Demand Calculation Methods; Thermal Exponential - GE Multilin F650 Instruction Manual

5 SETPOINTS
Function permission (Function): Enabling this setpoint allows to start the demand function.
Demand Method for Current values (CRNT Demand Method): Selection of the demand calculation method for current
values. Available methods are Thermal Exponential, Block interval, and Rolling Demand.
Demand Method for Power values (POWER Demand Method): Selection of the demand calculation method for power
values. Available methods are Thermal Exponential, Block interval, and Rolling Demand.
Demand Interval: Integration time, with a range of 5, 10, 15, 20, 30, 60 minutes. Measure integration is performed in the
period adjusted in the Demand Interval setpoint.
Demand Trigger: Operation mode selection for the Block Interval calculation method. This operation mode depends on
the Trigger Enabled setpoint. If trigger enabled is set as disabled, measure integration is made in the Demand Interval
period. IF trigger enabled is set as enabled, measure integration is made during the time interval between two consecutive
pulses of the input assigned to the demand, DEMAND TRIGGER INP, at Setpoint > Relay configuration > Protection
Elements
Snapshot Events: This setpoint enables or disables the snapshot event generation for the demand unit.

5.2.6.2 DEMAND CALCULATION METHODS

a) CALCULATION METHOD 1: THERMAL EXPONENTIAL
This method simulates the action of a peak demand thermal analog recorder. The relay measures the magnitude for each
phase (or three-phase, depending on the case) each second, and it assumes that the magnitude remains in that value until
the next update. It calculates the equivalent thermal demand based on the following equation:
Where:
DInput signal (constant).
d(t) Demand value after applying the input value during time t (in minutes)
K 2.3 / setpoint time d(t) reaches 90% of the signal entered in this time
If we assume that the input signal is monotonous increasing (each new value is higher than the previous value), with an
initial value of D different from zero, the previous equation becomes:
0,
Being D the demand value in the moment when the input signal starts to increase.
0
If the input signal decreases, time t restarts at 0 and the equation to be applied (cooling) will be:
GE Multilin
kt
–
d t ( ) ( )
D 1 e
= –
( )
D = V – D
S 0
kt
d t ( ) ( ) 1 e ( – )
= D – D – V –
0 0 S
F650 Digital Bay Controller
5.2 PRODUCT SETUP
5
5-13