27-08-2012, 12:27 PM
Computer Application In Power System
Computer Application.ppt (Size: 6.2 MB / Downloads: 249)
Introduction
The emphasis in modern power systems has turned from resource creation to resource management. The two primary functions of an energy management system are security and economy of operation and these tasks are achieved in main control centers.
In the present state of the art the results derived by the centre computers are normally presented to the operator who can then accept, modify or ignore the advice received. However, in the longer term the operating commands should be dispatched automatically without human intervention, thus making the task of the computer far more responsible.
In order of increasing processing requirements the main computer tasks involved in the management of electrical energy systems are as follows :-
Network analysis.
Automatic generation control (AGC).
Generation scheduling.
Supervisory control and data acquisition (SCADA).
Energy management is performed at control center, typically called system control centers, by computer systems called energy management systems /EMS/. Data acquisition and remote control is performed by SCADA.
AGC consists of two major and several minor functions that operate on –line in real time to adjust the generation against load at minimum cost. The major functions are load frequency control and economic dispatch, and the minor functions are reserve monitoring, which assures enough reserve on the system; interchange scheduling, which initiates and completes scheduled interchanges; and other similar monitoring and record functions /load forecast, fault allocation, trouble analysis/.
Generation control and ED minimize the current cost of energy production and transmission within the range of available controls. Energy management is a supervisory layer responsible for economically scheduling production and transmission on a global basis and over time intervals consistent with cost optimization.
LF and QV Control
Although there are many things to control in power system, majorly we control voltage and frequency by controlling other parameters of the generators, load and other devices in the system.
For efficient and secured power system- maintain reliability, security, stable, operate in most economical way, better quality (frequency with in the limit (3%), voltage (5% HV, 10% LV)).
Frequency is global phenomena ( same in one node and other), voltage is local phenomena (one point and another point is different). Eg. Change of frequency and voltage affect normal operation of the system.
Load Frequency Control
In a power system the load demand is continuously changing. In accordance with it the power input has also to vary. If the input - output balance is not maintained a change in frequency will occur. The control of frequency is achieved primarily through speed governor mechanism aided by supplementary means for precise control.
LFC consists of three major parts.
(i) Speed governing system
(ii) Rotating components (turbine-generator)
(iii) load and power system.
Single control area
In the previous sections models for turbine-generator, power system and speed governing systems are obtained. In practice, rarely a single generator feeds a large area. Several generators connected in parallel, located also, at different places will supply the power needs of a geographical area. Quite normally, all these generators have the same response characteristics in load demand. Such a coherent area is called a control area in which the frequency is assumed to be the same throughout in static as well as dynamic conditions.
In such a case, it is possible to define a control area, grouping all the generators in the area together and treating them as a single equivalent generator, i.e for purpose of developing a suitable control strategy, a control area can be reduced to a single speed governor, turbo-generator and load system. Putting together, the carious models derived so far a single control area can be conceived as shown below.
OPTIMAL POWER FLOW
ECONOMIC OPERATION /ED-Economic Dispatch/
The economic dispatch problem consists in allocating the total demand among generating units so that the production cost is minimized.
Generating units have different production costs depending on the prime energy source used to produce electricity (mainly coal, oil, natural gas, uranium, and water stored in reservoirs).
In addition to continuous decisions on how to allocate the demand among generating units, the economics of electricity generation also requires the calculation of an optimum time schedule for the start-up and shutdown costs of the generating units. (since the units’ start-up or shutdown costs can be significant, on/off scheduling decisions must be optimally coordinated with the ED of the continuous generation outputs.