• Home
        • Generation
        • Aurora works across a wide range of traditional power generation systems, from small CHP units up to large industrial power generation facilities. We have extensive experience in considering synchronous generators fault contribution into the network, as well as considering issues such as dynamic response and transient stability of synchronous generators.

        • Renewables & Energy Storage
        • Aurora provides a range of services to the Renewables and Battery Energy Storage Systems industries, and can provide advice on analysis on greenfield developments or integration into existing brownfield industrial facilities. We specialise in providing grid simulation and G99 compliance studies to support renewable connections to the UK network, and other European networks.

        • Transmission & Distribution
        • Aurora has extensive experience in the transmission and distribution sector, dealing with private 11kV and 33kV networks, iDNOs and DNOs and National Grid, for a variety of different design and analysis applications.

        • Oil, Gas and Petrochemical
        • Aurora has extensive experience in the Oil & Gas industry, and has undertaken a wide range of design activities, concept studies and simulation studies to support many large international EPC companies and service companies.

        • Industrial
        • Aurora works in light and heavy industry providing a range of services to help plant owners analyse and understand their networks, identify weak spots, providing guidance on system loadings, fault levels, earthing, protection coordination and arc flash.

        • Data Centres
        • Aurora has worked on a number of large data centres, providing a range of services to support existing specialist companies in this area, such as system analysis for fault levels, harmonic analysis, protection coordination and arc flash analysis.

        • Building Services
        • Aurora works in Building Services industry to support multiple M&E contractors in development of the HV aspects of their design, or integration of renewable technologies like roof top solar. ¬†Services include system analysis for fault levels, harmonic analysis, protection coordination and arc flash analysis.

        • Water
        • Aurora has extensive experience in the water industry and has worked fs, identify weak spots, providing guidance on system loadings, fault levels, protection coordination, motor starting earthing and arc flash. We also have extensive experience in helping water companies integrating renewalbe power and battery storge technologies into their sites.

        • Power System Analysis
        • Load flow, fault analysis, P28/2 voltage disturbance including flicker and transformer inrush, G5.5 Harmonics, G99 Grid studies, protection coordination, arc flash, dynamic and transient studies and electromagnetic transients.

        • Power System Design
        • Concept selection, contingency analysis, switchgear and transformer specification, SLD preparation, cable sizing, UPS sizing, substation layouts, protection scheme design, wiring modifications for EPC and M&E companies.

        • Power System Earthing
        • Earth potential rise (EPR) calculations and touch and step voltage calculations with either CDEGS or XGSLab, earthing layouts, soil resistivity testing, fall of potential tests, earthing inspections and resistance testing.

        • Power System Consultancy
        • Concept development and decarbonisation strategies, preparations of G99 and National Grid connection applications, review of ICP and vendor proposals, due diligence checks and client representative and failure investigations.

  • Case Studies
        • Team
        • As a consultancy our people are our greatest assets. Please follow the link above to meet the Aurora Team and find out more about us.

        • Careers
        • Are you interested in power system studies and analysis? Would you like to work for Aurora? If so click the above link to see our current vacancies.

  • News
  • Contact

G99 / Grid Code – Reactive Power Requirements

For Type C / D Generation sites in the UK, one of the most important studies to carry out in the early stages of a project is a reactive power capability assessment. This study is a specific type of load flow case, used, to confirm that the equipment is correctly sized, and the site can deliver the amount of active power (MW) and reactive power (MVAr) at the system entry point. Unfortunately many clients have problems at this point as they find there is a shortfall of reactive power (MVAr), and they must constrain their active power (MW) output to remain compliant.

The basic requirement for reactive power flow capability of a generating site, is the ability to produce reactive power when the host DNO / TSO system voltage is low, and to absorb reactive power when the host DNO / TSO system is high. Within the UK the requirement is to be able to operate at 0.95pf lag to 0.95pf lead, at the Connection Point, across a range of different DNO / TSO system voltages.

To demonstrate compliance there are a series of loadflow studies that must be carried out, at different loading, powerfactor and voltage. In many software packages that can be automated with a script. The standard shows two main sets of requirements: A VQ (Voltage-Reactive Power) diagram that defines the reactive capability when the site is operating at maximum power in relation to the DNO / TSO system voltage. A PQ (Active Power – Reactive Power) diagram that defines the reactive power capability across a range of different site power outputs. The VQ diagram is intended to show compliance at full power for different network voltages and the PQ diagram is to show compliance at intermediate loading levels.

Many companies get themselves into some difficult as they wrongly equate Registered Capacity with the amount of installed inverter capacity, forgetting that kW and kVA are not the same and that the site will have both active power losses, but also some significant reactive power consumption. Problems can then arise if the site cannot produce enough reactive power when operating at the required active power. This may need to inclusion of additional inverters, or MVAr compensation equipment.

Where things are made more complicated, is that the DNO connection agreements are specified at a given operating power factor (like 0.98 lag), so the need for reactive power capability across an active power range and voltage range can be confusing. The key thing to remember here is that the DNO can change the specified operating PF, so although it may be 0.98 lag now, they could change at a future date to 0.95, and the shortfall could be a problem. It is also possible that the DNO could request the site to operate in voltage control mode and thus the site RC would have to be restricted as it would be unable to meet the MVAr obligation.