T 4.1 Disruption of power supply

However supposedly secure a power supply is, power failures are actually a regular occurrence. In most cases of power failure, the power is down for less than a second so that it can escape notice. However, IT operations can be disrupted even by failures lasting as little as 10 ms. During measurements carried out at some 60 measuring points in Germany in 1983 approximately 100 power dips of this type were recorded. Of these, five failures lasted for up to 1 hour, and one had a duration of more than one hour. These interruptions were due solely to failures in the mains supply. Interruptions can also be caused by shutdowns for unannounced maintenance work or by cables damaged during underground engineering work.

It is not only direct users of electric power (PC, lighting, etc.) that depend on the power supply. All infrastructure installations nowadays are either directly or indirectly dependent on electric power, e.g. lifts, pneumatic post systems, air conditioning, alarm systems and telephone private branch exchanges. Even the water supply in high-rise buildings relies on electric power due to the use of pumps to generate pressure in the upper storeys.

Liberalisation of the electricity market has resulted in some industrial countries in a worsening of the level of supply. In Germany also the danger could arise of problems due to power supply failures or to switching operations at a national level.

Examples

• In a large industrial plant in southern Germany, the entire power supply was interrupted for several hours on account of technical problems at the power utility. This resulted in an interruption of production and in the failure of all computers of the development departments that had no auxiliary power supply.

• Due to a fault in the uninterruptible power supply of a computer centre, this did not switch back to normal operation after a brief power failure. Following discharge of the batteries, after around 40 minutes all computers in the server room affected crashed.

• At the beginning of 2001 there was a power emergency in California that lasted over 40 days. The power supply situation was so tight there that the Californian Independent System Operator (ISO) mandated rolling blackouts. These outages, which lasted up to 90 minutes, affected not only households but also high-tech industry. The power utilities did not publish timetables as to when the power would be down and where, because alarm systems and surveillance cameras were switched off during the power failures.