Re-rating a system for voltage variation

[desA]

A 230V~50Hz refrigeration system - let's say a heat-pump - is to be operated in a country which has 220V~50Hz power.

Assuming that the components were specc'd at 230V, but at 220V remain well within the manufacturers' specification window, what performance changes would we expect to see?

Things like compressor, fan, pump, performance. Cap tube length, or TXV selection/setting. System velocity & pipe sizing.

Anything else? Thanks everyone for your applied wisdom.

[mikeref]

desA, this is going to depend on the amount of voltage fluctuations in that country, as in load conditions at different times of the day. If the supply were constant at 220 volts, then some compensation will be expected in the amps drawn by the unit. I believe the higher amps will cause extra heat in the compressor and fan motors and transformer of the p.c., but not enough to cause problems. Ten volt drop is common here. Know of a situation where supply dropped to 208 on a normal voltage of 235 and air-cons failed to start.

[desA]

Thanks very much for your input, mikeref. I found an interesting link below.

http://www.kropla.com/electric2.htm


Many former 220 V countries have converted or are in the process of converting to the EU standard of 230 V

[Frikkie]

Goeie môre des,

The rotation speed of the motor is determined mainly by the supply frequency so the refrigeration output shouldn't change. The motor might be less efficient and run hotter with the lower voltage but manufacturers should allow for a 10% variation from the design voltage so it should not be a problem. If you are importing from Europe then maybe you should be concerned about the maximun ambient design temperature if you are you are selling in Natal.

[desA]

Goeie môre Frikkie. Alles van die beste.

Good points. I'm currently mapping the voltage in Durban metropol. So far today, it has swelled in the range 235-241V & back. Nominal is meant to be 220V~50Hz.

What has your experience with operating V & Hz been over the years?

[Frikkie]

I graduated engineering at Universiteit van Pretoria and worked with the railways for many years. I have understanding of LV AC (less than 1KV) and also high current DC motor systems but there are many new electronic systems around that I have no experience with and unfortunately I sometimes can't remember too well now as a young man like you but I like to help still when I can. I'm retired to my farm now at 75 years old but I tell everyone I am 65 so they don't talk to me as an old man.:D

Do the machines you have work with a built in modulated supply like an inverter to change the compressor speed? This would mean the supply voltage problem may be more with the inverter input itself than the motor of the compressor. The inverter would probably have a controlled output voltage which would change according to the frequency. Usually with an inverter the output voltage changes as a straight line graph with the output frequency.

Baie Geluk
Frikkie

[stufus]

Mitsubishi Elec stuff comes with a set of plugs that can be changed to deal with supply variations.
At least it used to, don't do installs any more.
According to mitsu it was all dealt with by the algorithms in the microprocessor.
But we all know manufacturers tell you what yo want to hear...
Cheers
Stu

[desA]

So far, the lowest voltage seen in Durban today was 232V - with a peak of 241V. From this perspective, the local voltage is now probably closer to 230V, than 220V.

I've heard a number of stories in SA, in regards to transformer balancing. I suspect that the over voltage during the day may be meant to counter large draws at peak load times & keep voltage > 220V.

So far, so good. Not sure what the rest of the country is like. Perhaps it's time to install under/over-voltage controls in these machines. SA seems to be going the way of most 3rd-world countries.

[mikeref]

[quote=desA;220266]So far, the lowest voltage seen in Durban today was 232V - with a peak of 241V. From this perspective, the local voltage is now probably closer to 230V, than 220V.
desA, in this area recently, electrical company fitted a transformer as voltage dropped too far(due to additional connections). What this did was to raise my voltage to 248, so i contacted them and they reduced it back to 239. Apparently appliances go bang after 252 volts:eek:.. Mike

[desA]

Had the reverse of this problem in Laos - voltage brown-outs as residents took up load. A decent voltage hi/lo cut-out works a treat at saving the compressor & other bits.

[chilliwilly]

In the UK and Europe the nominal voltage is 230 v + 10% - 6% (23v 14v) 50 hz + or - 10% (5hz). In the UK it is still typical for the voltage to be around 240 volts all day long, and above 250 volts in some areas, but is hardly evere measured at 230 volts, and in Europe probably doesn't get measured as high as 240v.

The frequency can be measured as low as 45 hz and as high as 55hz depending on the time of day, but if the frequency is at 45 hz for an hour, then it has to be at 55 hz for an hour to compensate for any synchronous applications. During that hour fluctuations of voltages occur due to the peak demands of each of the phases, and especially single phase loads.

I don't know much about power supplies in Africa but I'm sure that the grid supplier will monitor the load demand, and the distributor will manage the phase loading balance. Where the load is imbalanced the voltage between phases can somewhat differ with each other, especially at peak times.

This can cause the neutral to float and collect a voltage in excess of 30 volts to earth/ground in some extreme circumstances, depending on whether or not the star/wye point is suitably spiked to earth/ground. And the type and condition of the earth itself. And the condition and any adjustments made to the secondary winding of the sub.

The effect from the voltage difference to the applied load, needs to be very extreme to cause any instantaneous damage or cause a noticeable difference in the applied loads performance. The power companies say they will guarantee the supply parameters of 50 hz + or - 10 %, but if they supply a voltage over the stated value for long periods of time which has been known in some cases. A steady burnout of the applied load is resulted, but trying to prove it without any evidence is very hard to do.

I remeber when I was at school a light bulb was designed to be connected to a 250 volt supply, And hardly ever blew. Then I noticed over the years it changed to 240 volt, then 230 volt to harmonise with th EU. And they never last the average time of a thousand hours rating, due to the fact that the UK is still on a 240 volt supply (230v + 10% = 256v). 230 volt is now the rating of most domestic appliances and loads in the UK and the EU, and the constant 4.4% increase in voltage variation isn't always taken into consideration when designing the nominal voltage of the appliance. And it would be interesting to see if the same appliances in the EU result in the same failure (long term burnout) as quick as they do in the UK because of this variation.

[mikeref]

Interesting reading Chilli. Would a P.C.B transformer's output be a problem if voltage did reach 250 when designed for 230? As in stable low voltage supply to circuit.. Mike.

[desA]

Thanks so much 'chilliwilly', for your very useful post. I've learned something very useful.

[frank]

the UK is still on a 240 volt supply (230v + 10% = 256v).
oops.....

230 x 10% = 23

230 + 23 = 253

Lets hope the Bear isn't reading this.. :D:D

Interesting post Chilli

[chilliwilly]

Interesting reading Chilli. Would a P.C.B transformer's output be a problem if voltage did reach 250 when designed for 230? As in stable low voltage supply to circuit.. Mike.

I think it would depend on the quality of the components on the board. A factory where I used to work started to go through a phase where the pcbs were starting to burn out. This was in the early nineties, and the suppliers said the problem was due to over voltage on the secondary side of the tranny. Which had to mean the primary was over loaded. There was some minor discolouration around the bridge circuitry and regulators, and other components on the board.

The factory had two of its own 11 kv subs and dedicated tappings for certain machinery and plant, as well as the usual single and three phase general power supplies. We started by checking the general single phase voltage and three phase voltage that supplied the panels, and it was in the region of 241v-247v, and 414v-419v. No abnormal readings were found.

Anyway after some time was spent investigating the problem, we approached the suppliers and they said the voltage was too high. It should be no more than 230v and the 10v difference was causing the problem. We told them the new norm for the UK and Europe was now 230v+10-6%, and they should have considered this when they built the boards. They strongley disagreed and said the voltage in the UK was too high and needed to be dropped...? :confused:

But the problem boiled down to the tolerance values of the resistors not being matched to the other components, allowing them to sink too much current and burn them out. Anyway to cut a long story short, we modified the power supplies on the pcbs, and put a larger bridge network and linear voltage regulator network in there and solved the problem. Some of the smaller pcbs were just modified with a couple of zeners in parrallel to maintain a steady 5 or 10 volts. Eventually the company supplying the pcbs and small power supplies went out of business. ;)

:off topic:

They were a British company that claimed to specialise in control systems (DSL). They upgraded a tried and tested tradtional control system of a rubber compound process plant that had worked for years, but it never worked due to it never being tested and proved. It took all the maintenance team at least a week to salvage the old system and use what we could of the new one to get it back on line and in production again.:cool:

Basically looking at varying voltages affecting primary and secondary voltage. If I can remember the transformer basics.:o

Primary voltage = 240v.

Primary turns = 100 = 240v/100 = 2.4 v per turn.

Secondary voltage = 10v.

Secondary turns 24 = 240/10v = 24. 10v/24 0.42 volts per turn. 1:24 or 2:12 ratio.

250v primary = 0.25v per turn.

Secondary voltage = 250/24 10.42v 0.43v per turn.

So no secondary voltage increase to worry about. If the boards are burning out under normal operation, its more likely to be mismatched tolerence values of the components on the board. Or the gauge of the windings on the transformer are not 100% suited for the power rating of the tranny. Or the core material is substandard causing the pf to shift from a unity value, enough to cause under rating of the windings.:eek:

In the case of the light bulb.

250v @ 100W = 100/250 = 0.40 amp 250/0.40 = 625 ohms.

230v @ 100w = 100/230 = 0.44 amp 230/0.44 = 522 ohms.

100W lamp connected to a nominal 230v supply which will always be a 240v supply in the UK = 240/522 = 0.46 amp.

Actual wattage 0.46 x 240 = 110W.

:off topic:

Almost an 11 % increase in energy consumed and a light bulb that is overloaded due to the wrong voltage being supplied to it. And in turn shortening its lifespan. If there were 10 light bulbs on at the same time, thats the energy of one light bulb wasted, due to poor spec. As you can see in the UK, unless the 230v rating of appliances and loads have got a tolerence margin. Then they will burn out sooner than they would in the mainland EU. And in theory this means that the mainland EU has a lower carbon foot print than the UK, and maybe slightly cheaper electric bills if they are using GLS bulbs.

This is the kind of thing that manufacturers have been getting away with for a few years especially regarding the UK. Because they have deliberately misconstrued what harmonising documentation states. With me being a cynic on most things that don't make immediate sense. I honestly beleive that this has been done dliberately to increase profits in the form of increased sales, and increased recycling of waste glass and the costs associated with the management involved in reprocessing it.

I could go on about carbon footprinting, and the fact that a taxable revenue is skimmed of the profits associated with it. But nuff said for now, sorry if I've got carried away. ;)

[chilliwilly]

oops.....

230 x 10% = 23

230 + 23 = 253

Lets hope the Bear isn't reading this.. :D:D

Interesting post Chilli

:o :o.

A bear... I think a baby bear would have counted its berries more accurately than I did that!

[mikeref]

Nice one Chilli, definately alot to consider when it comes down to component failure, cause and effect... Sorry desA, seems i've taken over your thread:o... Mike.

[Magoo]

DesA
the compressor will run 16% slower sweap volume lower

[SeanB]

Going back to the effect on a motor, I have heard that the manufacturers are winding motors for 220V, as this saves the copper cost somewhat, and if you take this over a long run it adds up. Most will last long enough to get out of any warranty period, and most will probably run for a few years longer as they are not on all the time.

My local mains at work is steady at between 235 to 238 VAC, helped by the fact that there is a little 250kVA transformer in the rear, and the load is pretty constant during the day - almost all airconditioning. I used to live in Lyttelton, where the distribution system is the oldest in the country, and runs around 245-260VAC, as the original transformers were wound for 250V, and the replacements had to be the same as no metro wanted to change every one at the same time to harmonise due to the cost. Lovely for heaters and stoves, but murder on electronics and lights. It might have been changed by now, 20 odd years later.

About cooking electronics, most are designed well enough, but are then cost cutted so as to remove margins, and you get hot running resistors, diodes and transformers, along with toasty silicon. You might get a transformer run at the full rated power, but with no derating due to the bridge and reservoir capacitor, and the regulator being run at a high enough current and voltage drop so that the die inside is at near 140C, and has either no heatsink, or a small token that is mostly used to cook the local board and components. You often see a board that is black around the power supply, or is enclosed in a nice plastic case so that all parts get evenly roasted, with the case outside being hot enough to soften slightly and deform with time.