rwwengheaderGrid Code Compliance

With the advent of renewable energy projects taking place in RSA there are various requirements pertaining to the national grid code, which need to be adhered to. Specifically with regard to Quality of Supply, Voltage Response and Reactive Power requirements.

RWW Engineering has been involved in a number of installations and can offer the following services:

  • Power recordings and reporting on the compliance of a particular plant using class A recording equipment and latest government legislation and best practice.
  • Power system modelling with respect to quality of supply, harmonic emissions, voltage stability and Reactive Power requirements
  • Reactive Power Equipment design and engineering
  • Harmonic Filter equipment design and engineering
  • Dynamic voltage support
  • Supply and installation of Reactive Power and Harmonic filter equipment (turnkey installations)
  • STATCOM High Speed Reactive Power Systems and Active Harmonic Filtering

Explanation of some of the requirements and solutions

Typical Grid Code requirements

According to the certain grid code requirements, different voltages and power factors at the point of grid connection need to be considered to calculate the reactive power required from the renewable energy plant. It is important to know how much reactive power has to be supplied by each converter to fulfil the grid code requirements for the voltage control range for Renewable Power Plants (RPPs) at the PCC to correctly size the equipment.

Power control is necessary for all connection requirements for convertors, which vary widely according to the short circuit capacity of the system. The relative impedance for weak grids is high, so the impact of reactive power (Q) support is usually significant. If RPP’s are connected to a weak system, more power control is required to keep the system stable during and after a fault. This reactive power support can be quantified by completing a GC study.

Once a GC study has been completed, it can be seen whether the RPP can provide the reactive energy required or if it should be supplied by external substation based systems. The outcome of the study will be the reactive power capability curve of which an example can be seen in figure 3. In this case the convertors do not provide the required reactive power and need to be supported by external equipment.

In the case above external equipment made more economic sense than upgrading the convertors and PV modules to cater for this additional requirement. This equipment is supplied in the form of multiple step capacitor banks.

Another approach to complying with grid code requirements and ensuring maximum energy output is by installing a static synchronous compensator (STATCOM) at the point of common coupling (PCC). By applying a STATCOM system at the PCC, the plant owner or operator is able to automatically control the amount of reactive power, as well as address any voltage stability concerns.

A STATCOM will be able to quickly respond to grid events (with a response time of milliseconds), provides dynamic voltage control. Even on weak grids, the STATCOM device has the capability to control reactive power, limiting grid impedance, and ultimately enhancing the power output of a wind farm.

Active Harmonic Filtering, STATCOM and SVCHarmonic Filtering (Passive)