| To fully understand and appreciate the importance of | | | | such as blocks of flats), commercial or industrial. The |
| uninterruptible power supplies (UPS), it is crucial to | | | | physical point at which this happens is known as the |
| first understand how electricity is generated and | | | | Point of Common Coupling (PCC). In the UK, a |
| distributed in whatever country around the world you | | | | single-phase, 230Vac supply (more typically for |
| happen to be. In many Westernised societies it is | | | | residential consumer use) can be derived from the |
| tightly controlled, regulated and fairly reliable but in | | | | same substation (or incomer), by drawing on any one |
| other areas it is not and power protection at the final | | | | phase and neutral. In this way, the earth and neutral |
| point of consumption, whether business or residential, | | | | reference points are connected all the way back |
| needs to bare this in mind. It may be that what's | | | | along the distribution network to the substation. |
| needed is some form of micro-generation as well as | | | | Each country or region around the world has its own |
| uninterruptible power supply. | | | | set of grid transmission and distribution codes that |
| Electricity can be derived from a number of sources | | | | govern electricity generation and distribution. In |
| these days and the call for renewable technology in | | | | particular these stipulate minimum and maximum |
| response to environmental pressures means the list is | | | | voltage and frequency values allowed. |
| getting longer. Coal, gas-fired or nuclear generation | | | | For any site, the quality of power received through |
| stations have been the primary methods so far but | | | | its incomer is directly affected by the performance |
| wind, wave or solar power are beginning to make | | | | of the electrical distribution network upstream. Today |
| their mark. | | | | this can be intercontinental and span a range of |
| The phenomenon that generates electricity is termed | | | | political and cultural environments. Within a distribution |
| Electro-magnetic Induction. Its output is an alternating | | | | network power problems can be caused by: |
| current (ac) waveform. The process by which this | | | | - Network operation, grid switching, auto re-closers |
| happens utilises magnets on a shaft which rotate | | | | and fault tracing. |
| near to windings (usually three) into which electric | | | | - Network hardware failure, including transformer and |
| current is induced; referred to as Electro-motive | | | | breaker malfunctions. |
| Force. The process is the same in each case; the | | | | - Power shortages during peak demand periods when |
| only difference between each of the energy | | | | supply is restricted. |
| generation types is the fuel it uses to make the | | | | - Accidental severing of supply cables during |
| shaft spin. | | | | construction or street works. |
| The windings within a generator are separated by | | | | - Acts of terrorism, vandalism or deliberate sabotage. |
| 120 degrees of rotation, which creates a three-phase | | | | - Environmental activities such as lightning, heat, rain, |
| waveform comprising of P1 (phase 1), P2 (phase 2) | | | | snow, ice, wind or wildlife. |
| and P3 (phase 3) components. | | | | |
| The measurement of kV, at which electricity is | | | | On any site, a stable and clean electricity supply can |
| generated, varies around the world from country to | | | | be affected and influenced by local overloading, |
| country, region to region. In the UK, for example, it is | | | | simple switchgear faults and the operation of |
| typically 25kV, which is stepped up to 275/400kV | | | | industrial or commercial equipment and fittings - |
| before being distributed as a three-phase, 50Hz | | | | including mechanical presses, welding equipment, lifts, |
| supply. It needs to be distributed at a high voltage to | | | | escalators, air-conditioners, photocopiers and |
| overcome resistance (that might be in the network) | | | | fluorescent lights. All of these can induce power |
| or transmission losses. As it moves through the | | | | problems into a mains power supply that may have |
| network, however, to the point of use, the voltage | | | | been reasonably stable and clean beforehand. |
| is reduced. On the outskirts of major towns and | | | | A review of power generation and distributed and |
| cities, substations lower the voltage. In the UK this | | | | the effect it might have on power quality (alongside |
| would be to 132kV. These substations are connected | | | | other environmental, political and social unrest that |
| to even smaller substations that reduce the voltage | | | | may have an effect) has a baring on the size and |
| even further to typically 33kV and 11kV (UK). These | | | | type of uninterruptible power supply that may be |
| are found either within or close to the point of | | | | ideally suitable to an installation. |
| delivery. | | | | This article was compiled using information available in |
| It is at these substations that a neutral and earth | | | | The Power Protection Guide - the design, installation |
| reference are added so that, in the case of the UK, | | | | and operation of uninterruptible power supplies (ISBN: |
| a 400Vac, three-phase, plus neutral and earth | | | | 9 780955 442803). By Robin Koffler and Jason Yates |
| (TP+N+E) can be supplied to the incomer of a site or | | | | of Riello UPS. |
| building, which could be residential (larger buildings | | | | |