T 4.1 Disruption of power supply

In spite of high levels of service security, power supply failures still occur regularly at power distribution system operators and power supply companies. Most of these malfunctions are so short (less than one second long) that consumers do not even notice them. However, interruptions lasting longer than 10 ms can cause disruptions to IT operations. While taking measurements at about 60 measuring points in Germany in 1983, approximately 100 such power drops were registered. Of these failures, five lasted up to one hour, and one lasted even longer than an hour. These interruptions were due solely to failures in the power supply system. In addition, interruptions can also be caused by switching off the wrong equipment when performing scheduled maintenance or by cables damaged by excavation work.

Note that not only the obvious, direct consumers of electricity (PCs, lighting, etc.) depend on the power supply. All infrastructural equipment used today depends directly or indirectly on electrical power, e.g. lifts, pneumatic mail systems, air conditioning technology, alarm systems, security gates, automatic door closing units, sprinkler systems, and private branch exchanges for telephones. Even the water supply in high-rise buildings depends on electricity to generate water pressure in the upper floors using pumps.

The liberalisation of the electricity market in some industrial countries resulted in a poorer level of service. For this reason, the risk of problems due to failures of the power supply or due to switching operations at national power transfer points could increase, even in Germany.

Examples:

In a large industrial plant in southern Germany, the entire power supply was interrupted for several hours because of technical problems at the power utility company. Consequently, production was interrupted and all computers failed in the development departments not equipped with a backup power supply.

• Due to an error in the UPS of a computer centre, the UPS did not switch back to normal operation after a brief power failure. After about 40 minutes, the batteries were empty and all the computers in the affected server room failed.
• At the beginning of 2001, there was a power emergency in California that lasted over 40 days. The power supply situation was so tight that the Californian Independent System Operator mandated rolling blackouts. These power outages, which lasted up to 90 minutes, not only affected households, but also companies in the high-tech industry. Since the power failure also caused alarm systems and surveillance cameras to be switched off, the power supply company kept their rolling blackout timetables secret.
• In November of 2005, many communities in Lower Saxony and North Rhine-Westphalia were without power for days after heavy snowfall because numerous power line towers had collapsed under the weight of the snow and ice. It took several days to restore power.