Study on the Feeder Selection method for 10kV Regional Compensation Type Dynamic Voltage Restorer

This paper proposes the designing of regional compensation type Dynamic Voltage Restorer(DVR), and the topology of main circuit, the detection algorithm for voltage sag, the calculation method of reference voltage and pulse modulation method. Based on the different load types of the target substation and the sensitivity to voltage sags, the selection principle of the location of compensation line for regional compensation DVR is proposed, and the realization of substation feeder selection method is illustrated by taking a substation as an example. The compensation effect of the DVR under different fault types are simulated, and the validity and rationality of the designing are verified. Introduction With the continuous development of modern industrial technology and the extensive application of computer technology, more and more production processes such as semiconductor manufacturing, paper-making, computer integration adopt microprocessor chip based devices that are sensitive to power quality, even half cycle interruption or dips on the power supply would affect the operation of sensitive equipments, thus causes enormous losses [1,2] . Dynamic Voltage Restorer(DVR) is a device connected in series with the power source and the sensitive load. When the supply voltage is normal, DVR operates bypassed in hot standby state, and when the system voltage dips occurs, it will act quickly to compensate the voltage dips, thus can protect sensitive loads from the effects of voltage sags [3,4] . Currently researched and applied DVRs are almost of the low voltage level, and can compensate voltage drop for one or several the most sensitive devices of users load [5,6] . With the power supply voltage levels, the capacity and concentration rate of sensitive loads continue to increase, this point-to-point compensation form will be increasingly uneconomical. DVR developed to achieve regional voltage drop compensation will have important application value. Power distribution network includes many types of loads, such as industrial, manufacturing, commercial, residential, transportation, and telecommunications industries, etc. According to different requirements for supply reliability and the loss or affected degree of power interruption in the aspect of politics and economy, it divides into three categories, i.e. class I, II and III load [7,8] . However, on the point of sensitivity to voltage dips, the loads classification will vary. Taking into account the fact that the compensation capacity of current region-based DVR is limited, load distribution with different sensitivity to voltage drops is different. So the prime need is to determine the type of DVR regional protected area, select the line of work, after determine the area to be protected, then related hardware circuit design control strategies and protection work of DVR can be design. The research and application of the regional type DVR at home and abroad is rare and there are no studies on the feeder selection of regional type DVR. This paper presents the working principle Applied Mechanics and Materials Vol. 615 (2014) pp 290-297 © (2014) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMM.615.290 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 166.111.137.204-30/07/14,10:25:01) and the system wiring of regional type DVR. Then the feeder selection criteria and methods the regional type DVR are proposed based on the capacity and nature of the substation 10kV feeder and voltage sage monitoring statistics results. A 110kV substation is taken as an example to show the realization of the feeder selection method. Simulation results in PSCAD verifies the feasibility and effectiveness of the design of regional type DVR. Wiring diagram and working principle of regional type DVR System wiring and main circuit topology Since DVR based on cascaded multilevel topology has the advantages on system reliability, component selection, control complexity, overall efficiency over the other topologies [9-11] , the proposed main circuit topology based on multi-level cascade structure of regional type DVR for 10kV three-phase three-wire system is shown in Fig.1: Fig.1 Cascaded Multi-level Topology of DVR Inverter section uses three single-phase bridge configuration, each phase has 5 cascaded H-bridge; The rectifier uses a controllable rectifier bridge and discharge circuit; Energy storage unit powered from another 10kV bus in the same substation; Output filter and couple circuit uses LC filter. Voltage dip detection method The dq/αβ decomposition methods based on instantaneous reactive power have been widely used in devices such as DVR that are in highly requirement for time delay [12,13] . Fig.2 shows the block diagram of the voltage drop detection algorithm for the regional type DVR. Fig.2 Block diagram of three-phase voltage sag detection algorithm In Fig.2, e -sT represents time delay, and T=3.333ms;Ua, Ub, Uc represents the measured phase voltage respectively; Uad, Ubd, Ucd, Uaq, Ubq and Udq represents the dq components of the three-phase voltage respectively; Va, Vb, Vc represents three-phase voltage amplitude, and θ is the phase angle. The magnitudes of the voltage obtained are compared with a preset threshold, and the voltage dip can be determined when the voltage magnitudes drops below the 90% of the nominal voltage. Reference voltage calculation At present, the DVR compensation strategies mainly include: the same phase compensation, complete compensation and minimum power voltage compensation [14] . Applied Mechanics and Materials Vol. 615 291