Method, system and apparatus for fault detection in line protection for power transmission system
A method, system and apparatus of fault detection in line protection for a power transmission system. A voltage (u) at a measurement point on an electrical line is obtained. The measurement point is a point at which a protection device for the line protection is installed. A current (i) at the measurement point is further obtained and a differential value of the current is determined. Then, a voltage (u q ) at a setting point on the electrical line is determined from the voltage (u) at the measurement point, the current (i) at the measurement point and the differential value of the current (i) according to a time domain lumped parameter model for the electrical line. The voltage change between the determined voltage at the setting point during the fault period and a voltage at the setting point determined during a pre-fault period can be further determined. The fault detection can be performed based on the determined voltage change and a fault threshold. It can ensure voltage determination accuracy and detection reliability with a low sampling rate. Moreover, the solution can work right after the fault inception, almost no waiting time is required, and thus it may achieve a super-fast line protection.
1. A method for fault detection in line protection for a power transmission system, comprising:
obtaining a voltage at a measurement point, at which a protection device for the line protection is installed, on an electrical line;
obtaining a current at the measurement point;
determining a differential value of the current;
determining a voltage at a setting point on the electrical line from the voltage at the measurement point, the current at the measurement point and the differential value of the current according to a time domain lumped parameter model for the electrical line;
determining a voltage change between the determined voltage at the setting point during a fault period and a voltage at the setting point determined during a pre-fault period; and
performing the fault detection based on the determined voltage change and a fault threshold, wherein the fault threshold set such that the voltage change exceeds the fault threshold in response to an internal fault within a protection zone of the protection device, and such that the voltage change does not exceed the fault threshold in response to an external fault outside of the protection zone of the protection device.
2. The method of claim 1 , wherein the determining the voltage at the setting point is performed based on a differential equation.
3. The method of claim 2 , wherein the differential equation based on time domain lumped parameters includes:
u
q
(
t
)
=
u
(
t
)
-
R
*
i
(
t
)
-
L
*
di
(
t
)
dt
wherein u(t) represents the voltage at the measurement point; i(t) represents the current at the measurement point, R represents a resistance value of a resistor in the lumped parameter model, and L represents an inductance value of an inductor in the lumped parameter model and
di
(
t
)
dt
represents the differential value of the current i(t).
4. The method of claim 3 , wherein the obtaining the current at the measurement point comprises:
obtaining a phase current at the measurement point; and
removing, from the phase current, at least one of a capacitive current to ground or a capacitive current between phases.
5. The method of claim 2 , wherein the obtaining the current at the measurement point comprises:
obtaining a phase current at the measurement point; and
removing, from the phase current, at least one of a capacitive current to ground a capacitive current between phases.
6. The method of claim 1 , wherein the lumped parameter model comprises a Resistor-Inductor-Capacitor (RLC) model.
7. The method of claim 6 , wherein the obtaining the current at the measurement point comprises:
obtaining a phase current at the measurement point; and
removing, from the phase current, at least one of a capacitive current to ground or a capacitive current between phases.
8. The method of claim 1 , wherein the lumped parameter model comprises a Resistor-Inductor (RL) model.
9. The method of claim 1 , wherein the obtaining the current at the measurement point comprises:
obtaining a phase current at the measurement point; and
removing, from the phase current, at least one of a capacitive current to ground and a capacitive current between phases.
10. The method of claim 1 , wherein the fault threshold is a product of a reliable coefficient and a rating voltage of the electrical line.
11. The method of claim 1 , wherein the fault threshold is a product of a reliable coefficient and the voltage at the setting point determined during the pre-fault period.
12. A system for fault detection in line protection for a power transmission system, comprising:
one or more processors;
a memory coupled to at least one of the processors; and
a set of program instructions stored in the memory and executable by at least one of the processors to cause the system to:
obtain a voltage at a measurement point, at which a protection device for the line protection is installed, on an electrical line;
obtain a current at the measurement point;
determine a differential value of the current;
determine a voltage at a setting point on the electrical line from the voltage at the measurement point, the current at the measurement point and the differential value of the current according to a time domain lumped parameter model for the electrical line;
determine a voltage change between the determined voltage at the setting point during a fault period and a voltage at the setting point determined during a pre-fault period; and
perform the fault detection based on the determined voltage change and a fault threshold, wherein the fault threshold set such that the voltage change exceeds the fault threshold in response to an internal fault within a protection zone of the protection device, and such that the voltage change does not exceed the fault threshold in response to an external fault outside of the protection zone of the protection device.
13. The system of claim 12 , wherein the determining the voltage at the setting point is performed based on a differential equation.
14. The system of claim 13 , wherein the differential equation based on time domain lumped parameters includes:
u
q
(
t
)
=
u
(
t
)
-
R
*
i
(
t
)
-
L
*
di
(
t
)
dt
wherein u(t) represents the voltage at the measurement point; i(t) represents the current at the measurement point, R represents a resistance value of a resistor in the lumped parameter model, and L represents an inductance value of an inductor in the lumped parameter model and
di
(
t
)
dt
represents the differential value of the current i(t).
15. The system of claim 14 , wherein the lumped parameter model comprises a Resistor-Inductor-Capacitor (RLC) model.
16. The system of claim 14 , wherein the lumped parameter model comprises a Resistor-Inductor (RL) model.
17. The system of claim 12 , wherein the obtaining the current at the measurement point comprises:
obtaining a phase current at the measurement point; and
removing, from the phase current, at least one of a capacitive current to ground, and a capacitive current between phases.
18. The system of claim 12 , wherein the fault threshold is a product of a reliable coefficient and a rating voltage of the electrical line.
19. The system of claim 12 , wherein the fault threshold is a product of a reliable coefficient and the voltage at the setting point determined during the pre-fault period.
20. An apparatus for fault detection in line protection for a power transmission system, comprising:
a voltage obtainment module, configured to obtain a voltage at a measurement point, at which a protection device for the line protection is installed, on an electrical line;
a current obtainment module, configured to obtain a current at the measurement point;
a differential value determination module, configured to determine a differential value of the current;
a voltage determination module, configured to determine a voltage at a setting point on the electrical line from the voltage at the measurement point, the current at the measurement point and the differential value of the current according to a time domain lumped parameter model for the electrical line;
a change determination module, configured to determine a voltage change between the determined voltage at the setting point during a fault period and a voltage at the setting point determined during a pre-fault period; and
a fault detection module, configured to perform the fault detection based on the determined voltage change and a fault threshold, wherein the fault threshold set such that the voltage change exceeds the fault threshold in response to an internal fault within a protection zone of the protection device, and such that the voltage change does not exceed the fault threshold in response to an external fault outside of the protection zone of the protection device.
21. The apparatus of claim 20 , wherein the fault threshold is a product of a reliable coefficient and a rating voltage of the electrical line.
22. The apparatus of claim 20 , wherein the fault threshold is a product of a reliable coefficient and the voltage at the setting point determined during the pre-fault period.