Engineering Recommendation G5 Issue 5

An overview of the latest standard for harmonic voltage

distortions and the key updates.

The latest Engineering Recommendation (EREC) G5 issue 5 comes into effect for connection

offers issued from 17th June 2020. This latest revision, published by Energy Networks

Association (ENA), provides new harmonic planning levels and assessment processes for the

connection of harmonic sources and/or resonant plant to the network.

It is well recognised that harmonic voltages have the potential to interfere with communications, increase losses and cause damage to rotating plant and capacitors. Due to this, it is of upmost importance to ensure that the connection of new harmonic sources does not lead to excessive network harmonic levels. EREC G5 Issue 5 (G5/5) exists to define the assessment criteria, and subsequent harmonic limits, for the connection of harmonic generating loads. This document will outline the key updates of G5/5 compared to the previous issue G5/4. Revised Harmonic Limits The new issue brings about brand new harmonic planning and compatibility levels that were taken from the higher of those in the international standards or those in G5/4. Furthermore, the

voltage ranges have been revised to better match the GB system voltages.

Nominal Voltage (kV) THDv (%) ≤ 0.4 5

0.4 < and ≤ 25 4.5 25 < and ≤ 66 3.7

66 < and ≤ 230 3 > 230 3

Figure 1 – New Voltage Ranges and THD Limits

The above table shows the new voltage ranges and subsequent Total Harmonic Distortion (THD) voltage limits. As a straight comparison to those in G5/4, voltage ranges between 6.6kV and 66kV have a greater THD allowance, with the other voltages allowance remaining the same.

Extended Frequency Range In G5/4 harmonic compliance was considered up to the 50th order (2.5kHz), G5/5 has extended this up to the 100th order (5kHz). Revised Interharmonic Limits G5/5 includes revised limits for interharmonics based on IEC 61000-4-30 and IEC 61000-4-7.

Voltage ≤ 1kV

Voltage > 1kV

All voltage levels

Frequency (Hz) ≤ 95 ≤ 90 110-2490

2510-4990

Compatibility level

(% h=1)

IEC 61000-

2-2

0.2 0.5 0.3

Planning level (% h=1)

70.7% of

above

0.15 0.36 0.22

Figure 2 - G5/5 Interharmonic limits

The above table shows the new Interharmonic limits. The latest issue also gives a clear definition for the measurement of interharmonics. Limits for Voltage Notches Another change is for the limits associated with voltage notching. Voltage notching is caused by rectifier commutation, when two phases of the supply are effectively short circuited. Equipment that results in notching may only be connected if the PCC harmonic levels are compliant with G5/5, but it then must comply with the notching limits: - The notch depth (d) shall not exceed 15% of the

peak of the nominal fundamental voltage.

- The peak amplitude of oscillations due to commutation at the start and at the end of the notch shall not exceed 10% of the peak of the nominal fundamental voltage.

- The notch depth duration shall meet the

requirements of:

𝑡 ≤4032𝑑

Figure 3 - Depiction of voltage notching

Changes to stage 1, 2 and 3 assessment process In the new revision stage 1 assessments have been completely rewritten. The main aim of this was to make the process more understandable for those with limited experience in applying the harmonic standard. The stage 2 process has been made more systematic and now includes a defined assessment process flow as shown below in Figure 4.

Figure 4 - Stage 2 Assessment Flow

Finally, the stage 3 assessment now includes an appointment of harmonic headroom to define the limitations on new connections.

In Summary The new G5/5 standard provides clearer and more defined recommendations and assessment methods for the connection of harmonic generating loads. Stage 1 and 2 assessments feature similar limiting values, with some voltage levels benefiting from higher THD and voltage distortion allowances. When it comes to stage 3, connections must now comply with allocated headroom based on plant voltage level and power output – this could mean smaller harmonic allowances for some sites versus the allowance within G5/4. Enspec Power LTD. 6 Waterside Court, St Helens Technology Campus, Merseyside, WA9 1UA. www.enspecpower.com 01744 610945

We reserve the right to make technical changes or modify the contents of this document without prior notice. Enspec Power do not accept any responsibility whatsoever for potential errors or possible lack of information in this document.

We reserve all rights in this document and in the subject matter and illustrations contained therein. Any reproduction, disclosure to third parties or utilization of its contents – in whole or in parts – is forbidden without prior written consent of Enspec Power.