The question of how the volt drop limiting values were derived must be addressed. The PESs in England require that any load applied to their network by a consumer does not inflict a volt drop of more than 1% at the point of common coupling with their network for frequent load applications or 3% for infrequent load applications. Infrequent is defined as a load application or rejection not more than once in 3 hours this would be impractical to adopt for modern commercial/industrial systems thus the 1% figure is used exclusively.
This volt drop limit is to ensure that other consumers on the same network are unaffected by the switching on or off of loads by a consumer. The most obvious effect is that filament lamps would flicker or dim if the volt drop were excessive or it could cause a malfunction of other equipment, particularly equipment incorporating voltage sensitive components, on either the consumer’s or other consumers’ networks.
At one consumer’s site in Southern England where the volt drop had not been properly considered every cash till on the site had to be supplied via a local UPS to prevent their continuous malfunction.
The PES rule limiting the volt drop to 1% at the consumers point of common coupling is therefore adopted for switchboards on the consumer’s network as they are likely to feed lighting and small power systems where either lighting system flicker or equipment malfunction would rightly be judged as a design failure.
Motor Control Centres (MCCs) differ from switchboards in that they supply, or should only supply power to motors and devices associated with the motors for example solenoids. Motor control centres would also have control systems associated with the control of the motors, it is important that these systems operate properly at all times, excessive volt drops can cause malfunctions thus it is necessary to place a limit on the volt drop. The limit used for MCCs is 3% at the MCC busbars when a motor starts.
The motor circuit volt drop of 2.5% is taken from earlier editions (13th to 15th) of the IEE (Institution of Electrical Engineers and since 2006 the IET – Institution of Engineering and Technology) Wiring Regulations (BS7671) which give definitive limits for volt drops, the 16th and present 17th edition each print a lot of words regarding volt drop, however those words only give guidance regarding volt drops they do not give definitive limits.
The Wiring Regulations give no definitive limits for volt drop when a motor starts, the 10% limit for the starting volt drop of the motor circuit is to ensure adequate voltage at the motor terminals so that there is sufficient torque for the motor to start and run up to speed.
The volt drop in any part of the network will have a cumulative affect so, for example, a transformer no load voltage of 417V drops to 400V when it is fully loaded that is a 4.25% volt drop there is then the distribution network volt drop, the target of which is normally no more than 4% plus the motor circuit volt drop so the overall volt drop at the motor terminals when running can be 6.5% of the nominal voltage. However when added to the other volt drops of the network the actual volt drop at the motor terminals during starting may be as much as 14% of the nominal voltage.
Then there will be the PES MV network volt drops which must also be included in the calculations.
Volt drop is caused by the impedance of the circuit through which a current is flowing the energy lost due to volt drop is wasted energy, which manifests itself as heat, which is another reason for minimising the volt drop.
Electrical equipment manufactured for use at low voltage in the European Union has to, by statute (law), operate on a voltage tolerance of ±10% of the nominal voltage which is 400V between phases of a three phase system and 230V between phase and neutral of a single phase system. Note: If you divide 400 by √3 to obtain the phase voltage the result is 230.9401V thereby losing almost a volt by using the word nominal.
This tolerance level was introduced in 2008 it is a typical European Union political fudge, the limits were juggled to cover the standard voltages in use at that time throughout the European Union thereby creating a standard whereby no-one has to change to conform. It allows the politicians to state that the European Union has a common electrical voltage. In fact the politicians passed laws (the low voltage directives) to force the electrical equipment manufacturers to manufacture their equipment with a wider voltage tolerance band to cater for the voltage variations of the various countries of the European Union.
It should be noted that the politicians of the European Union have not yet managed to harmonise domestic plugs and sockets yet the solution is obvious. Use the IEC 60320 type C20 and C19 16A three pin plugs and shuttered sockets; and type C14 and C13 10A three pin plugs and shuttered sockets. If each fixed socket outlet was protected by an integral MCB or RCBO instead of a switch it would make the sockets suitable for use on ring and radial circuits making them suitable for the whole of the European Union, easy, but not to a politician!
Back to motors; therefore a 400V three phase motor will, or should, operate at any supply voltage from 360V to 440V at its terminals, however the full load current will change as the supply voltage changes.
Definition of a typical British career politician: An inferior sub-species of the human race that is held in complete contempt by the main species of the human race and is typified by the following characteristics:-
A two faced brain dead lying hypocrite, who is an inadequate human being, either male or female with no concept of honour, integrity or honesty and always on the look out for band wagons to jump on.
They speak with a forked tongue, talk a lot of rubbish, never listen to other people, are the masters of weasel words, and they never answer a question.
They love power and control over others, are full of their belief in their own self importance and are convinced that they are always right, their arrogance is unsurpassed by any other members of the human species, they see politics as an easy way of making money.
They normally have long snouts that go into a trough filled with other peoples (taxpayers) money.
Don’t forget the proverb the last refuge of a scoundrel is patriotism and politicians always claim to be patriotic.
Since most career politicians in England are graduates of English universities it proves the earlier point of just how poor the English education system is.
A warning whenever any politician opens their mouth expect a lie and you will then not be disappointed.
You would never let a paedophile look after your children so why do we let politicians look after our country.
Question, is the prime minister of England someone who has risen to the top or someone who has sunk to the bottom?