Island operation with paralleled generatorsįor the case of island mode operation with at least two generators connected in parallel to supply the load, the control of the voltage and the reactive power requirements have to be shared between the generators in parallel. This eliminates the undesired effect of lower than nominal voltages when in island operation.Ģ.3. The configuration above shows that by the operation of a simple contact the droop can be enabled or disabled, allowing the flexibility to disable it when in island operation and to enable it before connecting it to the grid. The diagram below presents the simple case described.įigure 4. Supply the load with the required reactive power and respond fast to any load changes to meet the demand at any time.Control the busbar voltage to the required nominal level.This is the simplest case in terms of AVR control, as there is only one active component in the circuit that can affect the busbar voltage and react to any reactive load changes.Ī single synchronous machine operating in island mode is only responsible for two actions: Island mode operation with a single generator These three scenarios are analysed separately below.Ģ.1. Operating in island mode, but in parallel with other generators.Operating in island mode as a stand-alone generator.So, in the diagram of figure 4, the increased reactive power demand QL causes the AVR set-point to increase from VG to VL because of the droop compensation control.Īccording to the network topology, the following operating scenarios can be identified: Any requirement for reactive power from the generator will result in the AVR internal voltage set-point V to change to meet the new demand. When a generator is directly connected to the grid, the grid voltage VG is fixed and cannot be controlled by the AVR. Representation of AVR control when connected to the grid. On the other hand, when connected to the grid, droop compensation is required and the droop characteristic is used below to explain the control of the AVR.įigure 2. Typically, a setting of 4-6% is chosen.ĭroop compensation is a control technique designed when the generator is connected to the grid, so it is not required when one generator is in island mode. Depending on the AVR, maximum reactive power is usually defined either as the reactive power exported at rated power factor, or as the MVA rating of the generator.ĭroop setting can be given values from 0%, which effectively disables the droop, to a maximum of usually 20%, which could cause VL to drop to 0.8 p.u. Droop compensation is set as percentage drop of the nominal voltage VN for maximum reactive power QL generated. The reactive power generated is calculated from the generator voltage and current signals, fed back to the AVR. If the initial AVR set-point is not changed, VL will be the voltage due to droop that the generator terminal voltage will reach operating in island mode against reactive load QL. The set-point in the AVR is chosen so that when the generator reactive power Q supplied is zero, the generator VN is equal to the nominal voltage. The interpretation of the above graph is that as the reactive power demand from the generator increases, the generator terminal voltage decreases. This set-point regulates the generator terminal voltage when in island mode. The droop characteristic represents a graph of the AVR voltage set-point V as a function of the generator reactive power produced.
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