Voltage versus VAr/power-factor regulation on synchronous generators
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.
Available from: Mostafa Eidiani
- "ﺑﺎ اﻣﺎ ﻳ اﮔ ﻛﻪ داﺷﺖ ﺗﻮﺟﻪ ﺪ ا از ﺮ ﻳ روش ﻦ ﺑﺮا ﺗﻨﻬﺎ ي ﺟﺒﺮاﻧﺴﺎز ي ﺷـﻮد اﺳﺘﻔﺎده ﻣﻘﺎ در ﻳ ﺟﺒﺮاﻧﺴـﺎز ﺑـﺎ ﺴـﻪ ي ﺧـﺎزﻧ ﻲ ﻧﺎﭘﺎ ﻳـ ﭘ و ﺪارﺗﺮ ﺮﻫﺰ ﻳ ﺑـﻮد ﺧﻮاﻫـﺪ ﺗـﺮ ﻨـﻪ .     "
اولين همايش منطقه اي مهندسي برق, Tehran, Iran; 01/2011
Available from: Pukar Mahat
- "However, when operated in the voltage control mode, it may cause either over or under excitation of the small generator as it will attempt to maintain the voltage at a set point with its continuously acting terminal voltage regulator . Also, an excessive reactive current may result in overload or loss of generator synchronism . According to , small generators' operation at the VAr/power factor control mode is justifiable. "
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ABSTRACT: Islanding operation of distribution systems with distributed generations (DG) is becoming a viable option for economical and technical reasons. However, there are various issues to be resolved before it can be a reality. One of the main issues is control of the DG. Control strategies, that may work fine while a DG is connected to a grid, might not work as desired while it is islanded and vise versa. This paper presents a strategy to operate distribution systems with a small gas turbine generator (GTG), which is capable of supplying local loads, in both islanding and grid connected conditions. Separate strategies are used to control the GTG while it is connected to the grid and while it is islanded. Switching between the control strategies is achieved through a state detection algorithm that includes islanding and grid re-connection detections. An existing islanding detection technique has been used and a grid re-connection detection algorithm has been developed. Simulation results show that the proposed method is effective in operating GTG optimally while it is either connected to the grid or islanded.
Transmission and Distribution Conference and Exposition, 2010 IEEE PES; 05/2010
Available from: Luis(Nando) Ochoa
- "New generation and load buses are also modeled as nodes, while any existing voltage-controlling generators are nodes. The new generators are run in constant power factor mode, as is common with distributed generation , with the power factors of all the new generators equal. It is reasonably straightforward to use voltage or other control modes instead . "
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ABSTRACT: This paper presents a novel method for determining the capacity of a network to accommodate new generation under network security constraints. The assessment is performed by maximizing the total generation capacity in an optimal power flow model; this is solved by gradually adding limited numbers of line outage contingencies, until a solution to the complete problem is obtained. The limit on the number of contingencies added is key to the method's efficiency, as it reduces the size of the optimization problems encountered. Moreover, varying this limit on contingencies added provides a simple and highly efficient means of searching for multiple local optima of the nonlinear optimization problem. The method has been tested on a modified version of the highly meshed IEEE Reliability Test System with N -1 security, where a significant reduction in the system's capacity for new generation is seen when security constraints are imposed. The method is generic and may be applied at any voltage level, for other security models and for other similarly structured problems such as the analysis of multiple resource availability scenarios.
IEEE Transactions on Power Systems 02/2010; 25(1):575 - 583. DOI:10.1109/TPWRS.2009.2036809 · 2.81 Impact Factor
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