POWER PLANT ENGINEERING (UNIT-6)

UNIT-6

 POWER PLANT ECONOMICS AND ENVIRONMENTAL CONSIDERATIONS: Capital cost, investment of fixed charges, operating costs, general arrangement of power distribution, load curves, load duration curve, definitions of connected load, maximum demand, demand factor, average load, load factor, diversity factor – related exercises. effluents from power plants and Impact on environment – pollutants and pollution standards– methods of pollution control.


Types of Loads

Residential Load This type of load includes domestic lights, power needed for domestic appliances such as radios, television, water heaters, refrigerators, electric cookers and small motors for pumping water.

Commercial Load It includes lighting for shops, advertisements and electrical appliances used in shops and restaurants, etc.

Industrial Load It consists of load demand of various industries.

Municipal Load It consists of street lighting, power required for water supply and drainage purposes.

Irrigation Load This type of load includes electrical power needed for pumps driven by electric motors to supply water to fields.

Traction Load It includes terms, cars, trolley, buses and railways.

Load Curve A load curve (or load graph) is a graphic record showing the power demands for every instant during a certain time interval. Such a record may cover 1 hour, in which case it would be an hourly load graph; 24 hours, in which case it would be a daily load graph; a month in which case it would be a monthly load graph; or a year (7860 hours), in which case it would be a yearly load graph. The following points are worth noting :
(i) The area under the load curve represents the energy generated in the period considered.
(ii) The area under the curve divided by the total number of hours gives the average load on the power station.
(iii) The peak load indicated by the load curve/graph represents the maximum demand of the power station.
Significance of Load Curves:

• Load curves give full information about the incoming and help to decide the installed capacity of the power station and to decide the economical sizes of various generating units.
• These curves also help to estimate the generating cost and to decide the operating schedule of the power station, i.e. the sequence in which different units should be run.

Load Duration Curve A load duration curve represents re-arrangements of all the load elements of chronological load curve in order of descending magnitude. This curve is derived from the chronological load curve. Figure shows a typical daily load curve for a power station.

It may be observed that the maximum load on power station is 35 kW from 8 AM to 2 PM. This is plotted in Figure .Similarly, other loads of the load curve are plotted in descending order in the same figure. This is called load duration curve

The following points are worth noting : 

 (a) The area under the load duration curve and the corresponding chronological load curve is equal and represents total energy delivered by the generating station. 

(b) Load duration curve gives a clear analysis of generating power economically. Proper selection of base load power plants and peak load power plants becomes easier.

Dump Power This term is used in hydroplants and it shows the power in excess of the load requirements and it is made available by surplus water. 

Firm Power It is the power which should always be available even under emergency conditions. 

Prime Power It is the power which may be mechanical, hydraulic or thermal that is always available for conversion into electric power. 

Cold Reserve It is that reverse generating capacity which is not in operation but can be made available for service. 

Hot Reserve It is that reserve generating capacity which is in operation but not in service. 

Spinning Reserve It is that reserve generating capacity which is connected to the bus and is ready to take the load.

Connected Load The connected load on any system, or part of a system, is the combined continuous rating of all the receiving apparatus on consumers’ premises, which is connected to the system, or part of the system, under consideration.

Demand The demand of an installation or system is the load that is drawn from the source of supply at the receiving terminals averaged over a suitable and specified interval of time. Demand is expressed in kilowatts (kW), kilo volt-amperes (kVA), amperes (A), or other suitable units.

Maximum Demand or Peak Load The maximum demand of an installation or system is the greatest of all the demands that have occurred during a given period. It is determined by measurement, according to specifications, over a prescribed interval of time.

Demand Factor The demand factor of any system, or part of a system, is the ratio of maximum demand of the system, a part of the system, to the total connected load of the system, or of the part of the system, under consideration.
Expressing the definition mathematically,                                                                             

                                                    

                                                    Demand factor = Maximum demand / Connected load

Load Factor The load factor is the ratio of the average power to the maximum demand. In each case, the interval of maximum load and the period over which the average is taken should be definitely specified, such as a “half-hour monthly” load factor. The proper interval and period are usually dependent upon local conditions and upon the purpose for which the load factor is to be used. Expressing the definition mathematically,

                                                                  

                                                              Load factor = Avg Load / Maximum demand    

Diversity Factor The diversity factor of any system, or part of a system, is the ratio of the maximum power demands of the subdivisions of the system, or part of a system, to the maximum demand of the whole system, or part of the system, under consideration, measured at the point of supply. Expressing the definition mathematically,

          Diversity factor = Sum of individual maximum demands / Maximum demand of entire group

Utilization Factor The utilization factor is defined as the ratio of the maximum generator demand to the generator capacity.

    

Plant Capacity Factor It is defined as the ratio of actual energy produced in kilowatt hours (kWh) to the maximum possible energy that could have been produced during the same period. Expressing the definition mathematically

                                           Plant capacity factor = ( E /  C* t)

where, E = Energy produced (kWh Plant Economy ) in a given period, 

 C = Capacity of the plant in kW, and 

 t = Total number of hours in the given period.

Plant Use Factor It is defined as the ratio of energy produced in a given time to the maximum possible energy that could have been produced during the actual number of hours the plant was in operation. Expressing the definition mathematically,

                                                         

                                                     Plant use factor = E / C*t'  

where, t' = Actual number of hours the plant has been in operation.