Norbert Becker

Novel 20-MW downhill conveyor system using three-level converters

This paper presents a very new drive system used to transport ore from the mine down to the concentrator plant in the copper mine Los Pelambres. Eight 2500 kW motors are driven by three-level inverters with GTOs. A three-level active front end (AFE) is used at the input side of each inverter. A GTO chopper is used to provide controlled electrical braking in case of line loss. The paper presents the requirements and alternatives for the drive system and the control strategies for the converters and the belt. A novel application of the selective harmonic elimination method is used to reduce the input current harmonics. Special attention is dedicated to the interaction with the electrical network. The most relevant features of the system are: (i) fuseless operation; (ii) adjustable power factor; (iii) reduced input current harmonics; and (iv) smooth transition between motoring and regenerating modes and 15 MW of regenerated power with more than six months of successful operation.

Regenerative drives in the megawatt range for high performance downhill belt conveyors

Downhill transport of ore from the mine to the beneficiation plant by means of belt conveyors introduces important advantages for the personnel and for the equipment. Furthermore, if the conveyor is equipped with a regenerative AC drive, the system generates an important amount of electrical energy for use in the process. This paper discusses the technical alternatives and the criteria used to select the solution with modern converter-inverter drives in the megawatt and medium voltage range. The considered drive alternatives are: (i) AC wound rotor induction motor drive with additional resistors, (ii) AC synchronous motor with cycloconverter, (iii) AC induction motor with current source inverter and (iv) induction motor with multilevel voltage source inverter. The study reveals that the use of a three-level active front end feeding a voltage source three-level inverter is the most appropriate alternative, considering the main technical criteria.

Operation of high power cycloconverter-fed gearless drives under abnormal conditions

This paper presents the behavior of large power mills (more than 10 MW each) that are fed by cycloconverters. Special attention is dedicated to the protection philosophy to avoid operational interruptions that can produce huge production losses and equipment damage. Several failure possibilities are considered: control failure, complete power outage, if a thyristor fails and cannot block reverse voltage, etc. Simulation studies and field measurements show that large currents and torque can occur under certain circumstances and that motor foundations must be able to support them. As a general conclusion, it can be said that proper protective design effectively avoids equipment damage

Resonances in a high-power active-front-end rectifier system

This paper presents the application of high-power three-level active-front-end rectifiers to regenerate energy in a downhill conveyor system. The selective harmonic elimination method is used to eliminate harmonics 11 and 13, working with very low switching frequency, where six-pulse harmonic orders 6k/spl plusmn/1 are eliminated by the delta-wye connection of the transformer. In this way, the input current at the mains is highly sinusoidal with small harmonics starting at frequencies of order 23 and 25. Resonances have been detected, originated mainly by the capacitances of feeding cables and noneliminated harmonics, which produce high-voltage distortion. Theoretical and field measurements present the problem and the solution by using a specially designed high-pass power filter.

Novel 20 MW downhill conveyor system using three-level converters

This paper presents a very new drive system used to transport ore from the mine down to the concentrator plant in the copper mine Los Pelambres. Eight 2500 kW motors are driven by three-level inverters with GTOs. A three-level active front end (AFE) is used at the input side of each inverter. A GTO chopper is used to provide controlled electrical braking in case of line loss. The paper presents the requirements and alternatives for the drive system and the control strategies for the converters and the belt. A novel application of the selective harmonic elimination method is used to reduce the input current harmonics. Special attention is dedicated to the interaction with the electrical network. The most relevant features of the system are: (i) fuseless operation; (ii) adjustable power factor; (iii) reduced input current harmonics; and (iv) smooth transition between motoring and regenerating modes and 15 MW of regenerated power with more than six months of successful operation.