• 대한전기학회논문지:전력기술부문A
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• 제52권9호
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• pp.500-505
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• 2003

The target of the ULTC(Under Load Tap Changer) control purpose is to minimize the operation number of the tap of the ULTC doing the error voltage which is the difference between the measured bus voltage End the reference bus voltage of the receiving end becomes less than the tolerance limits. The existing ULTC control method controls each ULTC considering only its bus voltage of the receiving end. However, this method did not cons der the coordinated control of the ULTCs of the system. In this paper, I proposed a coordinated control of the ULTC in :he loop power system using the Jacobian matrix. To show the validity of the proposed method, I made simulations for three cases: no action of the ULTC, the control of the ULTC by the existing control method, and the control of the ULTC by the coordinated control among the ULTCs of the system. The simulation result shows that the proposed method has more improvement of the operation of the ULTC than other methods.

• 전기학회논문지
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• 제58권7호
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• pp.1263-1269
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• 2009

Stable and sustainable power supply means maintaining a certain level of power quality and service while securing energy resource and resolving environmental issues. Distributed generation (DG) has become an essential and indispensable element from environmental and energy security perspectives. It is known that voltage violation is the most important constraint for load variation and the maximum allowable DG. In distribution system, sending voltage from distribution substation is regulated by ULTC (Under Load Tap Changer) designed to maintain a predetermined voltage level. ULTC is controlled by LDC (Line Drop Compensation) method compensating line voltage drop for a varying load, and the sending voltage of ULTC calls for LDC parameters. The consequence is that the feasible LDC parameters considering variation of load and DG output are necessary. In this paper, we design each LDC parameters determining the sending voltage that can satisfy voltage level, decrease ULTC tap movement numbers, or increase DG introduction. Moreover, the maximum installable DG capacity based on each LDC parameters is estimated.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 A
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• pp.230-232
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• 2000

To improve the voltage profile of the load bus, it is important that the coordinated controls among the reactive power compensators at the distribution substation. However, the conventional control scheme of the Under Load Tap Changer (ULTC) is not proper for coordinate control with Static Var Compensator (SVC). This paper proposes a new control model for ULTC and a new coordinated control scheme between ULTC and SVC. The numerical simulation verifies that the proposed system could improve the voltage profile on the load bus and could decrease the number of ULTC tap operation.

• 전기학회논문지
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• 제60권12호
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• pp.2206-2214
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• 2011

LDC(Line Drop Compensation) is widely used in controlling ULTC(Under Load Tap Changer) output voltage at distribution substation. However, LDC may experience some difficulties in voltage control due to renewable energy resources and distributed generations. Therefore, more advanced voltage control algorithm is necessary to deal with these problems. In this paper, a modified voltage control algorithm for ULTC and DG is suggested. ULTC is operated with the voltages measured at various points in distribution system and prevents overvoltage and undervoltage in the distribution feeders. Reactive power controller in DG compensates the voltage drop in each distribution feeders. By these algorithms, the voltage unbalance between feeders and voltage limit violation will be reduced and the voltage profile in each feeder will become more flat.

• 대한전기학회논문지:전력기술부문A
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• 제52권2호
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• pp.69-78
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• 2003

This paper presents a voltage analysis method of distribution systems interconnected with DG(Distributed Generation). Nowadays, small scale DG becomes to be introduced into power distribution systems. But in that case, it is difficult to properly maintain the terminal voltage of low voltage customers by using only ULTC(Under Load Tap Changer). This paper presents a voltage analysis method of distribution systems with DC for proper voltage regulation of power distribution systems with ULTC. In order to develop the voltage analysis method, distribution system modeling method and advanced loadflow method are proposed. Proposed method has been applied to a 22.9 kV practical power distribution systems.

• 전기학회논문지
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• 제63권2호
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• pp.224-229
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• 2014

This paper presents the novel voltage control method in power distribution system with distributed generators. The voltage in distribution systems is regulated by Under Load Tap Changer(ULTC) of substation and pole transformer of primary feeders. Recently, Step Voltage Regulator(SVR) is getting located at distribution feeders to regulate effectively voltage of primary feeders. But the effectiveness of SVR decreases due to independent operation between SVR and ULTC, and also the existing Line Drop Compensator(LDC) method considering the distributed generators may be not able to regulate the proper voltage in a permissible range. Thus, this paper presents a optimal voltage control algorithm of SVR by using the secondary voltage data of main transformer in substation.

• Journal of Electrical Engineering and Technology
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• 제4권3호
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• pp.330-336
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• 2009

This paper proposes an on-line voltage management and control solution for a distribution system which can improve the efficiency and accuracy of existing off-line work by collecting customer voltage on-line as well as the voltage compensation capability of the existing ULTC (Under Load Tap Changer) operation and control strategy by controlling the ULTC tap based on pattern clustering and recognition. The proposed solution consists of an ADVMD (Advanced Digital Voltage Management Device), a VMS (Voltage Management Solution) and an OLDUC (On-Line Digital ULTC Controller). An on-line voltage management emulator based on multi-thread programming and the shared memory method is developed to emulate on-line voltage management and digital ULTC control methodology based on the on-line collection of the customer's voltage. In addition, using this emulator, the effectiveness of the proposed pattern clustering and recognition based ULTC control strategy is proven for the worst voltage environments for three days.

• 대한전기학회논문지:전력기술부문A
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• 제55권6호
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• pp.242-248
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• 2006

This paper proposes a coordinated control method for under-load tap changers (ULTCs) with shunt capacitors to reduce the operation numbers of both devices. The proposed method consists of two stages. In the first stage, the dispatch schedule is determined using a genetic algorithm with forecasted loads to reduce the power loss and to improve the voltage profile during a day. In the second stage, each capacitor operates according to this dispatch schedule and the ULTCs are controlled in real time with the modified reference voltages considering the dispatch schedule of the capacitors. The performance of the method is evaluated for the modified IEEE 14-bus system. Simulation results show that the proposed method performs better than a conventional control method.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.27-28
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• 2008

For stable and sustainable energy supply, distributed generator (DG) has become an essential and indispensable element from environmental and energy security perspectives. However, installation of DG in distribution systems may cause negative affects on feeders because power outputs of DG could be changed irregularly. One of major negative affects is variation in voltage profile. In general, voltage regulation devices such as under load tap changer (ULTC) at distribution substation and step voltage regulator (SVR) along feeder in distribution system are used to maintain customers' receiving voltage within a predetermined range. These regulators are controlled by line drop compensation (LDC) method which calls for two parameters; the equivalent impedance and the load center voltage. Therefore, consideration of DG outputs in the LDC parameter design procedure may give large impact on the installable DG capacity. This paper proposes a method that estimates maximum Installable DG capacity considering LDC parameters of ULTC and SVR. The proposed algorithm is tested with model network.

• Journal of Electrical Engineering and Technology
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• 제2권2호
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• pp.152-156
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• 2007

This paper proposes a method for real-time control of both capacitors and ULTC in a distribution system to reduce the total power loss and to improve the voltage profile over the course of a day. The multi-stage consists of the off-line stage to determine dispatch schedule based on a load forecast and the on-line stage generates the time and control sequences at each sampling time. It is then determined whether one of the control actions in the control sequence is performed at the present sampling time. The proposed method is presented for a typical radial distribution system with a single ULTC and capacitors.