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Protection of transmission lines using GPS:

Protection of transmission lines using GPS Presentation by


1. INTRODUCTION A century has passed since the application of the first electro chemical over current relays in power system protection .

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Distance protection has played an important role in power line protection since it was first introduced in the early part of the century. It has many advantages over the power line protection techniques and can be adopted for fault location and back up protection. However , like other power frequency based protection techniques With the continuous development of modern technology, protection relays have advanced with the development of electromechanical, semiconductor, integrated circuits and microprocessor technologies.


History since the concept was first raised in the late 60’s relay technology has gone through rapid development. Digital techniques for transmission line protection have been quickly developed Modern development for power system network , the demand for fast fault clearance to improve system stability and the need for alternative protection principles have resulted in the search for methods to increase the speed of relay response . In the late 70’s this led to the development of “ultra high speed protection “ based on the use of traveling waves and super imposed components these relays offered the advantage of fast response , directionality , and where not affected by power swing and CT saturation. However many distinct advantages of the conventional protection techniques where not retained for eg . Inherent back up protection. In recent years, there is a growing interest in the use of fault generated transients for protection purposes

Extensive research work:

Extensive research work to develop new relaying principles and techniques based on there detection.. this led to the new concept of “transient based protection “(TBP). Among these the “positional protection” offers attractive solutions for power line protection. the actual portion of the fault on the line by measuring the traveling time of the high frequency transient voltage or current signals along the line . in contrast to the conventional traveling wave based protection techniques, this technique concentrates on the fault generated signals during arcing and their associated high frequency signals.


Functionality The positional protection uses its associated GPS scheme to determine the instant when it detects the fault generated high frequency transient signals and uses the power line communication system to communicate this information to the relays at the other substations. the system can also respond to the high frequency transient generated by switch gear operation, which provides an immediate opportunity for comprehensive self testing and calibration checking. Electro magnetic transient program(EMPT) software has been used to simulate a model EHV transmission system in order to examine the response of the protection scheme to a variety of different system and fault condition.


2. FAULT GENERATED TRANSIENTS AND ASSOSIATED PROTECTION TECHNIQUES A comparison of different protection techniques in the frequency domain is shown in fig . a power system fault indicates a variety of additional transient components in additional components contain extensive information about the fault and are spread through out the spectrum ranging from Dc to may kilohertz and even mega hertz.

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In conventional protection scheme , the high frequency signals are considered to be noise and filtered out and as a result, considerable research has been spent on the designing of the filters , protection schemes based on detection of fault generated transient, such as the “ ultra high speed protection ” schemes are generally limited by the band width of transducers used.

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The transient based protection technique operate by extracting the fault generated high frequency signals through specially designed detection devices and their associated algorithms. The high frequency current signal are directly extracted from the CT out puts . although conventional iron cored CT’s alternate the high frequency signals.


3. CHARECTERSTICS OF HIGH FREQUENCY CURRENT SIGNALS The theoretical aspects of the characteristics of the propagation of high frequency signals on transmission lines have been well documented.

3.1 detection of fault position and fault generated current transients:

3.1 detection of fault position and fault generated current transients when a fault occurs on a transmission line , wide band voltages and current signals propagate away from the fault point along the power conductors. , the fault position on the line , fault path resistance and the characteristics impedance of the power conductors .this propagation can be shown graphically. Here relays are located at all of the substations in the power system and independently monitor the power system. The frequency range of interest for monitoring these fault generated high frequency signals is between 40-80 KHz and the signal processing is designed as to determine the arrival of a high frequency transient characteristics of those generated by a fault.

3.2 Fault current transient detector:

3.2 Fault current transient detector The proposed scheme uses a specially designed transient current detector fed from the primary CTs . This extracts are high frequency signals associated with the fault generated current transients. A simplified block diagram of the detector arrangement is shown in the figure. The detector is designed to interrogate signals in the range of frequencies from 40-80KHz. analog circuit acts as a band pass filter which extracts the band of fault generated transient current signal from the line. as a result , the response of the scheme is not affected by the power frequency short circuit band at the busbar or the presise configuration of the source side networks .

3.3 Signal Processing Unit:

3.3 Signal Processing Unit model transformation is employed to decouple the signal in to their respective aerial modes. The signal mixing circuit receive the signal from the 3 phase CTs and continue these to form mode2 and mode3 signals. The sampling frequency of the analog to digital A/D converter is 1 Mz and the speed of propagation of the high frequency transient is similar to the speed of light. The digital processing includes filters sequence recording, amplitude comparison, counters and decision logic.


4. BASIC PRINCIPLES AND RELAY DESIGN A short circuit fault on a power transmission line generates voltages and current signals over a wide frequency range. They are Basic Principle Relay Design

4.1 Basic Principle :

4.1 Basic Principle The basic principle of the technique can be demonstrated by referring to the 400Kv, EHV transmission network, shown in figure.

4.2 Relay Design :

4.2 Relay Design A simplified block diagram of the relay unit is shown in fig.. the transient detector uni5t is connected to the line using three phase CVTs . these are able to detect the fault generated high frequency voltage signals.


5. MODELLING AND SIMULATION System Modeling : The response of the complete system was evaluated by modeling the transmission line system together with the relays in the scheme using the EMTP simulation program. simulation of line and transformer energization , load rejection and fault clearing which are done to help determine the required transformer , circuit breaker and other equipment charecterestics . Additional simulations used to develop recommended procedure for line and transformer energization . Comparison of several recorded waveforms with the result of EMTP simulation of same event s.


Primary system voltages Relay responses

<- Relay responses:

<- Relay responses


6.Conclusion A new technique for the protection of a transmission line network is presented in this paper. This uses a dedicated fault detector to extract the fault generated high frequency voltage transient signal and GPS system to time tag these signals. The traveling time of the transient high frequency signal from the point of fault to the adjacent substation is used to determine the fault positions.



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