Behavior of different distance relay characteristic on lines fed from type-1 and type-2 WTGU connected radially to grid: A case study

Line protection in HV/EHV/UHV lines is primarily by distance protection due to its selective, reliable and secure operation. With the wind farm penetration, the SIRs of lines are going to change drastically throughout the day. A case study has been performed in this paper to study the behavior of dynamic characteristics with respect to these changes. Analytically fault voltages and currents are calculated for the system. Distance relay implemented on hardware has been validated with these waveforms and inferences have been made to give recommendations for characteristics to be applied in practical systems for secure and reliable operation of distance relay.

I. Introduction

The wind generators of type-1 and type-2 are primarily induction machines. Due to their rugged performance and low maintenance, they are widely used when there is constant or near to constant wind speed. Most wind generators commissioned in the last decade are of this type. The most important difference between these machines and the conventional synchronous machines regarding behavior during fault. Synchronous machine provides support to the fault current by varying the transient impedances while these induction machines have constant armature impedances [1]. There are several technical papers and working group reports in the literature which give a good review of protection philosophy in the light of distributed generation [2], [3] and [4]. For a low voltage microgrid systems, typical protection is provided with co-ordinated directional over current relays. These days when these generators are connected to the grid at EHV level, the fault levels and their contribution is significantly low at for these EHV systems [5]. This makes the over-current or the conventional feeder protection hard to operate.