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Disclosed herein are an intelligent system and method for monitoring a generator reactive power limit using machine model parameters. The intelligent system and method for monitoring a generator reactive power limit using machine model parameters can calculate a maximum reactive power limit correspo

Disclosed herein are an intelligent system and method for monitoring a generator reactive power limit using machine model parameters. The intelligent system and method for monitoring a generator reactive power limit using machine model parameters can calculate a maximum reactive power limit corresponding to over-excitation and a generator terminal voltage corresponding to under-excitation, estimate a correct field current even when system variable are changed, and monitor the generator reactive power limit by using machine model parameters and a one-machine infinite bus, to thereby supply a maximum or minimum reactive power to a power system within an allowable generator reactive power limit and prevent a generator trip caused by the reactive power limit and a power failure over a wide area.

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What is claimed is: 1. An intelligent system for monitoring a generator reactive power limit using machine model parameter, the intelligent system comprising: a real-time phasor measurement system for converting data measured from a three-phase power line connected to a generator through a current

What is claimed is: 1. An intelligent system for monitoring a generator reactive power limit using machine model parameter, the intelligent system comprising: a real-time phasor measurement system for converting data measured from a three-phase power line connected to a generator through a current transformer and a potential transformer into phasors to calculate a terminal voltage, a terminal current, a reactive power and an active power in terms of root mean square (RMS) value; and a host computer for calculating the generator reactive power limit using the RMS data from the real-time phasor measurement system, a one-machine infinite bus, and the machine model parameters. 2. The intelligent system for monitoring a generator reactive power limit using machine model parameter according to claim 1, wherein the real-time phasor measurement system transmits the RMS data to the host computer at a predetermined time interval. 3. The intelligent system for monitoring a generator reactive power limit using machine model parameter according to claim 2, wherein the host computer calculates an infinite bus voltage using the one-machine infinite bus and the data measured by the real-time phasor measurement system. 4. The intelligent system for monitoring a generator reactive power limit using machine model parameter according to claim 3, wherein the host computer calculates an internal load angle and a field current of the generator using the machine model parameters and the data measured by the real-time phasor measurement system. 5. The intelligent system for monitoring a generator reactive power limit using machine model parameter according to claim 4, wherein the machine model parameters include at least one of a vertical axis synchronous reactance Xd, a horizontal axis synchronous reactance Xq, a vertical axis transient reactance Xd′, a horizontal axis transient reactance Xq′, an initial transient reactance X″, a leakage reactance Xl, saturation coefficients S(1.0) and S(1.2). 6. The intelligent system for monitoring a generator reactive power limit using machine model parameter according to claim 5, wherein the host computer calculates at least one of an infinite bus voltage, a maximum reactive power limit with respect to a field current of a generator over-excitation limiter (OEL), a terminal voltage of a generator under-excitation limiter (UEL), a maximum reactive power limit according to the OEL with respect to another generator active power, and reactive power limits according to generator over-voltage and under-voltage limits and indicates the calculated result on a generator reactive power capability curve. 7. A phasor calculating method of the real-time phasor measurement system of the intelligent system of claim 1, the phasor calculating method comprising the steps of: performing hardware configuration of the real-time phasor measurement system; measuring a current and a voltage through a current transformer and a potential transformer and reading a channel; reading a time stamp; calculating a phasor; and transmitting the calculated phasor to the host computer of the intelligent system. 8. An intelligent method for monitoring a generator reactive power limit using machine model parameters by means of using the intelligent system for monitoring a generator reactive power limit using machine model parameter comprising a real-time phasor measurement system and a host computer, the method carried out by the host computer comprising: a first step of constructing machine model parameters and system data; a second step of reading measured data from a real-time phasor measurement system and storing the read data; a third step of executing a reactive power limit calculating method according to a system condition; and a fourth step of visualizing the calculated reactive power limit, wherein, after the first step, it is checked whether the real-time phasor measurement system is operated: when the real-time phasor measurement system is not operated, it is checked whether a start signal is inputted and the constructed data is transmitted to the real-time phasor measurement system to perform the second step when the start signal is inputted, and the second step is carried out when the real-time phasor measurement system is operated. 9. The intelligent method for monitoring a generator reactive power limit using machine model parameters according to claim 8, wherein, after the second step, it is checked whether the machine model parameters and the system data need to be changed: the machine model parameters and the system data are changed and then the third step is executed when it is required to change the machine model parameters and the system data, and the third step is carried out when there is no need to change the machine model parameters and the system data. 10. The intelligent method for monitoring a generator reactive power limit using machine model parameters according to claim 9, wherein, after the fourth step, it is checked whether a stop signal is inputted or whether an error signal is generated: when the stop signal is not inputted and the error signal is not generated it is checked whether data request is finished and then the second step is executed when the data request is not finished, and calculated resources are deleted and then it is checked whether a start signal of the real-time phasor measurement system is inputted when the data request is finished, and when the stop signal is inputted or the error signal is generated the calculated resources are deleted and then it is checked whether the start signal of the real-time phasor measurement system is inputted. 11. The intelligent method for monitoring a generator reactive power limit using machine model parameters according to claim 8, wherein the third step comprises: a first step of inputting an initial condition (Po, Qo, Vto) and a system equivalent impedance; a second step of carrying out at least one of calculation of a generator internal field current ifdo and a load angle δo using machine model parameters, calculation of an infinite bus voltage Vinf, estimation and calculation of a terminal voltage Vto—OEL with respect to an OEL field current limit ifdo—OEL, calculation of reactive power limits with respect to a maximum operation terminal voltage Vto—max and a minimum operation terminal voltage Vto—n, calculation of a maximum limit reactive power value Qi—max corresponding to an output power Pi (i=1, 2, . . . ), calculation of a terminal voltage Vt—UEL with respect to an UEL limit minimum reactive power QUEL—lim, and calculation of a reactive power limit according to a variation in the infinite bus voltage Vinf; and a third step of checking whether the current operating point is included in a reactive power limit danger area, and performing warning of reactive power limit danger when the current operating point is included in the danger area or finishing the routine when the current operating point is not included in the danger area. 12. The intelligent method for monitoring a generator reactive power limit using machine model parameters according to claim 11, wherein the calculation of the terminal voltage Vto—OEL with respect to the OEL field current limit ifdo—OEL comprises the steps of: calculating an infinite bus voltage using the following Equation 1: P o + jQ o = V to ⁢ I to * = V to ⁡ ( V to - V inf ⁢ ⁢ _ ⁢ 0 jX s ) * [ Equation ⁢ ⁢ 1 ] where Po(MW) denotes the current active power, Qo(Mvar) denotes the current reactive power, Vto(kV) denotes the terminal voltage of the currently operating generator, and Xs denotes a system equivalent impedance (corresponding to the sum of a transformer impedance and a power transmission line impedance); and calculating the terminal voltage which allows a calculated generator field current to correspond to a field current set to an OEL, using an optimization technique corresponding to the least square method of the following Equation 2: 1 2 ⁢ min x = V t ⁢ ( i if ⁢ ⁢ _ ⁢ ⁢ OEL - f ⁡ ( x , V inf ⁢ ⁢ _ ⁢ ⁢ o , P o ) ) 2 [ Equation ⁢ ⁢ 2 ] where iif—cal=f(x) denotes the calculated generator field current, and ifd—OEL represents the OEL generator field current limit. 13. The intelligent method for monitoring a generator reactive power limit using machine model parameters according to claim 11, wherein the calculation of the terminal voltage Vt—UEL with respect to the UEL limit minimum reactive power QUEL—lim is carried out using the following Equation 3: P o + jQ UEL = V to ⁢ I to * = V t ⁢ ⁢ _ ⁢ ⁢ UEL ⁡ ( V t ⁢ ⁢ _ ⁢ ⁢ UEL - V inf ⁢ ⁢ _ ⁢ ⁢ 0 jX s ) * [ Equation ⁢ ⁢ 3 ] where Po(MW) denotes the current active power, QUEL(Mvar) denotes the current minimum reactive power limit, Vinf—o(kV) denotes an infinite bus voltage in the currently operating state, and Xs denotes a system equivalent impedance (corresponding to the sum of a transformer impedance and a power transmission line impedance). 14. The intelligent method for monitoring a generator reactive power limit using machine model parameters according to claim 11, wherein the calculation of the maximum limit reactive power value Qi—max corresponding to the output power Pi (i=1, 2, . . . ) is carried out calculating a maximum limit reactive power value at another generator power operating point by obtaining a terminal voltage which allows a calculated field current to correspond to a field current set to an OEL using an optimization technique corresponding to the least square method of the following Equation 4: 1 2 ⁢ min x = V t ⁢ ( i if ⁢ ⁢ _ ⁢ ⁢ OEL - f ⁡ ( x , V inf ⁢ ⁢ _ ⁢ ⁢ o , P i ) ) 2 [ Equation ⁢ ⁢ 4 ] where iif—cal=f(x) denotes the calculated generator field current, Pi (i=1, 2, L) represents another generator active power operating point, and ifd—OEL denotes the OEL generator field current limit. 15. The intelligent method for monitoring a generator reactive power limit using machine model parameters according to claim 11, wherein the calculation of the reactive power limits with respect to the maximum operation terminal voltage Vto—max and the minimum operation terminal voltage Vto—min is carried out using the following Equation 5: P o + jQ max / min = V max / min ⁢ I to * = V max / min ⁡ ( V max / min - V inf ⁢ ⁢ _ ⁢ 0 jX s ) * . [ Equation ⁢ ⁢ 5 ] 16. The intelligent method for monitoring a generator reactive power limit using machine model parameters according to claim 11, the method comprising: a first step of inputting machine model parameters and an initial condition (Po, Qo, Vto, Vinf—o, Xs); a second step of calculating an internal phase difference angle δ, splitting a stator current into a vertical axis current and a horizontal axis current, and calculating a generator field current ifd—cal; a third step of determining whether an optimization technique is to be applied, finishing the routine when the optimization technique is not to be applied, and determining whether a difference between an OEL generator field current limit ifd—OEL and a calculated generator field current ifd—cal is smaller than a generator induced electromotive force ε when the optimization technique is to be applied; and a fourth step of finishing the routine when the difference is smaller than the generator induced electromotive force ε, or performing the optimization technique and changing the terminal voltage Vt and executing the second step when the difference is greater than the generator induced electromotive force ε.