Protective Relaying Principles and Applications
4th Edition Blackburn Solutions Manual
questions and answers 2024
Element - in an electromechanical relay, an element is part of a relay unit, such as an
electromagnet, or damping magnet, or an induction disc that performs a specific
function. In a microprocessor-based relay, an element can be thought of as a formula or
small program that mathematically emulates a particular electromechanical relay
function
Fault - a short circuit between phases or phase-to-ground
Hand Reset - a qualifying term applied to a really indicating that following an operation
the contacts must be reset manually to their original positions
Heel Piece - the portion of a magnetic circuit of a relay that is attached to the end of the
core remote from the armature
Hertz - a term for cycles per second, abbreviated HZ
Hinge, Armature - a pivot provided by a joint, spring or rod that secures the armature to
the remainder of the relay frame or heel-piece
Impedance - generally speaking, the term impedance can be applied to resistance
alone, reactance alone, or a combination of the two
Impedance Relay - is a voltage-restraining overcurrent relay; the torque produced by a
current element is balanced against the torque of a voltage element; the current
element produces pick-up torque, whereas the voltage element produces re-set torque
Instantaneous Relay - a relay which operates and resets without intentional delay
Inverse Time - a qualifying term applied to a relay indicating that its time of operation
decreases as the magnitude of the operating quantity increases
Lock Out - a feature found in automatic reclose schemes which prevents further
automatic closing after a certain chosen sequence, or an auxiliary relay used to prevent
closing of certain circuit breakers or switches for presumed permanent faults
, Magnetizing Inrush - when a transformer is first energized, a transient magnetizing or
exciting current may flow; peak inrush current of 8 to 10 times full load peaks is not
uncommon
Make-Before-Break Contacts - double throw contacts so arranged that the moving
contact establishes a new circuit before disrupting the old one
Maximum Torque Angle - same as Characteristic Angle
Memory Action - obtained by a design in which current flow in a voltage polarizing coil
does not cease immediately when the voltage is instantly reduced to zero; the stored
energy in the voltage circuit causes sinusoidal current to flow in the voltage coil for a
short time
MHO Unit - a unit that has a voltage restraining element that opposes a different
element; in other words, a voltage restrained directional relay
Microprocessor-Based Relay - a multifunctional protection device using digital
technology to simultaneously monitor inputs such as current, voltage, analog, and digital
signals while supplying a variety of relay functions such as close, trip, alarm outputs and
remote communications
Mutual Impedance - the mutual impedance between two circuits is the ratio of the
voltage drop induced in one of the circuits to the current in the other circuit which
induces it
Negative Sequence Components - three vectors equal in magnitude and displaced 120
apart and rotating in a sequence ACB
Normal Condition - de-energized condition of the relay
Operating Time - the time which elapses between the instant of application of a
characteristic quantity and the instant when the relay operates
Operating Time Characteristic - the curve, or points on a curve, defining relay
performance in terms of the time which elapses for a relay to operate for different values
of characteristic quantity (usually expressed in terms of the pick-up value)
Operating Value - the limiting value of the characteristic quantity at which the relay
operates
Overcurrent Relay - a relay that operates when the current through its coil reaches a
predetermined value
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