This paper proposes a method to improve the frequency response of a power system during restoration. A Load Frequency Control (LFC) scheme with a PID controller is used. In the initial phase of restoration; the proposed control scheme helps to increase the amount of load pick-up. Presented method is capable of achieving better frequency response for a determined load step. The aim is to assess desired frequency response for different power plant. The proposed controller has been tested for different power plants, and simulation results show that the frequency controller can improve load pick-up.

This paper investigates the transient recovery voltages across vacuum circuit breakers used for the switching shunt capacitor bank in wind power plants, which are connected to the power system. Consideration has been given to high frequency models of all power system components, such as, the transformer, wind power plant generator, cable, surge arrester, vacuum circuit breaker and grounding system. The initial phase of study reproduced the results of previous work. In the second phase, the influence of different parameters, such as, the grounding system network, current injection point location to the grounding system, soil resistivity, grounding system length segment and soil ionization phenomena in the grounding system on transient recovery voltage, have been investigated via EMTP- RV. The results show that consideration of the high frequency behavior of the grounding system in wind power plants for prediction of transient recovery voltages is very important. Index Terms--Transient recovery voltage(TRV); Capacitor bank; Vacuum circuit breaker(VCB); Back to back switching;I.

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Original scientific paper One of the major problems in power system protection is current transformers saturation and inability of protective relays to recognize and compensate it. In this paper an approach is presented to identify current transformer saturation based on instantaneous flux density calculation. Also the calculated magnetizing current is used to saturation compensation. In the proposed algorithm, the instantaneous flux density and magnetizing current are calculated using Jiles-Atherton method. Using knee point flux density, a criteria is proposed to identify saturation phenomena in the current transformer and finally using calculated instantaneous magnetizing current, secondary current distortion has been compensated. To evaluate efficiency of the proposed algorithm, various types of faults, residual flux, fault occurring angle, CT burdens and DC components have been tested and the results evidence that the proposed algorithm is more accurate and reliable as well as faster than other algorithms and its error is obviously less than them.