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GE UR Series Instruction Manual Page 103

Line differential relay.
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5 SETTINGS
The relay measures current demand on each phase, and three-phase demand for real, reactive, and apparent power. Cur-
rent and Power methods can be chosen separately for the convenience of the user. Settings are provided to allow the user
to emulate some 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 (see below).
DEMAND TRIGGER
The relay can be set to calculate demand by any of three methods as described below:
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 the circuit quan-
tity remains at this value until updated by the next measurement. It calculates the 'thermal demand equivalent' based on the
following equation:
–kt
d(t) = D(1 – e
)
d = demand value after applying input quantity for time t (in minutes)
D = input quantity (constant)
k = 2.3 / thermal 90% response time.
See the 90% thermal response time characteristic of 15 minutes in the figure above. 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 will indicate 99% of the value.
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 (i.e. 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.
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.
If no trigger is assigned in the
culating method #2. If a trigger is assigned, the maximum allowed time between 2 trigger signals is 60 minutes. If
NOTE
no trigger signal appears within 60 minutes, demand calculations are performed and available and the algorithm
resets and starts the new cycle of calculations. The minimum required time for trigger contact closure is 20 µs.
CALCULATION METHOD 3: ROLLING DEMAND
This method calculates a linear average of the quantity (RMS current, real power, reactive power, or apparent power) over
the programmed demand time interval, in the same way as Block Interval. The value is updated every minute and indicates
the demand over the time interval just preceding the time of update.
GE Power Management
DEMAND TRIGGER
100
80
60
40
20
0
0
3
6
9
12
Time (min)
Figure 5–2: THERMAL DEMAND CHARACTERISTIC
DEMAND TRIGGER
setting and the
DEMAND TRIGGER
L90 Line Differential Relay
is set to "Off", Method 2 is used (see below). If
15
18
21
24
27
30
setting to program the input for the new
CRNT DEMAND METHOD
5.2 PRODUCT SETUP
CRNT
is "Block Interval", use cal-
5-19
5

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L90

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