UNIT-2-PPT- Real Power Frequency Control
- 1. 1 KONGUNADU COLLEGE OF ENGINERING AND TECHNOLOGY, TRICHY KONGUNADU COLLEGE OF ENGINEERING AND TECHNOLOGY (AUTONOMOUS) DEPARTMENT OF ELECTRICALAND ELECTRONICS ENGINEERING 20EE601- POWER SYSTEM OPERATION AND CONTROL UNIT-II REAL POWER AND FREQUENCY P.SRIDHAR,AP/EEE
- 2. KONGUNADU COLLEGE OF ENGINERING AN D TECHNOLOGY, TRICHY 2 UNIT II-REAL POWER-FREQUENCY CONTROL Basics of speed governing mechanisms and modeling - Speed load characteristics Regulation of two generators in parallel - Load Frequency Control (LFC) of single area system-Static and dynamic analysis of uncontrolled and controlled cases- LFC of two area system - Tie line modeling- Block diagram representation of two area system - Static and dynamic analysis-Tie line with frequency bias control-State variability model.
- 3. TECHNICAL TERMS Control area: Most power systems normally control their generators in unison. The individual control loops have the same regulation parameters. The individual generator turbines tend to have the same response characteristics then it is possible to let the control loop in the whole system which then would be referred to as a control area. Power Pool: An association of two or more interconnected electric systems having an agreement to coordinate operations and planning for improved reliability and efficiencies electric systems having an agreement to coordinate operations and planning for improved reliability and efficiencies KONGUNADU COLLEGE OF ENGINERING AND TECHNOLOGY, TRICHY 3
- 4. Prime Mover: The engine, turbine, water wheel, or similar machine that drives an electric generator; or, for reporting purposes, a device that converts energy to electricity directly (e.g., photovoltaic solar and fuel cell(s)). Pumped-Storage Hydroelectric Plant: A plant that usually generates electric energy during peak-load periods by using water previously pumped into an elevated storage reservoir during off-peak periods when excess generating capacity is available to do so. When additional generating capacity is needed, the water can be released from the reservoir through a conduit to turbine generators located in a power plant at a lower level. KONGUNADU COLLEGE OF ENGINERING AND TECHNOLOGY, TRICHY 4
- 5. Regulation: The governmental function of controlling or directing economic entities through the process of rulemaking and adjudication Reserve Margin (Operating):The amount of unused available capability of an electric power system at peak load for a utility system as a percentage of total capability. Restructuring: The process of replacing a monopoly system of electric utilities with competing sellers, allowing individual retail customers to choose their electricity supplier but still receive delivery over the power lines of the local utility. It includes the reconfiguration of the vertically-integrated electric utility. KONGUNADU COLLEGE OF ENGINERING AND TECHNOLOGY, TRICHY 5
- 6. Retail Wheeling: The process of moving electric power from a point of generation across one or more utility-owned transmission and distribution systems to a retail customer. Revenue: The total amount of money received by a firm from sales of its products and/or services, gains from the sales or exchange of assets, interest and dividends earned on investments, and other increases in the owner's equity except those arising from capital adjustments. Scheduled Outage: The shutdown of a generating unit, transmission line, or other facility, for inspection or maintenance, in accordance with an advance schedule. Real power: The real power in a power system is being controlled by controlling the driving torque of the individual turbines of the system. KONGUNADU COLLEGE OF ENGINERING AND TECHNOLOGY, TRICHY 6
- 7. LOAD FREQUENCY CONTROL The following basic requirements are to be fulfilled for successful operation of the system: The generation must be adequate to meet all the load demand The system frequency must be maintained within narrow and rigid limits. The system voltage profile must be maintained within reasonable limits and In case of interconnected operation, the tie line power flows must be maintained at the specified values. KONGUNADU COLLEGE OF ENGINERING AND TECHNOLOGY, TRICHY 7
- 8. BASICS OF SPEED GOVERNING MECHANISM AND MODELLING KONGUNADU COLLEGE OF ENGINERING AND TECHNOLOGY, TRICHY 8
- 9. Model of Speed Governor 9 Movement of C:
- 10. 10 Movement of D: Movement of ΔXE:
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- 13. Turbine Model 13 We are interested in the increased power generation ΔPG due to the increased steam value opening. There is incremental increase in turbine power ΔPT due to the change in valve position ΔXÊ, which will result in an increased generator power ΔPG. If the generator incremental loss is neglected, then ΔPT = ΔPG
- 14. Generator Load Model To develop the mathematical model of an isolated generator which is only supplying local load and is not supplying power to another area, suppose there is a real load change of ΔPD Due to the action of the turbine controllers, the generator increases its output by an amount ΔPG. The net surplus power (ΔPG - ΔPD) will be absorbed by the system in two ways. 14 1. By increasing the kinetic energy in the rotor at the at the rate / 𝒅 𝒅𝒕 (WK.E) 2. As the frequency changes, the motor load changes being sensitive to speed.
- 15. 15 By increasing the kinetic energy in the rotor at the at the rate / 𝒅 𝒅𝒕 (WK.E)
- 16. 16 2. As the frequency changes, the motor load changes being sensitive to speed.
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- 18. SPEED-LOAD CHARACTERISTICS (LOAD SHARING BETWEEN TWO SYNCHRONOUS MACHINES IN PARALLEL) 18
- 19. 19 Power output per MW Vs speed characteristics
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- 24. REGULATION OF ALTERNATORS 24 Regulation is defined as percentage rise in voltage when full load at the specified power factor is switched off, the excitation being adjusted initially to give normal voltage.
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- 26. 26 Necessity Alternators may be put in parallel because of the following reasons. 1. Local or regional power usè may exceed the power of a single available generator. 2. Parallel alternators allow one or more units to be shut down for scheduled emergency maintenance while the load is being supplied with power. 3. Generators are inefficient at part load, so shutting down one or more generators allows the remaining load to be carried with less machines that are efficiently loaded. 4. Load growth can be handled by added machines without disturbing the original installation. 5. Available machine prime movers and generators can be matched for economic cost and flexible use.
- 27. 27 Requirements for Parallel Operation Alternators to be operated in parallel should meet the following requirements. 1. They must have the same output voltage rating. 2. The rated speeds of the machines should be such as to give the same frequency. 3. The alternators should be of the same type so as to generate voltages of the same waveform. They may differ in their KVA rating. 4. The prime movers of the alternators should have same speed load drooping characteristics, so as to load the alternators in proportion to their output rating. 5. The alternators should have reactances in their armatures, otherwise, they will not operate in parallel
- 28. 28 Conditions for Proper Synchronising 1. The terminal voltage of the incoming machine must be exactly equal to that of the others, or of the bus-bars connecting them. 2. The speed of the incoming machine must be such that, its frequency equals bus-bar frequency. 3. The phase of the incoming machine voltage must be the same as that of the bus- bar voltage relative to the load 4. The phase sequence of the incoming
- 29. LOAD FREQUENCY CONTROL OF A SINGLE AREA SYSTEM 29 To analyse the LFC of an isolated system, first build mathematical model from the block diagram. Let ΔPC be the incremental control input. Let ΔPD be the incremental disturbance input. The incremental control input is due to the change in the speed changer setting, while the incremental disturbance input is due to the change in load demand. There are two responses: (i) Steady state or static response. (ii) Dynamic state response.
- 30. 30 Static Analysis or Steady State Response of Uncontrolled Case Consider the speed changer has a fixed setting. Under this condition ΔPC = 0 and the load demand changes. This is known as free governor operation.
- 31. 31 Using block reduction technique the block diagram is shown in figure
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- 33. 33 Applying final value theorem,
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- 35. 35 The system performance in terms of how the change in power affects the change in frequency is evaluated through AFRC.
- 36. 36 When several generators with governor speed regulations R1, R2, . . . . . . . . Rn are connected to the system, the steady state deviation in frequency is given by The droop of the load frequency curve is shown in Figure c is mainly determined by regulation.
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- 38. 38 Effect of Speed Changer on Speed Governor System A governor system can change the position of the main steam value which is actuated by the speed changer. Using this, we can restore the frequency to the initial value at various loads. (or output of generator). Let us consider 60% load. Nominal frequency = 50 Hz (i.e., 100% frequency) as depicted by the operating 'a', with an incremental load APD, the turbine speed drops and the new operating point is 'b' and the system frequency is 49.5 Hz (i.e., 99% frequency).
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- 40. 40 Effect of speed changer on speed governor system load frequency characteristics Now a controlling force ΔPC is applied to the speed changer and the characteristics is shifted upwards and the new operating point 'c' is shown in above Figure and the system is again operating at rated frequency. Hence, both controlling and disturbance forces are acting simultaneously.
- 41. 41 Static Analysis of Controlled Case In this case, there is a step change ΔPC force for speed changer setting and the load demand remains fixed i.e., ΔPD = 0.
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- 44. 44 Dynamic Response of Uncontrolled Case The static response of the ALFC loop yielded important information about frequency accuracy. The dynamic response of the loop will inform about "tracking" ability and stability of the loop. Assumptions: 1. Neglect the turbine dynamics. 2. The speed changer action is instantaneous. Put ΔPC(s) = 0, The block diagram reduces as shown in Figure
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- 46. 46 We can simplify the analysis by making the following assumptions.
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- 51. 51 • An interconnected power system is divided into a number of "control areas” for the purpose of load frequency control. • When subjected to disturbances like a small load change, all the generator - turbine units in a control area swing together with the other groups of generator turbine units in other areas. • Hence, all the units in a control area are represented by a single unit of equivalent inertia and characterized by a single (area) frequency. • Since all the network is strong, all the bus loads in a control area are assumed to act at single load point and characterized by a single equivalent load parameter. • The different control areas are connected by relatively "weak" tie lines. A typical n-area power
- 52. 52 For the optimal operation of an interconnected power system, the following points are to be considered. 1. Under normal operating condition, each control area should have the capacity to meet its own load from its own spinning generator, plus the scheduled interchange between the neighboring areas. 2. Under emergency condition, the energy can be drawn from the spinning reserves of all the neighboring areas immediately due to the sudden loss of generating unit. During normal operation of interconnected power system requires load frequency controller for each area which not only drives the area frequency deviation to zero but also the "net interchange" of that area to zero under steady state condition. Net interchange of area is defined as the algebraic sum of tie line flows between area i and other connected areas with tie line flow out of
- 53. 53 Two Area Load Frequency Control System Modelling
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