Fault current detection device for a D.C. network

Claim 2

A fault current detection device for a d.c. network, comprising: sampling means for obtaining a series of sample values by sampling, every sampling period, a current flowing through the d.c. network; first comparator means for comparing a current sample value I n obtained currently by said sampling means with a preceding sample value I n-1 to determine a sign of a deviation ΔI=I n =I n-1 ; calculation means for calculating a variable ΔI n representative of an amount of current variation with respect to said current sample value I n on the basis of a difference I n -J n-1 between said current sample value I n and a parameter J n-1 obtained by correcting, every sampling period, and weighting sample values within a preceding constant time period when said deviation ΔI is positive and on the basis of a difference I n -J n-1 between said current sample value I n and a new parameter J n-1 obtained by substituting said parameter J n-1 for said current sample value I n when said deviation ΔI is negative; and second comparator means for comparing said variable ΔI n with a preset value ΔI r to provide a fault current detection signal when ΔI n >ΔI r .

Claim 3

The fault current detection device as claimed in claim 1, wherein a positive set value ΔI r and a negative set value ΔI rm are set as a set value for said variable ΔI n related to a record in the past of load current and said parameter J n-1 is corrected every sampling period Δt when said variable ΔI n is negative and has a value lower than said negative set value ΔI rm .

Claim 4

The fault current detection device as claimed in claim 2, wherein a variable ΔI n ' related to the record in the past of load current is calculated by using a time constant different from said time constant of said parameter J n-1 .

Claim 5

A fault current detection device for a d.c. network, comprising: sampling means for obtaining a series of sample values by sampling, every sampling period, a current flowing through the d.c. network; first calculation means for calculating a current variation rate D n =dI/dt from a current sample value sampled currently by said sampling means and a preceding sample value; second calculation means, on the basis of said variation rate D n and a variable ΔI n-1 representative of a current variation amount D n-1 with respect to a preceding sampling period, for updating it to a new variable ΔI n when said current variation rate D n calculated by said first calculation means is positive and for removing said variable ΔI n-1 representative of said preceding current variation amount and making said new variable ΔI n with respect to a current variation rate D n zero when said variation rate D n is negative; and comparator means for comparing said new variable ΔI n obtained by said second calculation means with a predetermined set value ΔI r to provide a fault current detection signal when ΔI n >ΔI r .

Claim 6

A fault current detection device for a d.c. network, comprising: sampling means for obtaining a series of sample values by sampling, every sampling period, a current flowing through the d.c. network; first calculation means for calculating a current variation rate D n =dI/dt from a current sample value sampled currently by said sampling means and a preceding sample value; second calculation means, on the basis of said variation rate D n and a variable ΔI n-1 representative of a current variation amount D n-1 with respect to a preceding sampling period, for updating it to a new variable ΔI n when said current variation rate D n calculated by said first calculation means is positive and for removing said variable ΔI n-1 representative of said preceding current variation amount and making said new variable ΔI n with respect to a current variation rate D n zero when said variation rate D n is negative; and comparator means for comparing said new variable ΔI n obtained by said second calculation means with a predetermined set value ΔI r to provide a fault current detection signal when ΔI n >ΔI r .

Claim 7

The fault current detection device as claimed in claim 4, wherein a positive set value ΔI r and a negative set value ΔI rm are set with respect to said variable ΔI n related to said current variation amount and said variable ΔI n is made zero when said variable ΔI n is negative and has a value lower than said set value ΔI rm .

Claim 8

The fault current detection device as claimed in claim 5, wherein a variable ΔI n ' related to a current variation amount is calculated by using a time constant different from said time constant of said variable ΔI n .

Claim 9

A fault current detection device for each of a plurality of series arranged d.c. feeding lines for feeding an electric car running unidirectionally, comprising: sampling means for obtaining a series of sample values by sampling, every sampling period, a current flowing through said feeding line; means for calculating a variable ΔI n representative of an amount of current variation experienced on the basis of a difference between a currently sampled value I n and a previously weighted current value J n-1 so long as said currently sampled value I n obtained by said sampling means is not lower than a previously sampled value I n-1 by an amount substantially larger than a predetermined value D r ; means for calculating a newly weighted current value J n by using said variable ΔI n to update said current value J n-1 ; comparing means for comparing said variable ΔI n with a preset value ΔI r to provide a fault current detection signal when ΔI n >ΔI r ; means for providing a reset signal to an adjacent downstream feeding line to reset its current value J n-1 when said currently sampled value I n is lower than said previously sampled value I n-1 by an amount substantially larger than said predetermined value D r ; and means responsive to said reset signal from an adjacent upstream feeding section for substituting said previously weighted current value J n-1 for said currently sampled value I n prior to said calculation of said variable ΔI n .

Claim 10

A fault current detection device for each of a plurality of series arranged d.c. feeding lines for feeding an electric car running unidirectionally, comprising: sampling means for obtaining a series of sample values by sampling, every sampling period, a current flowing through said feeding line; means for calculating a variable ΔI n representative of an amount of current variation experienced on the basis of a difference between a currently sampled value I n and a previously weighted current value J n-1 so long as said currently sampled value I n obtained by said sampling means is not lower than a previously sampled value I n-1 by an amount substantially larger than a predetermined value D r ; means for calculating a newly weighted current value J n by using said variable ΔI n to update said current value J n-1 ; comparing means for comparing said variable ΔI n with a preset value ΔI r to provide a fault current detection signal when ΔI n >ΔI r ; means for providing a reset signal to an adjacent downstream feeding line to reset its current value J n-1 when said currently sampled value I n is lower than said previously sampled value I n-1 by an amount substantially larger than said predetermined value D r ; and means responsive to said reset signal from an adjacent upstream feeding section for substituting said previously weighted current value J n-1 for said currently sampled value I n prior to said calculation of said variable ΔI n .