How it works
The grid code sets what a plant must do at its point of connection. For frequency, it sets the band of normal operation and how output must respond when frequency strays, for example by reducing power when frequency rises above a threshold. For voltage, it sets a reactive power range, often expressed as a power factor or a share of rated MW, and how the plant must regulate voltage. Ramp-rate limits cap how fast output can rise or fall, in MW per minute.
During a fault, the voltage at the connection can collapse for a fraction of a second. Fault ride-through rules require the plant to stay connected through a defined voltage and time profile, and often to inject reactive current to help recovery. Compliance is shown first through simulation models submitted before connection, then by tests at commissioning, where the plant is stepped through setpoint changes and its responses are recorded. The grid operator may audit later, and settings must stay as approved.
Why it matters
The grid code shapes equipment choices from the start. Inverters, the power plant controller and sometimes extra equipment such as a STATCOM have to be sized to meet reactive power and fault ride-through rules. A plant that fails its compliance tests cannot start commercial operation, or may be held to a reduced output. Later changes to the code can require retrofits. Developers need these requirements priced into the design before procurement.
A worked example
A 200 MW solar plant must supply reactive power across a power factor range of 0.95 lagging to 0.95 leading at full output. The apparent power needed is 200 ÷ 0.95 = 210.5 MVA. The reactive power is √(210.5² − 200²) = 65.7 MVAr. Inverters rated at exactly 200 MVA cannot deliver it at full output. The developer must add 210.5 − 200 = 10.5 MVA of inverter capacity, or a separate source of reactive power.
Illustrative figures.
Across markets
In India, the Central Electricity Authority's technical standards for connectivity set the requirements, including fault ride-through and reactive power for wind and solar. In the US, rules come from FERC, NERC standards and each operator's interconnection requirements, and IEEE 2800 is being adopted for inverter-based plants. In the EU, the Requirements for Generators network code sets a common framework that each country fills in with its own values.