Testing of Travelling Wave Fault Locators

Travelling Wave Fault Location becomes more and more popular. Users worldwide praise the great accuracy of travelling wave fault location. Due to the principle of travelling wave fault location the accuracy of the fault location is based on an accurate time measurement of the travelling wave wavefronts. For travelling wave fault location, the time accuracy should be in the range of nanoseconds because a time inaccuracy of one microsecond would cause an error of 300 m for the fault location. For double ended travelling wave fault location this time accuracy needs to be maintained for both devices which can be placed several hundreds of kilometres away from each other. Before putting such travelling wave fault location systems into operation different tests should be performed to guarantee the performance of the system. Users should start with a factory acceptance test to prove the accuracy of the system in a lab environment. In the factory acceptance test many test cases should be applied to test the accuracy of the system for different fault types and fault positions on the line. The factory acceptance test should be performed with the exact propagation velocity of the line. The inaccuracy of the fault location in factory acceptance test should be independent of the fault position otherwise there could be a problem with the propagation velocity. The accuracy of fault location during the factory acceptance test should be constant over time to demonstrate the reliability of time synchronization. If the factory acceptance test is passed it is confirmed that the fault location system itself can fulfil the accuracy requirements without the influence of the primary system like instrument transformer and the wiring between instrument transformers and travelling wave devices. During the site acceptance test a focus should be given to the accuracy of the time synchronization of the travelling wave device on site. Beside this, it needs to be checked that all channels are wired correctly, and the trigger levels are appropriate. For enhanced accuracy the compensation for the propagation time between instrument transformer and travelling wave device needs to be tested. At site acceptance test switching operations of primary equipment can be used to check the proper behaviour of the travelling wave devices. This can be helpful to adjust trigger levels and check the propagation velocity of the line and the time synchronisation of the travelling wave devices at both ends of a line. Finally, the communication of the travelling wave devices to the central computer needs to be tested at the site acceptance test. The paper starts with a short introduction of travelling wave fault location, followed by a discussion of possible sources of inaccuracy for single ended and double ended travelling wave fault location. Factory acceptance test and site acceptance test are explained in detail using practical examples. The paper closes explaining how to verify the settings, especially the propagation velocity of the line. This can be done after putting the system into operation, using data from the first external faults.