WTGS Operation in Power Systems

Abstract

The connection of the wind turbine generator system to parallel operation with the electric power system influences the system state (operating point) and influences the load flow (real and reactive power). At the same time, nodal voltages and power losses themselves change, too. These quantities, defining the electric power system state, can be assumed to be basic but in fact the spectrum of factors influencing the electric power system as a result of the WTGS connection to the grid is much wider. The factors, which are considered in the following sections in a more detailed form, can be generally characterized as follows:

• • Location of the wind turbine in the electric power system. The way of connecting it to the electric power system (which in general is an AC system) highly influences the impact of the WTGS (or wind farm) on the power quality. As a rule, the impact on power quality at the consumer’s terminal for the WTGS located close to the load (i.e. connected to an MV system) is higher than one connected “electrically” far away (i.e. connected to an HV or EHV system).

• • Voltage variations of amplitude and frequency. The variations mainly result from the wind velocity, but other factors influencing the generator torque play an important part, too. Voltage variations are directly related to real and reactive power variations. The WTGSs equipped with an asynchronous generator with a squirrel-cage rotor or with a resistor connected to the rotor (in woundedrotor machines) are consumers of reactive power, which can cause additional negative problems for the grid.