Hitachi Relion 670 Series Applications Manual page 349

1MRK506375-UEN Rev. N
neutral. Current distortion is limited at the point of common coupling PCC to control the harmonic
current from the utility to the consumer. Thereby, the voltage distortion must be limited in order to
prevent it from spreading to other facilities.
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.
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.
Maintaining high power quality in traction system is very complex. The presence of non-linear loads
reduces the capability of the existing harmonic mitigation techniques. However, it is essential to
minimize the issues like harmonics, voltage sags and flicker to protect sensitive equipment affected
by the aforementioned issues produced by traction systems.
Various practical conditions which have dynamic characteristics like the speed of locomotion, load
and line condition will make this problem even worse. Harmonic current increases the heat
dissipation due to hysteresis and eddy currents, which causes stress on insulation materials.
Harmonic current increases transmission loss and the voltage drops.
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%.
Current harmonic limits vary based on the short circuit strength of the corresponding system they are
injected into. Harmonic current limit defines the maximum amount of harmonic current that can be
inject into the utility system. The difference between THD and TDD is used to calculate the
harmonics level during light load conditions.
15.11.4 Setting guidelines
The recommended limits for total harmonic distortion and individual harmonic distortion are available
in the IEEE 519-2014 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.
15.11.4.1 Setting procedure on the IED
Parameters for CHMMHAN function are set via the local HMI or PCM600.
Common base IED values for primary current (IBase) is set in the global base values for settings
function GBASVAL.
GlobalBaseSel: To select GBASVAL function for reference of base values.
Railway application RER670
Application manual
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Section 15
Monitoring
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