Intelligent load curtailment for low voltage electrical distribution systems

Abstract

This study aims to investigate, design, develop and test a load curtailment solution for low voltage electrical distribution systems having a limited incoming supply capacity. The objective is to demonstrate a practical solution for overloading during periods of high demand, and for making use of any spare standby generating power capacity to be used to energise non-essential loads. A Beckhoff CX8090 programmable logic controller (PLC) was used as the principal component of the intelligent priority-based energy management system. The controller monitors and manages the electrical installation in real-time through the use of bus terminals that transfer signals with current sensors, signal conditioning circuits and solid-state relays. All the data gathered by the PLC is transmitted to a human machine interface (HMI) to give the operator a visual representation of the current scenario of the installation. The interface shows the total current together with the essential current being consumed by the installation at that moment in time. A set of indicators also show the status of all the switchable loads connected to the distribution system. Through the HMI the user may also alter the priority levels and maximum current ratings of the controllable loads with these changes having an instant impact on the decision making procedures done by the system. The management system was tested under various possible scenarios, and from the results obtained it has shown that it has the capability to be a good practical solution to achieve the initial objectives set. This may be used as an economical alternative solution to increasing the incoming supply to larger ratings to combat overloading issues. The intelligent load curtailment system automatically sheds loads to limit the maximum demand during peak periods and allows non-essential loads to be utilised during a mains power disruption by making use of the spare standby generating capacity from the alternate sources.