A case study on the interoperability of the Direct Transfer Trip (DTT) technique with carrier signal protection schemes (PTT and DEF) and SCADA system between two utilities in Thailand

Abstract

This research paper presents a unique case study of a selected SPP named ABCD located in the eastern region in Thailand. ABCD currently earns revenue from selling the electricity to Thailand's Provincial Electricity Authority (PEA) via 115 kV substation of Electricity Generating Authority of Thailand (EGAT). Both PEA and EGAT somewhat require in monitoring and control how ABCD should operate and transfer the electricity through their own assets. The existing protection scheme in this SPP is very simple. There have been only distance and directional relays connected to EGAT bus and ABCD's ends without other teleprotection schemes. The interesting problem starts when ABCD want to increase its generation capacity from 92 MW to 119 MW. It is now required to meet EGAT's new protection regulation called direct transfer trip (DTT) technique and carrier signal protection schemes (both PTT-permissive transfer trip and DEF-directional earth fault transfer trip). PEA then also requests for monitoring and control the real-time protection operation via PEA SCADA system. This paper thoroughly elaborates the design concept and how to configure the proposed protection system and devices to meet EGAT and PEA requirements. To meet EGAT's new regulation, two teleprotection cabinets were added at both ends (EGAT and ABCD) in order to complete the communication between the two via PEA's fiber optics network. Another requirement to connect to PEA's SCADA system was done by adding another cabinet with gateway protocol converters (between PEA's DNP3 protocol and ABCD's internal IEC61850 ), remote terminal unit (RTU) and Ethernet switch at the ABCD's end. The PEA's fiber optic network has been used here via multiplexer (MUX). In order to validate that proposed scheme is capable of working properly, both FAT test and commissioning test are mandatory. What we have learned from this particular case study can be used as a very good example for the similar circumstance in Thailand.