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This paper aims at proposing novel methods for multi-terminal VSC HVDC system design and operation with large-scale wind farms. The paper is based on the hierarchical optimal power flow with small-signal stability constraint. Multi-terminal VSC HVDC (MTDC) system reinforcements are designed in the first step. The reinforcement capacities of the HVDC systems are designed by optimization process. Economic load dispatch in the reinforced system with MTDC is carried out in the next step. By the proposed method, multi-terminal VSC HVDC systems can be utilized more effectively even when wind production is not high. Several multi-terminal configurations are designed. Wind power hosting capacities, net present value, and profitability index of the systems are analyzed.

This paper proposes a fast and robust load flow method for balanced power distribution systems with distributed generation sources. The method formulates the power flow equations in PQ decoupled form with polar coordinates. Second-order terms are included in the active power mismatch iteration, and resistances are fully modeled without any simplifications. The impacts of zero-impedance branches are explicitly modeled through reconfiguring of the adjacent branches with impedances. Typical distribution generation models and distribution load models are included. A hybrid direct and indirect solution technique is used to achieve efficiency and robustness of the algorithm. Active power correction is solved by means of a sparse LU decomposition algorithm with partial pivoting, and the reactive power correction is solved by means of restarted Generalized Minimal Residual algorithm with incomplete LU preconditioner. The numerical examples on a sample distribution system with widespread Photovoltaic installations are given to demonstrate the effectiveness of the proposed method.

This paper proposes a hybrid current profile based fault location algorithm for double-line-to-ground (DLG) faults in a distribution system. The method uses both short-circuit fault current profile (average of fault currents recorded for the faulted phases) and during-fault load current profile (corresponding to the un-faulted phase) to estimate an accurate fault location. The method is extended to include the effects of fault resistance in determining the fault location. Both fault current profiles and load current profiles are simulated for different values of fault resistances. The profiles are also extrapolated for those fault resistances corresponding to which the simulated profiles are not available. Numerical examples on a sample distribution feeder with multiple laterals and load taps are provided to validate the proposed algorithm for its robustness.

This paper proposes a new method for determining single-phase-to-ground fault locations of ungrounded distribution systems based on the measurements collected from the feeder breakers and intelligent switches during the fault. The method first narrows down the possible faulted area into a specific feeder section based on the reactive power factors of residual powers determined for the breakers and switches. Then the power consumption of each individual load in the faulted section is determined based on measurements at the boundaries of the section, and load profiles for each individual load. The possible faulted line segment is determined using a forward sweep scheme to test a sign change of faulted phase voltages on terminal buses of line segments, and the possible fault point is determined by finding a location along the faulted segment having a zero voltage on the faulted phase. Numerical examples are given to demonstrate the effectiveness of proposed method.

This paper proposes a new method for determining the location of single-phase-to-ground faults of ungrounded distribution systems based on residual voltage distribution. The possible faulted line segment and fault location are determined by comparing the phase angles of faulted phase voltages against a faulted phase reference angle, and the faulted phase voltages are determined as the difference between the fault caused residual voltage of all phases and the shunt caused residual voltage of un-faulted phases. The method determines the fault location solely based on the voltages and currents measured during the fault, and associated series impedance and shunt impedances of line segments. It does not require any measurements or information for the load demands and prefault conditions. Numerical examples are given to demonstrate the effectiveness of the proposed method.

This paper proposes a hybrid three-phase load flow method for ungrounded distribution systems. Based on topology connectivity analysis, the system is partitioned into a mainline system and multiple tap systems. A Newton method with constant admittance matrix is used to solve the mainline system, such that zero impedance branches are merged into adjacent impedance branches to be considered, and constant active-power and voltage-magnitude (PV) buses with three-phase balanced voltages are transformed into single-phase PV buses to be modeled. A backward/forward sweep with loop compensation is used to solve the tap systems, such that a transformer and a voltage regulator is modeled using line-to-line voltages, a distribution line is simplified as a series branch, and loop compensation current is initialized based on loop downstream loads and the impedances of loop paths. Test results of sample systems are given to demonstrate the effectiveness of the proposed method.

This paper proposes a decoupled three-phase load flow analysis method for unbalanced distribution systems. The power flows are solved through nodal current injection mismatch equations written in rectangular coordinates. The voltage changes resulting from nodal current injection mismatches and nodal admittance matrix have been decoupled into one contribution from the real part, conductance matrix, and the other contribution from the imaginary part, susceptance matrix. The method determines voltage changes resulting from conductance and susceptance matrices respectively, and determines the voltages of a node as a linear combination of those voltage changes. The relative contributions are determined based on the diagonals of the conductance and susceptance matrices. The constant active power and voltage magnitude(PV) nodes have been converted into constant active and reactive power(PQ) ones based on a sensitivity matrix determined through Kron reduction of the nodal admittance matrix, and the corresponding reactive powers are adjusted after each solution has converged. The zero-impedance branches are merged with adjacent impedance branches, and the three phases of a balanced-voltage PV bus are merged into one single-phase PV bus to be modeled in the nodal admittance matrix. Numerical examples on IEEE 37 node test feeder and IEEE 123 node test feeder are presented to demonstrate the effectiveness of the proposed method.