ABSTRACT
A Study on the HVDC System and Fault Analysis of the
Northeast Asian Supergrid
MOON BYUNG-SOO
Advisor: Prof. Choi Hyo-Sang Ph.D.
Department of Electrical Engineering
Graduate School of Chosun University
The thesis's topic is “A study on the HVDC system and fault analysis of the
Northeast Asian Supergrid.”In the 21st century, as energy conversion
accelerates due to global warming and fossil fuel depletion, the establishment of
a supergrid linking power grids among countries is emerging as a major
concern. Northeast Asia is rich in renewable energy resources such as wind and
solar power in Mongolia and the interior of China, and is geographically
adjacent to large-scale power demands in Korea, Japan, and China, providing
favorable conditions for cross-border power supply and demand balancing. As a
result, strategies for securing energy security and realizing carbon neutrality by
2050 are being developed, and to achieve these goals, it is necessary to
establish measures to address the issues of frequency differences among AC
systems when linking power grids among countries and the increase in fault
current that occurs when connecting to high-voltage direct-current (HVDC)
systems. In this paper, the characteristics of fault currents generated in the
HVDC transmission system were analyzed, and the applicability of reduction
technology was reviewed.
In chapter 2, sections 1 and 2, the technical trends of the HVDC transmission
system, the transmission methods and interconnection schemes, and the basic
principles and modulation techniques of the VSC-HVDC system were examined
to present the system configuration direction suitable for HVDC connection.
Section 3 systematically summarized the principle of superconducting fault
current limiters (SFCLs), DC interruption theory, types of DC interruption
technologies, and the operating principles of DC circuit breakers (DCCBs).
Section 4 describes the fault analysis theory for the high voltage alternating
current (HVAC) system and the specification of fault current calculation based
on the IEC 60909. In addition, the basic theories of unbalanced faults such as
single-line-to-ground, double-line-to-ground, line-to-line, and three-phase faults,
and protection relay were described.
In chapter 3, PSCAD/EMTDC simulation design and interpretation were
conducted. In section 1, simulation parameters for the application of the
symmetric coordinate method were set up. Using this parameter, a symmetric
component (P–N–Z) analysis based on the x-axis was performed on the
three-phase asymmetric failure types of one-line ground fault, two-line ground
fault, and line-to-line short circuit. Using this, electrical characteristics such as
instantaneous values of voltage and current for each failure type, unbalance,
and change in symmetric components were analyzed. In section 2, an
VSC-HVDC grid based on the modular multi level converter (MMC) was
constructed between Weihai, China and Taean, Korea, and its parameters were
defined. In section 3, the DC voltage, current, and power graphs of MMC were
analyzed by steady-state simulation, and the voltage, current, and power
characteristics of AC1 (Weihai, China) and AC2 (Taean, Korea) were analyzed.
In section 4, a transient state simulation was executed in a PSCAD/EMTDC
environment, and the characteristics of the VSC-HVDC system based on a
MMC. Also the DC transmission system, and the AC1 and AC2 systems were
analyzed. By setting four fault points (F1-F4) in the HVDC ±500 kV, 350 km
transmission section, the DC ground current generated during the one-line
ground failure of the P (+) and N (-) poles, and the AC voltage, current, and
power characteristics of the sending point and the receiving point were
analyzed. In addition, the voltage, current, and power characteristics of the
AC1, AC2, and DC systems were analyzed in the event of a one-line ground
fault, two-line ground fault, between lines, and three-phase short circuits of
the AC1 and AC2 systems.
FULL THESIS:https://www.riss.kr/search/detail/DetailView.do?p_mat_type=be54d9b8bc7cdb09&control_no=58a12d105532aee7ffe0bdc3ef48d419&keyword=HVDC
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