Page 19 - Industrial Technology October/ November 2020 issue

Scope of G5-5 with variable speed drives below 28.9 A at the fifth
G5-5 is applicable to both new sites as well as harmonic for a 400 V connection would pass
modification to existing sites. G5-5 also includes new assessment, as would an 11 kV common coupling below
levels for planning and compatibility of harmonic 3.9 A at the fifth harmonic. Instead G5-5 divides the
distortion. The planning level represents a site’s voltage assessment over three stages with each divided
probability of disturbance within the operator’s electrical into subsequent levels.
network and the compatibility level is the point where An additional aspect of this now includes the
equipment failures can occur. combination of variable speed drive features, which were
According to G5-5, the network operator specifies a not previously taken into account. New to G5-5, the
level of voltage distortion at which connected equipment combination of drives with active front end (AFE) or
to the supply network is likely to be affected, based on harmonic filters and 6 or 12 pulse systems correspond to
percentage of total harmonic distortion (THD). G5-5 also different stages of assessment. Mitsubishi Electric and
includes a headroom calculation to determine additional PQM campaigned to ensure that drives without AFE but
distortion which could be added to the supply above the with active harmonic filters could be recognised as
background level but below the maximum permitted compliant to a G5-5 site-standard, providing that they
planning levels. achieve the same harmonic output as an equivalent drive
The amount of distortion already generated by other with AFE. Without this amendment, end users with
users on the network impacts the headroom value that 6 pulse drives above 22 kVA would have faced a
the operator will allow. significant challenge to achieve compliance.
Some allowance has also been made for medium
sized sites with their own transformer compared to the Impacts to industry
previous G5-4 recommendations. Some of the planning The implications of G5-5 will span all sectors,
levels above 400 V but below 33 kV have increased. particularly the water industry with many sites across the
There are no explicit current distortion levels set within country using high power drives and motors. While this
the document and the level of harmonic current sector is well-versed in harmonic compliance, end users
permitted is dependent on the calculated harmonic will now have to think more carefully about harmonic
voltage distortion for a supply and Fault Level. assessment. Increasing the volume of equipment and
drawing greater power means that considerations over
Amendments to the previous regulation headroom will have to take place as part of a harmonic
With G5-5, voltage distortion levels up to 2.5 kHz (50th survey and design. G5-5 also raises the bar for variable
harmonic) are assessed and equipment that generate speed drive manufacturers who will have to supply more
higher orders are evaluated up to 5 kHz (100th information on the harmonics they generate based on
harmonic), though in the latter case this is highly impedance and reactance in order to create an effective
unlikely to apply to most variable speed drives. A further model to help consultants and end users achieve
change for G5-5 also means that equipment that compliance.
generates a short burst of harmonic distortion such as All this may seem rather daunting but help is at hand
soft starters are now taken into account, with an and Mitsubishi Electric can provide a consultancy service
allowance of 314 kVA soft start total connected load for end users and system integrators to achieve G5-5
permitted for 400 V connections. compliance, providing modelling as well as the design
A key point is that individual items of equipment are and installation of active harmonic filtering to meet the
not assessed for compliance and that G5-5 is a site prescribed harmonic level. While the new
standard rather than a product standard. A significant recommendations provide a greater challenge to achieve,
change in practical terms is how the site standard is G5-5 is helping to create a better network for all
assessed and G5-5 is significantly more in depth than its stakeholders concerned.
predecessor. For example, with G5-4, in general a site gb3a.mitsubishielectric.com

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