A New Adaptive Inverse-Time Protection Scheme for Modern Distribution Systems with Distributed Generation

In the current times, penetration of distributed generation is increasing, which impacts coordination of relays in such a way that it requires change in the relays' settings. Inverse-time protection schemes based on only overcurrent sometimes fail to protect the distribution network with distributed generators(DGs), especially when the fault current is near or below the pickup current of the relay. This can happen in different fault situations, such as a fault in islanded mode, a fault with high impedance and a fault in grid-connected mode where a downstream relay senses low fault current due to limited fault current contribution by DGs. So, there is a need to overcome these limitations of overcurrent based inverse-time protection schemes and to devise a new inverse-time protection scheme which can work well in all these different fault situations. This paper proposes a new adaptive inverse-time protection scheme (AITPS) with a new computational method for the plug setting multiplier (PSM), which can serve as an effective measure when planning the protection in both grid connected and islanded modes, irrespective of types of fault and their fault impedances. The performance of the proposed protection scheme is tested on 13 feeder sample radial distribution network and IEEE 13-bus distribution network. To show the effectiveness of proposed method, operating times of relays obtained using proposed formulation are compared with the operating times calculated by using schemes based on only overcurrent. Results show that the proposed protection scheme is able to protect modern distribution systems with distributed generation in different fault situations, without changing the fundamental inverse relay characteristics.