SATEC EM920 Operation Manual - Manual (Page 76)

Chapter 5 Configuring the EM920
General Meter Setup
76 EM920 Power Quality and Revenue Meter
Power Calculation Modes
The power calculation mode option allows you to change the
method for calculating reactive and apparent powers in
presence of high harmonics. The options work as follows:
1. When the reactive power calculation mode is selected,
active and reactive powers are directly measured and
apparent power is calculated as:
2 2 Q P S + =
2. This mode is recommended for electrical networks with
low harmonic distortion, commonly with THD < 5% for
volts, and THD < 10% for currents. In networks with
high harmonics, the following method is preferable.
3. When the non-active power calculation mode is
selected, active power is measured directly, apparent
power is taken as product S = V x I, where V and I are
the RMS volts and amps, and reactive power (called
non-active power) is calculated as:
2 2 P S N − =
Tariff Control
The EM920 provides three options for switching tariff rates:
• automatic via a programmable TOU calendar schedule
(see Configuring the Daily Tariff Schedule for
information on configuring tariff change points)
• external via communications by writing a tariff number
to the meter tariff register (see the EM920 Modbus
Reference Guide for information on the active tariff
register location)
• external via digital inputs by providing a tariff code on
the meter tariff inputs
If a digital input option is selected, you can use 1 to 3
consequent digital inputs as tariff inputs. The following table
shows the number of inputs required depending on the
maximum number of used tariff rates.
Number of tariffs Number of tariff inputs
2 1
3 2
4 2
5 3
6 3
7 3
8 3
The following table shows code combinations that should be
provided on the tariff inputs to indicate an active tariff rate.