Abstract
To develop mechanical circuit breaker in high voltage direct current (HVDC) system, a fault current limiter is required. Traditional method to limit DC fault current is to use superconducting technology or power electronic devices, which is quite difficult to be brought to practical use under high voltage circumstances. In this paper, a novel concept of high voltage DC transmission system fault current limiter (DCSFCL) based on saturable core was proposed. In the DCSFCL, the permanent magnets (PM) are added on both up and down side of the core to generate reverse magnetic flux that offset the magnetic flux generated by DC current and make the DC winding present a variable inductance to the DC system. In normal state, DCSFCL works as a smoothing reactor and its inductance is within the scope of the design requirements. When a fault occurs, the inductance of DCSFCL rises immediately and limits the steepness of the fault current. Magnetic field simulations were carried out, showing that compared with conventional smoothing reactor, DCSFCL can decrease the high steepness of DC fault current by 17% in less than 10ms, which verifies the feasibility and effectiveness of this method.
Highlights
Due to rapid increase in global energy demand, distributed energy resources are widely applied in conventional power systems.[1,2,3] Compared with traditional AC system, DC system has overwhelming advantages in long distance and high power transmission
When a fault occurs, fault current of DC system is of great value and it doesn’t have zerocrossing point like AC systems do,[4,5,6] so we have to over-design the capacity of mechanical circuit breakers (MCB) for DC system to protect the whole devices from destructive damage, especially for high voltage direct current (HVDC) system of extremely large capacity.[7]
Superconducting technology based fault current limiter (SFCL) presents a variable resistance by switching between normal state and superconducting state to limit the DC fault current,[8,9] while solid state fault current limiter (SSFCL) performs a variable equivalent impedance to the system by controlling the conduction state of power electronic devices to limit the DC fault current.[10,11]
Summary
Due to rapid increase in global energy demand, distributed energy resources are widely applied in conventional power systems.[1,2,3] Compared with traditional AC system, DC system has overwhelming advantages in long distance and high power transmission. SFCL presents a variable resistance by switching between normal state and superconducting state to limit the DC fault current,[8,9] while SSFCL performs a variable equivalent impedance to the system by controlling the conduction state of power electronic devices to limit the DC fault current.[10,11] But the cost of SFCL is quite high and the realization of this method is very difficult, which limits the actual implementation of it. Except for SFCL and SSFCL, this new concept offers an alternative choice for building a DC FCL of lower cost and better high voltage adaptability
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