Power engineering - energy supply

In this paper the identifiability of synchronous generator’s parameters from time domain measurements at the terminals using a linearized equivalent is examined and a decoupled brute force algorithm for identification is presented. The generator model has two windings on both, the quadrature and the direct axis of the rotor. Measurements are carried out at the terminals; therefore the instantaneous values for rotor’s angle and rotational speed are unknown. A synchronous generator operating in a single machine infinite bus (SMIB) system was simulated. Field voltage was simulated to undergo a rectangular pulse change and the electrical quantities at the generator’s terminals were measured. To search the values of generator’s parameters brute force algorithm was used, since it provides an insight into all possible parameter sets which satisfy the identification criteria. After it has been established that some measured variables are insensitive to changes of certain parameters, a multistage approach was justified; without it, brute force search would not be feasible. Since the dynamics obtained with various parameter sets nearly coincides with that of the original simulation it is concluded that the synchronous generator’s parameter identification using the eighth order model in a linearized set up is not generally possible.

BOGOVIČ, J., MIHALIČ, R.
Flexible Alternating Current Transmission System Devices Compensator for Distribution System
KOMUNALNA ENERGETIKA / POWER ENGINERING, 171

abstract

One of the possible solutions for improving voltage conditions in an electric power system (EPS) is applying power electronics based or so called flexible alternating current transmission system (FACTS) devices. However, the appropriate inclusion of a FACTS device into the EPS is not a straightforward procedure. On the contrary, it requires several steps. One of the first steps is the power flow analysis, which requires an appropriate FACTS device modelling. In the past the models of FACTS devices for Newton-Raphson (NR) power-flow and current-injection calculation methods have been developed. The NR analysis, however, is not always suitable for distribution networks due to convergence problems. This is why new three-phase models of FACTS devices for the forward/backward sweep method are presented in this paper. Their application is demonstrated on an IEEE 34 and 123 bus test systems, in order to clearly present the approach virtues for FACTS modelling in distribution networks with included distributed generation units (DGs).

RUDEŽ, U., MIHALIČ, R.
Impact of Considered SVC Implementation in the Slovenian Power System on Inter-Area ENTSO-E Oscillation Damping
KOMUNALNA ENERGETIKA / POWER ENGINERING, 191

abstract

During the planning process of possible future investments into the Slovenian power system, a need arose for the comprehensive analysis related to low-frequency inter-area oscillation damping of a static var compensator (SVC) device. The SVC device was initially considered for solving local steady-state voltage issues on highest 220 kV and 400 kV voltage levels in the region. As the SVC device features fast dynamic response, it seemed reasonable to verify whether its implementation benefits the operation of the entire ENTSO-E interconnection as well. The presented analysis was performed using a complex model for dynamic studies, comprising publicly available ENTSO-E model and internally constructed Slovenian power-system model, which was successfully tested and verified in the past. Modelling of the SVC device was achieved by means of available research publications dealing with the subject, both foreign as well as domestic. By implementing a simple damping strategy, the results showed a positive effect on a small-signal stability and indicated which inter-area oscillations can be successfully damped when considered devices are connected to the Slovenian high-voltage transmission network.

MIHALIČ, R.

KOMUNALNA ENERGETIKA / POWER ENGINERING, 3

abstract

BOGOVIČ, J., MIHALIČ, R.
MODEL OF STATIC SYNCHRONOUS SERIES COMPENSATOR
KOMUNALNA ENERGETIKA / POWER ENGINERING, 12

abstract

This paper presents a model of Static Synchronous Series Compensators (SSSC) for load-flow calculations in a distribution system for the forward-sweep algorithm. The model of SSSC for forward-sweep algorithm is based on current model used in Newton-Raphson load-flow calculations. The model is modified that is used for forward-sweep algorithm, but all known properties are preserved. Since the distribution networks are mainly radial and unequally loaded by phases, a three-phase modeling of SSSC is presented. Models are verified on a test case.

AŽBE, V., MIHALIČ, R.
FAULT-CURRENT LIMITATION IN SLOVENIAN ELECTRIC-POWER TRANSMISSION SYSTEM
KOMUNALNA ENERGETIKA / POWER ENGINERING, 10

abstract

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

abstract

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.

RUDEŽ, U., MIHALIČ, R.
POSSIBILITIES FOR UPDATING UNDERFREQUENCY LOAD SHEDDING PROTECTION IN THE SLOVENIAN POWER SYSTEM
KOMUNALNA ENERGETIKA / POWER ENGINERING, 19

abstract

In recent decades, the advantages of a fast development in the communication and computer technology have been successfully harvested in the majority of technological areas for updating various mechanisms and processes. Power system control and protection is no exception. However, in certain other countries actual implementation of modern technologies into power system control and protection mechanisms takes less time compared to Slovenia. In case of a sudden major generation unit outage severe underfrequency conditions appear in the power system and only a centralized gathering of measurements and global actions (e.g. use of WAMS and GPS technology) can represent an appropriate approach to a global problem. In such circumstances, underfrequency load shedding is in many times the last resort tool for avoiding a total power system blackout. Consequently, its appropriate actions are of great importance both from technological and economical point of view. As a current status of an underfrequency load shedding protection in the Slovenian power system is still on the traditional level, in this paper authors summarize some of known developed mechanisms, among which some of them might be considered as an actual possibility for an upgrade of current underfrequency scheme in the Slovenian power system to an adaptive level.

AŽBE, V., MIHALIČ, R.
A SOFTWARE TOOL FOR PRESENTING FACTS DEVICES IN AN ELECTRIC POWER SYSTEM
KOMUNALNA ENERGETIKA / POWER ENGINERING, 21

abstract