Undervoltage is a decrease in voltage
below 90% of its nominal value for more than one minute. Undervoltage
is sometimes called a "brownout" although this term is not officially
defined. Brownout is often used when the utility intentionally reduces
system voltage to accommodate high demand or other problems. The
symptoms of undervoltage can range from none to daily equipment
malfunction or premature equipment failure. Undervoltage may go
unnoticed until new equipment is installed or the electrical system is
otherwise changed and the new combined load depresses (see Sags) the
voltage to a point where symptoms become apparent. Besides the obvious
malfunction of equipment, chronic undervoltage can cause excess wear on
certain devices like motors as they will tend to run overly hot if the
voltage is low. Undervoltage is generally a chronic problem
aggravated by a number of factors beyond the end user's control.
Electric utilities try to maintain voltage levels delivered to
customers at ±5%. However, factors like
weather, high demand and others can cause the utility voltage to fall
within a ±10% range. Even under ideal conditions, most customers will
see a drop in utility voltage levels over the course of the day as
demand begins to increase around 8 AM and peaks around 3 or 4 PM. Distribution
system characteristics can also contribute to chronically low voltage
situations. For example, customers at the end of a long line may be
subject to a permanent voltage drop due to line losses on top of the
utility voltage variations. |