Another option for older cables is something we have done recently which is Cable Cure Injection. The problem is, you need to take the cable out of service to inject them, but you don't need to replace. It will essentially rejuvenate the insulation, filling in any treeing that my have...
apower, The voltages range from 12KV to 34KV distribution. Often times we can not use switch grates do to the location, i.e. in town sidewalks, mowed lawn. On the transmission and especially in subs, we use the grates. The field personnell always wear gloves when operating switches, so the...
Hi Folks,
I am at an electric utility and an item that has continued to come up at our Union Labor Management meetings is if we are doing adequate initial grounding testing and adequate annual inspections of Load Break Switches. I would be very interested to hear what people do for initial...
Just FYI as well, a 750MCM, 15KV Riser on wood pole is a fairly commmon installation. There typically is not a whole lot of structural analysis that needs to occurr, unless you are talking an un-guyed structure. We typically use either 45' Class 3 or 50' Class 3 poles.
dpc, As it turned out, once upon a time, someone had a the idea of inserting an automatic throwover scenario between two seperate sets of bus pots. In my exploration of the AC, DC schematics, I failed to recognize this. It turns out the relay that would do the transfer was dropping out and...
We recently had a very large fault on one of our 34.5kV Subtransmission lines. It was a phase to phase fault (no ground involved), and the fault itself was about 11,000 Amps. As you can imagine there was contribution from a large number of sources, as it is a looped system. At one of the...
Howdy,
I am looking for sagging information with regards to spacer cable, in this case Hendrix. I normally use Sag 10 and PLS Cadd for transmission line design but have not had to design underbuild with Hendrix Spacer. I assume I am mostly interested in the sag of the steel messenger, along...
Thanks for the responses. I had checked the line balancing a few weeks ago and the current un balance was very minimal. Also, the line to neutral voltages are all equal very well balanced. It is only the line to line voltages that being affected, which I believe should only be due to the...
Folks,
I had posted a few weeks ago about a strange phase to phase voltage imbalance measured on the secondary of a three phase 12.47 x 277/480V transformer bank. We recently checked another bank further down the road and have the same issue, 208, 208 and 217. The 480 bank measured 480, 480...
Every state has different net metering rules (assuming your in the US) Here, we allow customers to install a unit at their residence, such as a windturbine up to 15KW,and run in parallel with the system. As everyone has mentioned, if you are generating more energy than the house is consuming...
wbd - The relay is actually set for 5% imbalance, so it shifts depending on the phase to phase voltages. The facility manager is looking into a similar relay with a 10% imbalance trip, but of course we still have the strange voltage issue that will cause motor winding heating.
I am at Green...
Thanks for the respones.
I am aware that this is not common practice to run similary phases in the same pipe. The pipes are all non-ferrous and do not have any ferrous material, i.e. condulators on them. I think we will end up having to do as Waross mentioned and isolate one end of the neutral...
Thanks for the responses.
I did check all the capacitors on the circuit, and all are in with no blown fuses.
Waross- I am going to look closely at the circuit loading and neutral current on the system to see if we in fact do have some heavy neutral current upstream. So, with the breaker...
I agree with you there. I was wondering if I had a phase angle shift caused by an impedance difference or a transformer ratio difference. We did TTR the transformers and got same ratio's and the nameplate has a percent Z of 4% on all three. I will be receiving the results tommorow of our...
Thanks for the response DPC. The relay is set at 5% imbalance, or 25 volts at 480. I did review the regulators and the taps were even, along with the datalogging in the control indicated they have been working properly. The confusing thing is, the line to ground voltages (277) are fairly...
One more question on a totally seperate issue. At one of our substations, we have 15KV cables coming off the low side of a 34.5 / 12.47 KV transformer. This feeds our low side bus which feeds the four feeders. The cables are Jacketed Concentric Neutral cables and there are 3 - 500MCM copper...
Folks,
We are having an interesting voltage problem at a water pumping facility and I was hoping someone might be able to shed some light. The setup is a a three phase overhead power bank, made up of three 167KVA, 12.47kv / 277/480Y service. The service enters the building into the main...
