Method for detecting fault in power transmission line and protection system using the same
A method for detecting fault in a power transmission line of a power transmission system and protection system using the same. The method includes: obtaining a system parameter of the power transmission system, adjusting protection reachability of a fault detecting element based on the obtained system parameter such that the adjusted protection reachability of the fault detecting element is applicable to a predetermined protection range, identifying whether there is an internal fault occurring on the transmission line using the adjusted fault detecting element, and generating a fault detection decision signal indicating the identified fault. If the predetermined protection range is desirable for the fault detecting element, its protection reachability may be adjusted in consideration of the influence imposed by the SIR such that the reach point of the adjusted fault detecting element can be extended to approach the end of the predetermined protection range. Consequently, the influence on its accuracy by various SIR values can be taken into account and accordingly the fault detecting solution can remove substantial errors as a result thereof.
1. A method for detecting fault in a transmission line of a power transmission system, including steps of:
(a) obtaining a system parameter of the power transmission system;
(b) adjusting protection reachability of a fault detecting element based on the obtained system parameter such that the adjusted protection reachability of the fault detecting element covers a predetermined protection range, wherein the protection reachability is a range of distance along the transmission line within which the fault detecting element is configured to detect fault conditions in the transmission line;
(c) obtaining instantaneous voltage values at a compensated point on the transmission line of the power transmission system for a series of time points;
(d) identifying whether there is an internal fault occurring on the transmission line using the adjusted fault detecting element by applying the obtained instantaneous voltage values at the compensated point to the adjusted fault detecting element for the identification of the internal fault, wherein the fault detecting element of the step (d) uses criteria:
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where U q and U q ′ respectively indicate the instantaneous voltage values for two of the series of time points, where U is U q ′ or U N , where U N indicates rated voltage of the transmission line, and K rei indicates reliability coefficient; and
(e) generating a fault detection decision signal indicating the identified fault.
2. The method according to claim 1 , wherein:
the step (b) of adjusting includes:
the reliability coefficient K rei of the fault detecting element is adjusted above a first threshold where the obtained system parameter is below a second threshold; and
the reliability coefficient K rei of the fault detecting element is adjusted below the first threshold where the obtained system parameter is above the second threshold.
3. The method according to claim 2 , further including:
(f) sampling current values and voltage values at one end of the transmission line for the series of time points;
wherein:
the step (c) includes computing the instantaneous voltage values at the compensated point on the transmission line from the current value samples and the voltage value samples based on a time domain lumped parameter differential equation based on RLC model or RL model for the transmission line for the series of time points.
4. The method according to claim 1 , wherein:
the system parameter is SIR; and
SIR=Z S /Z Set
where Z s is source impedance of the power transmission system, and Z set is impedance setting of the given transmission line.
5. The method according to claim 1 , further including:
(f) sampling current values and voltage values at one end of the transmission line for the series of time points;
wherein:
the step (c) includes computing the instantaneous voltage values at the compensated point on the transmission line from the current value samples and the voltage value samples based on a time domain lumped parameter differential equation based on RLC model or RL model for the transmission line for the series of time points.
6. The method according to claim 5 , wherein:
the step (b) of adjusting includes:
the reliability coefficient K rei of the fault detecting element is adjusted above a first threshold where the obtained system parameter is below a second threshold; and
the reliability coefficient K rei of the fault detecting element is adjusted below the first threshold where the obtained system parameter is above the second threshold.
7. A protection system for detecting fault in a transmission line of a power transmission system, including:
a processor, being configured to adjust protection reachability of a fault detecting element based on obtained system parameter of the power transmission system such that the adjusted protection reachability of the fault detecting element covers a predetermined protection range, identify whether there is an internal fault occurring on the transmission line using the adjusted fault detecting element, and generate a fault detection decision signal indicating the identified internal fault;
wherein:
the processor is further configured to apply obtained instantaneous voltage values at a compensated point to the adjusted fault detecting element for the identification of the internal fault, and the protection reachability is a range of distance along the transmission line within which the fault detecting element is configured to detect fault conditions in the transmission line, wherein the fault detecting element uses criteria:
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q
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K
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U
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=
U
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-
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′
where U q and U q ′ respectively indicate the instantaneous voltage values for two of the series of time points, where U is U q ′ or U N , where U N indicates rated voltage of the transmission line, and K rei indicates reliability coefficient.
8. The protection system according to claim 7 , wherein:
the reliability coefficient K rei of the fault detecting element is adjusted above a first threshold where the obtained system parameter is below a second threshold; and
the reliability coefficient K rei of the fault detecting element is adjusted below the first threshold where the obtained system parameter is above the second threshold.
9. The protection system according to claim 8 , further including:
a sampling device, being configured to sample current values and voltage values at one end of the transmission line for the series of time points;
wherein:
the processor is further configured to compute the instantaneous voltage values at the compensated point on the transmission line from the current value samples and the voltage value samples based on a time domain lumped parameter differential equation based on RLC model or RL model for the transmission line for the series of time points.
10. The protection system according to claim 7 , wherein:
the system parameter is SIR; and
SIR=Z S /Z set
where Z s is source impedance of the power transmission system, and Z set is impedance setting of the transmission line.
11. The protection system according to claim 7 , further including:
a sampling device, being configured to sample current values and voltage values at one end of the transmission line for the series of time points;
wherein:
the processor is further configured to compute the instantaneous voltage values at the compensated point on the transmission line from the current value samples and the voltage value samples based on a time domain lumped parameter differential equation based on RLC model or RL model for the transmission line for the series of time points.
12. The protection system according to claim 11 , wherein:
the reliability coefficient K rei of the fault detecting element is adjusted above a first threshold where the obtained system parameter is below a second threshold; and
the reliability coefficient K rei of the fault detecting element is adjusted below the first threshold where the obtained system parameter is above the second threshold.