Electrical Problems after Storms

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johnjar
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Electrical Problems after Storms

Post by johnjar » Tue Apr 17, 2018 7:27 pm

Nereus wrote:
Sat Apr 07, 2018 11:14 am
Dannie Boy wrote:
Sat Apr 07, 2018 10:02 am
Big Boy wrote:
Sat Apr 07, 2018 9:53 am
:banghead: First rain, first power cut :banghead:
Although I worked in the Power Generation business for over 40 years, I don’t understand the technical side of the distribution/domestic supply, but we have a 3 phase supply in our house and have some power and light circuits on and some off - maybe Nereus will provide the reasoning behind it all
Most small consumers are only supplied with single phase. If you have a 3 phase supply consider yourself fortunate.
The distribution system used in the street consists of 2 different types of electrical connections. The high voltage uses 3 wires and is connected in what is called "delta", or "mesh" if you are a Yank, and the triangle shape of the connection means that each of the 3 points of the triangle is 1 phase.

The voltage on each phase will be High Voltage, 6KV, 11KV, or whatever and of no use to a consumer. So a transformer has to be provided to "step down" the voltage to a useful level, in this country around 220 volts. The "primary" side winding of the transformer connects directly to the HV supply, one phase to each winding.

It is the secondary side of the transformer that is used for the consumer supply. Here the connection of the windings are connected in what is called "star", or "wye". This is a "Y" shaped connection with 1 phase available at each end of each leg of the "Y".

BUT, the connection also has a centre point, called the "star point". This point is where the "neutral" connection is made. If you look at the "star" you will see there are in fact 2 sets of windings in series across 2 phases. The voltage appearing here by transformer action is around 380 / 400 volts, which can be used to run 3 phase equipment. The voltage appearing across 1 phase and the centre, or star point, is 1,732 (root 3) of the phase to phase voltage.
Star-and-Delta-Connections.jpg

In a power failure situation it will depend on just where the failure occurs. If on the primary side of the transformer and just 1 phase fails, then the other still active phases will still provide for some output on the secondary side, but it may be at a reduced voltage, or "brown out". If the failure is on the secondary side of the supply it depends on which phase that the consumer is connected to wether or not you will still have a supply. That is the reason why if you have a 3 phase supply you may still have some single phase power, and your next door neighbor, who may be connected to a different single phase, still has power while you do not.

As always, TIT, so that is only the theory!
A good explanation as I could never understand why sometimes the telly is working but lights and fans are not.

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Re: Weather in Hua Hin & Thailand

Post by johnjar » Tue Apr 17, 2018 7:40 pm

Terry wrote:
Sun Apr 08, 2018 8:41 am
Absolutely everything if your power goes out after a drop of rain.

[Admin comment: then start another thread on electrical problems, this one is about the weather.]
Terry I agree electrical storms cause electrical problems :agree:

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Re: Electrical Problems after Storms

Post by Terry » Tue Apr 17, 2018 9:21 pm

Image

[Mod comment, final warning: Sly insults aimed at forum staff will get you suspended, and reposting them will make it happen faster. We will not stoop to such childishness so discuss the topic with civility or refrain from posting at all.]

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Re: Electrical Problems after Storms

Post by fft100 » Wed Apr 25, 2018 11:05 am

Nereus (or anyone else who understands this sort of thing),

I have read your posts on how single phase and 3 phase works. Outside on the street, we have 4 cables in parallel. As i understand it, the top one is earth, and the other 3 are phases 1,2 and 3. Each house is connected to the earth and one of the 3 phases. So, when our phase goes down, we have a problem, but our neighbours who are connected to a different phase do not. Presumably visa-versa as well.

1. Our phase seems to have more problems than the other 2 phases - any idea why that would be ? We get a lot of brown-outs, which I am sure doesn't do the lights and other electrical stuff any good.

2. What would it take to be connected to all 3 phases ? The transformer on the estate is about 100metres away.

Thanks

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Re: Electrical Problems after Storms

Post by HHTel » Wed Apr 25, 2018 12:16 pm

I can't answer your question but just a correction. The fourth wire is neutral. Earth wires (ground) are made locally (on site). Most modern houses have an earth rod of a couple of metres that provides earth to the rest of the house.

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Re: Electrical Problems after Storms

Post by Ginjaninja » Wed Apr 25, 2018 12:25 pm

you can't connect to all three phases as then you will have a 3-phase supply which is not suitable for your house.

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Re: Electrical Problems after Storms

Post by fft100 » Wed Apr 25, 2018 12:42 pm

Ginjaninja wrote:
Wed Apr 25, 2018 12:25 pm
you can't connect to all three phases as then you will have a 3-phase supply which is not suitable for your house.
What changes in the house would I need to make to be able to connect to all 3 phases ? Outside, I would think a new electricity meter - but inside ?

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Re: Electrical Problems after Storms

Post by Ginjaninja » Wed Apr 25, 2018 12:49 pm

^
I don't think there would be any point, if there is a problem with one phase (fault in the line?) then it would still affect the three-phase system.
Better wait for Nereus to respond, this is his domain. I've forgotten most of what I learnt and university (E&EE).
GN.

Edit: if your neighbours have a sound supply then it seems logical you tap into their source. What has P.E.A. said?
Last edited by Ginjaninja on Wed Apr 25, 2018 12:51 pm, edited 1 time in total.

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Re: Electrical Problems after Storms

Post by Nereus » Wed Apr 25, 2018 12:49 pm

Please refer to the previous post in the wrong thread: viewtopic.php?f=1&t=10540
Star-and-Delta-Connections.jpg
Star-and-Delta-Connections.jpg (46.28 KiB) Viewed 886 times
The 4 wires that you can see are the secondary (low voltage side) of the transformer, 3 active phases and a neutral, not an earth. The usual practice, which most likely does not apply here, is to connect each succeeding house in turn to a different phase. The idea being to try and "balance" the load evenly on the transformer. I have no idea what, if any, overload protection there may be, but good practice is to have each phase protected against overload / short circuit with its own separate fuse. It could be that there is too much load on the single phase that you are connected to, which is causing a "brown out". And yes, it can be very detrimental to equipment connected to such a phase.

Unless you are wanting to use some equipment that requires 3 phase to run, the biggest advantage is that at your own consumer unit(switchboard) you can spread your house circuits between 3 separate phases, so that if one supply phase fails you still have some power from the other still good phases.

To change it you would need a completely new consumer unit suitable for 3 phase, plus a new 3 phase cable run in from the street supply, and a new meter.

To further confuse the issue, the system used in Thailand is SUPPOSED to be what is termed MEN, which stands for "multiple earthed neutral". It means that ALL the neutral conductors in the system, including the neutral at the transformer, are bonded to earth, or the ground. As the usual practice here when installing something is to cut off the earthing conductor, do not expect this to be followed too closely!
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Re: Electrical Problems after Storms

Post by fft100 » Wed Apr 25, 2018 2:01 pm

Hi Nereus,

Thanks for the reply. I understand the practicalities re. load balancing, which is why some houses are more affected than others depending on which ones are lived in all the time, and run air-cons all day long etc etc.

I understand the other requirements, but what do you mean by 'you would need a completely new consumer unit suitable for 3 phase' ? What is a consumer unit ?

Thanks

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Re: Electrical Problems after Storms

Post by Nereus » Wed Apr 25, 2018 3:28 pm

What is a consumer unit ?
Its what I posted in the thread, followed by:(switchboard) :?
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Re: Electrical Problems after Storms

Post by Nereus » Wed Apr 25, 2018 3:50 pm

Another problem that can occur, not related to the weather, is excessive "voltage drop" on consumer supply lines.
This is just as likely to occur on developer type estates as it is on direct private connections. It is usually the result of undersized cabling, and / or undersized capacity transformers. A lot of private estates have had to provide their own transformer at their own cost, which will lead to buying the cheapest or minimal size, rather than one with a bit of spare capacity.

The PEA are also guilty of this where they keep loading up existing transformers as the demand increases, rather than providing a bigger unit. Coupled with this, both are also guilty of using undersized cables, rather than providing for future load increases.
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Re: Electrical Problems after Storms

Post by HHTel » Wed Apr 25, 2018 4:56 pm

My brain hurts!!

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Re: Electrical Problems after Storms

Post by Tunafish » Wed Apr 25, 2018 10:43 pm

These frequent "Brown Outs" are deadly. It is basic Ohm's Law: if the voltage goes down, then the current goes up.
Whereby any device which is active and has a coil in the input circuit ( a pump, a transformer, or a relay for example) gets overloaded and susceptible to being burned out. I have lost count of the number of replacement and repairs I have suffered due to this. In most countries, these sort of problems were eradicated 100 years ago, and here we are now talking about high speed railways....... It is scarey

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