Power Quality Issues – Part 2 – Dips and swells
Continuing on from the previous article on the issues of harmonics within an electrical installation, this month Julian Grant – General Manager at Chauvin Arnoux UK, discusses the symptoms and effects of dips and swells on the electrical network, and steps that can be taken to mitigate any problems.
When a subscriber purchases electrical energy, they are effectively buying a product. Like any other product it needs to meet the necessary prescribed quality standards to ensure it works properly, or in the case of electrical energy, that the equipment within the installation powered by it works properly and safely.
If electrical equipment is to operate correctly, it requires electrical energy to be supplied at a voltage (and frequency) that is within a specified range, and to that end European standard EN50160 “Voltage characteristics of electricity supplied by public distribution systems” was drawn up by CENELEC in November 1994. This standard gives the main characteristics of the voltage at a customers supply terminals in public low voltage and medium voltage electricity distribution systems under normal operating conditions.
The standard gives the limits or values within which the voltage characteristics can be expected to remain, but does not describe the typical situation in a public supply network. It is also the case that the limits are quite wide, 230V ± 10% for example, and it is acceptable for the voltage to drift outside ±10% for 5% of the time. Add to that the further complication that the UK electricity supply is actually specified as 230V +10% -6%.
The bottom line, as with all issues of power quality, is however, not whether the supply voltage meets or does not meet a standard, but the compatibility between the electricity supply and the loads that are connected to it. In other words, that an installation works safely, faultlessly and without interruption, to the requirements and satisfaction of the customer.