of a blackout. 27 is also used to initiate voltage correction measures, such as insertion of
shunt capacitor banks, to compensate for a reactive load and thereby to increase the
voltage.
27 can be used to disconnect from the network devices, such as electric motors, which are
damaged when subjected to service under low voltage conditions. 27 deals with low
voltage conditions at power system frequency. Low voltage conditions can be caused by:
• Malfunctioning of a voltage regulator or incorrect settings under manual control
(symmetrical voltage decrease)
• Overload (symmetrical voltage decrease)
• Short circuits, often as phase-to-ground faults (unsymmetrical voltage increase).
27 prevents sensitive equipment from running under conditions that could cause
overheating and thus shorten their life time expectancy. In many cases, 27 is a useful
function in circuits for local or remote automation processes in the power system.
4.5.2.7 Signals
Table 523: 27 Input signals
Name Type Default Description
V_A_AB SIGNAL 0 Phase to ground voltage A or phase to phase voltage AB
V_B_BC SIGNAL 0 Phase to ground voltage B or phase to phase voltage BC
V_C_CA SIGNAL 0 Phase to ground voltage C or phase to phase voltage
CA
BLOCK BOOLEAN 0=False Block signal for activating the blocking mode
Table 524: 27 Output signals
Name
Type Description
TRIP BOOLEAN Trip
PICKUP BOOLEAN Pickup
Section 4 1MAC059074-MB A
Protection functions
624 615 series ANSI
Technical Manual
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