what is meant by electrical transients?

electrical transients 

An electrical transient is a temporary excess of voltage and/or current in an electrical circuit which has been disturbed. Transients are short duration events, typically lasting from a few thousandths of a second (milliseconds) to billionths of a second (nanoseconds), and they are found on all types of electrical, data, and communications circuits. Your power distribution system and attached load equipment is under constant attack from various types of power line disturbances. The result is an estimated $26 billion-per-year cost to U.S. companies in lost time, equipment repair, and equipment replacement. Transient voltage surges comprise the most severe and immediate danger to sensitive electrical and electronic equipment, and are often a neglected aspect of facility design.
Studies have shown that approximately 80% of transient activity at a given facility may be internally generated. From the normal on-and-off switching of copiers, heating and ventilation, capacitor banks, and air conditioning systems to robotic assembly and welding machines, practically every industrial machine or system causes or is adversely affected by transients. Surges and transient power anomalies are potentially destructive electrical disturbances, the most damaging being over-voltage occurrences and short duration over-voltage events, and the cumulative effect of these transients is a major source of semi-conductor degradation and failure.
The installation of Surge Protection Devices (SPD) are crucial for all facilities where microprocessor based electronics and electrical machinery is in use. This protection is essential to reduce the risk of personal injury, physical equipment damage, and loss of operations. Although lightning can cause the most visible damage, it is not the primary cause of transient voltage surges.