GE L60 Instructions Manual page 327

Line phase comparison system
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CHAPTER 5: SETTINGS
The 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 the
user to emulate common electrical utility demand measuring techniques, for statistical or control purposes. If the
is set to "Block Interval" and the
DEMAND METHOD
is assigned to any other FlexLogic operand, Method 2a is used as follows.
TRIGGER
The relay can be set to calculate demand by any of the following three methods.
5.3.11.1 Calculation method 1: Thermal exponential
This 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 circuit
quantity remains at this value until updated by the next measurement. It calculates the 'thermal demand equivalent'
based on the following equation:
where
d = demand value after applying input quantity for time t (in minutes)
D = input quantity (constant)
k = 2.3 / thermal 90% response time
The figure shows the 90% thermal response time characteristic of 15 minutes. A setpoint establishes the time to reach
90% of a steady-state value, just as the response time of an analog instrument. A steady state value applied for twice the
response time indicates 99% of the value.
5.3.11.2 Calculation method 2: Block interval
This method calculates a linear average of the quantity (RMS current, real power, reactive power, or apparent power) over
the programmed demand time interval, starting daily at 00:00:00 (that is, 12:00 am). The 1440 minutes per day is divided
into the number of blocks as set by the programmed time interval. Each new value of demand becomes available at the
end of each time interval.
5.3.11.3 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) over
the interval between successive Start Demand Interval logic input pulses. Each new value of demand becomes available at
the end of each pulse. Assign a FlexLogic operand to the
demand interval pulses.
L60 LINE PHASE COMPARISON SYSTEM – INSTRUCTION MANUAL
DEMAND INTERVAL:
15 MIN
DEMAND TRIGGER:
Off
DEMAND TRIGGER
Figure 5-50: Thermal demand characteristic
DEMAND TRIGGER
Range: 5, 10, 15, 20, 30, 60 minutes
Range: FlexLogic operand
Note: for calculation using method 2a
is set to "Off," Method 2 is used as follows. If
setting to program the input for the new
PRODUCT SETUP
CRNT
DEMAND
Eq. 5-6
5
5-119

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