A new distributed generation protection scheme in Thailand using direct transfer trip technique and Mirrored Bits Protocol

Abstract

At present, most of the utility electrical power systems in Thailand are connected as a network. It is essential to gather many separated electrical power sources (from EGAT, PEA, MEA and private sectors i.e. IPP, SPP and VSPP) together to enhance the stability and reliability of Thailand’s power network. The appropriate protection scheme for a high voltage transmission system is indispensable. The current protection scheme that has long been used in most regions of Thailand’s network is a peer‐to‐peer protection scheme. Such a scheme has a big disadvantage when there is a fault at any point from only one power source in the network due to the lack of islanding mode of operation. For example, if there is a short circuit fault occurring in the region taken power from two sources, the protection relay will send out a signal to disconnect/cease the power from both ends, regardless of the fault locations. These circumstances happening quite often in many of Thailand’s networks and can cause a lot of damage from power outage, especially in industrial estate areas. Therefore, this research proposed a new technique for protection schemes to prevent the aforementioned circumstances called the direct transfer trip (DTT) protection scheme using the SEL Mirrored Bits® protocol. The principal idea is to have communication between the relay protection installed at any point of the network and the logic processor unit installed at the supplementary power source, such as IPP, SPP or VSPP, via a protocol called Mirrored Bits® through the fibre optic network. The key concept is that if there is a single fault occurring in any point of the network except from the main grid source, the generation systems of the supplementary power source must continue operating in order to avoid the power outage in the network. This paper elaborates the proposed protection scheme by examining and analysing the small power system network in the eastern region of Thailand. The single line diagram of such a network is presented here. The conceptual and detailed design of the proposed protection scheme is also elaborated. The design of such a logic processor unit is extensively explained. The simulation process was done using the computational simulation before the testing and commissioning process. The testing and commissioning results through the distributed control system (DCS) are satisfactory and are illustrated here.