POWER SYSTEM STABILITY USING FLYWHEEL ENERGY STORAGE SYSTEM
ABSTRACT:
• One of the most challenging aspects of today’s electricity grid is
that the amount of power generated and the amount consumed must be in
exact balance at all times. When imbalances occur, the frequency of
electricity (50 hertz) required by end users is not maintained,
adversely affecting grid stability. This constant balancing of power
demand and production to maintain frequency is called frequency
regulation.
• To maintain frequency regulation, FLYWHEEL ENERGY STORAGE SYSTEM is
used
.
• INTRODUCTION: • Generally the load connected to the power plant is not constant at all times.It is changed gradually at or near a constant value of voltage. Voltage is very important factor as the light output reduces very much when it is operated below a certain rated voltage.The induction motor draws more current for the same torque when operated at lower voltages and under extreme low voltage condition motors may stall under load. • One of the stabilities of the power system is steady state stability. • STEADY STATE STABILITY: • The steady state stability is the stability of the system under conditions of gradual or relatively slow change in load.The load is assumed to be applied at a rate which is slow when compared either with the natural frequency of oscillations of the major parts of the system or with the rate of change of field flux in the rotating machine in response to the change in loading. • WHAT HAPPEN IF THE LOAD IS CONTINUOUSLY VARYING? • If load is less than the power delivered then the extra energy generated will go as kinetic energy into the rotor of generator and the extra energy is wasted.If the load is more than the power delivered, then low voltage problem will be occurred.So, to overcome this, generation power should be changed according to the load requirement. • HOW THE DELIVERED POWER WILL BE CHANGED: • By changing generated emf and load angle only, the power delivered can be changed. • For small change in load,the input mechanical power cannot not be changed.Only the excitation of the alternator is to be changed to meet the load requirement. • To change the excitation, automatic voltage regulators are used. • One more method to meet the load requirement is FLYWHEEL ENERGY STORAGE SYSTEM. • To maintain frequency regulation, flywheel energy storage system can be used. • WHAT ARE FLYWHEEL ENERGY STORAGE SYSTEMS? • Flywheel Energy Storage systems act as mechanical batteries that store power kinetically in the form of a rotating mass, or "flywheel." • The flywheel energy storage system is connected to transmission lines before the grid through motors.These motors will come into existence when generation power is greater than load and the motors output mechanical energy is stored into flywheels as rotational energy.when load is greater than power delivered, the rotational energy stored in flywheels acts as mechanical energy to generators and power is supplied to grid. • When the grid goes down, the power stored by the rotating flywheel is converted to electrical energy through the flywheel’s integrated electric generator. The system provides the DC energy to the Uninterruptible Power Supplies system until grid power is restored or the facility's back-up power generator can be started. Once either the utility is restored or the genset provides power to the input of the Uninterruptible Power Supplies, the Flywheel Energy Storage system will be re-charged by taking some current from the DC bus of the Flywheel Energy Storage until it is back up to full speed. • DESIGN OF FLYWHEEL SYSTEM Motor/generator Transformation between rotational kinetic energy and electrical energy is performed with a shaft-mounted PM brushless 3 kW Motor/generator. The rotor component consists of a 4-pole PM array, banded by a graphite–fiber shell. The stator component consists of a set of copper coils that are cooled by thermal conduction through an aluminum housing to the top of the vacuum chamber. The power electronics will be capable of providing 3-phase 208 V output to a nongrid-connected electrical load. Containment Safety containment for the flywheel is through a cylindrical array of vertical steel S-brackets, as shown unenclosed in the upper left in figure. These brackets have been enclosed by an annular shell to reduce the virtual leak to the vacuum system. In the unlikely event of catastrophic failure of the rotor, the rotor debris impacts the inner wall of the annular shell, and the initial deformation of the S-brackets acts to form a cavity in which the debris can continue to circulate and dissipate energy internally through collisions between debris particles, keeping the debris completely within the outer vacuum shell. Vacuum: The rotor, bearing components, and M/G stator are enclosed by a steel vessel that is evacuated. Initial evacuation of the chamber is done by a roughing pump. Afterward, the roughing pump is removed, and the chamber is continually evacuated by a 70 l s−1, 24 Vdc, turbomolecular pump and associated backing pump. • FLYWHEEL ENERGY STORAGE PROJECT OVERVIEW • This project demonstrates a flywheel energy storage system designed to respond to a regional transmission operator signal to quickly add or subtract power from the grid in a frequency regulation support mode. Using this concept, the flywheel recycles energy (store energy when generation exceeds loads; discharge energy when load exceeds generation) instead of trying to constantly adjust generator output. • THE PURPOSE OF FLYWHEEL ENERGY STORAGE PROJECT • This project is being sponsored to determine the relative benefits of having faster responding generation resources. Additionally, understanding the response time of a flywheel storage system as compared to traditional generator response time will provide a better determination of the required sizing for flywheel and other fast response systems. • When aggregated to reach appropriate output/input levels there are many benefits that flywheel energy storage can offer to the electric grid. The primary benefits are: • Increased Available energy: Because present day generators need to be operated below their maximum capability to provide regulation, they are not available to provide their maximum power. Typically generators need to be below their maximum capacity by 2 times the amount of regulation in order to provide headroom for safe operation. If all regulation were accomplished by flywheel energy storage system, then there would be an additional 2-4 % generation capacity without adding new generators. • Support Distributed Generation and Decentralized Energy projects with Local Voltage Support: Several Projects have already shown the benefits of using flywheels for local voltage support. This includes a project on the NY City transit system, where ten 1.6 KWh flywheels provide support between train stations. As flywheel storage increases, as will be demonstrated by this project, the feasibility of larger scale application of flywheel energy storage system for local voltage support will be more practical. HOW FLYWHEEL ENERGY STORAGE IS BEING APPLIED? • The flywheel energy storage system consists of an array of flywheel energy storage modules and power conversion electronics packaged in a standard 12’ x 40’ shipping container. This mobile container would interface with the grid’s three-phase 480-volt cables via a step up transformer. This matrix is capable of storing and recycling 250 kWh’s of energy. The rated discharge rate of a matrix is 1 MW therefore each container will provide rated power for 15 minutes or lower power for an extended period. • Monitoring and data acquisition has been specified such that system availability and power/energy parameters will be accessible via the website. Any time the system is operated, the kilowatts supplied or absorbed by the storage unit and the total system efficiency will be viewable via graphical display by day, week, month, etc. • While performing Frequency Regulation, the flywheel energy storage system will receive two input signals from the System Operator. • Regulation Signal (RS): This will be the amount of regulation to be provided over the next time step. This value will be between (-)100KW and (+) 100KW. Minus refers to absorbing 100kW of power from the Grid. Plus refers to injecting 100 kW of power to the grid. The regulation signal refers to the amount of power being absorbed or injected relative to a base set point as described by signal 2. The amount of power being injected or absorbed will be as measured downstream of the flywheel energy storage system and upstream of the step up transformer. This regulation signal will be updated every 4 seconds. • Set Point (SP): This will be the nominal level of power being removed from the grid during the time on regulation. It will be a percentage of the full regulation signal and will be a variable during the demonstration phase of testing. This setting will remain constant over an agreed to time period – usually one to 24 hours. In addition to the set point and regulation signal the master controller will have input from the flywheel controller to know how much energy is in each flywheel. The system controller will then send a signal to the flywheel controllers, and load bank to control the power flow within and to and from the flywheel energy storage system based on these inputs. ADVANTAGES: • The flywheel energy storage system will follow the regulation signal within a fraction of a percent. Unlike generation based Frequency Regulation, no fuel is consumed, and no emissions are generated. Analysis of presently used Frequency Regulation signals indicates that an energy storage module, which can store or deliver 1 MW for 15 minutes, would provide regulation services superior to services currently provided by generators. After development testing is completed the flywheel energy storage system and will be commissioned and put on automatic control. CONCLUSION: Now a day’s automatic voltage regulators are using to vary generated voltage. But the flywheel energy storage system is another method to compensate the continuous varying loads. For example, though we are having fuses, circuit breakers are being used. The more protective devices used the more safety we give to power systems. REFERENCES: El-Wakil, M.M. 1984. Powerplant Technology. New York, NY: McGraw Hill. ISBN 9780070192881. * Sheahen, T.P. 1994. Introduction to High-Temperature Superconductivity. New York, NY: Plenum Press. ISBN 9780306447938.
• INTRODUCTION: • Generally the load connected to the power plant is not constant at all times.It is changed gradually at or near a constant value of voltage. Voltage is very important factor as the light output reduces very much when it is operated below a certain rated voltage.The induction motor draws more current for the same torque when operated at lower voltages and under extreme low voltage condition motors may stall under load. • One of the stabilities of the power system is steady state stability. • STEADY STATE STABILITY: • The steady state stability is the stability of the system under conditions of gradual or relatively slow change in load.The load is assumed to be applied at a rate which is slow when compared either with the natural frequency of oscillations of the major parts of the system or with the rate of change of field flux in the rotating machine in response to the change in loading. • WHAT HAPPEN IF THE LOAD IS CONTINUOUSLY VARYING? • If load is less than the power delivered then the extra energy generated will go as kinetic energy into the rotor of generator and the extra energy is wasted.If the load is more than the power delivered, then low voltage problem will be occurred.So, to overcome this, generation power should be changed according to the load requirement. • HOW THE DELIVERED POWER WILL BE CHANGED: • By changing generated emf and load angle only, the power delivered can be changed. • For small change in load,the input mechanical power cannot not be changed.Only the excitation of the alternator is to be changed to meet the load requirement. • To change the excitation, automatic voltage regulators are used. • One more method to meet the load requirement is FLYWHEEL ENERGY STORAGE SYSTEM. • To maintain frequency regulation, flywheel energy storage system can be used. • WHAT ARE FLYWHEEL ENERGY STORAGE SYSTEMS? • Flywheel Energy Storage systems act as mechanical batteries that store power kinetically in the form of a rotating mass, or "flywheel." • The flywheel energy storage system is connected to transmission lines before the grid through motors.These motors will come into existence when generation power is greater than load and the motors output mechanical energy is stored into flywheels as rotational energy.when load is greater than power delivered, the rotational energy stored in flywheels acts as mechanical energy to generators and power is supplied to grid. • When the grid goes down, the power stored by the rotating flywheel is converted to electrical energy through the flywheel’s integrated electric generator. The system provides the DC energy to the Uninterruptible Power Supplies system until grid power is restored or the facility's back-up power generator can be started. Once either the utility is restored or the genset provides power to the input of the Uninterruptible Power Supplies, the Flywheel Energy Storage system will be re-charged by taking some current from the DC bus of the Flywheel Energy Storage until it is back up to full speed. • DESIGN OF FLYWHEEL SYSTEM Motor/generator Transformation between rotational kinetic energy and electrical energy is performed with a shaft-mounted PM brushless 3 kW Motor/generator. The rotor component consists of a 4-pole PM array, banded by a graphite–fiber shell. The stator component consists of a set of copper coils that are cooled by thermal conduction through an aluminum housing to the top of the vacuum chamber. The power electronics will be capable of providing 3-phase 208 V output to a nongrid-connected electrical load. Containment Safety containment for the flywheel is through a cylindrical array of vertical steel S-brackets, as shown unenclosed in the upper left in figure. These brackets have been enclosed by an annular shell to reduce the virtual leak to the vacuum system. In the unlikely event of catastrophic failure of the rotor, the rotor debris impacts the inner wall of the annular shell, and the initial deformation of the S-brackets acts to form a cavity in which the debris can continue to circulate and dissipate energy internally through collisions between debris particles, keeping the debris completely within the outer vacuum shell. Vacuum: The rotor, bearing components, and M/G stator are enclosed by a steel vessel that is evacuated. Initial evacuation of the chamber is done by a roughing pump. Afterward, the roughing pump is removed, and the chamber is continually evacuated by a 70 l s−1, 24 Vdc, turbomolecular pump and associated backing pump. • FLYWHEEL ENERGY STORAGE PROJECT OVERVIEW • This project demonstrates a flywheel energy storage system designed to respond to a regional transmission operator signal to quickly add or subtract power from the grid in a frequency regulation support mode. Using this concept, the flywheel recycles energy (store energy when generation exceeds loads; discharge energy when load exceeds generation) instead of trying to constantly adjust generator output. • THE PURPOSE OF FLYWHEEL ENERGY STORAGE PROJECT • This project is being sponsored to determine the relative benefits of having faster responding generation resources. Additionally, understanding the response time of a flywheel storage system as compared to traditional generator response time will provide a better determination of the required sizing for flywheel and other fast response systems. • When aggregated to reach appropriate output/input levels there are many benefits that flywheel energy storage can offer to the electric grid. The primary benefits are: • Increased Available energy: Because present day generators need to be operated below their maximum capability to provide regulation, they are not available to provide their maximum power. Typically generators need to be below their maximum capacity by 2 times the amount of regulation in order to provide headroom for safe operation. If all regulation were accomplished by flywheel energy storage system, then there would be an additional 2-4 % generation capacity without adding new generators. • Support Distributed Generation and Decentralized Energy projects with Local Voltage Support: Several Projects have already shown the benefits of using flywheels for local voltage support. This includes a project on the NY City transit system, where ten 1.6 KWh flywheels provide support between train stations. As flywheel storage increases, as will be demonstrated by this project, the feasibility of larger scale application of flywheel energy storage system for local voltage support will be more practical. HOW FLYWHEEL ENERGY STORAGE IS BEING APPLIED? • The flywheel energy storage system consists of an array of flywheel energy storage modules and power conversion electronics packaged in a standard 12’ x 40’ shipping container. This mobile container would interface with the grid’s three-phase 480-volt cables via a step up transformer. This matrix is capable of storing and recycling 250 kWh’s of energy. The rated discharge rate of a matrix is 1 MW therefore each container will provide rated power for 15 minutes or lower power for an extended period. • Monitoring and data acquisition has been specified such that system availability and power/energy parameters will be accessible via the website. Any time the system is operated, the kilowatts supplied or absorbed by the storage unit and the total system efficiency will be viewable via graphical display by day, week, month, etc. • While performing Frequency Regulation, the flywheel energy storage system will receive two input signals from the System Operator. • Regulation Signal (RS): This will be the amount of regulation to be provided over the next time step. This value will be between (-)100KW and (+) 100KW. Minus refers to absorbing 100kW of power from the Grid. Plus refers to injecting 100 kW of power to the grid. The regulation signal refers to the amount of power being absorbed or injected relative to a base set point as described by signal 2. The amount of power being injected or absorbed will be as measured downstream of the flywheel energy storage system and upstream of the step up transformer. This regulation signal will be updated every 4 seconds. • Set Point (SP): This will be the nominal level of power being removed from the grid during the time on regulation. It will be a percentage of the full regulation signal and will be a variable during the demonstration phase of testing. This setting will remain constant over an agreed to time period – usually one to 24 hours. In addition to the set point and regulation signal the master controller will have input from the flywheel controller to know how much energy is in each flywheel. The system controller will then send a signal to the flywheel controllers, and load bank to control the power flow within and to and from the flywheel energy storage system based on these inputs. ADVANTAGES: • The flywheel energy storage system will follow the regulation signal within a fraction of a percent. Unlike generation based Frequency Regulation, no fuel is consumed, and no emissions are generated. Analysis of presently used Frequency Regulation signals indicates that an energy storage module, which can store or deliver 1 MW for 15 minutes, would provide regulation services superior to services currently provided by generators. After development testing is completed the flywheel energy storage system and will be commissioned and put on automatic control. CONCLUSION: Now a day’s automatic voltage regulators are using to vary generated voltage. But the flywheel energy storage system is another method to compensate the continuous varying loads. For example, though we are having fuses, circuit breakers are being used. The more protective devices used the more safety we give to power systems. REFERENCES: El-Wakil, M.M. 1984. Powerplant Technology. New York, NY: McGraw Hill. ISBN 9780070192881. * Sheahen, T.P. 1994. Introduction to High-Temperature Superconductivity. New York, NY: Plenum Press. ISBN 9780306447938.
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