Journey of Implementation of Line Differential Protection at Distribution Utility “Tata Power Delhi Distrbution Limited”

Protection Relays and the Communication Systems brain and heart of a power system network. Utilities in India have been using electro-mechanical and static protection relays since a very long time and have already adopted conventional protection schemes. With the advancement in Protection Relay technology, a shift is however imperative to achieve efficiency and cost optimization in an ever growing distribution network. Being a front-runner in the adoption of latest technologies in the utility space, TATA Power-DDL has successfully revamped its Protection and Communication Infrastructure by commissioning modern numerical relays having capability to integrate on IEC 61,850 communication protocol. A Smart grid roadmap has now been adopted by TPDDL and various technologies have already been successfully implemented like Grid Substation and Distribution Automation, SCADA/ADMS, GIS, AMI, DSM, Smart Meters, Communication Infrastructure and RF Canopy. Traditional protection schemes have worked successfully alongside all the recent advancements in technology as stated above. One of such schemes is Line Differential Protection wherein Line Differential Relays are installed at both ends of a transmission line and communicate with each other through a medium.

In TATA Power-DDL network, there are around 200 sub-transmission line circuits, most of them being of short length (2–3 km). Initially, these lines were protected by Back-Up protection—Over Current and Earth Fault Relays. But difficulties started to be observed while doing relay coordination based on current and time margin. Some cases of cascaded tripping were also experienced, resulting in MU loss and customer dissatisfaction. However, Distance Protection scheme had already been implemented as Main Protection in Boundary Line Feeders. But, the reliability and selectivity of distance protection is lost in the following cases:-

Taking the fact into consideration that TPDDL network is having significant Circuit-Kilometers as compound (Overhead and Underground Cable) sub-transmission lines, distance protection relay may operate inadvertently. Hence, the organization decided to shift to Line Differential Relays. Ever since, two major revamping projects have been implemented in TATA Power-DDL, based on the type of Communication technology adoption. The two technologies currently in service are:-

Technological Upgradation in tele-protection systems got our attention and we decided to implement the IP-MPLS infrastructure. The IP-MPLS based Line Differential communication offered us following advantages:-

Moreover, all the IED project files of Line Differential Relays have been kept in a secured central server for easily accessing Fault Data Records and checking relay communication.

This major advancement has improved our reliability indices and have played an important part in reducing Uncoordinated Trippings.