• Journal of international Conference on Electrical Machines and Systems
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• v.2 no.4
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• pp.405-412
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• 2013

This paper includes new protection concepts and practices to avoid mechanical damage of three-phase transformer by asynchronous operation of synchronous generator. this failure is often caused just after synchronous generator was connected to the grid because of a malfunction of the controller or misconnections of the synchronous devices. The results of the studies on the analyzing the phenomenon of asynchronous operation experienced in Korea and rapidly detecting asynchronous state are descrived.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.11
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• pp.47-52
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• 2015

This paper derives the problems that occur when asynchronous transfer in case of phase, frequency, voltage between the emergency generator and the grid and proposed the countermeasure to solve this problem when the transfer switch replace ATS(Automatic Transfer Switch) with CTTS(Closed Transition Transfer Switch) for the non-interrupting switching. In order to simulate above cases, modelling was used the transient analysis program PSCAD/EMTDC. By using this, the customer installed emergency generator and the grid was implemented. We compared three cases of asynchronous transition based on the basic case and proposed improvement by controlling the governor of emergency generator.

• Journal of Power Electronics
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• v.10 no.5
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• pp.538-547
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• 2010

This paper deals with a stand-alone wind energy conversion system (WECS) with an isolated asynchronous generator (IAG) and voltage and frequency (VF) control feeding three-phase four-wire loads. The reference generator currents are estimated using the instantaneous symmetrical component theory to control the voltage and frequency of an IAG system. A three-leg voltage source converter (VSC) with an isolated star/delta transformer is used as an integrated VSC. An integrated VSC with a battery energy storage system (BESS) is used to control the active and reactive powers of the WECS. The WECS is modeled and simulated in MATLAB using the Simulink and the Sim Power System (SPS) toolboxes. The proposed VF controller functions as a voltage and frequency regulator, a load leveler, a load balancer and a harmonic eliminator in the WECS. A comparison is made on the rating of the VSC with and without ac capacitors connected at the terminals of an IAG. Simulation and test results are presented to verify the control algorithm.

• Journal of Mechanical Science and Technology
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• v.14 no.6
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• pp.590-596
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• 2000

Cause of excessive vibration with twice the rotational speed of a two-pole generator rotor for the fossil power plants was investigated. The two-pole generator rotor, treated as a typically asymmetric rotor in vibration analysis, produces asynchronous vibration with twice the rotational speed, sub-harmonic critical speeds, and potentially unstable operating zones due to its own inertia and/or stiffness asymmetry. This paper introduces a practical balancing procedure, and presents the results of the investigation on sources of the excessive vibration based on the experimental vibration data of the asymmetric two-pole rotor in balancing.

• Journal of Power Electronics
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• v.8 no.1
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• pp.81-90
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• 2008

This paper presents an investigation of a voltage and frequency controller for an isolated asynchronous generator (IAG) driven. by a wind turbine and supplying 3-phase 4-wire loads to the isolated areas where a grid is not accessible. The control strategy is based on the indirect current control of the VSC (voltage source converter) using the frequency PI controller. The proposed controller consists of three single-phase IGBT (Insulated Gate Bipolar Junction Transistor) based VSC, which are connected to each phase of the IAG through three single phase transformers and a battery at their DC link. The controller has the capability of controlling reactive and active powers to regulate the magnitude and frequency of the generated voltage, harmonic elimination, load balancing and neutral current compensation. The proposed isolated system is modeled and simulated in MATLAB using Simulink and PSB (Power System Block-set) toolboxes to verify the performance of the controller.

• Journal of Power Electronics
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• v.9 no.1
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• pp.43-50
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• 2009

This paper deals with a novel solid state controller (NSSC) for an isolated asynchronous generator (IAG) feeding 3-phase 4-wire loads driven by constant power prime movers, such as uncontrolled pico hydro turbines. AC capacitor banks are used to meet the reactive power requirement of the asynchronous generator. The proposed NSSC is realized using a set of IGBTs (Insulated gate bipolar junction transistors) based current controlled 2-leg voltage source converters (CC- VSC) and a DC chopper at its DC bus, which keeps the generated voltage and frequency constant in spite of changes in consumer loads. The neutral point of the load is created using aT-configuration of the transformers. The IAG system is modeled in MATLAB along with Simulink and PSB (power system block set) toolboxes. The simulated results are presented to demonstrate the capability of the isolated generating system consisting of NSSC and IAG driven by uncontrolled pico hydro turbine and feeding 3-phase 4-wire loads.

• International Journal of Fluid Machinery and Systems
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• v.2 no.1
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• pp.92-101
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• 2009

The purpose of this paper is to gain a greater understanding of the performance of practical wind turbine generating systems with differing output power controllers and controlling means for wind turbine speed. Subjected wind turbines, both equipped with an asynchronous power generator, are located at two sites and are defined as wind turbine A and wind turbine B in this study, respectively. Their performance differences are examined by measuring wind speed and electric parameters. The study suggests that both wind turbines have a clear linkage between current and output power fluctuations. Comparison of the fluctuations to wind speed fluctuation, although they are triggered primarily by wind speed fluctuation, clearly indicates the specific behaviors inherent to the respective turbine control mechanisms.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.10
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• pp.1542-1547
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• 2012

Asynchronous phenomenon occurs on the synchronous generators under power system when a generator's amplitude of electromagnetic force, phase angle, frequency and waveform etc become different from those of other synchronous generators which can follow instantly varying speed of turbine. Because the amplitude of electromagnetic force, phase frequency and waveform differ from those of other generators with which are to be put into parallel operation due to the change of excitation condition for load sharing and the sharing load change, if reactive current in the internal circuit circulates among generators, the efficiency varies and the stator winding of generators are overheated by resistance loss. When calculation method of protection settings and logic for protection of generator asynchronization will be recommended, a distance relay scheme is commonly used for backup protection. This scheme, called a step distance protection, is comprised of 3 steps for graded zones having different operating time. As for the conventional step distance protection scheme, zone 2 can exceed the ordinary coverage excessively in case of a transformer protection relay especially. In this case, there can be overlapped protection area from a backup protection relay and, therefore, malfunctions can occur when any fault occurs in the overlapped protection area. Distance relays and overcurrent relays are used for backup protection generally, and both relays have normally this problem, the maloperation, caused by a fault in the overlapped protection area. Corresponding to an IEEE standard, this problem can be solved with the modification of the operating time. On the other hand, in Korea, zones are modified to cope with this problem in some specific conditions. These two methods may not be obvious to handle this problem correctly because these methods, modifying the common rules, can cause another coordination problem. To overcome asynchronizing protection, this paper describes an improved backup protection coordination scheme using a new logic that will be suggested.

• Journal of Power Electronics
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• v.9 no.6
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• pp.874-883
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• 2009

This paper deals with an integrated voltage and frequency (VF) controller for isolated asynchronous generators (IAG) driven by a constant power pico-hydro uncontrolled turbine feeding three-phase four-wire loads. The proposed VF controller is used to control the frequency and voltage of an IAG with load leveling. Such a VF controller is also known as an integrated electronic load controller (IELC) which is realized using an isolated star/polygon transformer with a voltage source converter (VSC) and a battery at its DC bus. The proposed generating system with a VFC is modeled and simulated in MATLAB along with Simulink and Simpower system (SPS) toolboxes. The simulated results are presented to demonstrate the performance of an isolated asynchronous generator feeding three-phase four-wire loads with neutral current compensation.

• Journal of KSNVE
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• v.9 no.4
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• pp.835-840
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• 1999

Cause of excessive vibration signals with twice the rotational speed of a 2-pole generator rotor in balancing for fossil power plants was investigated. The 2-pole generator rotor is treated as a typically asymmetric rotor in vibration analysis, and produces asynchronous vibration with twice the rotational speed for its own inertia and stiffness asymmetry. This paper introduces practical balancing procedure and experimental vibration data of the asymmetric 2-pole rotor in balancing, and presents the results of investigation into sources of the excessive vibration signals.