GE B30 Instruction Manual page 301

5 SETTINGS 5.6 GROUPED ELEMENTS
In this scheme, the normal voltage level halts the differential element. An actual bus fault operates the undervoltage ele-
ment, thereby permitting the differential element to operate. This can be applied for bus configurations of up to five feeders
with the voltage signal available. If applied, use the undervoltage function to supervise the main differential output with an
AND gate in the FlexLogic equation before driving the output contact.
Using the drop-out undervoltage operand as the Block input to the differential element is not recommended. The differential
element includes the saturation detector that responds to certain time relationships between the differential and restraining
currents, and therefore, it must be operational all the time in order to function properly.
This element may be used to give a desired time-delay operating characteristic versus the applied fundamental voltage
(phase-to-ground or phase-to-phase for wye VT connection, or phase-to-phase for delta VT connection) or as a definite
time element. The element resets instantaneously if the applied voltage exceeds the dropout voltage. The delay setting
selects the minimum operating time of the phase undervoltage. The minimum voltage setting selects the operating voltage
below which the element is blocked (a setting of "0" will allow a dead source to be considered a fault condition).
5
Figure 5–66: PHASE UNDERVOLTAGE1 SCHEME LOGIC
GE Multilin B30 Bus Differential System 5-167