Hello:
I work for a US government agency.
We recently replaced our 30 year old substations in our administrative building.
Quite recently a grounded\shared neutral situation caused a feeder ground fault relay to trip the feeder breaker.
To remedy the situation we will have to revise the...
Hello:
A small pump house building was recently connected to our 4.16kV overhead distribuition system. Basicall the system consists of a 150kVa pad mounted transformer (4.16kV Delta Pri - 208Y/120V Sec.
At the pole cutouts the surge arresters are tied to a ground rod at the pole base. The...
Hello:
In the US the two main fire codes (IFC and UFC)impose a limitation of 50 gal of electrolyte for UPS VRLA battery systems.
Apparently the official interpretation is that the 50 gal of electrolyte is the aggregate sum of the battery systems in a specific space (data center, battery room...
Hello:
A decision was made by my management to install surge arresters at every other pole of a 69kV line thats 3200 feet long between the utility metering point and the main substation 69kV incoming switch. The distance between poles is 200 ft. The line has a guard wire.
Also the surge...
Hello:
We recently specified Doble testing (tip-up) on a 750/1000kVA dry-type transformer (20+ years old) as part of a comprehensive test regimen. Our NETA certified test company said that they would do it, but would not be able to get any useful information because the transformer is a...
Who can legally perform power systems and arcflash studies?
Can they be performed by technicians who will then use the study results to set protective relays and select fuses.
Hello:
A 12.470kV/4.16kV, 3750kVa trafo is being used at our campus facility to supply sundry loads at 4.16kV through a secondary VCB with 50/51 relay protection. It was decided by some of our technicians to use it as a step up transformer to supply a 12.47kV load while a new feeder is being...
Hello:
We have Westinghouse Power Centers in one of our buildings. These centers have ASLR dry type transformers (12.47kV,500/666kVA, 150 degree C rise, Sharon Plant, 1978)). Recently one of these transformer caught fire and released a lot of smoke over a period of 1/2 hour. Our fire dept...
Hi:
Our local utility does not transpose its HV lines (as far as I can see by looking at its transmission and subtransmission lines).
Is there a need to be worried about this as far as overcurrent relaying is concerned?
Thank you kindly,
hidalgoe
HellO:
What have been the results of recent engineering debacles, like Boston's Big Dig concrete section that fell and killed some folks in a car or Katrina meant for PE's as far as liability and ethics are concerned?
Hello:
We recently replaced our old main substation electromechanical relaying system with a SEL 351S/351A system. The 351A relays are for feeder protection and the 351S relays serve as main secondary breakers.
Our substation consists of 2ea power transformers (69kV/12.47kV, 15/20MVA ABB)...
Our Main Substation transformers (15MVA, 69kV/12.47kV)have S&C Trans-Rupters with overcurrent protection on the 69kV side. What would be the best placement for the CTs used with the overcurrent relays: on the line side of the Trans-rupters or on the load side of the Transrupters.
One of our transformers (ABB 15/20MVA, 67/12.47kV, 8.46% @ nominal tap, primary 33 step OLT) recently was taken off line manually because of unbalanced voltage condition accompanied by inrush like noise. We have no primary SCADA sensing, but our secondary voltage waveforms revealed a 20%...
Hello:
At my federal agency we have a 12.47kV overhead line that is strung using individual insulators on each utility wooden pole. The poles are spaced at approx. 150' from each other and is about 2 miles long. On each run between cables large insulating balls were installed to avoid phase...
Hello:
I would like to find technical information on the nature, calculation and structural analysis of electromagnetic forces generated during short circuit conditions for three phase, phase to phase and phase to ground faults.
For example how do you calculate and represent the forces acting...
Hi:
Recently a phase conductor on a 3-Ph, 480Vac system suffered some damage due to overtemp caused by a loose breaker terminal lug.
Rather than replace the feeder, we chose to temporarily splice a new conductor length to replace the damaged section that was cut off.
Some folks in my...
The power engineers whom I work with have been debating whether to do the usual load flow study first, then the short circuit study or the other way around. One group favors load flow first because it gives you the pre-fault and angle values to use in your short circuit study. Others say a...
I would like to know if the various codes affecting arc flash studies require each and every live electrical panel at a site to be considered.
I work at a federal aviation lab center. Thousands of panels exit here. Some "experts" here are of the opinion that existing power panels are...
