“ EFFECT OF GRID DISTURBANCE ON PLANT DYNAMICS OF A NUCLEAR POWER PLANT ” <ul><li>By – G DIVYA DEEPAK </li></ul><ul><li>M.Engg– Mechanical Engineering </li></ul><ul><li>(University of Windsor) </li></ul>
GRID ELECTRICAL DISTURBANCE <ul><li>A grid electrical disturbance (GED) is characterized by variances in voltage and frequency </li></ul><ul><li>It is a function of changes in load, generation, or the connection between two via the transmission network. </li></ul><ul><li>Voltage and frequency variations serve as a measure of the severity of the disturbance. </li></ul><ul><li>Ability of a power system to recover from a GED is directly related to the response of the grid system’s protective relaying </li></ul>
DISTURBANCE TYPE AND CHARACTERISTICS <ul><li>LOAD DISTURBANCES : </li></ul><ul><li>Small random fluctuations superimposed on slowly varying loads. </li></ul><ul><li>EVENT DISTURBANCES : </li></ul><ul><li>Faults on a transmission lines due to equipment malfunctions or natural phenomena such as lightning strikes. </li></ul><ul><li>Cascading events due to protective relay action following severe overloads or violation of operating limits. </li></ul><ul><li>Generation outages due to loss of synchronism or malfunction </li></ul>
DEPICTION OF NUCLEAR POWER PLANT RESPONSE DURING A GRID ELECTRICAL DISTURBANCE
Prototype Fast Breeder Reactor (PFBR) <ul><li>PFBR is а 500 MWe, sodium cooled, pool type, mixed oxide ( МОХ) fuelled reactor with two secondary loops </li></ul><ul><li>МОХ fuel is selected on account of its proven capability of safe operation to high burnup,ease of fabrication and proven reprocessing </li></ul><ul><li>Pool type concept is adopted due to its inherently high thermal inertia of the large mass of sodium in the pool which eases the removal of decay heat. </li></ul>
ANALYSIS OF PUMP PERFORMANCE CONSTANT VOLTAGE AND VARIATION OF FREQUENCY FOR PFBR BOILER FEED PUMP There is a linear relationship between stator current and torque. As the stator current increases by 10 percent the torque increases by 15 percent.
CONSTANT FREQUENCY AND VARIATION OF VOLTAGE FOR BFP As the supply voltage decreases from 6.6 kV to 4 kV the stator current increases by 9 percent. Thus, there is linear increase in stator current as the supply voltage decreases
ANALYSIS OF GENERATOR PERFORMANCE CONSTANT FREQUENCY AND VARIATION OF VOLTAGE It is seen that as the supply voltage decreases the stator current required for the excitation of generator windings starts increasing. Here, when voltage decreases by 10 percent the stator current increases by 4 percent
CONSTANT VOLTAGE AND VARIATION OF FREQUENCY The decrease of the supply frequency has a direct effect on the stator current of the generator. Here, as the supply frequency decreases the torque required increases and to provide this increased torque more amount of stator current is drawn. In the above graph as the supply frequency decreases by 10 percent the stator current increases by 8 percent.
IMPACT OF GRID FREQUENCY VARIATION ON PROCESS DYNAMICS <ul><li>Thus, frequency variation power supply to motors proportionally affects the flow supplied by pumps. </li></ul><ul><li>Maximum temperature difference across fuel channels in PFBR is ~ 170 0 C. </li></ul><ul><li>Thus, 3 % variation in flow affects the coolant temperature at the outlet of fuel channels by 5 0 C. Alarm will be generated when the coolant temperature increases by this value. </li></ul><ul><li>In order to overcome this process constraint, primary and secondary sodium pumps are provided with variable frequency drives with a speed controller designed to control the speed within 1 rpm. </li></ul><ul><li>frequency drives are not provided for boiler feed pumps, condensate extraction pumps and condensate cooling water pumps. </li></ul><ul><li>Feed water flow is manipulated by a control valve to control the sodium temperature at the outlet of steam generator. </li></ul>
<ul><li>Apart from this, level controller provided for the deaerator manipulates the feed water flow supplied by the condensate extraction pumps to the deaerator. With this control system in place, the flow supplied by condensate cooling pumps also becomes insensitive of grid frequency variation. </li></ul><ul><li>Turbine is provided with speed as well as pressure control systems. Under a grid frequency variation, the turbine controller will enter into an oscillating mode of operation due to the conflicting requirements of speed and pressure control systems. </li></ul>
CONCLUSION <ul><li>Due to the variable frequency drives provided for the drive motors of primary and secondary sodium pumps, there will not be any impact on the flow supplied these pumps due to supply frequency variation </li></ul><ul><li>Condenser cooling will be impaired due to frequency variation of power supply to condenser cooling pumps. However, this will have negligible impact on the overall process dynamics . </li></ul><ul><li>Sodium temperature and deaerator level controllers provided for manipulating feed water flow (supplied by boiler feed pumps) and condensate flow (supplied by extraction pumps), make these systems insensitive to grid frequency variation. </li></ul><ul><li>Impact of grid electrical disturbance on the operation of motors and generators has been found to be benign. </li></ul>
REFERENCES <ul><li>N.Theivarajan “Grid electrical disturbances and expected responses of PFBR systems”PFBR/5100/DN/1003/R-A,1995. </li></ul><ul><li>B.L Theraja “Fundamentals of Electrical & Electronics Engineering”, 1991 (pp 158-193). </li></ul><ul><li>Kuffel.E “High voltage Engineering”, 2000 (pp150-170). </li></ul><ul><li>K. Wallace et al, “Nuclear plant response to grid electrical disturbance”, 1995. </li></ul><ul><li>Acha.E “Power Electronic control in electrical systems” ,2002. </li></ul><ul><li>U.A Bakshi “Electrical Machines-II” (pp 220-250),2009. </li></ul><ul><li>M. Venkataratnam “Conceptual design of variable speed drive for sodium pumps”PFBR/52400/DN/1003/R-G,1997. </li></ul><ul><li>M.S Naidu “High voltage Engineering”,1992. </li></ul><ul><li>A. Venkatesan et al, “Conceptual design of reactor power control”PFBR/60000/1011/R-A,2001. </li></ul><ul><li>Kuffel “ Power Electronic Circuit,Devices application in electrical system” 1990. </li></ul>