Monitoring and control of a filter in a power network

Claim 3

A method according to claim 1, wherein the forming of the state signal in dependence on said quotient SUTGn and said quotient SITGn further comprising the steps of: multiplying said quotient SUTGn by said quotient SITGn and adding the result to "ONE" to form a summation; and generating the difference between said quotient SUTGn and said quotient SITGn and dividing said difference by said summation and forming the state signal in dependence on the resultant division.

Claim 4

A method according to claim 1, wherein the frequency of the selected tone is determined as the product of a selected integer and a sensed value of the fundamental frequency associated with the power network.

Claim 7

A method according to claim 4, wherein the forming of the state signal in dependence on said quotient SUTGn and said quotient SITGn further comprising the steps of: multiplying said quotient SUTGn by said quotient SITGn and adding the result to "ONE" to form a summation; and generating the difference between said quotient SUTGn and said quotient SITGn and dividing said difference by said summation and forming the state signal in dependence on the resultant division.

Claim 8

A method according to claim 4, further comprising the steps of: forming, for each one of the plant components, a signal in dependence on the phase difference; and supplying said signal to the alarm unit for comparison with a signal formed in dependence on the mean value of the phase difference for more than one of the plant components connected to the power network.

Claim 9

A method according to claim 4, wherein the frequency of the selected tone is determined as the product of a selected integer and a sensed value of the fundamental frequency associated with the power network.

Claim 12

A method according to claim 8, wherein the frequency of the selected tone is determined as the product of a selected integer and a sensed value of the fundamental frequency associated with the power network.

Claim 13

A method according to claim 8, wherein the step of forming said amplitude values further comprises the steps of: respectively square said signals SUCOSn, SUSINn, SICOSn and SISINn; summing the squares of said signals SUCOSn and SUSINn and taking the square root of the resultant summation to form a signal SUn; summing the squares of said signals SICOSn and SISINn and taking the square root of the resultant summation to form a signal SIn; and forming said amplitude value for the selected tone of said sensed voltage in dependence on said signal SUn and forming said amplitude value for the selected tone of said sensed current in dependence on said signal SIn.

Claim 14

A method according to claim 10, further comprising the step of supplying said calculating unit with a value related to the operating temperature of at least the capacitive impedance elements, for example the operating temperature of the plant component, to be included as a parameter in the calculation of the value of the capacitance of the capacitive impedance element.

Claim 15

Apparatus for monitioring and controlling a plant component, for a tunable filter for harmonic filtering in a converter plant for high-voltage direct current, connected to an electric power network with a fundamental frequency corresponding to a period T, said component having a reactive impedance changeable via a control member, comprising: means for sensing a voltage occurring in the plant component and a current flowing through the plant component; means for forming the phase difference between a selected tone of said sensed voltage and of said sensed current, the selected tone having a frequency equal to an integer multiple of said fundamental frequency (n×2πt/T, where n is a positive integer); means for forming a state signal SUITGn in dependence on said phase difference; and means for supplying the state signal to the control member for changing the reactive impedance of the plant component such that the magnitude of said phase difference is minimized; wherein said means for forming the phase difference further comprises: (a) means for forming a sine and a cosine signal, both of a frequency equal to the frequency of the selected tone; (b) means for forming a first product R1 in dependence on the product between the sensed value of said voltage and the sine signal, means for forming a second product R2 in dependence on the product between the sensed value of said voltage and the cosine signal, means for forming a third product R3 in dependence on the product between the sensed value of said current and the sine signal, and means for forming a fourth product R4 in dependence on the product between the sensed value of said current and the cosine signal; (c) means for integrating each of said first, second, third and fourth products over at least one of a time equal to said period and a multiple of said period; and (d) means for forming respective signals SUCOSn, SUSINn, SICOSn and SISINn in dependence on the integrated first, second, third and fourth products, and forming the state signal in dependence on a quotient SUTGn of the signal SUSINn and the signal SUCOSn and on a quotient SITGn of the signal SISINn and the signal SICOSn.

Claim 16

Apparatus for monitioring and controlling a plant component, for a tunable filter for harmonic filtering in a converter plant for high-voltage direct current, connected to an electric power network with a fundamental frequency corresponding to a period T, said component having a reactive impedance changeable via a control member, comprising: means for sensing a voltage occurring in the plant component and a current flowing through the plant component; means for forming the phase difference between a selected tone of said sensed voltage and of said sensed current, the selected tone having a frequency equal to an integer multiple of said fundamental frequency (n×2πt/T, where n is a positive integer); means for forming a state signal SUITGn in dependence on said phase difference; and means for supplying the state signal to the control member for changing the reactive impedance of the plant component such that the magnitude of said phase difference is minimized; wherein said means for forming the phase difference further comprises: (a) means for forming a sine and a cosine signal, both of a frequency equal to the frequency of the selected tone; (b) means for forming a first product R1 in dependence on the product between the sensed value of said voltage and the sine signal, means for forming a second product R2 in dependence on the product between the sensed value of said voltage and the cosine signal, means for forming a third product R3 in dependence on the product between the sensed value of said current and the sine signal, and means for forming a fourth product R4 in dependence on the product between the sensed value of said current and the cosine signal; (c) means for integrating each of said first, second, third and fourth products over at least one of a time equal to said period and a multiple of said period; and (d) means for forming respective signals SUCOSn, SUSINn, SICOSn and SISINn in dependence on the integrated first, second, third and fourth products, and forming the state signal in dependence on a quotient SUTGn of the signal SUSINn and the signal SUCOSn and on a quotient SITGn of the signal SISINn and the signal SICOSn.

Claim 17

Apparatus according to claim 12, wherein the means for forming the state signal in dependence on said quotient SUTGn and said quotient SITGn further comprising: means for multiplying said quotient SUTGn by said quotient SITGn and means for adding the result to "ONE" to form a summation; and means for generating the difference between said quotient SUTGn and said quotient SITGn and dividing said difference by said summation and forming the state signal in dependence on the resultant division.

Claim 18

Apparatus according to claim 12, further comprising means for determining the frequency of the selected tone as the product of a selected integer and a sensed value of the fundamental frequency associated with the power network.

Claim 19

Apparatus for monitoring at least two plant components, for harmonic filters in a converter station for high-voltage direct current, connected to an electric power network with a fundamental frequency corresponding to a period T, comprising: means for sensing, for each one of the at least two plant components, a voltage occurring in the plant component and a current flowing through the plant component; means for forming the phase difference between a selected tone of said sensed voltage and of said sensed current, the selected tone having a frequency equal to an integer multiple of said fundamental frequency (n×2πt/T, where n is a positive integer); means for forming a state signal SUITGn in dependence on said phase difference; and means for supplying the state signal to an alarm unit for comparison with a state signal formed in dependence on phase differences for more than one of the plant components connected to the power network; wherein said means for forming the phase difference further comprises: (a) means for forming a sine and a cosine signal, both of a frequency equal to the frequency of the selected tone; (b) means for forming a first product R1 in dependence on the product between the sensed value of said voltage and the sine signal, means for forming a second product R2 in dependence on the product between the sensed value of said voltage and the cosine signal, means for forming a third product R3 in dependence on the product between the sensed value of said current and the sine signal, and means for forming a fourth product R4 in dependence on the product between the sensed value of said current and the cosine signal; (c) means for integrating each of said first, second, third and fourth products over at least one of a time equal to said period and a multiple of said period; and (d) means forming respective signals SUCOSn, SUSINn, SICOSn and SISINn in dependence on the integrated first, second, third and fourth products, and forming the state signal in dependence on a quotient SUTGn of the signal SUSINn and the signal SUCOSn and on a quotient SITGn of the signal SISINn and the signal SICOSn.

Claim 20

Apparatus for monitoring at least two plant components, for harmonic filters in a converter station for high-voltage direct current, connected to an electric power network with a fundamental frequency corresponding to a period T, comprising: means for sensing, for each one of the at least two plant components, a voltage occurring in the plant component and a current flowing through the plant component; means for forming the phase difference between a selected tone of said sensed voltage and of said sensed current, the selected tone having a frequency equal to an integer multiple of said fundamental frequency (n×2πt/T, where n is a positive integer); means for forming a state signal SUITGn in dependence on said phase difference; and means for supplying the state signal to an alarm unit for comparison with a state signal formed in dependence on phase differences for more than one of the plant components connected to the power network; wherein said means for forming the phase difference further comprises: (a) means for forming a sine and a cosine signal, both of a frequency equal to the frequency of the selected tone; (b) means for forming a first product R1 in dependence on the product between the sensed value of said voltage and the sine signal, means for forming a second product R2 in dependence on the product between the sensed value of said voltage and the cosine signal, means for forming a third product R3 in dependence on the product between the sensed value of said current and the sine signal, and means for forming a fourth product R4 in dependence on the product between the sensed value of said current and the cosine signal; (c) means for integrating each of said first, second, third and fourth products over at least one of a time equal to said period and a multiple of said period; and (d) means forming respective signals SUCOSn, SUSINn, SICOSn and SISINn in dependence on the integrated first, second, third and fourth products, and forming the state signal in dependence on a quotient SUTGn of the signal SUSINn and the signal SUCOSn and on a quotient SITGn of the signal SISINn and the signal SICOSn.

Claim 21

Apparatus according to claim 15, wherein the means for forming the state signal in dependence on said quotient SUTGn and said quotient SITGn further comprising: means for multiplying said quotient SUTGn by said quotient SITGn and adding the result to "ONE" to form a summation; and means for generating the difference between said quotient SUTGn and said quotient SITGn and dividing said difference by said summation and forming the state signal in dependence on the resultant division.

Claim 22

Apparatus according to claim 15, further comprising: means for forming, for each one of the plant components, a signal in dependence on the phase difference; and means for supplying said signal to the alarm unit for comparison with a signal formed in dependence on the mean value of the phase difference for more than one of the plant components connected to the power network.

Claim 23

Apparatus according to claim 15, further comprising means for determining the frequency of the selected tone as the product of a selected integer and a sensed value of the fundamental frequency associated with the power network.

Claim 24

Apparatus for monitoring a plant component comprising at least one capacitive impedance element, comprising at least one of a filter for harmonic filtering and a capacitive bank for generating reactive power in a converter plant for high-voltage direct current, connected to an electric power network with a fundamental frequency corresponding to a period T, comprising: means for sensing a voltage occurring in the plant component and a current flowing through the plant component; means for forming amplitude values for a selected tone of said sensed voltage and of said sensed current, the selected tone having a frequency equal to an integer multiple of said fundamental frequency (n×2πt/T, where n is a positive integer); means for supplying the amplitude values, a value of the frequency of the selected tone or the corresponding period T/n thereof, a known value of the resistance of the plant component, and a known value of he inductance of the plant component to a calculating unit for calculating the value of the capacitance of the capacitive impedance element in dependence on said supplied values; and means for supplying said calculated value of the capacitance of the capacitive impedance element to an alarm unit for comparison with a predetermined reference value; wherein said means for forming the amplitude values further comprising: (a) means for forming a sine and a cosine signal, both of a frequency equal to the frequency of the selected tone; (b) means for forming a first product R1 in dependence on the product between the sensed value of said voltage and the sine signal, means for forming a second product R2 in dependence on the product between the sensed value of said voltage and the cosine signal, means for forming a third product R3 in dependence on the product between the sensed value of said current and the sine signal, and means for forming a fourth product R4 in dependence on the product between the sensed value of said current and the cosine signal; (c) means for integrating each of said first, second, third and fourth products over at least one of a time equal to said period and a multiple of said period; and (d) means for forming respective signals SUCOSn, SUSINn, SICOSn and SISINn in dependence on the integrated first, second, third and fourth products, and means for forming the state signal in dependence on a quotient SUTGn of the signal SUSINn the signal SUCOSn and on a quotient SITGn of the signal SISINn and the signal SICOSn.

Claim 25

Apparatus for monitoring a plant component comprising at least one capacitive impedance element, comprising at least one of a filter for harmonic filtering and a capacitive bank for generating reactive power in a converter plant for high-voltage direct current, connected to an electric power network with a fundamental frequency corresponding to a period T, comprising: means for sensing a voltage occurring in the plant component and a current flowing through the plant component; means for forming amplitude values for a selected tone of said sensed voltage and of said sensed current, the selected tone having a frequency equal to an integer multiple of said fundamental frequency (n×2πt/T, where n is a positive integer); means for supplying the amplitude values, a value of the frequency of the selected tone or the corresponding period T/n thereof, a known value of the resistance of the plant component, and a known value of he inductance of the plant component to a calculating unit for calculating the value of the capacitance of the capacitive impedance element in dependence on said supplied values; and means for supplying said calculated value of the capacitance of the capacitive impedance element to an alarm unit for comparison with a predetermined reference value; wherein said means for forming the amplitude values further comprising: (a) means for forming a sine and a cosine signal, both of a frequency equal to the frequency of the selected tone; (b) means for forming a first product R1 in dependence on the product between the sensed value of said voltage and the sine signal, means for forming a second product R2 in dependence on the product between the sensed value of said voltage and the cosine signal, means for forming a third product R3 in dependence on the product between the sensed value of said current and the sine signal, and means for forming a fourth product R4 in dependence on the product between the sensed value of said current and the cosine signal; (c) means for integrating each of said first, second, third and fourth products over at least one of a time equal to said period and a multiple of said period; and (d) means for forming respective signals SUCOSn, SUSINn, SICOSn and SISINn in dependence on the integrated first, second, third and fourth products, and means for forming the state signal in dependence on a quotient SUTGn of the signal SUSINn the signal SUCOSn and on a quotient SITGn of the signal SISINn and the signal SICOSn.

Claim 26

Apparatus according to claim 19, further comprising means for determining the frequency of the selected tone as the product of a selected integer and a sensed value of the fundamental frequency associated with the power network.

Claim 27

Apparatus according to claim 19 wherein the means for forming said amplitude values further comprises: means for respectively squaring said signals SUCOSn, SUSINn, SICOSn and SISINn; means for summing the squares of said signals SUCOSn and SUSINn and taking the square root of the resultant summation to form a signal SUn; and means for summing the squares of said signals SICOSn and SISINn and taking the square root of the resultant summation to form a signal SIn; and means for forming said amplitude value for the selected tone of said sensed voltage in dependence on said signal SUn and forming said amplitude value for the selected tone of said sensed current in dependence on said signal SIn.

Claim 28

Apparatus according to claim 21, further comprising: means for supplying said calculating unit with a value related to the operating temperature of at least the capacitive impedance elements, for example the operating temperature of the plant component, to be included as a parameter in the calculation of the value of the capacitance of the capacitive impedance element.