Voltage drop solved

[Naam]

Your thingy will have no idea that the mains voltage is low

if yew shparkies are wrong i vill haff vasted kvite zome monny shudd i go for shtabbilising oll mine phasis

Zee shparkies r korrekt.

But you need a sparks who knows what he's doing, particularly if using three single-phase units.

if i do it then i go for an individual unit for each phase.

[RichCor]

Can someone explain how these AVR's work when the grid goes low? I understand transformers but what I don't understand is how something can transform from nothing? Like if the grid goes low on amps (coulombs) then how can an AVR which needs more amps to up the voltage work? Seems like a case of diminishing returns. 'splain it to me Lucy.

We're really only concerned with available Wattage. Power companies use fixed Step-Up and Step-Down transformers to vary the "Volt x Amps" ratio of Wattage.

An AVR is designed use a similar feature with the use of a broad-voltage transformer and a constantly moving variable 'tap' to perpetually seek and provide a given output voltage. The available amperage may continues to vary wildly, but so long as there is enough total Wattage for the load, it works.

It's only changing the Volt x Ampere ratio by constantly moving the transformer tap.

If at a certain point the AVR cannot continue to compensate (Transformer input voltage out of range, high heat, low amperage, etc,) then the unit should shut down until the input source comes back into it's working range.

[redandyellow]

Thanks for posting this. Your excellent post is an example why I like TV, along with the lowest common denominator of course, of which I am probably in the running..

Kind Regards

[Crossy]

Can someone explain how these AVR's work when the grid goes low? I understand transformers but what I don't understand is how something can transform from nothing? Like if the grid goes low on amps (coulombs) then how can an AVR which needs more amps to up the voltage work? Seems like a case of diminishing returns. 'splain it to me Lucy.

OK, let's go back to basics.

A transformer is two coils if wire on an iron core. The transformer ratio of input:output is determined by the number of turns on each coil.

Let's say we have two coils of 220 turns (1:1 transformer). If we apply 220V to one then 220V appears on the other, if we then pull 1A from the output side then 1A flows into the input side (assuming a 100% efficient transformer). Watts out = Watts in (220V x 1A = 220W on both sides)

If the input falls to 200V then the output will follow to 200V, if we want to get back to 220V we need to add more turns to the output making it 200:220 or 1:1.1. If we now draw our 1A from the output the input now draws 1.1A from the now 200v supply. Watts out 220V x 1A = 220W still equals Watts in 200V * 1.1A = 220W.

Obviously we need to constantly adjust the ratio to follow the variations of the input. Several way of doing this, our AVRs use either fixed taps at various ratios, the correct tap being chosen by relays and some electronics checking the output or we can use a variable ratio transformer (Google - variac) driven by a servo motor and more electronics.

As you suspect, there is a potential issue of course. If the grid is seriously overloaded (causing the low voltage) the increased load current could pull the supply lower, causing still more current to be drawn by the AVR etc. etc. eventually the supply will collapse (the grid breakers will open on over current). Most AVRs give up at about 150-160V input (input current is about 1.5 x the output current) and so reduce the possibility of killing the supply dead.

[bankruatsteve]

Thanks for the replies. Where I thought I was going with my question though, is how effective will an AVR be in a grid brown-out situation? Or, over demand on a remote transformer? IE: would an AVR really help the OP situation? Oops - that was another topic I think. Whatever.

And, where are the "grid breakers" found?

[RichCor]

How effective an AVR will be in a grid brown-out depends on the brown-out. How much total wattage is still available, and if the input operating voltage is workable.

IMHO mentioned his "single phase 20kVA stabilizer says 150-250V input range on the front, but when we tested it initially, it was still stabilizing 130V mains to 220V".

That's a pretty good working range. Hopefully your service wouldn't ALWAYS operate that low, but some don't have a choice of what's being delivered so need the AVR.

Grid Breakers are usually found near step-down transformers, switching stations and generating station. They're usually also placed so a 'leg' or 'branch' of users can be easily isolated when an issue occurs so the rest of the grid can continue to operate. While most Grid Breakers will be housed in some large metal box, some are just large fuses spurred off each phase line, hanging off a pole in mid-air like a knife switch, placed prior to feeding a step-down transformer, or placed prior to a branch circuit.

Interesting short article (with pictures):

Edison Tech Center - Lightning and Fault Suppression

Lightning Arresters, Fuses, Surge Arresters, Air Terminals, Disconnectors, Breakers/Interrupters, Reclosers and Horns

[IMHO]

Thanks for the replies. Where I thought I was going with my question though, is how effective will an AVR be in a grid brown-out situation? Or, over demand on a remote transformer? IE: would an AVR really help the OP situation? Oops - that was another topic I think. Whatever.

And, where are the "grid breakers" found?

Yesterday we had a brown-out with 78VAC at the meter - the stabiliser shut down. So far 130VAC is the lowest I've seen it be able to stabilize. As for over-demand, I assume that's exactly the problem it fixes for me at all other times

Not sure what you mean by grid breaker, but the stabilizer has it's own 2 pole breaker on the front, which in my setup allows me to kill all power to everything.

[carlyai]

I've just gone thru the process of installing 3 single phase 10000 KVA Lioa AVR's on my 3 phase system and it didn't work.

I installed them between the Safe-T-Cut (SC) and the consumer unit.

Installed one AVR on phase 1 with no load, all OK.

Installed one AVR on phase 2 with no load, all OK.

Didn't install the 3rd AVR as thought for testing two would be enough.

Adjusted the SC to 30 ma and applied load to AVR 1 all OK.

Applied load to AVR 2 all OK.

This is with our 3 phase water heaters switched off.

Manually tripped the SC but it would not reset with the AVR's connected.

On another thread Crossy explained why he thought that was.

I found out last night, that while I was away for 3 months the Sparky did try to put the 3 single phase AVR's on the incoming mains before we had the SC installed and it didn't work.

Emailed Lioa and they said that you can't put 3 single phase AVR's on a 3 phase system but have to use a 3 phase AVR.

As a Guess:

It may be to do with the three phase AVR having only one servo motor and the single phase AVR's having one servo motor but when you install them across the 3 phase mains there are 3 servo motors adjusting the transformer taps for the best phase voltage.

If the 3 phase AVR worked on the same principal it would have 3 servo motors, so this is my guess as to why it doen't work, or it may work if you didn't have a SC installed.

To try and be clearer, I am saying the 3 single phase AVR's across my 3 phase supply didn't work because it tripped my Safe-T-Cut.

[Forkinhades]

Is it just the safety cut that is stopping the units from working?

Whether upstream or downstream? ie AVR before or after Safety Cut?

[RichCor]

Is it just the safety cut that is stopping the units from working?

Whether upstream or downstream? ie AVR before or after Safety Cut?

I was surprised to read that the Safe-T-Cut was installed upstream of the AVRs.

I thought the original proposed idea was to have the 3-phase heaters tap off the mains first, then come the AVRs, then the transfer Switch, then the Safe-T-Cut and the CU (breaker box).

[Crossy]

In order to work out what's going wrong carlyai we need to know exactly how it was wired when it didn't work, no guessing, wire for wire drawing please.

Apart from possibly power-on surges I can see no reason why using 3 single-phase AVRs wouldn't work as advertised.

Have you investigated the AVRs to verify that the marked neutral really is the neutral (passed directly from input to output)?

EDIT and that the AVRs are all wired the same.

[Forkinhades]

^ +1 Xy

[carlyai]

Is it just the safety cut that is stopping the units from working?

Whether upstream or downstream? ie AVR before or after Safety Cut?

The AVR's were tested downstream of the SC.

The sparky evidently tried the 3 AVR's on the 3 phase input to the house before the CU, before the SC was installed and it didn't work.

I appreciate all the great advice and good information and it has helped me a great deal, but I'm going to buy a 3 phase AVR and install that.

[carlyai]

Is it just the safety cut that is stopping the units from working?

Whether upstream or downstream? ie AVR before or after Safety Cut?

I was surprised to read that the Safe-T-Cut was installed upstream of the AVRs.

I thought the original proposed idea was to have the 3-phase heaters tap off the mains first, then come the AVRs, then the transfer Switch, then the Safe-T-Cut and the CU (breaker box).

That was the original proposal.

While I was away back in Aus the sparky installed the 3 AVR's on the mains incoming, before I had a Safe-T-Cut installed.

Evidently it didn't work. Not too sure of the details.

Needs a lot further investigation, exact wiring diagram etc as Crossy rightly suggests.

[carlyai]

In order to work out what's going wrong carlyai we need to know exactly how it was wired when it didn't work, no guessing, wire for wire drawing please.

Apart from possibly power-on surges I can see no reason why using 3 single-phase AVRs wouldn't work as advertised.

Have you investigated the AVRs to verify that the marked neutral really is the neutral (passed directly from input to output)?

EDIT and that the AVRs are all wired the same.

Yes you are correct. An exact wiring diagram is the thing that has been missing a along.

[Forkinhades]

15kva for a single phase 63A main switch on 30/100 supply should be fine

What's your loads? ie how many air con, water heaters etc.

[carlyai]

I went today to my local GH and they had the 15kvA ones no mention of the 20 kva, the price quoted was +/- 25k THB. Would this be enough for a whole house system with a meter of 30/100 Single Phase with a Main Breaker of 63 amps ?

Thx

I found GH good.

I bought my 2 10 KVA in Rayong, and they then searched Thailand for one more and found it somewhere and sent it to Roi-et for me to pick up.

They will also order them in for you.

[Forkinhades]

No problem,

15kva/220 = 68 A (approx)

[Crossy]

Sorry Guys if this has already been answered or doesn't really belong here, if so my sincere apologies.

How is an AVR protected against surges, as to my understanding the AVR goes between your meter and your CU, so any surge passes through this device ?

An AVR protects against long term under and over voltages (they can take several seconds to react) although they will take the edge of fast surges due to their inherent inductance. Fast surges / transients (such as from lightning) need a faster acting device such as a MOV (metal oxide varistor), these are discussed in several threads in this forum.

For comprehensive protection you need to look at both, the MOV is essential for pretty well everyone in Thailand.

[Crossy]

Thanks C,

But I think I need to rephrase my question (sorry)

Will a Surge not destroy a AVR as it will pass through it ?

It may upset the electronics, the transformer is pretty robust any surge that would damage it is likely to have much more spectacular effects.

Put MOVs in front of the AVR (where they should be anyway) to protect it.

[RichCor]

Thanks C,

But I think I need to rephrase my question (sorry)

Will a Surge not destroy a AVR as it will pass through it ?

An AVR in many instances is just a Heavy Duty Transformer (but the number of windings used on the secondary is variable). Transformers are very robust. Generally the only thing that affects them are sustained high heat.

The AVR detects input voltage and is designed to either compensate the secondary (if within design parameters) or shut down.

A quick Power Surge would normally ride straight through and be received on the secondary (unless filters for voltage spikes and surges were used to trap them). An electrical spike large enough to vaporize metal or jump an air gap are another thing altogether.

As Crossy mentioned, AVRs also have associated electronics for running the adjustments of the AVR. They can be affected by large or out-of-spec power surges as well.

How A Transformer Works

A simple transformer consists essentially of two coils of insulated wire. In most transformers, the wires are wound around an iron-containing structure called the core. One coil, called the primary, is connected to a source of alternating current that produces a constantly varying magnetic field around the coil. The varying magnetic field, in turn, produces an alternating current in the other coil. This coil, called the secondary, is connected to a separate electric circuit.

The ratio of the number of turns in the primary coil to the number of turns in the secondary coil—the turns ratio—determines the ratio of the voltages in the two coils. For example, if there is one turn in the primary and ten turns in the secondary coil, the voltage in the secondary coil will be 10 times that in the primary. Such a transformer is called a step-up transformer. If there are ten turns in the primary coil and one turn in the secondary the voltage in the secondary will be one-tenth that in the primary. This kind of transformer is called a step-down transformer. The ratio of the electric current strength, or amperage, in the two coils is in inverse proportion to the ratio of the voltages; thus the electrical power (voltage multiplied by amperage) is the same in both coils.

[IMHO]

15kva for a single phase 63A main switch on 30/100 supply should be fine

What's your loads? ie how many air con, water heaters etc.

Predicted max. load is around 50 amps (rough calculation)

OK, so that 's 11kVA - next question: what's the predicted min. mains voltage?

If your mains drops to say, 150V under full load, your mains load will be over 73 Amps, making the 15kVA unit too small.

All that said, I'd just spend the extra on the 20kVA unit that and forget about the calcs, or wondering just how low the mains can/will go

[Forkinhades]

Personally I would measure the voltages throughout the day on load. Especially during peak times, which in my village is around 6 - 8 pm, where my measured voltage is around 200V

[Forkinhades]

Yes indeed, and very unlikely the voltage drops to 150V, even if it did, it would not be long periods, and as said 'everything' will not be on at the same time.

[crs]

We have a small (2kVA) AVR which feeds the technology via a UPS, handy when the supply is down to 150V.

If you have regular low voltage you may want to consider a two-pronged attack:-

1. An AVR to supply stuff like your TV, freezer etc.
2. A low volt cut-off to protect your A/C and other things that you can afford to have powered off for a while.

Means you can use a smaller (cheaper) AVR.

Apache704, how big is your 45A unit? A photo would be great. Our breaker box is in the lounge, got to avoid annoying wifey

Crossy - re. low volt cut-off - searched around Thaivisa and your home lec site but not seen an explanation or link to a device that does this. Would appreciate if you can give some more info (or a link to where you already have) please. (Eg, pic, link, price.)

My situation...

Just moved in - had 63A Safe T Cut CU (with RCBO) fitted, added earthed circuits for this and that with wiring upgraded where necessary. (Just ordered a DIM MOV which I can hopefully squeeze into the CU too.)

(4x small aircon, 2x 4.5kw showers, fridge freezer, microwave combi, 250W Well Pump, other usuals.)

Down village soi, on single phase, towards the end of what looks like a long, congested spur from the transformer (>400m away). Volts drop down to 200ish on the evenings = low fan speeds and a slightly moody PC UPS. Not seen bad drops to to <190 as of yet, but worse brownouts might happen so am interested in some low voltage protection if not too expensive/difficult.

Also, they're building a new apartments thing just over the road and guess they'll need to run 3 phase in for power. If there's a way for me to get in on this somehow, can my CU be worked for 3 phase?

Cheers.

[Crossy]

We are using one of these http://www.ebay.co.uk/itm/Adjustable-Over-Under-Voltage-Protective-Relay-/221381033800?hash=item338b567f48 also available as 3-phase. Similar units are available in Thailand.

Note that the unit above cannot directly switch heavy loads and must be used with a contactor (big relay).

The new apartment block will likely have its own transformer so you'll not be able to piggy-back on their supply

[crs]

We are using one of these http://www.ebay.co.uk/itm/Adjustable-Over-Under-Voltage-Protective-Relay-/221381033800?hash=item338b567f48 also available as 3-phase. Similar units are available in Thailand.

Note that the unit above cannot directly switch heavy loads and must be used with a contactor (big relay).

The new apartment block will likely have its own transformer so you'll not be able to piggy-back on their supply

Right, so if I get:

a MOV like this: http://www.ebay.com/itm/370724479666?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

An over/under voltage protector like this: http://www.ebay.co.uk/itm/Adjustable-Over-Under-Voltage-Protective-Relay-/221381033800?hash=item338b567f48

And a contactor like this (found a link you'd given in another thread): http://www.ebay.co.uk/itm/Schneider-15959-CT-Double-Pole-25a-NO-Contactor-240v-Coil-Used-/151031227579?pt=UK_BOI_CircuitBreakers_RL&hash=item232a29a4bb

I could put them in a bare DIM box and wire in pre CU as lightening, under and over voltage protection? (Don't think I can be bothered with AVRs.)

A wiring diagram plus any setting recommendations/necessaries for the individual items to show my electrician guy would be great, if you could...

RE. 3 phase - ah, true...

[SPJ]

Apache704, can you please send the contact details of where you bought your unit from as we have the same problem here. Thank you!!!

[Crossy]

Apache704, can you please send the contact details of where you bought your unit from as we have the same problem here. Thank you!!!

Post #1 says he got his AVR in Global House