High-Power Regenerative Converter for Ore Transportation under Failure Conditions J. Pontt*, J. Rodríguez, R. Huerta, P. Newman Department of Electronics Technical University Federico Santa María Av. España 1680 - Valparaíso - CHILE * E-mail: jorge.pontt@usm.cl Werner Michel FH Darmstadt University of Applied Sciences Haardtring 100 64295 Darmstadt - Germany Christian Lastra Compañía Minera Los Pelambres Ahumada 11, Piso 7 Phone: +56-2-4408810 Santiago, Chile Abstract— The use of three-level neutral point clamped (3L- NPC) voltage source inverters for drive applications in the megawatt range is becoming a standard solution. In combination with the same converter circuit in rectifier operation as Active Front End (AFE) it is able for four-quadrant operation. An existing plant, which has been in operation with eight converters since several years, has shown some failures, which lead to considerations of failure mechanisms and failure rates. All failures were on the AFE. A first failure of a power semiconductor leads to subsequent breakdown of others. Some failures are analyzed and failure conditions are described. Some failure reasons can be excluded and a probable reason is pointed out. Finally, a recommended solution is described and its result after its implementation is discussed. I. INTRODUCTION Nowadays a large amount of industrial facilities are incorporating high-power Active-Font-End (AFE) converters and medium level voltage systems, for handling larger amounts of energy more efficiently and safely. Previous reports have presented the incorporation of these systems especially in the mining industry, where line-side PWM converters can provide reduced network interaction, unity power factor and bidirectional power flow capability [1]-[4]. Three-Level neutral-point-clamped configuration (NPC) is employed increasingly for high-power applications, because its inherent capability for medium-voltage operation, concerning, low switching frequency and power semiconductors utilization, as discussed in [5] - [7]. However, despite the advanced stage of the semiconductor technology, burning issues of semiconductors devices are still a concern. Some critical application requirements impose very strong specifications to the semiconductors like minimum “on- stage” current, high blocking voltages, low switching losses, etc. Many mining facilities are located at high-level altitudes above sea level. This condition introduces extremely high stressing environment to the power systems and power semiconductors devices [8, 12]. This work presents a report of failures presented in an industrial high power medium voltage level downhill conveyor, including the study of semiconductor’s failure mechanisms and a solution for the recurrent failures presented by the downhill conveyor at the line side active-front-end converters. The main contribution of this work is to resume some situations on power semiconductors working in highly rough environment conditions. II. DESCRIPTION OF THE SYSTEM The conveyor system here described consists of three individual conveyors, where two of them have three AC-Drives each and the third one has two AC-Drives only. The three conveyors have a length of 5905, 5281 and 1467 meters. The average inclination is about 11% downhill. With a transport capability of 5800 tons/h, a total of 15 MW can be regenerated to the network keeping unity power factor. Fig. 1 presents the single-line diagram of the electrical system. The conveyors are named as CV005, CV006 and CV007. CV005 and 006 have three motors each, meanwhile CV007 only two. This could be an important fact because of the harmonic issue concerning power quality and some important operational considerations. Fig. 2 shows a diagram of one conveyor system (CV006). The fourth drive is not present in the actual implementation, but will allow upgrading in the future. Conveyor 3 has only two motors, as it is only 1467 meters long. The motors are induction motors of 2.5 MW each operated by three-level neutral point clamped converters (3L-NPC) with a second 3L- NPC at the line side acting as active front-end rectifier (AFE). 23kV - network system 140 m n: 5 9.5 Q/Mvar: 5 4 Qf: 5 3 BUS 1; 23kV 170 m 60 MVA 9% Overhead line 168 km Overhead line 168 km 1.4 km OHL n.c. 5.0 km 6.2 km 23kV - network system 200 m n: 5 9.5 Q/Mvar: 5 4 Qf: 5 3 BUS 2; 23kV 150 m 60 MVA 9% 1.4 km OHL n.c. 1 km 23kV - network system n: 5 9.5 Q/Mvar: 5 4 Qf: 5 3 BUS 3; 23kV 150 m 60 MVA 9% 12.2 km 220 kV 1.4 km OHL Shovel #1 Shovel #2 Conveyor 7 CV007 Conveyor 6 CV006 Conveyor 5 CV005 Concentrator Tie - Breaker 1 km 2.5 km 1.4 km 2 AFE + INV 3 AFE + INV 3 AFE + INV Bus 10 Conveyor Filter Circuit San Isidro U=220 kV f=50 Hz Sk*= 3389 MVA Figure 1. Electrical single-line diagram of the complete plant 0-7803-8487-3/04/$20.00 (C) 2004 IEEE