Voltage versus VAr/power-factor regulation on synchronous generators
ABSTRACT When paralleled to the utility bus, synchronous generators can be controlled using either terminal voltage or VAr/power factor (PF) control. Selection is dependent upon the size of the generator and the stiffness of the connecting utility bus. For large generators where the kVA is significant, these machines are usually terminal voltage regulated and dictate the system's bus voltage. When smaller terminal voltage regulated generators are synchronized to a stiff utility bus, the system voltage will not change as the smaller generator shares reactive loading. However, if the system voltage changes significantly, the smaller generator, with its continuous acting terminal voltage regulator, will attempt to maintain the voltage set point. As the voltage regulator follows its characteristic curve, it may cause either over or under excitation of the smaller generator. Excessive system voltage may cause a small generator to lose synchronizing torque, while low system voltage may cause excessive heating on the generator or excessive overcurrent operation of the excitation system. Maintaining a constant reactive load on the smaller generating unit can reduce the generator field current variations and, thus, reduce the maintenance of the collector rings and brushes. This paper illustrates the effect of changing system bus voltage on small generators utilizing voltage versus VAr/PF regulation.
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ABSTRACT: The paper presents the digital realization of a model of reactive power flow (QFM) in a steam power plant using a programmable logic controller (PLC). The steam power plant (SPP) model is developed for pre-commissioning validation testing of the coordinated reactive power-terminal voltage (Q-V) control system. The SPP QFM includes a model for a synchronous generator, an excitation system, a step-up transformer, and the generator's droop characteristic modeled through the automatic voltage regulator (AVR). A QFM synthesis is based on a series of experiments performed on site. The parameters of the generator and AVR are estimated from recorded generator voltage and current time responses to a step change in voltage reference of the AVR. To get a complete QFM, transformers and network reactances are also included. In order to calculate reactive power (Q) flows more accurately, the generator Q output is adjusted by taking into account its real power output. Standard PLC hardware, as industrial grade equipment appropriate for on site testing, is used for practical QFM implementation after discretization of the continuous mathematical model. The developed QFM response is verified through a series of experiments performed in the laboratory.IEEE Transactions on Power Systems 11/2011; 26(4):2256-2263. · 3.53 Impact Factor
Conference Paper: Control of large scale wind power plants[Show abstract] [Hide abstract]
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ABSTRACT: The paper proposes a decentralised approach to guarantee an optimal voltage profile along the feeders of a distribution system with Distributed Generation (DG) from renewable sources. The goal is achieved by using a reactive power closed-loop control scheme for the DG device. The reference value is designed by solving a minimisation problem, which is formulated using only local measurements and avoiding any data exchange with other control systems in the grid. Variations of the operating conditions of the distribution system are estimated to update the formulation of the minimisation problem. Numerical results are presented to give evidence of the effectiveness of the proposed approach.Energy Conference and Exhibition (ENERGYCON), 2012 IEEE International; 01/2012