# Demand - GE L90 Instruction Manual

L90 line current differential system ur series.

5.2 PRODUCT SETUP
PATH: SETTINGS
PRODUCT SETUP

## DEMAND

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
5
following equation:
where: d = demand value after applying input quantity for time t (in minutes)
D = input quantity (constant), and k = 2.3 / thermal 90% response time.
The 90% thermal response time characteristic of 15 minutes is illustrated below. A setpoint establishes the time to reach
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.
5-42
DEMAND
CRNT DEMAND METHOD:
Thermal Exponential
POWER DEMAND METHOD:
MESSAGE
Thermal Exponential
DEMAND INTERVAL:
MESSAGE
15 MIN
DEMAND TRIGGER:
MESSAGE
Off
d t ( )
Figure 5–3: THERMAL DEMAND CHARACTERISTIC
L90 Line Current Differential System
Range: Thermal Exponential, Block Interval,
Rolling Demand
Range: Thermal Exponential, Block Interval,
Rolling Demand
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 (see below). If
DEMAND TRIGGER
kt
(
)
=
D 1 e
Time (minutes)
setting to program the input for the new
DEMAND TRIGGER
5 SETTINGS
5.2.10 DEMAND
(EQ 5.6)
842787A1.CDR
GE Multilin
CRNT  