Uninterruptible Power Supply - Electricity Generation & Distribution

To fully understand and appreciate the importance of uninterruptible power supplies (UPS), it is crucial to first understand how electricity is generated and distributed in whatever country around the world you happen to be. In many Westernised societies it is tightly controlled, regulated and fairly reliable but in other areas it is not and power protection at the final point of consumption, whether business or residential, needs to bare this in mind. It may be that what's needed is some form of micro-generation as well as uninterruptible power supply.

Electricity can be derived from a number of sources these days and the call for renewable technology in response to environmental pressures means the list is getting longer. Coal, gas-fired or nuclear generation stations have been the primary methods so far but wind, wave or solar power are beginning to make their mark.

The phenomenon that generates electricity is termed Electro-magnetic Induction. Its output is an alternating current (ac) waveform. The process by which this happens utilises magnets on a shaft which rotate near to windings (usually three) into which electric current is induced; referred to as Electro-motive Force. The process is the same in each case; the only difference between each of the energy generation types is the fuel it uses to make the shaft spin.

The windings within a generator are separated by 120 degrees of rotation, which creates a three-phase waveform comprising of P1 (phase 1), P2 (phase 2) and P3 (phase 3) components.

The measurement of kV, at which electricity is generated, varies around the world from country to country, region to region. In the UK, for example, it is typically 25kV, which is stepped up to 275/400kV before being distributed as a three-phase, 50Hz supply. It needs to be distributed at a high voltage to overcome resistance (that might be in the network) or transmission losses. As it moves through the network, however, to the point of use, the voltage is reduced. On the outskirts of major towns and cities, substations lower the voltage. In the UK this would be to 132kV. These substations are connected to even smaller substations that reduce the voltage even further to typically 33kV and 11kV (UK). These are found either within or close to the point of delivery.

It is at these substations that a neutral and earth reference are added so that, in the case of the UK, a 400Vac, three-phase, plus neutral and earth (TP+N+E) can be supplied to the incomer of a site or building, which could be residential (larger buildings such as blocks of flats), commercial or industrial. The physical point at which this happens is known as the Point of Common Coupling (PCC). In the UK, a single-phase, 230Vac supply (more typically for residential consumer use) can be derived from the same substation (or incomer), by drawing on any one phase and neutral. In this way, the earth and neutral reference points are connected all the way back along the distribution network to the substation.

Each country or region around the world has its own set of grid transmission and distribution codes that govern electricity generation and distribution. In particular these stipulate minimum and maximum voltage and frequency values allowed.

For any site, the quality of power received through its incomer is directly affected by the performance of the electrical distribution network upstream. Today this can be intercontinental and span a range of political and cultural environments. Within a distribution network power problems can be caused by: 

• Network operation, grid switching, auto re-closers and fault tracing.
• Network hardware failure, including transformer and breaker malfunctions.
• Power shortages during peak demand periods when supply is restricted.
• Accidental severing of supply cables during construction or street works.
• Acts of terrorism, vandalism or deliberate sabotage.
• Environmental activities such as lightning, heat, rain, snow, ice, wind or wildlife.

On any site, a stable and clean electricity supply can be affected and influenced by local overloading, simple switchgear faults and the operation of industrial or commercial equipment and fittings - including mechanical presses, welding equipment, lifts, escalators, air-conditioners, photocopiers and fluorescent lights. All of these can induce power problems into a mains power supply that may have been reasonably stable and clean beforehand.

A review of power generation and distributed and the effect it might have on power quality (alongside other environmental, political and social unrest that may have an effect) has a baring on the size and type of uninterruptible power supply that may be ideally suitable to an installation.

This article was compiled using information available in The Power Protection Guide - the design, installation and operation of uninterruptible power supplies (ISBN: 9 780955 442803). By Robin Koffler and Jason Yates of Riello UPS.