I. Introduction
With the development of society and economy and the rapid rise of industry, the number of 10KV power distribution systems has increased significantly. The simplicity, reliability, safety, energy efficiency and cost-effectiveness of power distribution systems have become particularly important.
Currently, traditional 10kV power distribution systems still use relay systems and distributed monitoring and metering, as well as distributed control methods. However, adopting PLC (Programmable Logic Controller) systems for centralized control and centralized monitoring and metering is beneficial for improving the automation level of power distribution system operation and management, ensuring the safety and stability of power distribution, reducing the workload of operating personnel, and improving safety and reliability.
II. Comparison of Relay Systems and PLC Systems
PLCs (Programmable Logic Controllers) are a new type of industrial controller developed in recent decades. They are more flexible in programming, feature-rich, widely applicable, simpler to control than relay systems, easier to use, have stronger anti-interference capabilities, higher cost-effectiveness, and longer service life. They are also characterized by their small size, light weight, and low power consumption. Relay systems have significant drawbacks: large size, low reliability, short service life, and difficulty in troubleshooting. In particular, because they rely on hard-wired logic to construct the system, wiring is complex, adaptability to changes in production processes is poor, and centralized control is inconvenient. PLCs, on the other hand, are easy to install and wire in the field. Their internal soft relays can simplify the complex intermediate links of relay systems, enabling soft-wired logic systems that facilitate centralized control. In addition, PLCs have self-diagnostic, fault alarm, fault alarm type display, and network communication functions, making them convenient for operators and maintenance personnel to inspect.
III. Examples of Centralized Control and Centralized Monitoring Metering in 10kV Primary Distribution Systems
In a 10kV primary power distribution system, two 1000kVA transformers operate in parallel. Figure 1 shows the schematic diagram of this primary power distribution system.
3.1 The Role of PLC in Centralized Control
In primary power distribution systems, relay systems are mainly concentrated in the main receiving cabinet and transformer distribution cabinet. Using a PLC system to replace the relay system can reduce hard wiring between cabinets, eliminate many relays, simplify the manufacturing process, lower system production costs, and improve the reliability, safety, and energy efficiency of the power distribution system. A PLC system block diagram is shown in Figure 2.
The PLC is the nerve center of the entire system. All control, protection, and operational status indications are accomplished through virtual relays within the PLC via soft connections and externally provided switching quantities and signals. Controlling the voltage below safe levels improves operational safety; operating away from high-voltage rooms prevents operator error; and one-stop control increases work efficiency and reduces worker workload. Signal transmission throughout the system can be achieved using only two fieldbuses. The PLC's operational status and alarm indications facilitate troubleshooting for both operators and maintenance personnel. Furthermore, compared to relays, PLCs offer higher maintenance-free operation and a longer service life.
3.2 PLC I/O Allocation
In a 10kV primary power distribution system, in addition to power-on and power-off control, there are also overcurrent, undervoltage, and gas protection for the transformer. Taking an Omron CAMP2AH40-point PLC as an example, the I/O allocation is shown in Table 1. Power-on and power-off control is a switching function, which can be achieved using control buttons. Overcurrent, undervoltage, and gas protection involve automatic detection technology, which is implemented using intelligent sensors to improve the reliability of the protection.
Table 1 PLCI/O Allocation Table
Design of centralized control, centralized monitoring and metering for 3.310kV primary power distribution system
The power distribution system is the nerve center of the power grid. Its normal operation is inseparable from our daily lives and work order, requiring higher reliability. The intelligent, energy-saving, easy-to-operate, and convenient-to-maintain nature of the power distribution system is a necessity for rapid economic development. Users desire higher safety standards, lower labor intensity, and higher cost-effectiveness for equipment during operation and maintenance. Based on these considerations, we have made the following improvements to the 10kV primary power distribution system: applying PLC for centralized control of the main receiving cabinet and distribution cabinets, and applying digital instruments for centralized monitoring and metering. The improved 10kV primary power distribution system block diagram is shown in Figure 3.
After the improvement, with the integrated cabinet as the working platform, staff in the duty room can control the operating status of the high-voltage room, which is both convenient and safe. Staff can also record and inspect the monitoring instruments, metering instruments, and working or alarm status at any time, which is convenient, timely and clear, and can also reduce labor intensity.
In summary, using a microcomputer PLC to operate the relay protection and control system greatly improves the system's automation level and reliability. It also facilitates centralized control and monitoring, promotes information management, significantly reduces costs, and increases work efficiency, making it worthy of widespread application.
