In my blog “Electricity: a living energy flow”, I explained how electricity was the result of living, proactive particle energy desires. That part was mostly about direct current (d.c.). This part is a continuation of that theme but dealing with alternating current (a.c.). supplies and particularly with the u.k’s mains supply.
You might think that reversing voltage pressures and inviting electrons to move back and forth in a wire some 50 times a second, as happens in the u.k. mains supply, would fail to provide the energy an appliance needs to function but not so.
An a.c. mains circuit may be well over a 100 miles in length but as we learnt in part 1, electron movements are a response to light speed energy interactions. Each 1/100th’s of a second, an electrons is moving in one direction, we might regard as variable d.c. In that time a photon emitted by an electron if not absorbed by and influencing other electrons could travel 1,860 miles. Electron moves are rapid and marginally reduce that distance. The more tightly held electrons in the heating elements of your toaster, kettle or cooker more than 50 miles away from the source feel its energy pressure and decide it is best to move, so creating heat.
But how does the energy dissipated in the heating elements of your home and that dispersed in billions of applications like that trigger an increase in source input? It’s because the light speed photons encouraging electron motions are also conveying the resistance (reverse pressure if you like) they feel back to the source. To maintain source pressure the source has to work harder. In the case of a substation generator we arrange for any slowing in its speed to be accompanied by an increase in its energy input, thereby maintaining its 25,000 volt output pressure.
Supply and Transmission
Energy sources feeding the grid in the u.k. are diverse with wind power and gas contributing most, nuclear, biomass and imported energies making a moderate contribution and smaller inputs from hydro, solar and stored energies. The latter are mainly inputs from batteries used to store energy from other sources, like wind and solar.
To bring the energy needs to even a small community at low voltage direct current (d.c.) would require massive conducting cables so the very few d.c. supplies there are, are at high voltage. The vast majority of supplies are three phase and conveyed at National Grid voltages of 400,000 or 275,ooo volts a.c. that are then stepped down to lower voltages at grid stations nearer demand locations. On the pylon shown the top wire is a protective earth wire. The three wires on each side of the pylon are the phase wires, each set coming from separate generators.
The high voltages mean we can transmit high rates of energy (power) along the relatively small wires we see on transmission pylons. Its being a.c. means we can use transformers at substations to change voltages. We step them down to 132,000 volts, then to 33,000 volts, to 11,000 volts and then in final substations to 415 volts.
All of the above mentioned voltages are 3 phase. It provides an arrangement in which voltages always sum to zero. By balancing loads across the three phases we can also have currents that at any one time sum up directionally to near zero. The phase wires act alternatively as circuit supply and return wires.
Three phase windings can be connected in either a star or delta arrangement. The source generator’s star arrangement has an earthed neutral. Its step up transformer will be star to delta. The transformers that step down voltages will be delta to delta except as below for the consumer output.
At the final substation transformer the delta wired input becomes a star wired 3 phase and neutral, as illustrated. It has 415 volts between any two of its phase wires and 240 volts between any one of its phase wires and the star arranged neutral.
Industrial and many commercial premises will have such a 3 phase supply. Three phase motors and appliances that use it will naturally balance phase energies. Some effort will be made to balance non three phase and 240 volt supplies by the connecting them to chosen three phase terminals and neutral.
Domestic Mains Energy
Domestic properties are generally supplied using a single phase wire and a neutral. Balancing the load that domestic premises place on a local substation is achieved by connecting equal numbers of properties to each of its three phases. To stop voltages floating, the neutral, as one pole of the supply is bonded to earth at the local substation, as shown in the diagram. If that were not done any highly dangerous voltage making contact with its wired circuits could in fault conditions deliver fatalities.
The live wire voltage relative to the neutral is sinusoidal, and over a cycle its positive and negative peaks are about 339 volts and its average is zero, so you might well ask where the 240 comes from. It is the a.c. voltage that outputs the same heat from your toaster element as that of a 240 volt d.c. voltage. Mathematically it is the root of the mean of all the squared cycle values.
The domestic distribution board shown here has a residual current device (RCD). It compares current flows in live and neutral wires. If they are not the same it is indicative of some leakage to earth. It might be through you; the power is shut off.
If neutral and earth are connected at the substation why do we need an earth wire. Couldn’t the neutral do that job?
Consider using a neutral wire to earth a metal toaster. If we plugged the toaster into a wall connection with its neutral detached our toaster wouldn’t work. But its live would be connected via the heater element and its neutral to the toasters metalwork. Touch the toaster frame and we get a shock as we complete the circuit back to supply earth.
Perhaps the most important concept to take away from this blog is that photon energies are not just going from source to destination. Particle resistances opposing them are being conveyed by them right back to the original energy source. This concept is not just applicable in wired circuits. It is a fundamental part of the photon interaction between protons and electrons and also a fundamental behaviour of the photons in space that we see as electromagnetic waves and call light.