ABB Relion 670 Series Applications Manual page 407

1MRK 505 370-UUS Rev. K
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
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
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.
14.10.4 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.
14.10.4.1 Setting procedure on the IED
Parameters for CHMMHAI(ITHD) 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: It is used to select GBASVAL function for reference of base values.
MaxLoadCurr: Maximum demand load current at PCC for total demand distortion calculation. When the
point of common coupling (PCC) is considered at the service entrance or utility metering point, IEEE
519-2014 standard recommends that the maximum demand load current must be calculated as the
average current of the maximum demand for the preceding 12 months.
WrnLimitTDD: It defines the warning limit for the calculated total demand distortion. The difference
between THD and TDD is helpful to find the harmonics level during light load conditions. According to
standard IEEE 519-2014, harmonic current distortions on a power system with short circuit strength less
than 20 is limited to 5% total demand distortion (TDD).
tDelayAlmTDD: It defines the alarm time limit for the calculated total demand distortion which is applied
after the warning signal pickup and depends on its sustainability.
Busbar protection REB670
Application manual
rd th
, 6 , and 9
Minimum and maximum current limit is set as 5% of the IB and 300.0% of IB
respectively. If the current is outside the above range, the calculation of total harmonic
distortion, individual harmonic distortion, total demand distortion and crest factor are
blocked, and outputs are provided as zero.
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th
) harmonics in the phase currents does not cancel out.
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harmonic).
Section 14
Monitoring
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