UNIT I: INTRODUCTION System load variation load characteristics load curves and load duration curve (daily, weekly and annual) load factor diversity factor. Importance of load forecasting and simple techniques of forecasting. An overview of power system operation and control and the role of computers in the implementation.(Qualitative treatment with block diagram).

1 Recent trends in real time control of power system

Real time control of power system means the system in working state. While the power system is in process control the machine at that time in the working field.

The size of turbo generator units has increased. So it is difficult to operate them near critical parameters. Hence, it is necessary to acquire a large volume of data pertaining to plant and to process them immediately. It is essential to take necessary control actions within critical time. Higher cost of fuels, environmental protection and rising inflationary spiral have placed a strain on the utility return on investment. New plant equipment and construction costs rise at an alarming rate. This means, more peak load demand must be met by older plants. Thus, monitoring and control systems must be f ast enough to protect generation equipments against overloads, false and dangerous operating conditions, conventional electrical instruments can handle the situation, if information receiving is one at a time. But when a flood of information hit all at once, a fast data processing equipment or system is required. Thus the computer is essential for the efficient and economic operation and control.

Some of the major benefits of computerized operation and control of plant are:

Increased plant safety.More equipment life. Increased plant availability. Higher plant efficiency.Minimum operating errors.

In 1982, the United States derived its electricity from the following sources. 72 % from coal, gas, oil, 15 % from hydro power and 13 % from nuclear. But no ener gy form is entirely risk free. Use of energy made possible our present life styles. Thus the major goals for the future are to develop new primary resources which promote better means of generation and transmission and emphasis less wasteful use of electri city.

Computer Configuration Trend:

The computer system used at power plant station has been undergoing continuous development over the years. Formerly, all the functions such as data acquisition, logging display, control and performance calculations were performer by computer processing unit (CPU). In such system failure of any of the elegant leads to the total system breakdown. Thus, the need for a dual computer configuration arose which is quite costly.

The further advancement in communication technology and powerful microprocessors has resulted in the cheap and reliable microprocessor based Distributed Processing System (DPS). It is based on the principle of LAN. Today, in all process industries including power plant, this system is employed for data a cquisition and control. DPS consists of a number of microprocessors connected through data highway, which is passive in nature. Each processor is assigned a specific task independently. So, the failure of one of the processors does not disturb the function of the other processors.

Advantages of DPS

Better reliability.Greater processing power. More responsiveness.Longer survivability. Better modularity.More system expandability. Easier maintenance.

Functions and Facilities

The function of the data acquisition and control system is to provide the operator with current plant information through graphic displays, group displays, alarms annunciations and so on, for the safe operation of plant. The DPS further provides detailed historical information for diagnostic / review purposes in case of outage and plant performance. The data acquisition and control system performs the following general functions.

Data acquisition and validation. Real time variable computations. Alarm monitoring and display.Performance and deviation calculation. Trends, events, reports and logs.Sequential control.Modulating control.Other related functions.

In order to carry out these functions, some facilities are required. They are:

Data Processing System

The process input / output requirements are high resolution digital inputs, low resolution digital inputs, analog inputs 4 20 mA DC, thermo couple inputs, RTD inputs, pulse inputs, analog outputs and contact outputs.

Computer System Design Requirement for Power Plant:

Power plant is a complex system which includes the boiler, turbo generator, cooling tower and the reheat system. The operating parameters of the plant are largely governed by the grid connected to it. Thus, DPS at power plant must have the following features:

High availability. Good expandability. High data rate.Geographic distance spanning.Ability to support several hundred independent devices. Stability under high control.Self diagnostic.Ease of reconfiguration and maintenance and low cost.

Non Conventional Energy Resources:

i Solar power.ii. Wind, wave, geothermal and tidal power.

iii. Fossil fuel.

Future Generating Equipment:

current densities used in rotor and stator windings. Major efforts are used to develop superconducting machines, where the winding temperature is kept close to absolute zero. The enormous current and flux densities achieved in such machines coiled possibly increase 1 GW size unit to(5 6) GW. This w ould mean better generating economy.

Automation

It is the term used to describe a broad array of processes, products and systems working in harmony to automate manufacturing. It includes elements of factory and plant automation such as robotics, drives, PLC and computerized numerical control, production, planning process optimization, open control systems; human machine interfaces vision systems and industrial networks. It is only in the last few years the companies have started incorporating software sys tems at all levels of production.

Modularity & Reconfigurability:

Design of machinery demands, connectivity solutions, which are reliable and simple to use.At higher levels of plant automation, it will become possible to run overseas factories on the

e web browser used to control domestic production.

Field Bus Networks

In many factories, hard wired control systems are still the norm. They are used to control level to allow communication with the operation level.

Decentralized Control:

As control is being transferred to the field devices, electronic motor control can take place at the motor itself. Electrical connections are integrated in connectors that largely eliminate

wiring errors and allow motors to be connected and disconnected wi thout any use of tools. All the components of a decentralized automation system will be fed by a continuous common connection system for data and power.

2 What are system level and plant level controls?

The function of an electric power system is to convert energy from one of the naturally available forms to electrical from and to transport it to points of consumption.

A properly designed and operated power system should meet the following fundamental requirement.

sent to meet the active and reactive powerdemand2. Minimum cost with minimum ecological impact.3. The power quality must have certain minimum standards within the tolerance or limit such as

Constancy of frequency.Constancy of voltage (Voltage magnitude and load angle). Level of reliability.

Factor affecting power quality:

Switching surges. Lightning.Flickering of voltage.Load shedding.Electromagnetic interference.Line capacitance and line inductance. Operation of heavy equipment.Welding machine operation.

The three main controls involved in powers are: Plant

Level Control (or) Generating Unit Control.2 System Generation Control.3 Transmission Control.

1. Plant Level Control (or) Generating Unit Control

The plant level control consists of:

i Governor control or Prime mover control.ii. Automatic Voltage Regulator (AVR) or Excitation control.

i Governor control or Prime mover control

Governor control or Prime mover controls are concerned with speed regulation of the governor and the control of energy supply system variables such as boiler pressure, temperature and flows. Speed regulation is concerned with steam input to turbine. With

ariation in load, speed of governor varies as the load is inversely proportional to speed. The speed of the generator varies and the governor senses the speed and gives a command signal, so that, the steam input of the turbine is changed relative to the load requirement.

ii Automatic Voltage Regulator (AVR) or Excitation control

The function of Automatic Voltage Regulator (AVR) or Excitation control is to regulate generator voltage and relative power output. As the terminal voltage varies the excitation control, it maintains the terminal voltage to the required standard and the demand of the reactive power is also met by the excitation control unit.

These controls are depicted in given figure

Figure 1: Plant and System Level Controls

2. System Generation Control

The purpose of system generation control is to balance the total system generation against system load and losses, so that, the desired frequency and power interchange with neighboring systems are maintained. This comprises of:

i Load Frequency Control (LFC).ii. Economic Dispatch Control (EDC).

iii. System Voltage Control.iv. Security control.i Load Frequency Control (LFC).

This involves the sensing of the bus bar frequency and compares with the tie line power frequency. The difference of the signal is fed to the integrator and it is given to speed changer which generates the reference speed for the governor. Thus, the frequency of the tie line is maintained as constant.

ii Economic Dispatch Control (EDC).

When the economical load distribution between a number of generator units is considered, it is found that the optimum generating schedule is affected when an incremental increased at one of the units replaces a compensating decrease at every other unit, in term of some incremental cost. Optimum operation of generators at each generating station at various station load levels is known as unit commitment.

iii System Voltage Control

This involves the process of controlling the system voltage within tolerable limits. This includes the devices such as static VAR compensa tors, synchronous condenser, tap changing transformer, switches, capacitor and reactor.

The controls described above contribute to the satisfactory operation of the power system by maintaining system voltages, frequency and other system variables within their acceptable limits. They also have a profound effect on the dynamic performance of power system and on its ability to cope with disturbances.

iv Security control

The main objective of real time power system operation requires a process guided by control and decisions based on constant monitoring of the system condition. The power system operation is split into two levels.

LEVEL 1: Monitoring and Decision

The condition of the system is continuously observed I the control centres by protective relays for f aults or contingencies caused by equipment trouble and failure. If any of these monitoring devices identifies a sufficiently severe problem at the sample time, then the system is in an abnormal condition. If no such abnormality is observed, then the system is in a normal condition.

LEVEL 2: Control

At each sample, the proper commands are generated for correcting the abnormality on protecting the system from its consequences. If on abnormality is observed, then the normal operation proceeds for the next sample interval.

Central controls also play an important role in modern power systems. Today systems are composed of interconnected areas, where each area has its own control centre. There are

many advantages to interconnections. The interconnected areas can share their reserve power to handle anticipated load peaks and unanticipated generator outages. Interconnected areas can also tolerated large load changes with smaller frequency deviations at spinning reserve and standby provides a reserve margin.

The central control centre information including area frequency, generating unit outputs and tie line power floes to interconnected areas. This information is used by automatic load frequency control in order to maintain area frequency at its scheduled values

3 Explain (i) Load Forecasting, (ii) Unit Commitment and (iii) Load Scheduling.

1 Load forecasting

The load on their systems should be estimated in advance. This estimation in advance is known as load forecasting. Load forecasting based on the previous experience without any historical data

Classification of load forecasting:

Forecasting Lead Time Application

Very short time Few minutes to half an hour Real time control, real time security evaluation.

Short term Half an hour to a few hoursAllocation of spinning reserve, unit commitment,maintenance scheduling.

Medium term Few days to a few weeks Planning or seasonal peak winter, summer.

Long term Few months to a few years To plan the growth of the generation capacity.

Need for load forecasting:

To meet out the future demand.Long term forecasting is required for preparing maintenance schedule of the generating units, planning future expansion of the system.For day t day operation, short term load forecasting demand and for maintain ing the required spinning reserve.Very short term load forecasting is used for generation and distribution. That is, economic generation scheduling and load dispatching.Medium term load forecasting is needed for predicted monsoon acting and hydro availability and allocating.

2 Unit Commitment

The unit commitment problem is to minimize system total operating costs while simultaneously providing sufficient spinning reserve capacity to satisfy a given security level. In unit commitment problems, we consider the following terms.

A short term load forecast. System reserve requirements. System security.Startup costs for all units.Minimum level fuel costs for all units. Incremental fuel costs of units.Maintenance costs.

3 Load Scheduling (Load Dispatching)

Loading of units are allocated to serve the objective of minimum fuel cost is known as load scheduling. Load scheduling problem can be divided into:

i Thermal scheduling.ii. Hydrothermal scheduling.

i Thermal scheduling

The loading of steam units are allocated to serve the objective of minimum fuel cost. Thermal scheduling will be assumed that the supply undertaking has got only form thermal or from steam stations.

ii Hydrothermal scheduling.

Loading of hydro and thermal units are allocated to serve the objective of minimum fuel cost is known as hydrothermal scheduling.

Scheduling of hydro units are complex because of natural differences I the watersheds, manmade storage and release elements used to control the flow of water are difficult.

During rai ny season, we can utilize hydro generation to a maximum and the remaining period, hydro generation depends on stored water availability. If availability of water is not enough to generate power, we must utilize only thermal power generation. Mostly hydroel ectric generation is used to meet out peak loads. There are two types of hydrothermal scheduling.

) Long range hydro schedulingb) Short range hydro scheduling.

) Long range hydro scheduling

Long range hydro scheduling problem involves the long range forecasting of water availability and the scheduling of reservoir water releases for an interval of time that depends on the reservoir capacities. Long range hydro scheduling involves

b

from I week to I year or several years. Long range hydro scheduling involves optimization of statistical variables such as load, hydraulic inflows and unit availabilities.

) Short range hydro scheduling.

Short range hydro scheduling involves from one day to one week or hour by hour scheduling of all generation on a system to achieve minimum production cost foe a given period.

Assuming load, hydraulic inflows and unit availabilities are known, for a given reservoir level, we can allocated generation of power using hydro plants to meet out the demand, to minimize the production cost.

The largest category of hydrothermal system includes a balance between hydroelectric and thermal generation resources. Hydrothermal scheduling is developed to minimize thermal generation production cost.

4 Explain the need for voltage and frequency regulation in power system.

A power system is said to be well designed if it gives a good quality of reliable supply, which means that the voltage levels must be within reasonable limits. Practically, all the equipments on the power system are designed to operate satisfactorily within voltage variations of around 5 %. If the voltage variation is more than a pre specified value, the performance of the equipments is also sacrificed.

The voltage at the generating stations and the frequency decides the KW loading of the generating stations and the loading through the interconnectors.

Need f r Voltage Regulation in Power System

Knowledge of voltage regulation helps in maintaining the voltage at the load terminals within prescribed limits under fluctuating load conditions, by employing suitable voltage control equipment. The following points are to be considered.

The transmission lines and the distribution lines need voltage control at various stages to maintain the voltage at the last consumers premises within permissible limits.Variations in supply voltage are detrimental in various aspects.Below normal voltage substantially reduces the light output from incandescent lamps. Above normal voltage reduces the life of the lamps.Motors operated at below normal voltage draw abnormally high currents and may overheat, even when carrying no more than the rated horse power load.If the voltage of the system deviates from the nominal value, the performance of the devices suffers and its life expectancy drops.The real line losses depend as much upon the reactive line as upon the real time power flow. The reactive line flow depends upon line end voltages.

f

By adjusting the excitation of the generator at the sending end below a certain limit may result in instability of the system and excitation above certain level will result in overheating of the rotor.Service voltages are usually specified by a nominal value a nd the voltage maintained is ± 5 % of the nominal value.

Need f Frequency Regulation in Power System

Knowledge of frequency regulation helps in maintaining the system frequency that is speed of the alternator within prescribed limits under fluctuating load conditions, by using speed governor and integral controller. In a network, considerable drop in frequency occurs due to high magnetizing currents in induction motors and transformers. The following points to be considered.

receiving end voltage. If we connected two systems in parallel, it will spoil the system.The generator turbines, particularly steam driven ones are designed to operate at a very precise speed.Most of AC motors rub at speeds that are directly related to the frequency.The overall operation of a power system can be much better controlled if the frequency error is kept within strict limits.A large number of electrically operated clocks are used. They are all driven be synchronous motors and the accuracy of these clocks is a function not only of a frequency error, but actually of the integral of this error.Constant turbine speed is an important requirement. The velocity of the expanding steam is beyond our control and the turbine efficiency requires perfect speed match.Unusual deviations in the frequency can be detected earlier.When two systems working at different frequencies are to be tied together to make same frequency, frequency converting stations or links are required.

5 Draw and explain the basic P f and Q v control loops.

BASIC PF AND QV CONTROL LOOPS

S i in the real bus power affect the bus phase angle and not the bus voltage magnitudes. This change affects the real line flows and not the reactive line flows.

i in the reactive power affect the bus voltage magnitudes and the phase angle. This change affects the reactive line flows and not the real line flows.A static change in the reactive bus power affects the bus voltage at the particular bus and has little ef ect on the magnitude of voltage.

QV Control Loop:

The automatic voltage regulator circuit or QV control loop as shown in given figure 2

This loop is used for voltage control. This bus bar voltage is stepped down using a potential transformer to a small value of voltage. This is sent to the rectifier circuit which converts the

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AC voltage into DC voltage and a filter circuit used in this removes the harmonics. The voltage Vi, thus rectified is compared with a reference voltage V ref in the comparator and a voltage error signal is generated. The amplified form of this voltage gives a condition for the exciter to increase the field current based on its polarity. The output of the generator is stepped up using a transformer and fed to the n=bus bar. Thus the v oltage is regulated and controlled in this control circuit.

PF Control Loop

This control loop circuit is divided into primary and secondary Automatic Load Frequency Control (ALFC) loop structures as shown in given figure 2

Figure 2: Automatic load frequency and voltage regulator control loops

Primary ALFC:

The circuit primarily controls the steam valve leading to the turbine. A speed sensor senses the speed of the turbine. This is compared with a reference speed, governor whose main activity is to control the speed of the steam by closing and opening of the control valve. That is, if the differential speed is low, then the control valve is opened to let out the steam at high

eed in turncontrols the frequency.

Secondary ALFC:

This circuit involves a frequency sensor that senses the frequency of the bus bar and compares it with Tie line power frequencies in the signal mixer. The output of this is an Area Control Error (ACE) w hich is sent to the speed changer through integrator. The speed changer gives the reference speed to the governor. Integral controller is used to reduce the steady state frequency change to zero. After this part of the circuit, is the introduction of the Primary ALFC loop whose function has already been described.Thus, the two loops together help in controlling the speed which in turn controls the

Using the relation, Speed N 120 f P

Where, f is frequency in Hz and P is number of poles.

6 Draw the load curve and load duration curve. Explain the importance of these curves in ection with economic operation of power system?

The generating stations may be steam, hydro, nuclear, diesel or any other type. This factor mainly depends upon the natural sources available in the areas. The power station should be as near as possible to the centre of the load so that the transmission cost and losses are minimum. The scheme employed should be such that extension could be made to meet with the increase in demand in future, without incurring heavy expenditure.

LOAD CURVES:

Load Curves:

Load on the power system is seldom constant. It varies from time to time. The curve showing the variation of load on the power station with respect to time is known as a load curve. It can be plotted on a graph taking load on Y axis and time on X axis.

Daily Load Curve:

The curve showing the variation of load on a whole day i.e., 24 hours with respect to time is known as daily load curve. The load variations are recorded half hourly or hourly on a whole day (24 hours). Typical daily load curve is as shown in figure 3.

Monthly Load Curve:

The curve showing the variation of load of the month with respect to time is known as monthly load curve.

It can be obtained from the daily load curves of that month. It can be plotted by calculating the average values of power over a month at different times of the day. It is used to fix rate of energy tariff.

Yearly or Annual Load Curve:

The curve showing the variation of load of the year with respect to time is known as yearly or annual load curve.

It can be obtained from the monthly load curves of that year. It is used to determine the annual load factor.

Figure 3: Daily load curve

The load curves supply the following informations:

The variation of the load during different hours of the day.The area under the curve represents the total number of units generated in a day.The peak of the curve represents the maximum demand on the station on the particular day.The area under the load curve represented is divided by the number of hours, gives the average load on the power station.The ratio of the area under the load curve to the total area of the rectangle in which it contained, gives load factor.

LOAD DURATION CURVE

This is another type of curve which indicated the variation of load, but with the loads arranged in descending order of magnitude, i.e., the greatest load on the left and lesser loads towards right. From this curve, the load fact or of the station can also be determined. Typical load duration curve is as shown in figure 4.

Figure 4: Load duration curveImportant Terms for Deciding the Type and Rating of Generating Plant:

Connected Load:

For deciding the type and rating of generating plant, it is necessary that engineering may be familiar with the following important terms.

The sum of the continuous ratings of all the electrical equipment connected to the supply system us known as connected load.

Maximum Demand

Thecalled the maximum demand. It is the maximum demand which determines the sixe and the cost of the installation.

Demand Factor:

The ratio of actual maximum demand on the system to the total rated load connected to the system is called the demand factor. It is always less than the unity.

Demand Factor =

Average Load or Demand:

Maximum Demand Connected Load

The average load or demand on the power station is the average of loads occurring at various events

Daily Average Load =

Monthly Average Load =

Annual Average Load =

Load Factor

KWhr Supplied in a day 24

KWhr Supplied in a month24 30

KWhr Supplied in a year 24 365

Load factor is defined as the ratio of average load to the maximum demand during a certain period of time such as a day or a month or a year is called the load factor.

Maximum Sum of individualDemand on the < maximumpower station demands

Load Factor = Average Demand Maximum Demand

If the plant is operated for T hours,

Load Factor = Average Demand T Units Generated in T hour Maximum Demand T Maximum Demand T

T = 24 for daily load curve.T = 24 × 7 for weakly load curve. T = 24 × 365 for annual load curve.

Significance of Load Factor:

Load factor is always greater than u nity, because average load is smaller than maximum demand.It is used to determine the overall cost per unit generated. If the load factor is high, cost per unit generated is low.

Diversity Factor:

The ratio of sum of the individual maximum demands of all the consumers supplied by it to the maximum demand of the power station is called the diversity factor.

Diversity Factor =

Sum of individual maximum demands Maximum Demand of power station

It is always greater than the unity.Because of maximum demand of different consumers do not occur at same time. Therefore,

If diversity factor is more, the cost of generation of power is low.

Factors to improve the diversity factor:

Giving incentives to some consumers to use electricity in the night or light load periods.Using day ligh t saving. Staggering the office timings.Having two part tariff in which consumer has to pay an amount dependant on the maximum demand of consumer uses.

Coincidence Factor

The reciprocal of the diversity factor is called the coincidence factor.

Coincidence Factor =

Maximum Demand of power station Sum of individual maximum demands

It is always less than the unity.

Capacity Factor or Plant Factor:

Capacity factor is defined as the ratio of the average load to the rated capacity of the power plant.

Capacity Factor =

Average DemandRated Capacity of the power plant

Units or KWhrs generatedPlant Capacity Number of Hours

Utilisation Factor:

It is a measure of the utility of the power plant capacity and is the ratio of maximum demand to the rated capacity of the power plant. It is less than the unity.

Utilisation Factor =

Maximum Demand on the power station Rated Capactiy of the power station

Plant Operating Factor (or) Plant Use Factor:

It is defined as the ratio of the actual energy generated during a given period to the product of capacity of plant and the number of hours the plant has been actually operated during the period.

Plant Use Factor =

Total KWhr GeneratedRated Capacity of the plant Number of operating hours

Reserve Capacity:

It is the difference between plant capacity and maximum demand.

Reserve Capacity = Plant Capacity Maximum Demand.

7 What is spinning reserve and does this reserve help in operating a power system efficiently? How is clod reserve different from hot reserve?

In any area, the kind of fuel available cost, availability of suitable sites for a hydro station, the nature of load to be supplied, are considered by choosing the type of generation. The minimum capacity of the generating station must be such as to meet the maximum demand.

Installed Reserves

Installed reserve is that generating capacity which is the power intended to be always available.

Installed reserve can be kept low by the achievement of good diversity factor.

Spinning Reserves:

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

Cold Reserves

Cold reserve is that reserve generating capacity which is available for service but is not in operation.

Hot Reserves:

Hot reserve is that reserve generating capacity which is in operation bus is not in service.

ASSIGNMENT QUESTION

8 A generating station has the following daily load cycle :Time (Hours) 0 6 6 0 0 2 2 6 6 20 20 24Load (MW) 20 25 30 25 35 20Draw the load curve and calculate,(1) Maximum demand, (2) Units generated per day, (3) Average load, (4) Load factor

9 A power station has to meet following demand:

Group A: 200 KW between 8 A.M and 6 P.M Group B: 100 KW between 6 A.M and 10 A.M Group C: 50 KW between 6 A.M and 10 A.MGroup D: 100 KW between 10 A.M and 6 P.M and then between 6 P.M and 6 A.M

Plot the daily Load curve and determine diversity factor, units generated per day and load factor.

10. (i) The maximum demand on a power station is 100 MW. If the annual load factor is 40%, calculate the total energy generated in a year.(ii) If the maximum demand on the station is 2500 KW and the number of KWh generated per year is 45 × 106, determine (1) Diversity factors, (2) Annual load factor

PART A 1 What i load curve?

The drawn between the variations f load the power station with reference t time i known load There three types, Daily load curve Monthly load curve Yearly load

2 What i daily load curve?

The drawn between the variations f load with reference t various time period f day i known daily load

3 What i monthly load curve?

It i obtained from daily load Average value f the power t month for different time periods calculated and plotted i the graph which i known monthly load

4 What i yearly load curve?

It i obtained from monthly load which i used t find annual load factor.

5 What i connected load?

It i the f continuous ratings f all the equipments connected t supply systems.

6 What i Maximum demand?

It i the greatest demand f load the power station during given period.

7.What i Demand factor?

It i the ratio f maximum demand t connected load. Demand factor= (max demand)/ (connected load)

8 What i Load factor?

The ratio f average load t the maximum demand during given period i known load factor.

Load factor (average load)/ (maximum demand)

9 What i Average demand?

The average f loads occurring the power station i given period (day month year) i known average demand.

Daily erage demand (no f units generated per day)/ (24 hours)Monthly erage demand (no f units generated i month)/ (no f hours i month)Yearly erage demand (no f units generated i year)/ (no f hours i year)

11. What i Diversity factor?

The ratio f the f individual maximum demand power station i known diversityfactor.Diversity factor (sum f individual aximum demand)/(maximum demand).

12. What i Capacity factor?

This i the ratio f actual energy produced t the maximum possible energy that could have been produced during given period.Capacity factor= (actual energy produced)/ (maximum energy that have been produced)

13. What i Plant factor?

It i the ratio f units generated t the product f plant capacity and the number f hours for which the plant i operation.Units generated per average load hours i year

14. What i Load duration curve?

When the load elements f load arranged i the order f descending magnitudes the then obtained i called load duration

14 What i the necessity f voltage regulation?

All equipments i power system designed t operate satisfactorily only when the voltage level the system correspond t their rated values. S voltage regulation i very important.

15 What the disadvantages f voltage regulation?

The disadvantages f voltage regulatio are,i) If voltage variation i then pre specified value, the performance f equipments i poorii) Life i most f the equipments i also sacrificed.

16 Give category f load device

The categories f load devices are, Motor devices 70%

b Heating and lighting 25% Electronic devices 5%

17 Why the frequency regulation i very important?

Since the speed f induction motors depend upon the system frequency, regulation f power system frequency i very important.

18 How the multitudes f devices characterized?

The multitude f devices characterized by,Size

b Symmetry (single three phase)Load constancy (in respect t time, frequency and voltage)

d Use cycle (regular random use).

19 What the effects f load dependency voltage and frequency?

The effects f load dependency voltage and frequency are, Serious problems created i HP motors.

b If efficiency and power factor increases, current decreases Generators lead t shut d

20 What i load management?

A generator capacity has increased i price (to much $1000 per kilowatt) and the fuel shortages put extra squeeze them, many electric utilities finding it worthwhile t try t

the load peaks. This i referred t load management.

21 Give the two major control loops f large generators?

The two major control loops f large generators are, Automatic Voltage Regulator (AVR)

b Automatic Load Frequency Control (ALFC)

22 Write about AVR loop.

The automatic voltage regulator (AVR) loop controls the magnitude f the terminal voltage (Vt) The latter voltage i continuously sensed, rectified and smoothed. This DC signal, the resulting after amplification and signal shaping the input t the exciter which finally delivers the voltage (Vf) t the generator field winding.

23 How the ALFC loop i affected by AVR loop?

AVR affect the magnitude f generated EMF (Eg) This generated EMF affects the generated real power Therefore changes i AVR loop affect ALFC loop.

24 Write about load frequency mechanism.

The frequency i closely related t the real power balance i the overall network. Under normal operating conditions the system generators synchronously and generate together the power t each moment i being drawn by all loads plus the real.

25 Give important for voltage control.

The real line losses depend much upon the reactive upon the real line power flow. It i possible t minimize these losses by selecting optimum power flow, i terms f real and reactive powers S the voltage control i very important.

26 What i the distinct difference between P f and Q V control?

The surplus f MEGAVARS tends t increase the frequency f system The changes not uniform but will b greatest t the buses where the Q surplus i the greatest. This i distinct difference between P f and Q lVl control