UFC 3 -520-01
June 10, 2002
Definition and Function
AC Circuit Breaker is a device that is used to close and interrupt an ac
power circuit under normal conditions or to interrupt this circuit under fault
or emergency conditions.
excitation to build up during starting or that functions when the machine
voltage has built up to given value.
High-Speed DC Circuit Breaker is a circuit breaker that starts to reduce the
current in the main circuit in 0.01 second or less, a fter the occurrence of
the dc overcurrent or the excessive rate of current rise.
Power Factor Relay is a device that operates when the power factor in an
ac circuit becomes above or below a predetermined value.
Field Application Relay is a device that automatically controls the
application of the field excitation to an ac motor at some predetermined
point in the slip cycle.
Short-Circuiting or Grounding Device is a power or stored energy operated
device that functions to short-circuit or to ground a circuit in response to
automatic or manual means.
Overvoltage Relay is a device that functions on a given value of
Voltage Balance Relay is a device that operates on a given difference in
voltage between two circuits.
Current Balance Relay is a device that operates on a given difference in
current input or output of two circuits.
Time-Delay Stopping, or Opening, Relay is a time-delay device that serves
in conjunction with the device that initiates the shutdown, stopping, or
opening operation in an automatic sequence.
Ground Protective Relay is a device that functions on failure of the
insulation of a machine, transformer or of other apparatus to ground, or on
flashover of a dc machine to ground. This function is assigne d only to a
relay that detects the flow of current from the frame of a machine or
enclosing case or structure of a piece of apparatus to ground, or detects a
ground on a normally ungrounded winding or circuit. It is not applied to a
device connected in the secondary circuit or secondary neutral of a CT, or
CTs, connected in the power circuit of a normally grounded system.
AC Directional Overcurrent Relay is a device that functions on a desired
value of ac overcurrent flowing in a predetermined direction.