GE PQMII, Instruction Manual

Page: 95 / 216

CHAPTER 5: SETPOINTS
PQMII POWER QUALITY METER – INSTRUCTION MANUAL 5–11
• POWER DEMAND TYPE : Three real/reactive/apparent power demand calculation
methods are available: thermal exponential, block interval, and rolling interval (see the
Demand Calculation Methods
table below). The three phase real/reactive/apparent
power demand is calculated.
• POWER DEMAND TIME INTERVAL : Enter the time period over which the power
demand calculation is to be performed.
• ENERGY COST PER kWh : Enter the cost per kWh that is charged by the local utility.
• TARIFF PERIOD START TIME : Enter the start time for each of the three tariff period
calculations.
• TARIFF PERIOD COST PER kWh : Enter the cost per kWh for each of the three tariff
periods.
Table 5–2: Demand Calculation Methods
Method Description
Thermal
Exponential
This selection emulates the action of an analog peak-recording
thermal demand meter. The PQMII measures the average quantity
(RMS current, real power, reactive power, or apparent power) on each
phase every minute and assumes the circuit quantity remains at this
value until updated by the next measurement. It calculates the
“thermal demand equivalent” based on the following equation:
(EQ 5.1)
where:
d
= demand after applying input quantity for time
t
(in min.)
D
= input quantity (constant)
k
= 2.3 / thermal 90% response time
The graph above shows the thermal response characteristic for a
thermal 90% response time 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 will indicate 99% of the value).
Block Interval
This selection calculates a linear average of the quantity (RMS
current, real power, reactive power, or apparent power) over the
programmed demand
TIME INTERVAL
. Each new value of demand
becomes available at the end of each time interval.
Rolling Interval
This selection 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.
d t ( ) D 1 e
kt
–
–
( )
=
T i me ( m in)
0
20
40
60
80
100
0 3 6 9 12 15 18 21 24 27 30
Dema
nd
(%)