4–258 869 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUALPROTECTION CHAPTER 4: SETPOINTSFrequency Rate ofChange (81R)There is one Frequency Rate of Change protection element which can respond to rate ofchange of frequency with voltage, current and frequency supervision.The Rate of Change element may be set as an instantaneous element with no time delayor as a definite time delayed element. The rate of change element has the programmableminimum operating voltage and current thresholds to prevent undesired operation underspecific system conditions.The settings of this function are applied to each source to produce Pickup and Trip flags.The Frequency Rate of Change Pickup flag is asserted when the calculated frequency rateof change of the specified source is above the PKP value, the voltage and current areabove the MINIMUM levels, and the frequency is within a certain range. The FrequencyRate of Change Trip flag is asserted if the element stays picked up for the time defined bythe Pickup time delay. The element instantaneously drops from Pickup without operation, ifthe frequency rate of change drops below 96% of the Pickup value, before the time foroperation is reached.The minimum voltage and current thresholds select the minimum voltage and currentbelow which the element is blocked.The minimum and maximum frequencies set the operating frequency range out of whichthe element is blocked.Path: Setpoints > Protection > Group 1(6) > Frequency > Frequency Rate of Change 1(X)FUNCTIONRange: Disabled, Trip, Alarm, Latched Alarm, ConfigurableDefault: DisabledThe selection of the Trip, Alarm, Latched Alarm, or Configurable setting enables theelement.When the Trip function is selected and the element operates, output relay #1 “Trip” willoperate but the “ALARM” LED will not turn on.When the Alarm function is selected and the element operates, the “ALARM” LED willflash; it will self-reset, when the operating conditions are cleared.When the Latched Alarm function is selected, and the element operates, the “ALARM”LED will flash during the TOC operating condition, and will be steadily lit after theconditions are cleared. The “ALARM” LED can be cleared by issuing a Reset command.Output relay #1 “Trip” will not operate if the Alarm or Latched Alarm setting is selected.When the Configurable function is selected, neither the Trip output, nor the ALARM LEDwill turn on automatically. They must be configured using their own menus andFlexLogic operands.The selected output relays #3 to #7 will operate if the Trip, Latched Alarm, Alarm orConfigurable setting is selected and the element operatesTRENDRange: Decreasing, Increasing, Bi-directionalDefault: DecreasingThe setting allows configuring of the element to respond to increasing or decreasingfrequency, or to a frequency change in either direction.
