HV and EHV voltage variations are defined in the ESQCR and will normally be repeated in the connection agreements.  For HV supplies below 132kV the requirement is +/- 6% and for supplies of 132kV and over its +/-10%.   

After that its up to the designer.  Normally once you go above 11kV the transformers would have on line tap changers controlled by suitable relays to keep the secondary voltage within pre-set limits.

And whether or not the cable between the transformer secondary and your first load  or disboard is included in the sums or not.

For a house in the street the volt drop sums start at the meter board, not at the transformer terminals, the voltage drop in the street mains is very real but it  "belongs" to the DNO - they only guarantee to hit somewhere between 208 to 253 at your cut out (and are usually quite well in, but not always)

When you have a bit more control, you can usually do quite a bit better than that.

Normally drop at HV can be neglected because the voltage  loss is scaled by the transformation ratio. (11kV/400 or whatever)

Mike

Peter Hartley said:

It also applies to Extra Low Voltage (ELV) ranges and Low Voltage (LV) ranges, across a variety of frequencies.

yes, so in those cases, the v.d. is from the transformer (or converter) for those sources.

Regs 525.1 and 525.201 also still apply ... but in this case, the designer can take into account vd on both sides of the source to achieve those requirements, or use a "regulated" source (SMPSU for DC, for example). In any event, the source is not a public LV supply according to ESQCR, but in the case of ELV, you might ask whether the other "deemed to comply" models work too - I don't think they would always be valid TBH ... what's perhaps more pertinent here, is where a constant current driver is used as a source.

Energy efficiency measures may also take precedence !

In what situations would voltage drop be less relevant than energy efficiency? 

AMK said:

In what situations would voltage drop be less relevant than energy efficiency? 

Well ... since you ask ... Power over Ethernet is a good example.

But in general:

(a) voltage drop can be controlled with power converters or transformers;

(b) where constant current (or constant power) is used, voltage drop to an extent can be ignored, and energy efficiency measures (perhaps whole lifecycle cost) could be considered.

Just to add, power converters and transformers are not without disadvatages. For instance, they can cause power losses. Also will make the system more expensive, bulky, and complicated. Therefore, power converters and transformers may not be the optimal choice for voltage drop.

True - and in many cases, a fatter cable is the way to go, but if you have to get 1kW over more than say 1km, then it is less lossy to install step up step down transformers at both ends - there is a reason there is an EHV national grid ;-)

As a very rough rule of thumb, when the distance in metres is comparable to the voltage between the lines, it becomes worth considering, and when it is several times further, a change of voltage  is pretty much the only practical solution..

Mike

In what situations would voltage drop be less relevant than energy efficiency? 

In the general situation too - 5% v.d. represents a 5% loss in energy too - so and increase in consumption to have the same effect.  Say you had a constant 1kW load - 5%  would mean a loss of a 438kWh a year - or say £131.40 at 30p/kWh - over say a 30 year installation lifetime that's £3,942 - which could justify going up a cable size or three if you could reduce the losses by a few percent. Similar reckoning for say 3kW for 8 hrs/day (heat pump) or 7kW for 4hrs/day (EV).

   - Andy.