Sylwester Robak

Power system stability screening for long-term planning of transmission network development

Stability analyses of a power system are performed at short-term and mid-term planning of transmission network development. Increased load demands and market economics are pushing transmission networks closer and closer to their operational limits. Therefore it is necessary to perform even a simplified power system stability assessment also at long-term planning. The article shows that very simple criteria of angle stability and voltage stability based on short-circuit power can be used as screening filters for fast contingency selection. The suggested criteria have been verified for a real large-scale system.

Contingency selection for power system stability analysis

Transmission expansion planning requires static and dynamic analyses. Planning criteria include the selection of contingencies consisting of faults and their clearing, performance standards, transmission system adjustments, and corrective action plan. Performance standards relating to power system dynamics mainly concern the voltage ride through and transient angle stability i.e. retaining synchronism after the occurrence of the contingencies mentioned. The selection of planning contingencies, for which performance standards must be complied with, is important in terms of capital expenditures in transmission network expansion and secure power system operation. This paper discusses planning contingencies accepted by various transmission network operators worldwide and describes a set of planning contingencies proposed by the authors.

Automatic Alleviation of Overloads in Transmission Network by Generation Curtailment

For economic reasons, expansions of transmission networks are based on a compromise between capital cost and security of power system operation. At the same time, the power system must withstand typical highly likely contingencies. Various emergency state control systems, also called special protections, prevent emergencies following less likely contingencies. This paper describes overloads emergency state control (OLEC) used for the alleviation of overload in transmission networks near a power plant. Such control uses the functions of automated power reduction of generating units and has been implemented for a large steam power plant. The OLEC presented here uses different methods of generation curtailment for steam generation units. A case study illustrates the efficiency of the proposed control method.

Automatyka odciążająca sieć przesyłową oparta na zaniżaniu wytwarzania

For financial reasons expansion of transmission networks is based on the compromise between investment costs and ability of power system to withstand disturbances. It is assumed, that power system must withstand typical credible and non-credible disturbances. To avoid blackouts following extreme disturbances the power systems are equipped with emergency control also referred to as special protection. In this paper an overload emergency control is described. It has been designed and implemented in order to alleviate overloads in transmission lines in the vicinity of large steam power plant. It utilizes capability of steam generating units to curtail automatically real power. (Overload emergency state control of transmission network based on generation curtailment) Słowa kluczowe: automatyka odciążająca, sieci przesyłowe, łagodzenie przeciążeń, zaniżanie wytwarzania.

Selected issues of cable link designing in HVAC and HVDC submarine power grids

Submarine (offshore) HVAC and HVDC cable power grids will play bigger and bigger role in the nearest future. In particular it will be connected with development of offshore wind farms and establishment of submarine transmission interconnections between the various national power systems. It results in necessity to elaborate proper procedures of designing of cable links (lines) which are part of HVAC and HVDC submarine power grids. Concept of offshore cable power grids in the context of introducing (injecting) of power generated in offshore wind farms to on-shore power grids and intersystem power exchange have been described in the paper. Submarine cable link as an element of submarine power grid have been described. Examples of existing submarine cable links and the ones that are being designed, as well as examples of offshore power grids have been given. Then technical characteristic of HVAC and HVDC submarine power cables have been presented. In the further part of the paper general power system requirements concerning cooperation of submarine cable link and on-shore power grid have been formulated. The main part of the paper concerns designing process of HVAC and HVDC submarine cable links. General and detailed rules of designing of both types of submarine cable links, considering difficulties well known from practice, have been described. At the end of the paper summary and final conclusions have been presented.

Short-circuit power as important reliability factor for power system planning

Detailed stability analyses of a power system are performed at short-term and mid-term planning of transmission network development. At long-term planning, due to the uncertainty of power system data, the stability analyses are either omitted or performed in a simplified method. Currently, due to the economical and ecological reasons, the power system operators are interested to use the transmission network as close as possible to the thermal and stability limits. Therefore it is necessary to perform even a simplified power system stability assessment also at long-term planning. The paper shows that very simple criteria of angle and voltage stability based on short-circuit power can be used for the sake of long-term planning. The suggested criteria were verified for a real large-scale power system.

Selected problems of frequency control for a multi-area power system with heterogeneous generation structure

In perspective, by 2030, a change of the fuel/ technology structure of capacity power will take place during the next dozen or so years in many countries of the European Union. Such changes are also planned in the Polish Power System (NPS) structure of capacity power which, in addition to the economic and environmental is also reflected under the angle of frequency control and tie-line power in interconnected power systems. The submitted paper discusses the proposed changes in the structure of capacity power on the example of the NPS. Moreover, some results of system frequency and tie-line power control (load and frequency control) in a heterogeneous generation power system are presented.