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G5/5 regulations bring important changes for VSD installations

G5/5 regulations bring important changes for VSD installations

With the exception of the light bulb, virtually every electronic device will generate harmonics of some description. And when we consider non-linear loads such as variable speed drives, the harmonics they generate can be enough to disrupt the operation of other devices connected to the supply.

Recognising that there are increasing numbers of non-linear loads looking to be connected, the regulations governing their connection have been updated, with Engineering Recommendation (EREC) G5/5 superseding G5/4 as of June this year.

Wayne Turtill, product manager for variable speed drives, servos and low voltage at Mitsubishi Electric, says: “G5/5 is applicable for all new users and supply applications and modifications. The network operator (NO) is responsible for the overall coordination of the disturbance levels on its network and for assessing the impact of the new user’s relevant equipment. The user is responsible for complying with the conditions the NO places on them to comply with this engineering recommendation.”

G5/5 considers voltage distortion levels of up 2.5kHz (the 50th harmonic) as standard, while equipment generating high harmonic orders or ‘interharmonics’ may require an assessment up to 5kHz (the 100th harmonic). For VSD users, Turtill notes: “Off-the-shelf VSD are very unlikely to cause interharmonic issues.”

He adds: “G5/5 also sees the NO specifying a level of voltage distortion at which equipment connected to the supply is likely to be affected. If you have 8% or more voltage distortion at 400V, your equipment is more likely to fail.” There are no explicit current distortion levels set within the document. The level of harmonic current permitted is dependent on the calculated voltage distortion for a supply voltage and fault level.

Along with variable speed drives, the changes in G5/5 mean it now considers soft starters as well. “G5/4 did not, so in theory you could have added any number of soft starters to the system,” comments Turtill. “In G5/5 soft starters have to be included in the calculation.”

The assessment process has also been updated, maintaining the three-stage approach of G5/4 but breaking these stages down further. And Turtill comments: “You have to do your assessment calculations based on the technology you are using. Equipment up to 16A per phase and compliant with BS EN 61000-3-2 can be added freely, but does add to total loading.”

Stage 1 assessments are still reserved for LV connections and are generally only suitable for small loads. Stage 2 considers connection of systems greater than LV but less than 33kV, or equipment exceeded in the Stage 1 assessment or where the limits cannot be met. Turtill notes: “Measurement of the background distortion is required for existing sites.”

There may be a need for a Stage 3 assessment or calculation if the values exceed the specified limits. Failure at this stage requires mitigation and/or a higher PCC. Where any proposed equipment could affect the network with voltage distortion greater than planning levels, the NO can refuse connection until a solution is agreed. “You have to remember that the network operator is both judge and jury, and their decision is final,” comments Turtill. “They don’t have to grant you a connection.”

He stresses that Mitsubishi Electric is there to help. “Mitsubishi Electric can offer full harmonic surveys that benchmark harmonic content, provide information on where and when energy is being used, and a seven day survey compliant with G5/5 using compliant metering,” he says. “And we can offer the recommendations if any mitigation is required and identify potential energy savings.

“Once we know your issues, we can offer products to help mitigate the problem. It may be as simple as fitting a choke to your non-linear load. This can as much as halve the generated distortion from an inverter and is a very cost-effective solution.

“If you need something larger, we can escalate the solution to fit an active filtration system, not only mitigating new loads but also cleaning up potential issues that are already impacting the site.”

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