In order for power to be usable (e.g. high-quality), its characteristics must be within the tolerances of the supplied load. Therefore it is not enough for power to be present. Let’s take this necessary condition as the starting point for the analysis.

Information on electrical power quality is somewhat scarse. The main independent sources of information considered here are:

• European Network of Transmission System Operators for Electricity (ENTSO-E);
• The Italian Regulatory Authority for Electricity and Gas;
• Leonardo Energy (LE).

The available statistics respectively refer to High Voltage lines, Low Voltage lines and power quality within the system used. In fact, high-quality power supplies are frequently compromised by consumers’ loads within their own plants, such as non-linear loads or loads with high inrush current. Unfortunately, the lack of information on Medium Voltage lines, which is of extreme relevance to all consumer loads connected via transformer to the grid, does not allow for a complete analysis. The reason probably stems from the fact that individual quality standards are defined in Medium Voltage.

The ENTSO-E Statistical Yearbook 2008 provides an overview of electricity exchanges between European nations and lists the major periods of unavailability, classified according to the reason:

• Maintenance
• New construction
• Overload
• Failure in protection devices
• Outside impacts (animals, plants)
• Atmospheric agents
• Other reasons/unknown

The bottom line is that in 2008, the total downtime of international tie lines of 220 to 380 kV with rated power from 300 to 1745 MVA between Italy and neighbouring countries amounted to approximately 6500 hours.

However as regards low-voltage lines, the Regulatory Authority informs us that in 2007 in Italy, each user experienced 4.73 power outages of between 1 second and 3 minutes and 2.16 power outages of over 3 minutes’ duration, giving a total downtime of 58 minutes.

Tech Info – Jan/Feb  2010

POWER QUALITY OBSERVATORY

by

MATTEO GRANZIERO

Technical Communication Specialist

 SOCOMEC UPS