Implementation Techniques of Substation Control System of Switching-Unit Substations for Increasing Reliabilities of Customer Substations Under Mea's Scada Constraints

In MEA's distribution system, customer substations typically have one incoming-line which is tapped on an open-loop transmission line according to normal conditions at that time. Nowadays, an environment of MEA's distribution area has changed such as severe traffic jam, a high number of high constructions, and a high number of high advertising boards resulting in higher chance of overhead-transmission-line faults than before. For switching operations, MEA also has installed three remote-controlled switches at any tap point for quickly switching in some urgent situations such as a faulty preferred line has a location-known fault. So MEA is able to remotely transfer customer's load to another emergency line within a short time by a dispatching center.

However, some faults happen with an indistinct location, MEA has to take time to find and clear them before switching causing long outage duration especially during severe traffic jam. A lot of solutions to detect a fault's location from a line-tap point of view are tried out but they are not long-term solutions due to several constraints such as FCI (Faulted Circuit Indicator) often is malfunction in high temperature or long-sight CCTVs are not able to detect some faults locations.

Consequently, Metropolitan Electricity Authority (MEA) has to create a project to build a switching-unit substation for any large customer who has a substation with one incoming line from MEA for increasing customer's reliability and also MEA's reliability. The large customers need electric reliability due to their lifeline depends on their productions whether are on schedule or not. Several large customers joining the project also support building area and some budget for building a switching-unit substation due to them realize benefits of a switching-unit substation. The switching-unit substation actually is a small-unmanned switching substation which has two incoming lines and one/two/three outgoing lines for customer substations. For faster switching operation, the switching-unit substation have to has proper protective relays and a substation control system allowing MEA's SCADA is able to control and monitor especially in an urgent situation. However, number of switching-unit substations is originally not on a design of MEA's SCADA resulting in a number of spared SCADA channels is not enough for all switching-unit substations today. Thus, a solution has been created and will be described The paper will present useful techniques to implement a composite substations control system among substations with IEC61850 over WAN for controlling the switching-unit substations during a fault occurs. The paper will also describe how to apply IEC61850 messaging to create a high-speed line transfer function between substations for automatic load transfer function resulting in higher availability.