Page 1 Objectives In this lecture you will learn the following What are the transient processes before system frequency settles down to steady state ? We have seen the effect of speed droop settings on sharing of excess load between generators in steady state. Although we have considered only the steady state conditions, it is to be noted that governors, turbines and generators (and practically all constituents of a power system) are governed by dynamic equations. This means that steady state is not reached instantaneously. Indeed, if the transient processes are not stable, the system will not settle down to the steady state. Thus it is important to consider the dynamical equations which govern the physical structures, especially the prime mover system. While dynamical modelling of components is beyond the scope of this course, we will briefly discuss the working of a steam governor. A speed governor is a device which senses speed deviation from its reference value and appropriately changes control valve position in a steam turbine or gate position in a hydraulic turbine. This is achieved in older units using mechanical and hydraulic arrangements (mechanical hydraulic governors), while in modern units, the sensing and computing functions are done electrically (electrohydraulic governors). A speed governor should allow us to change the governor gain (or equivalently the droop) and also change the speed and/or load reference. A governor may also have additional parameters which tailor its dynamic response so that instability does not take place. A student is referred to the book "Power System Stability and Control" by P. Kundur, McGraw Hill, New York, 1994, for further reading on this subject. We study the frequency transients for a simplified two generator system with speed governing, by an example. onsider 2 identical generators supplying 2 loads as shown in the figure below. Module 3 : Frequency Control in a Power System Lecture 15 : Speed Governor Page 2 Objectives In this lecture you will learn the following What are the transient processes before system frequency settles down to steady state ? We have seen the effect of speed droop settings on sharing of excess load between generators in steady state. Although we have considered only the steady state conditions, it is to be noted that governors, turbines and generators (and practically all constituents of a power system) are governed by dynamic equations. This means that steady state is not reached instantaneously. Indeed, if the transient processes are not stable, the system will not settle down to the steady state. Thus it is important to consider the dynamical equations which govern the physical structures, especially the prime mover system. While dynamical modelling of components is beyond the scope of this course, we will briefly discuss the working of a steam governor. A speed governor is a device which senses speed deviation from its reference value and appropriately changes control valve position in a steam turbine or gate position in a hydraulic turbine. This is achieved in older units using mechanical and hydraulic arrangements (mechanical hydraulic governors), while in modern units, the sensing and computing functions are done electrically (electrohydraulic governors). A speed governor should allow us to change the governor gain (or equivalently the droop) and also change the speed and/or load reference. A governor may also have additional parameters which tailor its dynamic response so that instability does not take place. A student is referred to the book "Power System Stability and Control" by P. Kundur, McGraw Hill, New York, 1994, for further reading on this subject. We study the frequency transients for a simplified two generator system with speed governing, by an example. onsider 2 identical generators supplying 2 loads as shown in the figure below. Module 3 : Frequency Control in a Power System Lecture 15 : Speed Governor Page 3 Objectives In this lecture you will learn the following What are the transient processes before system frequency settles down to steady state ? We have seen the effect of speed droop settings on sharing of excess load between generators in steady state. Although we have considered only the steady state conditions, it is to be noted that governors, turbines and generators (and practically all constituents of a power system) are governed by dynamic equations. This means that steady state is not reached instantaneously. Indeed, if the transient processes are not stable, the system will not settle down to the steady state. Thus it is important to consider the dynamical equations which govern the physical structures, especially the prime mover system. While dynamical modelling of components is beyond the scope of this course, we will briefly discuss the working of a steam governor. A speed governor is a device which senses speed deviation from its reference value and appropriately changes control valve position in a steam turbine or gate position in a hydraulic turbine. This is achieved in older units using mechanical and hydraulic arrangements (mechanical hydraulic governors), while in modern units, the sensing and computing functions are done electrically (electrohydraulic governors). A speed governor should allow us to change the governor gain (or equivalently the droop) and also change the speed and/or load reference. A governor may also have additional parameters which tailor its dynamic response so that instability does not take place. A student is referred to the book "Power System Stability and Control" by P. Kundur, McGraw Hill, New York, 1994, for further reading on this subject. We study the frequency transients for a simplified two generator system with speed governing, by an example. onsider 2 identical generators supplying 2 loads as shown in the figure below. Module 3 : Frequency Control in a Power System Lecture 15 : Speed Governor The generator mechanical ("swing") equations have already been discussed before. The natural transients associated with the electrical network/loads are assumed to be fast compared to the electro-mechanical transients; therefore the network and loads are represented by their sinusoidal steady state equations. The solution of the problem is given in the following slides. Solution: Page 4 Objectives In this lecture you will learn the following What are the transient processes before system frequency settles down to steady state ? We have seen the effect of speed droop settings on sharing of excess load between generators in steady state. Although we have considered only the steady state conditions, it is to be noted that governors, turbines and generators (and practically all constituents of a power system) are governed by dynamic equations. This means that steady state is not reached instantaneously. Indeed, if the transient processes are not stable, the system will not settle down to the steady state. Thus it is important to consider the dynamical equations which govern the physical structures, especially the prime mover system. While dynamical modelling of components is beyond the scope of this course, we will briefly discuss the working of a steam governor. A speed governor is a device which senses speed deviation from its reference value and appropriately changes control valve position in a steam turbine or gate position in a hydraulic turbine. This is achieved in older units using mechanical and hydraulic arrangements (mechanical hydraulic governors), while in modern units, the sensing and computing functions are done electrically (electrohydraulic governors). A speed governor should allow us to change the governor gain (or equivalently the droop) and also change the speed and/or load reference. A governor may also have additional parameters which tailor its dynamic response so that instability does not take place. A student is referred to the book "Power System Stability and Control" by P. Kundur, McGraw Hill, New York, 1994, for further reading on this subject. We study the frequency transients for a simplified two generator system with speed governing, by an example. onsider 2 identical generators supplying 2 loads as shown in the figure below. Module 3 : Frequency Control in a Power System Lecture 15 : Speed Governor The generator mechanical ("swing") equations have already been discussed before. The natural transients associated with the electrical network/loads are assumed to be fast compared to the electro-mechanical transients; therefore the network and loads are represented by their sinusoidal steady state equations. The solution of the problem is given in the following slides. Solution: where ?Psi is a state of the system. Solution (Con td..): The initial conditions of the various state are as follows: Initial Conditions: Page 5 Objectives In this lecture you will learn the following What are the transient processes before system frequency settles down to steady state ? We have seen the effect of speed droop settings on sharing of excess load between generators in steady state. Although we have considered only the steady state conditions, it is to be noted that governors, turbines and generators (and practically all constituents of a power system) are governed by dynamic equations. This means that steady state is not reached instantaneously. Indeed, if the transient processes are not stable, the system will not settle down to the steady state. Thus it is important to consider the dynamical equations which govern the physical structures, especially the prime mover system. While dynamical modelling of components is beyond the scope of this course, we will briefly discuss the working of a steam governor. A speed governor is a device which senses speed deviation from its reference value and appropriately changes control valve position in a steam turbine or gate position in a hydraulic turbine. This is achieved in older units using mechanical and hydraulic arrangements (mechanical hydraulic governors), while in modern units, the sensing and computing functions are done electrically (electrohydraulic governors). A speed governor should allow us to change the governor gain (or equivalently the droop) and also change the speed and/or load reference. A governor may also have additional parameters which tailor its dynamic response so that instability does not take place. A student is referred to the book "Power System Stability and Control" by P. Kundur, McGraw Hill, New York, 1994, for further reading on this subject. We study the frequency transients for a simplified two generator system with speed governing, by an example. onsider 2 identical generators supplying 2 loads as shown in the figure below. Module 3 : Frequency Control in a Power System Lecture 15 : Speed Governor The generator mechanical ("swing") equations have already been discussed before. The natural transients associated with the electrical network/loads are assumed to be fast compared to the electro-mechanical transients; therefore the network and loads are represented by their sinusoidal steady state equations. The solution of the problem is given in the following slides. Solution: where ?Psi is a state of the system. Solution (Con td..): The initial conditions of the various state are as follows: Initial Conditions: The results of the numerical integration (Runge-Kutta 4th order method with time step of 0.01) are shown below. A MATLAB/SIMULINK simulation model files to do the same can be downloaded from here (init.m, governor.mdl). First run the file init.m by typing init at the MATLAB prompt. After that, run the SIMULINK file. For the step increase in load 1 by 10% (i.e., the load resistance at bus1 reduces by 10%), note the following: a) Changes in generator speeds. Notice the aggregate movement as well as the relative motion (swings). b) Power output of both machines c) Voltages at both load buses d) Power Flow through the tie line between buses 1 and 2 (it changes : why?) (click on images to enlarge)Read More

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