Xia Chengjun

Analysis on commutation failure caused by AC faults in multi-infeed HVDC systems

Commutation failure (CF) is one of the common faults in HVDC system, a new issue arising in multi-infeed HVDC systems is whether all the inverters will suffer from commutation failures concurrently, and the interaction between AC and DC systems is much more complicated. According to the mechanism of commutation failure, influencing factors and judgment basis, this paper proposed a commutation failure detection method based on the critical multi-infeed interaction factor (CMIIF). A three-infeed HVDC system was modeled in PSACD/EMTDC, The simulation results of the test system and an actual system proved the accuracy and validity of the proposed method.

Analysis of inrush current and over-voltage with HVDC AC filters switching on

The number of the faults caused by AC filters has been reached 8 times in a HVDC system of CSG. The AC Filter may produce inrush current and over-voltage when switching on, which will occasionally damage the filters, make protection malfunction and threat the system. The paper introduces a simulation based on Monte Carlo algorithm and PSCAD User-definition model in order to analysis the problem. This paper makes simulations about inrush current and the zero sequence current to research three-phase unbalanced inrush current in the inverter side. Based on these results, some methods which solve the effect of inrush current has been proposed, like erecting POW, locking the unbalanced protection temporarily.

Travelling-wave-based on-line fault location scheme for 110kV power cable

This paper presents a novel wavelet-based fault location scheme for 110kV cable when the digital fault recorded data are available at the two terminals of each cable. Three phase current signals are decoupled into two aerial modes and one zero mode with the phase-mode transformation. The theory of wavelet singularity detection is applied to extract the arrival time of the travelling wave from the aerial mode which are necessary for fault location. The proposed scheme can determine the fault location without the support of GPS and has the ability to eliminate the uncertain factor including wave velocity and transition impedance. Characteristics of the proposed fault location scheme are studied with some simulation cases by using PSCAD/EMTDC. The results indicate that the proposed scheme has acceptable accuracy for fault location.

On-line fault location scheme for power cable based on Arc characteristic

In this paper, a novel fault location scheme for 110kV XLPE cable based on wavelet analysis is presented. Three phase fault currents are collected by the fault recorders installed at the two terminals of the cable. One zero mode and two aerial modes are obtained after the recorded current signals are decoupled with phase-mode transformation. The arrival time of the travelling wave can be identified precisely with the α aerial mode by using the wavelet singularity detection technology. The proposed algorithm can position the fault without GPS and is independent of the wave velocity and fault transition impedance. This will help to solve the problem of cable changing parameters, especially the change of wave velocity due to the changing relative permittivity with age. Arc characteristics are considered by establishing the Cassie arc model. Several simulation cases are studied by using PSCAD/EMTDC and the results indicate the proposed scheme is feasible and reliable for application.

Analysis of transformer inrush under unbalanced three-phase parameters

The phase A of No.1 main transformer broke down in a certain 500kV substation and the standby has been lost, in order to maintain normal operation, phase B of No.2 main transformer has been used as a replacement, thus result in the unblanced three-phase parameters of No.1 transformer. Existing relay protection principle is based on balanced three phase parameters, to study the impacts on relay protection caused by unbalanced three-phase parameters, inrush current as a key element in relay protection be selected, a brief analysis of principle and characteristics of inrush current is given, then a simulation model for computing statistical transformer inrush current based on Monte Carto and user-defining function of the PSCAD/EMTDC software is established, based on the real data, comparison of inrush current between balanced and unbalanced is conducted. It is pointed that short-circuit impedance unbalance has little impact on inrush current while the different of saturation characteristic has a greater influence.