Fault protection of HVDC transmission lines
View Patent ↗A protection system for high voltage direct current, HVDC, transmission lines is provided. The protection system includes a direct current, DC, bus, a device configured to connect an HVDC transmission line to the bus, at least one DC circuit breaker arranged for disconnecting the transmission line from the bus upon reception of a trip signal, current and voltage sensors, an inductor arranged such that the current through the transmission line passes the inductor, and a fault detection unit. The fault detection unit is arranged for assessing, on the basis of current and/or voltage measurements, whether a fault exists on the transmission line, and sending, if a fault is detected on the transmission line, a trip signal to the circuit breaker. The additional inductance limits the rise in fault current and facilitates a selective fault detection. Further, a method of fault protection for an HVDC transmission line is provided.
1. A high voltage direct current, HVDC, fault protection system comprising:
an HVDC unit comprising:
a direct current, DC, bus,
means for connecting at least one HVDC transmission line to the bus, and
at least one DC circuit breaker being arranged for disconnecting the transmission line from the bus upon reception of a trip signal, and
a protection unit comprising:
a current sensor being arranged for measuring a current I(t) through the transmission line,
a voltage sensor being arranged for measuring a voltage U(t) between the transmission line and ground,
an inductor or inductors being arranged such that the current through the transmission line passes the inductor or inductors, and
a fault detection unit arranged for:
assessing whether a fault exists on the transmission line by deriving at least one fault measure from the voltage and/or current and comparing the fault measure with a predetermined value, and
sending, if a fault is detected on the transmission line, a trip signal to the circuit breaker, and wherein
the fault detection unit is further arranged for assessing whether a fault exists on the transmission line by:
evaluating S=[U(t 2 )−U(t 1 )]×[I(t 2 )−I(t 1 )], where t 1 and t 2 are consecutive sampling times, and
deciding that a fault exists on the transmission line if S<−S 0 , where S 0 is a predetermined positive value.
2. The system according to claim 1 , wherein the inductor is connected in series with the transmission line.
3. The system according to claim 1 , wherein the inductor is connected in series with the DC bus.
4. The system according to claim 1 , wherein the fault detection unit is further arranged for:
comparing the measured voltages U(t 1 ) and U(t 2 ) to a positive threshold value U 0 , and
enabling the trip signal to be sent, only if the measured voltages are smaller than the threshold value U 0 .
5. A high voltage direct current, HVDC, switchyard comprising a fault protection system according to claim 1 .
6. A high voltage direct current, HVDC, converter station comprising a fault protection system according to claim 1 .
7. A high voltage direct current, HVDC, grid comprising a fault protection system according to claim 1 .
8. A method of fault protection for a high voltage direct current, HVDC, unit comprising:
a direct current, DC, bus,
means for connecting at least one HVDC transmission line to the bus, and
at least one DC circuit breaker being arranged for disconnecting the transmission line from the bus upon reception of a trip signal,
wherein an inductor or inductors are arranged such that a current through the transmission line passes the inductor or inductors, the method comprising:
measuring the current I(t) through the transmission line,
measuring a voltage U(t) between the transmission line and ground,
assessing whether a fault exists on the transmission line by deriving at least one fault measure from the voltage and/or current and comparing the fault measure with a predetermined value, wherein said assessment whether a fault exists comprises
evaluating S=[U(t 2 )−U(t 1 )]×[I(t 2 )−I(t 1 )], where t 1 and t 2 are consecutive sampling times, and
deciding that a fault exists on the transmission line if S<−S 0 , where S 0 is a predetermined positive value, and sending, if a fault is detected on the transmission line, a trip signal to the circuit breaker.
9. The method according to claim 8 , further comprises:
comparing the measured voltages U(t 1 ) and U(t 2 ) to a positive threshold value U 0 , and
enabling the trip signal to be sent, if the measured voltages are smaller than the threshold value U 0 .
10. The system according to claim 2 , wherein the fault detection unit is further arranged for:
comparing the measured voltages U(t 1 ) and U(t 2 ) to a positive threshold value U 0 , and
enabling the trip signal to be sent, only if the measured voltages are smaller than the threshold value U 0 .
11. The system according to claim 3 , wherein the fault detection unit is further arranged for:
comparing the measured voltages U(t 1 ) and U(t 2 ) to a positive threshold value U 0 , and
enabling the trip signal to be sent, only if the measured voltages are smaller than the threshold value U 0 .
12. A high voltage direct current, HVDC, switchyard comprising a fault protection system according to claim 2 .
13. A high voltage direct current, HVDC, switchyard comprising a fault protection system according to claim 3 .
14. A high voltage direct current, HVDC, switchyard comprising a fault protection system according to claim 4 .
15. A high voltage direct current, HVDC, converter station comprising a fault protection system according to claim 2 .
16. A high voltage direct current, HVDC, converter station comprising a fault protection system according to claim 3 .
17. A high voltage direct current, HVDC, converter station comprising a fault protection system according to claim 4 .
18. A high voltage direct current, HVDC, grid comprising a fault protection system according to claim 2 .
19. A high voltage direct current, HVDC, grid comprising a fault protection system according to claim 3 .
20. A high voltage direct current, HVDC, grid comprising a fault protection system according to claim 4 .