Pilot project: Line differential protection over Ethernet

Sweden, with approximately 1000 regional grid substations. The primary protection function for 130 kV power lines, according to company philosophy, is Line Differential Protection

(LDP). Today, LDP communication use the IEEE C37.94 serial protocol, encapsulated and transported over the packet-based company wide area network with Multi-Protocol Label

Switching (MPLS) technology. Emulating serial links over a packet-based network poses several challenges.

Recently, protection equipment featuring a new communication interface for LDP has been introduced, eliminating the need for a serial interface. A general description is that the time tagged current phasors is being transported in UDP streams carried by Ethernet. The UDP traffic can be connected to the network and routed as any other high priority service. The LDP function has to be externally time synchronized. A modern approach is to use Precision Time

Protocol (PTP). Our company has decided to test a packet-based solution without protocol conversion to evaluate a less complex and standardized solution. This paper will describe the implementation of LDP over Ethernet in two different stages, according to our process for technical development. Stage one is a Proof Of Concept performed in a laboratory environment. Stage two is the execution of a Pilot Project in live substations protecting a 130 kV power line, implemented in two substations on the west coast of Sweden. PTP is distributed to both substations over the company wide area network (WAN) using the PTP

Telecom Profile from ground based atomic clocks. The paper describes the relationship between PTP and the LDP function, how different PTP attributes affects the function. The paper includes test results and experience from operation in two regional grid substations.