Can i damage the power companies pole transformer with repeated inrush? - Page 1
Forum section: electronics / projects

author: CopperCone
author_rank: Super Contributor
timestamp: June 12, 2018, 02:03:21 pm
content: So my idea was to make a circuit that does peak voltage or otherwise worst case switching.If it was not setup right (i intend to put it close to the panel on its own breaker) say set into some kind of stupid load that would cause peak currents but not trigger the breaker, could the surge damage the pole pig?As far as i know its just a big oil cooled air transformer, and the average current can be low, but can some kind of mechanical damage be forseen? I dont want to destroy power company property due to stupidity

author: David Hess
author_rank: Super Contributor
timestamp: June 12, 2018, 02:38:13 pm
content: If you can damage the pole pig, then it was defective anyway.I have heard of pole pigs being destroyed by excessive surge current but they were all related to big induction motor loads.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 12, 2018, 02:48:05 pm
content: No.If you tried, the recloser upstream would break the circuit. (Hopefully. If you actually tried putting an axe into your drop, it may not be low enough resistance to properly fault the circuit.)It's fuses all the way down, to paraphrase.Tim

author: jmelson
author_rank: Super Contributor
timestamp: June 12, 2018, 07:00:47 pm
content: Quote from: T3sl4co1l on June 12, 2018, 02:48:05 pmThe pole transformers typically have a lever-actuated circuit breaker on the secondary side, that should protect the transformer from any overload. The primary side typically has a metal fuse with a det-a-cord to blow out the arc. This is usually fused way higher than the KVA rating of the transformer, and is only to protect the HV main from being tripped off at the substation due to a single failed transformer.Jon

author: CopperCone
author_rank: Super Contributor
timestamp: June 12, 2018, 07:09:30 pm
content: I was more worried like some kind of mechanical damage from the surge current causing it to rumble the windings and grind itself down to short out turns or cause crimps to loosen and tensioned wires to short out, I don't really understand the vibrations that can result from it, I assume the thermals are averaged well and protected.I know transformers sometimes make rumbling noises with the right load. It seems bad for them, but its just a hunch. I think the oil might have a good dampening effect on ware though? And it lubricates between the windings to reduce their friction? They wont start cavitating or some crazy shit will they?I just figured maybe they don't design em for repeatedly handling surges like they do for expected averaged currents or heat.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 12, 2018, 07:20:09 pm
content: There is a slight chance to upset the transformer with too much DC current drawn by odd waveforms. More modern toroid shape or amorphous core transformers to not like DC current very much an might saturate. This might blow the primary side fuse and also cause some noise.

author: chris_leyson
author_rank: Super Contributor
timestamp: June 12, 2018, 07:24:32 pm
content: QuoteIf your load is a transformer then worst case switching is at zero crossing.EDIT: That's not right, must be thinking of something else

author: jmelson
author_rank: Super Contributor
timestamp: June 12, 2018, 09:40:49 pm
content: Quote from: chris_leyson on June 12, 2018, 07:24:32 pmNo, it IS right! If you switch on at the zero crossing, then the transformer iron has a complete half-cycle to integrate flux.Normally, the transformer integrates flux DOWN TO ZERO during the rising side of the voltage, then integrates up on the falling side of the wave. Thus, the flux lags a quarter wave behind the voltage, and the flux reaches zero right at the voltage peak. But, if you start integrating from zero at the voltage zero crossing, then you end up with TWICE the integrated flux, and the transformer saturates.Jon

author: CopperCone
author_rank: Super Contributor
timestamp: June 12, 2018, 09:54:05 pm
content: the idea is that you program it to switch whereever, to give maximum problem for the circuit being tested (time delay up to 1 cycle from zero crossing detection, adjust to 50 or 60 or whatever Hz, I guess 400Hz too)

author: David Hess
author_rank: Super Contributor
timestamp: June 12, 2018, 10:20:23 pm
content: That switching at the zero crossing causes the transformer to saturate is just not that big a deal.On the other hand if you have a poorly behaving load like a rectifier and capacitor input power supply, switching on at the peak creates a massive surge current from charging the capacitor much greater than switching on at the zero crossing so pick your poison or for testing purposes; do both and everything in between.

author: CopperCone
author_rank: Super Contributor
timestamp: June 12, 2018, 10:30:35 pm
content: I think the idea would be to like do a buncha samples and pick the one that looks the worst then do it alot

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 13, 2018, 04:09:37 am
content: Quote from: David Hess on June 12, 2018, 10:20:23 pmA toroidal transformer will easily draw as much when it saturates.Better still, a toroidal transformer with attached cap-input filtered rectifier will do both no matter what phase of the line you switch it on. Yay!Tim

author: jbb
author_rank: Super Contributor
timestamp: June 13, 2018, 05:10:42 am
content: Repeated stress cycles may age the transformer windings or connections. No idea to what extent. The most concerning thing to me is making a connection go high resistance. It then heats up and can set the transformer (full of oil...) on fire.You may have more trouble with any fuses in the system ageing and then blowing at less than rated current.

author: timpattinson
author_rank: Contributor
timestamp: June 13, 2018, 12:35:17 pm
content: Is the pole transformer just feeding your house or others as well? Equipment damage aside, some people may not take kindly to a slight brownout on the supply.Sent from my SM-G930F using Tapatalk

author: CopperCone
author_rank: Super Contributor
timestamp: June 13, 2018, 01:52:56 pm
content: Lol covert operations to putloggingmeters on neighbors house exterior outlets to determine smallest allowable choke sizeThis is getting a bit ridiculous but so is not knowing the behavior of your designs!Are there any fusesin a typical home install? Here circuit breakers are the standard. They should be uneffected right?I guess you would want to aim a laser at the pole to monitor it for abnormalities?Need togo for a walk to see what the companies system is wired like here

author: timpattinson
author_rank: Contributor
timestamp: June 13, 2018, 02:21:19 pm
content: The magnetic trip of the breaker *could* be activated with a high enough in rush.Do you have to do a physical test, and does it have to be with continuous AC? A rotary phase converter or similar could provide isolation from breaking anything in the building or the pole, and it won't fry as easily as rectifying and re-inverting your AC source.If what you're testing could be approximayed with some kind of correctly timed pulse, that could be an easier way to go.Sent from my SM-G930F using Tapatalk

author: CopperCone
author_rank: Super Contributor
timestamp: June 13, 2018, 03:03:07 pm
content: Its supposed to test worst case conditions of startup if the startup protection circuitry is not functioning or not present with anyac powered electrical device of my choosing.I mostly like small stuff and instrumentation so it should be completely non issue but i want to know the contingencies.I want the lowest price and line impedance possible and i want the device to run afterwords. I want the test to be as realistic as possible.The rotary converter idea is interesting i would like one for things like long term tests with a lisn etc. The tests i had in mind running from a converter would be to minimize line noise and change of line transients destroying my expensive spectrum analyzers and shit.Do you have some kind of idea od what kind of surges i can get from a rotary converter (i would like something like a 2000a peak)Another purpose of these tests is to test destructive failure modes of components so i can do things like evaluate power electronics blast shields, plasma damage containment from exploding fuses etc on ac vircuits (for dc i can use big capacitors for this)Its kind of rough because i dont have a rogawski coil to measure surge currents near the panel of my house so i cant give a spec but its between 500a to 4500a for shre

author: tpowell1830
author_rank: Frequent Contributor
timestamp: June 13, 2018, 04:17:36 pm
content: Quote from: CopperCone on June 12, 2018, 02:03:21 pmYou are the reason for zoning in cities, someone who takes house current and tries an industrial testing, LOL. Joking aside, if you stress your breakers in your house as you say, these can and will explode dramatically when overloaded as you describe, even for a millisecond at those kind of loads. However, as far as the transformer on the pole, the inductive reactance of the transformer is a hedge against such damage occurring to the transformer. If your breakers don't explode and given that you don't do thousands of these tests, I would unofficially say that you have no worries.Also, as someone said, if you are on a pole transformer exclusively for your home alone, you don't have to worry about the neighbors getting brownouts. If you are going to do these tests over a long period of time and in the thousands, I recommend that you get an industrial solution from the power company, i.e. an industrial sized transformer exclusive to your location and needs.Power On CopperCone!Hope this helps...

author: CopperCone
author_rank: Super Contributor
timestamp: June 13, 2018, 04:25:37 pm
content: How bad is a breaker explosion for a home? I was hoping the circuit box is designed to contain it, i wonder if i should stop leaving clothing on top of the dryerwhich is placed under it.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: June 13, 2018, 04:45:30 pm
content: Quote from: CopperCone on June 13, 2018, 04:25:37 pmTrust me, I have seen breakers explode and take out the metal box that holds them into small pieces of shrapnel that went 10s of meters away from ground zero. You don't want this to happen in your home.EDIT: The best way to keep this from happening in your home is to use your electrical equipment within the designed capabilities of the system. If this is not clear enough, DON'T DO THOUSANDS OF AMPS TESTING IN YOUR HOME!

author: CopperCone
author_rank: Super Contributor
timestamp: June 13, 2018, 07:41:11 pm
content: hmm maybe I should have combined the threads, but to restate (not at you particularly) I don't intend to do the worst case kind of testing with ridiculous loads like giant flash lamps, only realistic circuits I would build...If I get the full burst from that inrush, I expect my circuit to explode, my wallet to feel lighter, etc... I don't have a assembly line of circuits and parts to explodeBut for that kind of explosion to happen, you would need two breakers to fail right? The main feed breaker (200A or whatever), and the secondary breaker (20-40A)? (I still intend to use 10kA breakers )What kind of failure mode leads to such a explosion? I am a bit concerned about my basement.

author: james_s
author_rank: Super Contributor
timestamp: June 13, 2018, 09:11:28 pm
content: The only time I've ever seen a pole pig be damaged was when lightning struck a line nearby.Well unless you count the occasional car accident or storm that knocks down a pole causing the thing to smash in the street.