4-30
Protection and Control
BE1-951
Figure 4-16. Under/Overvoltage Element
Time delay settings entered in cycles are converted to seconds or milliseconds (per the nominal frequency
setting stored in EEPROM) before being stored. See Section 3,
Input and Output Functions, Voltage
Measurement Functions for more information about this setting. If the nominal frequency setting is being
changed from the default (60 hertz) and time delay settings are being set in cycles, the frequency setting
should be entered and saved before making any time delay settings changes.
27X/59X/159X Auxiliary Under/Over Voltage Protection
Figure 4-16 illustrates the inputs and outputs of the auxiliary under/overvoltage elements. Element operation
is described in the following paragraphs.
The auxiliary elements have two outputs: 27X/59X/159XPU (pickup) and 27X/59X/159XT (trip). When the
monitored voltage increases above the pickup setting, the pickup output becomes TRUE and the element
starts timing toward a trip. The trip output becomes TRUE when the element timer times out.
The Block (BLK) input is used to disable protection. A BESTlogic expression defines how the BLK input
functions. When this expression is TRUE, the element is disabled by forcing the outputs to logic 0 and
resetting the timer. This feature functions in a similar way to the torque control contact of an
electromechanical relay.
The 27X, 59X, and the 159X elements are enabled or disabled by the Mode input. Four modes are available.
Selecting Mode 0 disables protection. Mode 1, 2, or 3 enables the element, as described in this section
under
BESTlogic Settings for the Auxiliary Under/Overvoltage Element.
The pickup setting determines the voltage pickup level of the element. The time delay setting controls how
long it takes for the trip output to become TRUE after the pickup output becomes TRUE. When the monitored
voltage increases above the pickup threshold, the pickup output becomes TRUE and the timer starts. If the
voltage remains above the pickup threshold for the duration of the time delay setting, the trip output becomes
TRUE. If the voltage decreases below the 59X/159X dropout ratio of 98 percent, or increases above the 27X
dropout ratio of 100%, the timer is reset to zero.
If the 60FL element trip logic is true, and V block is enabled for 3VO blocking (N), the 27X/59X/159X
functions will be blocked if they are set to mode 2. For more information on the 60FL function, see the
paragraphs later in this section.
If the target is enabled for the 59X/159X element, the target reporting function will record a target when the
trip output is TRUE and the fault recording function trip logic expression is TRUE. See Section 6,
Reporting
and Alarm Functions, Fault Reporting Functions for more information about target reporting.The overcurrent
elements have adaptable targets. If one is set for directional control, it will report a 67 target. If one is set
for non-directional control it will report a 59 target.
BESTlogic Settings for the auxiliary Under/Overvoltage Elements
Logic settings for the 27X/59X/159X function are made using the SL-27X (settings logic–undervoltage)
command or the SL-59X and SL159X (settings logic–overvoltage) command. The settings of these
commands determine whether the elements are enabled or disabled. The SL command also provides
