CHAPTER 5: SETTINGS GROUPED ELEMENTSD30 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL 5-2535These 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 thedrawn current, which can cause dangerous overheating in the motor. The undervoltage protection feature can beused to either cause a trip or generate an alarm when the voltage drops below a specified voltage setting for aspecified time delay.• Permissive functions — The undervoltage feature can be used to block the functioning of external devices byoperating an output relay when the voltage falls below the specified voltage setting. The undervoltage feature canalso 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 can be generated to transfer a loadfrom 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 curveoperates when the voltage drops below the pickup level for a specified period of time. The time delay is adjustable from 0to 600.00 seconds in steps of 0.01. The undervoltage elements can also be programmed to have an inverse time delaycharacteristic.The undervoltage delay setting defines the family of curves shown as follows.Eq. 5-23whereT = operating timeD = undervoltage delay setting (D = 0.00 operates instantaneously)V = secondary voltage applied to the relayVpickup = pickup levelFigure 5-141: Inverse time undervoltage curvesAt 0% of pickup, the operating time equals the PHASE UNDERVOLTAGE DELAY setting. AUXILIARY UV1See page 5-257 AUXILIARY UV3 AUXILIARY OV1See page 5-258
