Dragutin Vojković, M.Sc.E.E.
1. “Chopper forced-commutation circuits”
was the title of my graduation thesis (FACULTY OF ELECTRICAL ENGINEERING IN ZAGREB, 1973).
I have theoretically elaborated a few chopper forced-commutation circuits, compared them and showed that it is not possible to describe them uniformly (with the same differential equations) but it is necessary to analyse each circuit separately.
2. Estimation of an inductance for a filter placed on the DC terminals of a diode
bridge rectifier connection in an electric locomotive (KONČAR – INSTITUTE FOR ELECTRICAL ENGINEERING, 1974).
I have proved that, with existing characteristics of a transformer and other elements, the mounted inductor with 5 mH was the best solution as regards harmonics contents (their influence on the power dissipation and interference on telecommunication lines).
3. Development of high power rectifiers for railway substations (KONČAR – INSTITUTE FOR ELECTRICAL ENGINEERING, 1975)
In order to replace a few old mercury rectifiers in some substations (train, tram) it was necessary to develop semiconductor rectifiers without replacing existing transformers.
I have selected the diodes (parallelly or serially connected in each branch of a three phase bridge rectifier connection), the fuses for diode protection, the RC elements, etc.
4. Development of the single phase rectifier connection for special purposes
(KONČAR – INSTITUTE FOR ELECTRICAL ENGINEERING, 1976)
(Similarly to point 3)
5. Laboratory examination of a three phase thyristor rectifier for an excitational system of a synchronous generator
(functional, load and short circuit tests); (KONČAR – INSTITUTE FOR ELECTRICAL ENGINEERING, 1977)
6. “Diode rectifier selection on the base of short circuit characteristics”
was the title of my master’s thesis. (FACULTY OF ELECTRICAL ENGINEERING IN ZAGREB, 1977)
The paper deals with the external and internal short circuit currents in the three phase bridge rectifier connection for railway substations and in the single phase bridge rectifier connection for electric locomotives.
On the base of the mathematical analyses, programs for the computation of the development of short circuit current and (I2t) values were written. The method for valve and fuse selection was suggested on the base of short circuit characteristics.
7. Development of the rectifier for a new thyristor locomotive
(KONČAR – INSTITUTE FOR ELECTRICAL ENGINEERING, 1977)
I have selected the thyristors, the fuses and the RC elements for single phase double rectifier connection. Also, I made a program for a digital-computer simulation of that rectifier connection.