5-104 L60 LINE PHASE COMPARISON SYSTEM – INSTRUCTION MANUALPRODUCT SETUP CHAPTER 5: SETTINGS5The relay measures current demand on each phase, and three-phase demand for real, reactive, and apparent power.Current and Power methods can be chosen separately for the convenience of the user. Settings are provided to allow theuser to emulate common electrical utility demand measuring techniques, for statistical or control purposes. If the CRNTDEMAND METHOD is set to "Block Interval" and the DEMAND TRIGGER is set to “Off,” Method 2 is used as follows. If DEMANDTRIGGER is assigned to any other FlexLogic operand, Method 2a is used as follows.The relay can be set to calculate demand by any of the following three methods.5.3.10.1 Calculation method 1: Thermal exponentialThis method emulates the action of an analog peak-recording thermal demand meter. The relay measures the quantity(RMS current, real power, reactive power, or apparent power) on each phase every second and assumes that the circuitquantity remains at this value until updated by the next measurement. It calculates the 'thermal demand equivalent'based on the following equation:Eq. 5-6whered = demand value after applying input quantity for time t (in minutes)D = input quantity (constant)k = 2.3 / thermal 90% response timeThe figure shows the 90% thermal response time characteristic of 15 minutes. A setpoint establishes the time to reach90% of a steady-state value, just as the response time of an analog instrument. A steady state value applied for twice theresponse time indicates 99% of the value.Figure 5-41: Thermal demand characteristic5.3.10.2 Calculation method 2: Block intervalThis method calculates a linear average of the quantity (RMS current, real power, reactive power, or apparent power) overthe programmed demand time interval, starting daily at 00:00:00 (that is, 12:00 am). The 1440 minutes per day is dividedinto the number of blocks as set by the programmed time interval. Each new value of demand becomes available at theend of each time interval.5.3.10.3 Calculation method 2a: Block interval (with start demand interval logic trigger)This method calculates a linear average of the quantity (RMS current, real power, reactive power, or apparent power) overthe interval between successive Start Demand Interval logic input pulses. Each new value of demand becomes available atthe end of each pulse. Assign a FlexLogic operand to the DEMAND TRIGGER setting to program the input for the newdemand interval pulses. DEMAND INTERVAL:15 MINRange: 5, 10, 15, 20, 30, 60 minutes DEMAND TRIGGER:OffRange: FlexLogic operandNote: for calculation using method 2a
