ABB Relion 670 Series Applications Manual page 275

1MRK 511 407-UUS Rev. J
Voltage harmonic distortion levels can vary drastically, depending on the configuration of system.
These voltage harmonics can damage the equipment as they are designed to operate for certain
range of voltage inaccuracy.
Moreover, in four-wire distribution systems (three-phase and neutral), the currents in the three
phases will return via the neutral conductor, a 120 degree phase shift between corresponding
phase currents that causes the currents to cancel out in the neutral, under balanced loading
conditions. When nonlinear loads are present, any 'Triplen' (3
currents does not cancel out. However, they will be added cumulatively in the neutral conductor,
which can carry up to 173% of phase current at a frequency of predominately 180 Hz (3
harmonic).
In case of electric traction systems, it generates various power quality problems that have an
important impact on its distribution network. DC traction loads, fed through AC/DC rectifiers,
generates non-linear voltages and currents on the AC system, that will result in harmonic voltage
distortion of the power supply system. Traction power supply system creates power quality
problems to the corresponding grid, which can cause:
• Poor power quality
• Increase in operational cost due to less productivity
• Damage to sensitive equipment in nearby facilities.
In general, harmonics can cause reduced equipment life if a system is designed without
considering the harmonics and if the equipment is not designed to withstand harmonics. Hence, it
is important to measure and monitor harmonics in power systems. Harmonic voltage distortions
on 161 kV power system and above is limited to 1.5% of total harmonic distortion (THD), in with
each individual harmonic is limited to 1.0%.
16.11.3 Setting guidelines
The recommended limits for total harmonic distortion and individual harmonic distortion are
available in the IEEE 519 standard. The limits are based on measurements which are done at the
point of common coupling. It should not be applied to either individual pieces of equipment or at
locations within a user's facility. In most cases, harmonic voltages and currents at these locations
could be found to be significantly beyond recommended limits at the PCC due to the lack of
diversity, cancellation, and other phenomena that tend to reduce the combined effects of multiple
harmonic sources to levels below their algebraic summation.
16.11.3.1 Setting procedure on the IED
Parameters for VHMMHAI(VTHD) function are set via the local HMI or PCM600.
Common base IED values for primary voltage (
function GBASVAL.
GlobalBaseSel : It is used to select GBASVAL function for reference of base values.
WrnLimitTHD : It defines the warning limit for the calculated total harmonic distortion.
Phasor measurement unit RES670
Application manual
Minimum and maximum voltage limit is set as 5% of the
respectively. If the voltage is outside the above range, the calculation of total
harmonic distortion, individual harmonic distortion and crest factor are blocked
and outputs are provided as zero.
© Copyright 2017 Hitachi Power Grids. All rights reserved
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Section 16
Monitoring
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