Wavelet Based Protection Scheme for Multi Terminal Transmission System with PV and Wind Generation

A hybrid generation is a part of large power system in which number of sources usually attached to a power electronic converter and loads are clustered can operate independent of the main power system. The protection scheme is crucial against faults based on traditional over current protection since there are adequate problems due to fault currents in the mode of operation. This paper adopts a new approach for detection, discrimination of the faults for multi terminal transmission line protection in presence of hybrid generation. Transient current based protection scheme is developed with discrete wavelet transform. Fault indices of all phase currents at all terminals are obtained by analyzing the detail coefficients of current signals using bior 1.5 mother wavelet. This scheme is tested for different types of faults and is found effective for detection and discrimination of fault with various fault inception angle and fault impedance.


I. INTRODUCTION
An electrical power system consists of utility grid and hybrid energy sources like wind and photovoltaic. The heavy short circuit currents are likely to cause damage to equipment if suitable protective relays and circuit breakers are not provided for the protection of each section of the power system. A fault in a power system can lead to abnormal currents and voltages [4,6]. During a three phase short circuit, the currents may become excessively large and the voltages may go to zero. The system must be protected against such occurrences, and steps must be taken to remove a fault as quickly as possible [10]. An integration scheme of solar photovoltaic combination with a wind energy system of large capacity doubly excited induction generator is described in this paper. Protection must required to respond both utility grid and renewable energy sources. If the fault is on the utility grid, the desired response may be to isolate the hybrid energy sources from the main utility as rapidly as possible to protect the system [5]. If the fault is within the hybrid source, the protection scheme isolates the energy source section of the system to eliminate the fault. In order to cope with the bi-directional energy flow due to large numbers of sources new protection schemes are required [7]. Reliable protection schemes can reduce costs for distributed generation, providing for more options in the overall mix of power sources. Mixed communications, different terminal arrangements, and accommodation of communication failure provides protection engineers with necessary options to improve overall system operation The proposed algorithm describes the general operating principle of multi terminal transmission line protection [1]  current signals are identified and then sum of the detailed coefficients are calculated by make use of bior1.5 mother wavelet at each terminal. This is compared to a threshold value of current signal in order to provide security against external faults. The protection scheme is simple if all the information is available at each terminal in order to provide high-speed tripping of each faulty terminal [3]. The test results can clearly shows that the variation in the value of fault index of the healthy phase in the presence of hybrid energy sources in the path along one terminal towards the other terminal with variations in fault inception angle and resistance.

II. HYBRID ENERGY SYSTEM
Distributed generation technologies applicable for hybrid energy sources may include emerging technologies such as wind turbine, solar PV, micro-hydropower, diesel generators. Hybrid generation consists of low voltage distribution systems with distributed energy resources, such as wind turbine and photovoltaic power systems, together with storage devices [9]. Solar PV generation involves the generation of electricity from solar energy. Due to enormous improvement in inverter technologies, PV generation is now preferred worldwide as Distributed Energy Resources. Solar energy can be utilized by collecting and converting it directly into electrical energy using photo voltaic system. Rapid progress in increasing the efficiency and reducing the cost of PV cells has been made over the past few decades [8]. Their terrestrial uses are now widespread, particularly in providing power for communications, lighting and other electrical appliances in remote locations where a more conventional electricity supply would be too costly. Wind turbine converts kinetic energy of winds motion into electrical energy using the energy conversion systems. Usually doubly fed induction generators are used in WECSs [2]. The main part of the wind turbine is the tower, the rotor, and the nacelle. The nacelle provides the mechanical transmission and the generator. Wind velocities between 4 m/s and 30m/s are used for driving wind turbine generator shaft and producing electrical energy .Turbine captures the wind energy flow through rotor blades and transfers the energy to the induction generator through the gearbox. The generator shaft is driven by the wind turbine to generate electric power.

III. SYSTEM MODELING AND ANALYSIS
Single line diagram of Four terminal transmission line with hybrid Energy source of wind and PV generation included in the system as illustrated in Figure 1 and description about the details of the system are represented in table1.

IV. RESULTS AND DISCUSSIONS
The wavelet based Fault classifier modules are tested using data sets consisting of fault cases. Fault index, fault inception angle, distance and fault resistance were changed to investigate the effects on the performance of the proposed algorithm.
A .Test results of single phase to ground faults (LG)

V. CONCLUSION
The accuracy and reliability of algorithm and wavelet analysis for fault classification for shunt faults on multi terminal transmission line fed from sources with two end terminals and hybrid energy sources like wind and PV system at other two terminals is presented in this work. The online data sheet used to input to the algorithm employs the fundamental components of three phase currents of each section measured at all end terminals, thus require less communication and data acquisitions. The wavelet detailed coefficient based classification algorithm provides automatic detection and discrimination of fault type, faulted phases less than half cycle from the inception of fault at any fault resistance. The variation of fault parameters such as line distance, fault inception angle and fault resistance on multi terminal transmission with hybrid energy system protection scheme is effectively done. The performance of the proposed protection scheme has been investigated by a number of classified short circuit fault conditions are analyzed.The complexity of the possible types of faults of transmission line, varied fault inception angles from 0 to 180°,fault resistance (0-50Ω) are identified and tested at different distances.