|
|
AŽBE, V., MIHALIČ, R.
FAULT-CURRENT LIMITATION IN SLOVENIAN ELECTRIC-POWER TRANSMISSION SYSTEM
KOMUNALNA ENERGETIKA / POWER ENGINERING, 10
Reinforcement of electric-power systems (EPS) with construction of new power lines, additional interconnections between networks, a growth in generating capacity and upgrade to a higher voltage levels (e.g., from 220 kV to 400 kV) is a natural and logical way of development of EPS in order to improve the stability and reliability. However, on the other side, these reinforced networks can reach or even exceed their limits with respect to the short-circuit current withstand capability. The problem of too high fault currents can be firstly expected in reinforced networks that supply big cities. This paper presents and discusses various methods for limiting these fault currents in 110 kV electric-power network. These methods can be either passive (i.e., increase of impedance at nominal and fault conditions) or active (i.e., small impedance at nominal load and fast increase of impedance at fault occurrence). As typical structure of substation at 110 kV level is in the form of double busbar with two transformers, special attention is paid on inserting fault-current limiters at the position of bus coupler. The results of application of various fault current limiters are presented on the case of Slovenian EPS for the year 2030.
AŽBE, V., MIHALIČ, R.
CHARACTERISTICS OF DOUBLY-FED MOTOR-GENERATOR DURING THE FAULT
KOMUNALNA ENERGETIKA / POWER ENGINERING, 12
Doubly-fed motor-generator (DFMG) will be included in pumping-storage plants in Slovenia—one of them is already in operation— and they will become an important part of Slovenian electric-power system, so it is important to know the behavior of these machines. This paper presents the characteristics of a large doubly-fed motor-generator during and after the fault. During the fault—where DFMG operates as an asynchronous machine—the machine meets the saturation and in combination with the network-voltage reduction this largely affect the electrical torque of the machine. The difference between static and dynamic power-to-speed characteristic is presented with the application of trajectories of rotor speeds. Besides various resistances of crow-bar protection were considered. Results of simulations show that during a fault a crow-bar resistance has an important role—in order to increase the transient stability of DFMG, proper value of crow-bar resistance should be applied.
AŽBE, V., MIHALIČ, R.
A SOFTWARE TOOL FOR PRESENTING FACTS DEVICES IN AN ELECTRIC POWER SYSTEM
KOMUNALNA ENERGETIKA / POWER ENGINERING, 21
The effects of Flexible AC Transmission System (FACTS) devices on an electric-power system (EPS) depend on many parameters. As a result, an easily understood and at the same time comprehensive explanation of these effects can be a difficult task. For this reason we have developed a computer program that can graphically represent the active and the reactive power and the phasors of the voltages and currents in a longitudinal EPS incorporating various FACTS devices. The design of the program makes it easy to change the parameters of the FACTS devices and the parameters of the EPS while the charts are simultaneously refreshed. The program is available, free of charge, on the web (http://lpee.fe.uni-lj.si/index.php?option=com_content&view=category&layout=blog&id=42&Itemid=29). To demonstrate the applicability of the program, a comparison between two similar—but when considering certain parameters, very different—FACTS devices has been performed. Using this program a user can gain a new insight into the effect of FACTS devices on an EPS, i.e., by changing the EPS's parameters and the parameter of a FACTS device, and by observing the changes in the power flow and the movement of the phasors of the voltages and currents. As the numerical results are also available "on-line", the program can be used as a simple control of plausibility of the results for other—more detailed— calculations.
|