This paper proposes a new on-line measuring method for tan δ of insulation based on passive current sensors. The new method avoids the difficulties encountered during producing sensors with high precision for ratio error and phase displacement error, thus it is cost-effective and of high accuracy. Combining a phase difference algorithm with the computer technology, the method is suitable for micro-controller unit （MCU）. The practicability of the method is validated by field tests, thus its anti-interference ability is confirmed.
In the north part of China, the power outputs of many wind farms are limited by the load following capacity （LFC） of traditional generators. This paper proposes a mixed-integer programming formulation to assess the maximum LFC of a power system. The objective of the formulation is to maximize the total spare spinning capacity of all generators in the valley load period, which is subjected to constraints including power balance, unit on/off status and generator power limits at both peak and valley load levels. Based on the formulation, a method for evaluating wind power penetration limit is also introduced considering the error of the wind power prediction and the wind power curtailment. For given installed wind capacity, the annual wind power curtailment can be simulated. By presetting the maximum proportion of wind curtailment, the allowable wind power integration capacity is acquired by a golden section search method. The proposed method has been tested on a practical power system. Simulation results show t
This paper presents a replacement strategy for an aged transformer based on condition monitoring and system risk. The condition monitoring measurements are used to estimate the insulation age of the transformer. The unavailability because of transformer aging failure is calculated using the insulation age instead of the traditional natural age. The system risk is assessed using the total unavailability from both aging and repairable failures. The expected damage cost and benefit due to delaying the replacement of the transformer are evaluated. The best replacement timing is determined as the year when the replacement of the transformer reaches the maximum net benefit. A case study for two aged transformers in a utility system demonstrates the effectiveness of the proposed method.
A current source converter based multi-terminal direct current（DC）wind energy conversion system（WECS）is proposed.The current source DC/DC converter is adopted to connect a wind turbine to an inverter with maximum power point control.Each turbine is associated with a DC source by parallel-connected to a common DC link.After DC power collection,a current source inverter（CSI）using gate turn-off components is used for the grid connection due to its flexible reactive power control and short circuit protection capabilities.For such a parallel connection configuration,the CSI operates in an input voltage control mode,which maintains the DC link voltage constant.The dynamic responses of combined mechanical and electrical systems are investigated with three different operation cases.Simulation and experimental results demonstrate the feasibility and stability of the current source DC/DC converter based multi-terminal DC WECS.
A new adaptive single-pole autoreclosure technique based on the magnitude of fault point voltage is presented.After fault phase tripping,the fault point voltage of transient faults is essentially different from that of permanent faults,so the magnitude of fault point voltage is used to distinguish fault nature.Fault point voltage can be calculated through uniform transmission line equation.Considering that fault point voltage changes with fault location and transition resistance,a concept of real-time action voltage setting is put forward.The technique solves the problem that criterions based on terminal voltage could be easily affected by inductive coupling voltage and transition resistance.Simulation results show that the method is reliable.
A simulation framework is proposed to evaluate the voltage stability of power systems incorporating wind power intermittency.Firstly，the power output modelings of three types of wind turbines are discussed.Secondly，the Jensen model is employed to simulate the wind farm with the wake effect.The Monte Carlo based technique is used to conduct the voltage stability evaluation incorporating the randomness of the wind speed based on the Weibull probability distribution.Thirdly，the relative sensitivity index（RSI）is calculated to identify weak buses during analysis.Finally，case studies with different simulation scenarios are carried out.Some statistical results involving weakness probability，expected value and variance of RSI as well as preliminary conclusions are drawn based on numerical simulation results.