Network Protection in a changing system

16 September 2025, by Volker Leitloff, Chair of SC B5

Introduction

The increasing number of Renewable Energy Resources (RES), and other installations, like energy storage, connected via converters, has given raise to concerns about the performance of the different protection and automation functions. Installations connected to the electric network with power electronic based converters are also known as Inverter Based Resources (IBR).

Initially, IBR consisted mainly in RES connected to the distribution network, either as distributed energy sources on normal feeders also supplying conventional loads, or on dedicated feeders for bigger installations. IBR can nowadays be found on all voltage levels of the network, including on transmission level, with installations ranging up to several hundreds of MW.

Impact of changing network on protection

The impact of IBR on network protection is a hot topic and numerous publications have analysed this impact and investigated possible improvements or workarounds for the identified issues. The most impacted protection functions are the distance protections, mainly used on transmission level and the overcurrent protections, mainly used on distribution level. The identified issues can increase the risk of false or non-selective tripping or, on the contrary, delayed tripping or fail-to-trip. They are related to the inherent characteristics of inverters including

low contribution to short circuit current;
low or no contribution to inertia, limited to control algorithms of the converter, if no stored energy resource is used;
heterogenous behaviour for negative and zero sequence components. This is aggravated by the reaction delay of the converter control. Even if the control provides sequence components under steady state conditions, an inevitable delay of several tens of milliseconds to adjust under transient conditions is observed. This is longer than the expected reaction time of most instantaneous protections;
lacking interoperability with existing voltage control and reactive power management algorithms on distribution and transmission level. In principle, these algorithms are based on the assumption of synchronous generators;
high level of injected harmonics, potentially up to high harmonic ranges. In addition to deterioration of the power quality seen by the users, this also can put considerable thermal constraints on HV equipment, lines and cables;
implementation of phase-locked loop frequency estimation algorithms without sufficient fault ride through capacity in the converter control, potentially resulting in serious frequency excursions of the converter under constraint network conditions;
specific and manufacturer dependent transient behaviour different from that of synchronous machines.

In some papers, the possibility to limit the impact on the network protection by enforcing adequate requirements for the connecting converters has been discussed. Many papers compare the behaviour of a given protection function between classical networks and networks with a high penetration of RES. In this context, the correct modelling and simulations of converters and their control algorithms presents a major difficulty. In most cases, this model is not available and/or cannot be validated for the different simulation scenarios.

Mitigation and developments

Some experts have conducted a high-level analysis. The most pragmatic approach proposed is to modify (i.e. often simplify) protection functions in order to make them independent of the source characteristics. In general, transient based protections (Travelling Waves) and, with some limitations, differential protections are protection functions which are not impacted at all by IBR.

The general recommendations are:

to only use known electrotechnical properties of the lines and cables which are independent of the IBR,
not to use assumptions about IBR behaviour, which is not standardised and depends on the manufacturer,
to increase knowledge and consciousness for all stakeholders within utilities, regulators and IBR operators about the constraints and impacts on network protection,
to take advantage of algorithms which can be hosted by digital protection IED in order to overcome limitations of protection functions stemming from the electromechanical era.

No specific requirements related to protections are normally included in the IBR connection specifications. The general philosophy is that the protections have to adapt to the network. This approach has been challenged for the connection of IBR, but it is not likely that this situation changes in the foreseeable future, given the number of deployed systems, the difficulty to obtain consensus for requirements and the lacking acceptability to increase costs or decrease performance of IBR due to protection constraints.

Attempts to improve the situation by introducing cost neutral requirements, such as standardised behaviour under transient conditions and standardised control for negative and zero sequence components are being undertaken, but they will not change the situation in a close future for similar reasons.

The choice of protection functions which are not or only slightly affected by the issues related to IBR seems thus the most sensible approach for utilities, as mentioned above.

For the same root causes, issues with recloser function, power swing blocking, islanding detection or frequency-based algorithms in networks with high IBR penetration have been reported.

Study Committee B5 activity

The impact of IBR on network protections was also the main subject of many recent conference sessions, including

Preferential Subject (PS) 2 of SC B5 in the CIGRE Paris Session in 2022: Addressing protection related challenges in network with low-inertia and low fault-current levels
PS 1 of the CIGRE symposium in Trondheim in 2025: Integration of renewable energy resources to the grid. Several papers in the B5 track discussed impacts on network protection and automation, and there were also other papers, namely in the C4 track, covering this issue.
Several papers discussed this subject under the PS 3 in the recent SC B5 symposium 2025 in Osaka: “Sharing of best practices on revised principles enabled by modern protection IEDs”

The selected PS for SC B5 in the Paris session 2026 and the B5 colloquium in 2027 will also cover this subject.

In addition to this several B5 working groups are active in this field, including

WG B5/ C4.61 “Impact of Low Inertia Network on Protection and Control”
WG B5.65 “Enhancing Protection System Performance by Optimizing the Response of Inverter Based Resources”
WG B5.78 “New requirements of network protection and control for renewable energy integration”
WG B5/C4.79 “IBR Protection Roadmap”

There are also already Technical Brochures from SC B5 available which are discussing aspects related to the subject: