GSR036 Security and Quality of Supply Standard (SQSS) System Access Reform Authority Decision
Outcome of proposed changes to the National Electricity Transmission System Security and Quality of Supply Standard (SQSS), to ease upper operational pre and post fault voltage limits for the 200 kV to 300 kV network.
The Authority approves the proposed changes to the SQSS.
Start date
10 working days after the Authority decision
Code modification description
The code modification is the first change to the SQSS stemming from the System Access Reform programme and addresses the voltage limits that apply to operational timescales on the 200 kV to 300 kV transmission network. Section 6 of the SQSS defines the upper voltage limit applicable to the 275 kV network as +9%. This limit was reduced from +10% to +9% in 2017 following the Fundamental SQSS Review and was then extended to the wider 200 kV to 300 kV voltage range. This change was informed by asset standards in place at the time. The +9% limit has become a primary driver of outage rejections, particularly where large power stations are unavailable or voltage control equipment is out of service alongside major network reinforcement works. The modification increases the upper operational pre-fault and post-fault voltage limit for the 200 kV to 300 kV network from +9% to +10%, such that operation up to +10% becomes compliant within the SQSS standard. Operation above +10% remains non-standard and would continue to be managed through existing SQSS and Grid Code arrangements, requiring agreement with all affected parties.