5.5 GROUPED ELEMENTS
These protection elements can be used for a variety of applications such as:
Undervoltage Protection: For voltage sensitive loads, such as induction motors, a drop in voltage increases the drawn
current which may cause dangerous overheating in the motor. The undervoltage protection feature can be used to either
cause a trip or generate an alarm when the voltage drops below a specified voltage setting for a specified time delay.
Permissive Functions: The undervoltage feature may be used to block the functioning of external devices by operating an
output relay when the voltage falls below the specified voltage setting. The undervoltage feature may also be used to block
the functioning of other elements through the block feature of those elements.
Source Transfer Schemes: In the event of an undervoltage, a transfer signal may be generated to transfer a load from its
normal source to a standby or emergency power source.
The undervoltage elements can be programmed to have a Definite Time delay characteristic. The Definite Time curve oper-
ates when the voltage drops below the pickup level for a specified period of time. The time delay is adjustable from 0 to
600.00 seconds in steps of 10 ms. The undervoltage elements can also be programmed to have an inverse time delay
characteristic. The undervoltage delay setting defines the family of curves shown below.
where: T = Operating Time
D = Undervoltage Delay Setting
( D = 0.00 operates instantaneously)
V = Secondary Voltage applied to the relay
= Pickup Level
At 0% of pickup, the operating time equals the
SETTING GROUP 1(8)
Figure 5–55: INVERSE TIME UNDERVOLTAGE CURVES
L90 Line Differential Relay
5.5.17 VOLTAGE ELEMENTS
% of V pickup
80 90 100 110
GE Power Management