Unit-5&6Lecture 32
Load management:
Load management, also known as demand side management (DSM), is the process of balancing the supply of electricity on the network with the electrical load by adjusting or controlling the load rather than the power station output.
This can be achieved by direct intervention of the utility in real time, by the use of frequency sensitive relays triggering circuit breakers (ripple control), by time clocks, or by using special tariffs to influence consumer behavior.
Load management allows utilities to reduce demand for electricity during peak usage times, which can, in turn, reduce costs by eliminating the need for peaking power plants. In addition, peaking power plants also often require hours to bring on-line, presenting challenges should a plant go off-line unexpectedly.
Load management can also help reduce harmful emissions, since peaking plants or backup generators are often dirtier and less efficient than base load power plants. New load-management technologies are constantly under development — both by private industry and public entities.
Economic loading of generators and interconnected stations:
Optimum economic efficiency is achieved when all the generators which are running in parallel are loaded in such a way that the fuel cost of their power generation is the minimum. The units then share the load to minimize the overall cost of generation.
This economical approach of catering to the load requirement is called as ‘economic dispatch’. The main factor in economic operation of power systems is the cost ofgenerating the real power. In any EPS, the cost has two components as under:
• The Fixed Costs: Capital investment, interest charged on the money borrowed, tax paid, labour, salary, etc. which are independent of the load variations.
• The Variable Costs: which are dependant on the load on the generating units, the losses, daily load requirements, purchase or sale of power, etc.
The current discussion on economic operation of power systems is concerned about minimizing the variable costs only.
Further, the factors affecting the operating cost of the generating units are: generator efficiency, transmission losses, fuel cost, etc. Of these, the fuel cost is the most important factor. Since a given power system is a mix of various types of generating units, such as hydal, thermal, nuclear, hydro-thermal, wind, etc., each type of unit contributes its share for the total operating cost. Since fuel cost is a predominating factor in thermal (coal fired) plants, economic load dispatch (ELD) is considered usually for a given set of thermal plants in the foregoing discussion.
PROBLEM OF ECONOMIC LOAD SCHEDULING:
There are two problem areas of operation strategy to obtain the economic operation of power systems. They are: problem of economic scheduling and the problem of optimal power flow.
* The problem of economic scheduling: This is again divided into two categories:
• The unit commitment problem (UCP):Here, the objective is to determine the various generators to be in operation among the available ones in the system, satisfying the constraints, so that the total operating cost is the minimum. This problem is solved for specified time duration, usually a day in advance, based on the forecasted load for that time duration.
• The economic load dispatch (ELD):Here, the objective is to determine the generation (MW power output) of each presently operating (committed or put on) units to meet the specified load demand (including the losses), such that the total fuel cost is minimized.
* The problem of optimal power flow: Here, it deals with delivering the real power to the load points with minimum loss. For this, the power flow in each line is to be optimized to minimize the system losses.
Dept. of EEE, NIT-RaichurPage 1