can I damage my home analog power meter with repeated inrush? - Page 1
Forum section: electronics / projects

author: CopperCone
author_rank: Super Contributor
timestamp: June 12, 2018, 07:16:38 pm
content: How does the home power meter deal with it? I have a mechanical one. Will it degrade? I don't want my electrical bill going up or having the meter guy think I am trying to pull a wise one on the power company.I mean the full force of the transformer, as much as is possible with the circuit breaker and cable run going a few feet away from my circuit panel, so between 1000-4000 A.Thought this merited its own thread as its fairly different then transformers.

author: Belrmar
author_rank: Regular Contributor
timestamp: June 13, 2018, 01:29:47 am
content: those meters should be rated to be able to deal with the amount of power your power controll switch installed by the company, worst case it would burn the coils insed it so is their fault for not using a correctly sized power meter

author: C
author_rank: Super Contributor
timestamp: June 13, 2018, 01:50:09 am
content: Your main power breaker is there to protect the power feed to you house. Cable from pole pig transformer and meter.The breaker that connects your cable & load is there to protect the cable that connects your load.As stated the pole pig transformer often has a breaker on the secondary to protect against cable shorts.And the pole pig transformer primary has a fuse.Keep in mind that a nasty load could cause a higher meter charge. If you want cheapest power you want your load to look like a resistor with zero volt load changes and smaller peak loads. This also helps keeping breakers from tripping.PFC is there to let the power company save money while suppling you power. It also would let you run your load with smaller generator.C

author: David Hess
author_rank: Super Contributor
timestamp: June 13, 2018, 04:15:16 am
content: The only way you could damage the meter is to apply a continuous low power factor at high current to it. I have heard stories of this happening where the voltage measures correct, a current measurement shows high current, but the power meter shows no power because the power factor was zero while smoke was coming out of it.

author: jbb
author_rank: Super Contributor
timestamp: June 13, 2018, 05:05:09 am
content: Enough stress cycles may age the meter coils. No idea if this is practically relevant...

author: cat87
author_rank: Regular Contributor
timestamp: June 13, 2018, 06:26:07 am
content: A few years back a friend told me he was experimenting with some huge flash tubes (huge as in half a meter or a meter long ) which were pulsed, straight from the wall socket. Now the current pulses were not large enough to rupture the old breakers in the house, but the mechanical meter he had went bananas during every one of those pulses. It only lasted for a few hours until it gave up the ghost.The power company came and changed it and this new one only lasted for something like 1 week of further experimenting with the tubes.Of course, after the power company changed the meter a second time, the guy stopped as to not raise toocmany eyebrows.So in conclusion, yes, you can damage the mechanical meters with high pulses.

author: JS
author_rank: Frequent Contributor
timestamp: June 13, 2018, 06:50:56 am
content: How much is inrush? 50A? 300A?How much is your connection rated for? 3kVA? 30kVA?How often?And if I can ask... WHY??You could started just one topic on this, for the power meter and transformer, I don't see a point in starting 2, we already have one too many topics going on...JS

author: mac.6
author_rank: Regular Contributor
timestamp: June 13, 2018, 07:42:25 am
content: mechanical meter can only slow down with age and malfunction (for example three phase powermeter with one phase out, cannot be seen easily but cut bill in 3).That's why there is a rush into "smart" meters as huge inventory of old mechanical power meters mean huge unbilled money in the end.

author: Gyro
author_rank: Super Contributor
timestamp: June 13, 2018, 07:56:28 am
content: Is this not just the same topic ashttps://www.eevblog.com/forum/projects/can-i-damage-the-power-companies-pole-transformer-with-repeated-inrush/Surely you're just asking if you can damage something in your mains supply chain with repeated inrush surges, you may as well throw in breakers, cables and connections too.

author: CopperCone
author_rank: Super Contributor
timestamp: June 13, 2018, 01:58:20 pm
content: The meter seems particularly complicated because it has moments and real mechanics. The other stuff you listed will fall under the transformer thread.I thought the rotating bit and the dials and all the gears and shit in it merit a seperate discussion look how much more responses this thread got.I figured the device is rather unconventional compared to the bread and butter electronics.I knew about fuse aging but i did not think there were any fuses in a modern domestic electrical system.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: June 13, 2018, 04:39:46 pm
content: Quote from: CopperCone on June 12, 2018, 07:16:38 pmAs I said in your other thread, with the currents that you are doing, there can't be an answer to this when you are using the system beyond the rated capabilities. The stresses that you are proposing are not normal operating conditions, so, again, I recommend that you work with the power company to get the proper equipment setup to do your testing. We can't (and won't) answer these questions because you are trying to operate outside of the system's rated capabilities.I would think that you will need your own specialized setup with your own isolated transformer in order to properly do this type of testing. I am not going to pretend to design such a system at your location, that is what electrical engineers at your power company are for, to work with you to isolate you from their grid and for you to accomplish your testing.I might also add that I would love to be there when you do these tests (in a protected, safe place of course)!Power ON CopperCone!Hope this helps...

author: CopperCone
author_rank: Super Contributor
timestamp: June 13, 2018, 07:29:41 pm
content: I thought that they might be accounted for, since sometimes you do get big ass surge loads like big saws, compressors?, etc.. just not commonly stated as it would only confuse customers and be of interest to fairly hardcore reliability engineers.What is said about the xenon lamps concerns me though. Thankfully I don't expect such loads to be tested often (or at all, I don't even know what I could build that would tax the system so much)Will take me a while to do anything I am just fleshing out a bunch of ideas I have to find direction.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: June 13, 2018, 08:03:06 pm
content: Quote from: CopperCone on June 13, 2018, 07:29:41 pmCompressors and motors that you would use at home do have inrush currents, it is true, but no where near the currents that you are proposing (2000 to 4000 amps). The curves on the inrush for the motors mentioned are well known and accounted for in the system analysis.Okay, I get it, you are merely speculating, asking yourself "what if", but this is where the engineering discipline is called a discipline. Lives and livelihoods are at stake.

author: CopperCone
author_rank: Super Contributor
timestamp: June 13, 2018, 09:03:31 pm
content: Uh, So If I wanted to limit current to the design specification with some kind of reactor, how many amps should the max inrush be set to?Partly why I thought it was more robust is because the breakers are rated for 10kA

author: james_s
author_rank: Super Contributor
timestamp: June 13, 2018, 09:06:40 pm
content: I have a couple of old power meters kicking around. The coils are made of gigantic solid copper bar, I'd estimate about 6AWG that are welded to the terminal then pass up to make a couple of loops around part of the stator core then the other end is welded to the output terminal. I would be shocked if one of these things could be damaged without tripping the main breaker, unless it's possible to accelerate the rotor violently enough to cause mechanical damage to the gear train.

author: najrao
author_rank: Regular Contributor
timestamp: June 14, 2018, 08:55:51 am
content: My home is also my lab, and is fed by two separate meters, one spinning disc single phase and the other a newly installed "smart" three phase job. This latter almost certainly senses phase and neutral currents separately by small toroidal current transformers (I can read the values on real time basis, scrolled for display). I should add that the feed is at 400V 50Hz, the line-neutral voltage at 230 being sent through the single phase meter.Now, I have a dc load of 2kW to feed at about 300V, and I want to do this using a three phase-to-neutral half wave rectifier which gives 280V average (I will deal with the peaks and the filtering). Would this half wave, possibly discontinuous, load cause 1. Any damage to the meter or the 250kVA pole transformer, 2. The smart meter to read low (not so smart after all)? If the meter is smarter than this, how does it handle the unidirectional currents through the CT's?

author: jbb
author_rank: Super Contributor
timestamp: June 15, 2018, 02:54:35 am
content: Najaro: Half wave rectifiers are bad news. They may cause your smart meter to ‘tamper’ I.e. your power company gets angry with you.Also DC current can make distribution transformers unhappy due to saturation. How much current ? I don’t know, it depends...Let’s ball park: 2 kW @ 300V is 6.7A DC. Each diode is on 1/3 of the time, so per phase DC offset is 2.2A.250 kVA @ 230V (3 phase) is 362ASo that’s 0.6% DC current. I wouldn’t try it.Alternatives:1- use 50Hz step down transformer (maybe with isolation)2- use VARIAC3- use 550V DC bus (direct 3 phase rectifier)4- use thyristors to make controlled rectifier5- add switch mode stage to 550 V DC bus e.g. buck converter or something isolated.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 15, 2018, 04:46:29 am
content: I'm under the impression that 3 phase transformers are constructed such that a DC bias current, if equal in all 3 phases, effectively cancels out. Although for a mere 2kW, it would probably make more sense to just use a bridge rectifier on one phase and eliminate the need to bring in a 3 phase supply.Quite a few heating appliances simply add a series diode for the half power setting.

author: hamster_nz
author_rank: Super Contributor
timestamp: June 15, 2018, 05:16:46 am
content: Quote from: NiHaoMike on June 15, 2018, 04:46:29 amOh... How cheap and nasty (but also effective).

author: najrao
author_rank: Regular Contributor
timestamp: June 15, 2018, 08:13:03 am
content: I want answers to:Would this half wave, possibly discontinuous, load cause 1. Any damage to the meter or the 250kVA pole transformer, 2. The smart meter to read low (not so smart after all)? If the meter is smarter than this, how does it handle the unidirectional currents through the CT's?Thanks for that, wise ones. 0.8mm