Yew Ming Yeap

Wavelet based fault analysis in HVDC system

HVDC system has become practically mature over the years but it is still met with some protection issues which should be discussed, for example, the circuit breaker (CB) should be selective to not trip if the transient is temporary, such as overcurrent due to load change. This paper addresses the problem with identifying the type of faults in a HVDC system using wavelet transform (WT). The wavelet transform is proven to be able to capture the distinctive feature of the fault pattern, specifically fault current rising time and oscillation pattern, which are helpful to form a basis for the tripping decision. Three phase-to-ground fault and DC fault are of concern in this paper as their effects are the most detrimental to the system. The point-to-point HVDC system is simulated using PSCAD, and the simulation result is subsequently processed in MATLAB to perform the wavelet transform.

Simulation and analysis of faults in high voltage DC (HVDC) power transmission

Modern civilization depends heavily on the consumption of electrical energy for industrial, commercial, agricultural, domestic and social purposes. However, for the current HVDC system, proper protection devices and logic are not yet as mature as the AC counterpart. This paper presents the fault analysis for the protection of the HVDC (65-765 kV range) grid, using PSCAD. Faults in the DC transmission line are analyzed. This paper also looks into the response of the system to each kind of faults. It is observed that the AC and DC faults have different signatures allowing us to tell them apart. The rise time of the fault current is presented here. Analysis of load changes is also done comparatively with the fault cases.

Differentiation of fault and load change in HVDC system using Amplitude Tracking Square Wave

For a HVDC system, a reliable power system protection should be quick and precise in identifying fault. It is also equally important to ensure some events that could be mistaken for fault to not trigger false alarm, for example load change. Wavelet transform is one of the well-known tools that is able to achieve this purpose. In this paper, the fault analysis using a novel Amplitude Tracking Square Wave (ATSW) is studied. The algorithm is very easy to be implemented, as only time-domain analysis is involved. Notwithstanding the low complexity, it can work as effective as the wavelet transform, as proven by comparing the results obtained from these two signal processing techniques.

Fault detection in HVDC system using Short Time Fourier Transform

The protection of HVDC system is an important topic for stable transmission. When fault happens, DC breaker opens the circuit electronically unlike AC breaker, therefore, its operation is very fast. Besides that, it is also equally important to design a fast fault detection method. This paper investigates the application of Short Time Fourier Transform (STFT) to not only detect but also differentiate types of disturbance. For this application specifically, one needs to compromise frequency resolution in exchange for better time resolution. As a result, we are no longer able to find the frequency components in fault signal. To address that, a parameter is proposed to capture the pattern of the side lobes in frequency domain. It is seen that STFT, with that parameter, can effectively detect the DC fault very fast (<;1.5ms), as well as differentiate it from AC fault and load change. A two-terminal Modular Multilevel Converter (MMC) HVDC system is used to simulate fault in PSCAD/EMTDC. The DC current is exported to MATLAB to perform STFT.

STFT analysis of high frequency components in transient signals in multi-terminal HVDC system

High voltage DC (HVDC) system is important transmission technology, with several advantages over the AC transmission system. Transient analysis plays an important role in the power systems, in particular for the multi-terminal DC (MTDC) system. In DC systems, the DC line fault can result in extremely fast rising current compared to its AC counterpart due to absence of the line inductance. Therefore, the analysis of fast transients is of great interest in the HVDC system, in particular for MTDC system. In this paper, the application of Short Time Fourier Transform (STFT) in transient analysis of current signals in the MTDC system has been investigated. Because of uncertainty principle with the STFT, finer time resolution has been chosen at the expense of frequency resolution, allowing for faster detection. The CIGRE B4 multi-terminal DC grid system has been modeled in PSCAD/EMTDC, and transient events are simulated. The steady-state and the transient currents in the different terminals are monitored and analyzed using the STFT.

Analysis and validation of wavelet transform based DC fault detection in HVDC system

Abstract Fault detection plays an important role in both conventional AC and upcoming DC power systems. This paper aims to study the application of discrete wavelet transform (WT) for detecting the DC fault in the high voltage DC (HVDC) system. The methods of choosing the mother wavelet suited for DC fault is presented, based on degree of correlation to the fault pattern and the time delay. The wavelet analysis is performed on a multi-terminal HVDC system, built in PSCAD/EMTDC software. Its performance is judged for critical parameter like the fault location, resistance and distance. The analysis is further extended to validation using results from experiment, which is obtained from a lab-scale DC hardware setup. Load change, one of the transient disturbances in power system, is carried out to understand the effectiveness of the wavelet transform to differentiate it from the DC fault. The noise in the experimental result gives rise to non-zero wavelet coefficient during the steady-state. This can be improved by removing the unwanted noise using right filter while still retaining the fault-induced transient. The wavelet transform is compared with short-time Fourier transform to highlight the issue with window size and noise.

Comparative evaluation of power loss in HVAC and HVDC transmission systems

Researches on renewable energy sources have been carried out and ways to reduce energy consumption and energy wastage have been discussed and studied to tackle the worlds power shortage problems. Wind farm, one of the prominent renewable sources, is usually remotely far from onshore and needs long transmission to bring generated power to populated areas. This paper covers the analysis of the traditional high voltage alternating current (HVAC) transmission system and comparison of the aforementioned system with high voltage direct current (HVDC) transmission in terms of power loss. In this paper, the converter that used in HVDC transmission system is voltage source converter (VSC). To observe and evaluate the power losses, the HVAC and HVDC transmission models are simulated in PSCAD. It is seen that cable contributes to large portion of losses in HVAC system, increasingly so with longer transmission distance. Whereas for HVDC system, converter loss is found to outweigh cable loss.

Circulating current controller in dq reference frame for MMC based HVDC system

This paper presents a phase shifted triangular carrier pulse width modulation technique for control of modular multilevel converter (MMC) based HVDC system. This switching modulation technique has reduced average switching frequency when compared to conventional method where switching state changes in each sampling period or control cycle. A dq reference frame based circulating current controller (CCC) is implemented to suppress the double line frequency arm circulating currents of MMC. Details regarding the outer loop power control and DC bus voltage control for transmitting desired amount of power through HVDC system are also discussed. A detailed matlab simulink model of eight submodules (SM) per arm MMC based HVDC system was developed and the corresponding simulation results are presented. Simulation studies with and without CCC are carried out and the corresponding variation in arm currents, SM capacitor voltages are also discussed.

Fault location estimation for VSC-HVDC system using Artificial Neural Network

Recent developments in high voltage direct current (HVDC) transmission have had a positive impact on the research community. HVDC transmission offers superior power quality and low transmission loss, however, the fault location and clearance technology is not as mature as its AC counterpart. This paper aims to propose a fault location technique on a 200 km two-terminal VSC-HVDC system using wavelet transform (WT) and artificial neural networks (ANN). The HVDC system is modeled in PSCAD and the results are treated with WT and ANN using MATLAB. The fault of concern in this paper is pole-to-pole fault. The simulation is repeated by varying fault resistance and location along 200 km to test the influence of these two parameters on the proposed fault location method. The result demonstrates reasonably high reliability in predicting the fault location with low error.

Fault and load change differentiation in High Voltage Direct Current (HVDC) system

High Voltage Direct Current (HVDC) system has come a long way to shift the direction of power transmission in future. With respect to that, the protection is still one of the hot topics that need to be addressed, particularly the DC fault detection method. This paper presents the fault simulation study of a two-terminal HVDC system. DC fault and load change are of interest here. With the help of wavelet transform, these two cases can be differentiated by determining the wavelet coefficient of DC line current. Details regarding synchronous reference frame dq current controller at source terminal, RMS method controller at load terminal are also discussed and the corresponding obtained simulation results for steady state, load change and fault conditions using Matlab/Simulink are presented.