Water and Energy Abstracts
Year : 2004, Volume : 14, Issue : 1
First page : ( 31) Last page : ( 32)
Print ISSN : 0021-1672.

77. Electrical Braking of Hydro Generator Realized Through Excitation System with Digital Voltage Regulator

Brkljac Blazenka, Pertinic Marijan

(Proceedings, Hydro 2003, Vol. I, Croatia, pp. 601–607).

Abstract

In the paper the basic principles of electrical braking of hydro generators with employment of standard excitation system are described. The basic requirements on the equipment and principle scheme are given. The characteristics of electrical braking and its advantages in comparison with mechanical braking are stated. Electrical braking has found its major practical application in reversible hydro power plants and peak power plants with a need for daily frequent stopping and starting of generator set. It can be also used on other hydro power plants having long normal stopping time because of technical advantages, reduced maintenance of hydraulic brakes and relatively small additional investing expenses for its realization. A mathematical program for PC, intended for electrical braking behaviour calculation “ELKOC” is developed. Diagrams and oscillograms of site tests of electrical braking are given and the comparison to the calculating results from mathematical model is shown. The principle of electrical braking is applied with potential-source controlled-rectifier excitation system with the digital voltage regulator type “DRN”. Necessary modifications of the plant project and design have been carried out. The control sequence of electrical braking has been implemented in the digital voltage regulator application program as an independent module. Results of analyses made on site and those obtained through mathematical model “ELKOC” show that the below given statements are as true for those hydroelectric power plants where frequent stopping of generator sets is required as for those where there are not such requirements. During electric braking time required for stopping the generator is considerably shortened; a lifetime of bearings is expanded and possible damages which may be caused by “dry friction” are reduced to minimum; during stopping of the generator distribution of mechanical strains and vibrations is rather equalized; a lifetime of brake linings is considerably expanded and their strains as well as their failures (faults) are reduced to the minimum (breaking of brakes can cause great damages in stator and rotor windings); the problems with dust are here insignificant. The electrical braking transformer is designed to allow spare supply of generator excitation in case of an excitation transformer failure. It can be also used to supply independently the excitation system during testing the generator protection system. In that way, hard and dangerous temporary reconnections of cables are avoided. The changeover to the excitation system spare supply is carried out with de-excited generator. Realization of electrical braking through modular digital voltage regulator enables a complete automation, high efficiency, reliable and easily maintainable equipment, which increases availability and reliability of the plant. Use of computers and application of mathematical program “ELKOC” proved to be useful in making calculations of electrical braking of the generator set. The results obtained by calculations agree with the recorded ones, which justifies further usage of the model for similar calculations.

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Keywords

Electrical braking, Practical application, Maintenance, ELKOC, Digital voltage regulator.

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