230V/240V Question

[JohnW2]

"(b)in the case of a low voltage supply, a variation not exceeding 10 per cent above or 6 per cent below the declared voltage at the declared frequency;"

I've commented/questioned about this in the other thread. However, I've only just noticed the last few words (emboldened above). What happens if (as is far from impossible at the extremes of voltage), the frequency differs from the declared frequency (within the ±1% permitted variation). Are the voltage limits then different? If not, what is the significance of those last few words?

Kind Regards, John

 

[stillp]

The frequency might be somewhat different at the extremes of voltage. The tolerances are with respect to the nominal voltage and frequency.

 

[stillp]

Apart from the different plug shapes, *nothing* I have taken has had the slightest difficulty working on the local voltage without any pre-setting whatsoever.

A lot of the latest electronics (laptop and mobile-phone chargers, for example) come with switched-mode power supplies which will accept a wide range of supply voltages by nature of their design, often over a range of about 90 to 270V, so they'll generally have no problems whatsoever on anything from the (nominal ) 100V supplies in places like Japan up the 250V in some parts of Africa and, I believe, India.

And they won't even have problems dealing with changes of frequency, e.g. 50/60Hz.

 

[JohnW2]

And they won't even have problems dealing with changes of frequency, e.g. 50/60Hz.

Indeed. In fact, many/most of them can probably cope with DC!

Kind Regards, John

 

[JohnW2]

The frequency might be somewhat different at the extremes of voltage. The tolerances are with respect to the nominal voltage and frequency.

Yes, I understand that - but the voltage tolerance is quoted 'at nominal frequency', which begs the question as to what the voltage tolerance becomes at other (permitted) frequencies, doesn't it?

Kind Regards, John

 

[PBC_1966]

I think we would all accept that under certain conditions loading across the network which causes sags in frequency would also be quite likely to cause drops in voltage as well. But as John asks, what does that really have to do with the legislation adding that qualifying clause "at the declared frequency" to the allowable tolerances? What's the purpose of adding that clause?

 

[bernardgreen]

Indeed. In fact, many/most of them can probably cope with DC!

Many won't as they use a capacitor in series with the supply to limit the amount of power that the switch mode circuit can take from the supply.

 

[JohnW2]

Indeed. In fact, many/most of them can probably cope with DC!

Many won't as they use a capacitor in series with the supply to limit the amount of power that the switch mode circuit can take from the supply.

Yes, some do, but many I've dissected the have the supply going straight to the rectifier.

Kind Regards, John

 

[stillp]

The frequency might be somewhat different at the extremes of voltage. The tolerances are with respect to the nominal voltage and frequency.

Yes, I understand that - but the voltage tolerance is quoted 'at nominal frequency', which begs the question as to what the voltage tolerance becomes at other (permitted) frequencies, doesn't it?

Kind Regards, John

No, because it is quoted at nominal frequency.

 

[JohnW2]

The frequency might be somewhat different at the extremes of voltage. The tolerances are with respect to the nominal voltage and frequency.

Yes, I understand that - but the voltage tolerance is quoted 'at nominal frequency', which begs the question as to what the voltage tolerance becomes at other (permitted) frequencies, doesn't it?

No, because it is quoted at nominal frequency.

So do I take it that the regulations give absolutely no indication of permitted voltage tolerances when the frequency is not exactly equal to the 'nominal' value (which, strictly speaking, will almost never be the case - 50.000000000000000000000000... Hz would be a distinct rarity!).

Kind Regards, John

 

[stillp]

You can, I'm sure, read the regulations yourself, but I'm not sure you'll benefit until you can understand the basic principles of specification for engineering quantities. You seem to be struggling with the statistics as well - a series of measurements of frequency would appear as a normal distribution, centered on 50.000... however many zeroes you care to add.

 

[Gerrydelasel]

I think what JohnW2 is saying is that the last part of the following sentence is redundant:
"a variation not exceeding 10 per cent above or 6 per cent below the declared voltage at the declared frequency"
Surely the voltage tolerance is +10/-6% around nominal, regardless of the frequency. The frequency is a separate issue with its own tolerance, so why did they bother to mention frequency in that sentence?

 

[stillp]

The frequency will vary slightly as the voltage varies. However in order to be able to express the voltage tolerance in a meaningful and measurable way, the specification for the voltage tolerance is given at the nominal frequency. It's a bit like the specification for many products, which give an operating temperature range of, for example, 0 to 55° C, but performance characteristics are quoted at 25° C.

 

[Gerrydelasel]

The frequency will vary slightly as the voltage varies. However in order to be able to express the voltage tolerance in a meaningful and measurable way, the specification for the voltage tolerance is given at the nominal frequency.

Ah, so they mention frequency because, if the frequency dropped outside the acceptable range, it would be pointless to specify or demand an 'acceptable' voltage, since the system is already faulty.

 

[JohnW2]

You can, I'm sure, read the regulations yourself, but I'm not sure you'll benefit until you can understand the basic principles of specification for engineering quantities.

I guess I'm naive. It seems that when I see a specification which says ""a variation not exceeding .... at the declared frequency" I am making the mistake of assuming that it means what it says!

You seem to be struggling with the statistics as well - a series of measurements of frequency would appear as a normal distribution, centered on 50.000... however many zeroes you care to add.

As you know only too well, I am in at least as strong a position as anyone else here to understand the statistics. As I'm sure you are aware, if one has a Normal distribution with a mean of 50, the probability of any item/measurement/whatever having a value of exactly 50 is zero (or, more correctly, 'infinitely small').

Kind Regards, John