standards with respect to reliability. But if the AHJ sees the area as historically prone to power outages, he/she might require another emergency backup source or better still, an engine-driven fire pump.
NewtonLaw
Senior Member
- Location
- Honesdale, PA USA
kwired
Electron manager
- Location
- NE Nebraska
And if the utility transformer isn't deemed large enough I would sure think that could also be considered a reliability issue. That said, when considering if it is adequate they likely do allow it to run until it fails, just like the fire pump itself.
Also keep in mind the larger the fire the more sprinkler fuses melt and activate the heads, the more flow is demanded from the fire pump which means more load on the supply. But the larger the fire may get the more likely other loads on the system are either shut down intentionally, automatically or they just fail and are taken off line leaving more capacity for the fire pump.
- Status