1-2
General Information
BE1-951
Each current sensing circuit is low burden and isolated. Neutral (residual) and negative sequence current
magnitudes are derived from the three-phase currents. An optional independent ground current input is
available for direct measurement of the current in a transformer neutral, tertiary winding, or flux balancing
current transformer.
Contact Sensing Inputs
Four programmable contact sensing inputs (IN1, IN2, IN3, and IN4) with programmable signal conditioning
provide a binary logic interface to the protection and control system. Each input function and label is
programmable using BESTlogic. A user-meaningful label can be assigned to each input and to each state
(open and closed) for use in reporting functions.
Contact Outputs
Five programmable general purpose contact outputs (OUT1, OUT2, OUT3, OUT4, and OUT5) provide a
binary logic interface to the protection and control system. One programmable, fail-safe contact output
(OUTA) provides an alarm output. Each output function and label is programmable using BESTlogic. A
user-meaningful name can be assigned to each output and to each state (open and closed) for use in
reporting functions. Output logic can be overridden to open, close, or pulse each output contact for testing
or control purposes. All output contacts are trip rated.
Protection and Control Functions
Protection functions consist of Overcurrent, Voltage, Frequency, Breaker Reclosing, Fuse Loss, and Breaker
Failure protection and general purpose logic timers. Setting Groups and Virtual Control Switches make up
the control functions. The following paragraphs describe each protection and control function.
Directional Overcurrent Protection
Directional overcurrent protection is provided by six instantaneous overcurrent functions and four
time-overcurrent functions. Digital signal processing filters out unwanted harmonic components while
providing fast overcurrent response with limited transient overreach and overtravel.
Each instantaneous overcurrent function has a settable time delay. Phase elements include 50TP and
150TP. Neutral elements include 50TN and 150TN. Negative Sequence elements include 50TQ and 150TQ.
Inverse time-overcurrent functions are provided for phase, neutral, and negative sequence protection. A 51P
phase element, 51N and 151N neutral elements, and a 51Q negative sequence element are provided.
Time-overcurrent functions employ a dynamic integrating timing algorithm covering a range from pickup to
40 times pickup with selectable instantaneous or integrated reset characteristics. Time-overcurrent curves
conform to the IEEE PC37.112 document and include seven curves similar to Westinghouse/ABB CO
curves, five curves similar to GE IAC curves, a fixed time curve, and a user programmable curve. Phase
time-overcurrent functions can be voltage restrained or controlled for generator backup applications.
Each overcurrent element can be individually set for forward, reverse, or non-directional control.
Voltage Protection
One volts per hertz protective element provides overexcitation protection for a generator and/or transformer
(24).
One phase overvoltage and one phase undervoltage element provides over/undervoltage protection (27P,
59P). Phase overvoltage protection can be set for one of three, two of three, or three of three logic. When
a four-wire voltage transformer connection is used, overvoltage protection can be set for either phase-to-
phase voltage or phase-to-neutral voltage.
Two auxiliary overvoltage and one auxiliary undervoltage element provides over/undervoltage protection
(27X, 59X, 159X). Auxiliary voltage protection elements can be set to individually monitor the auxiliary
voltage fundamental, third harmonic, or phase 3V
0
voltages. Ground unbalance protection is provided when
the optional auxiliary voltage input is connected to a source of 3V
0
such as a broken delta VT.
