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2.7 Harmonic Measurement Connections
Harmonic measurements can be made only on signals that are present on the
instrument inputs . In some of the 3-wire configurations, there may be one of inputs
missing, so the user might not get the appropriate readings.
4-wire Configurations
In 4-wire configurations, no special considerations are necessary. All harmonic
quantities will be measured correctly. In the '4Ln3', '4LL3', '3Ln3' or '3LL3' wiring
modes, harmonic voltages will represent line-to-neutral voltages. In '3Ln3' or '3LL3'
wiring modes, harmonic voltage will be measured only for two phases and the total
power harmonics will be calculated inaccurately.
3-wire Direct Connection
In a 3-wire Direct Connection, harmonic voltages will represent the three phase line-
to-neutral voltages that appear on the instrument input transformers. If the system
load is not symmetrical, the voltage readings will have no meaning. In the case of the
symmetrical load, harmonic voltages will not reflect all the multiples of order 3
harmonic.
Using 2 CTs, harmonic currents will be measured only for two phases and the total
power harmonics will be calculated inaccurately.
3-wire Open Delta Connection
Readings for harmonic voltages will represent two line-to-line voltages L12 and
L23. Current harmonics will be taken using 2 or 3 CTs, according to the wiring
configuration.
Total harmonic powers will be measured properly using two input line-to-line
voltages and two currents.
Installation
17
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