The switching on and off of press plates is a core operation item for secondary equipment. By switching press plates on or off, the protection operation mode can be adjusted to match the operation modes of different primary equipment, ensuring that the protection system operates correctly when faults occur in primary equipment. When a protection device malfunctions or undergoes maintenance, the corresponding press plate can be promptly switched off to prevent protection misoperation or refusal to operate. In the operation of relay protection, accidents caused by incorrect or missing switching of press plates, which lead to protection misoperation or refusal to operate, occur from time to time, seriously affecting the safe and stable operation of the power grid.

Recently, after a switching operation at a 220kV substation of a power supply company under the State Grid, the bus differential outlet press plate of a bay was not switched on. Subsequently, a hidden danger line clip broke due to strong winds, causing a bus grounding fault. As a result, the faulty bay failed to trip, while the opposite-side bay tripped instead.

At present, the correctness of press plate switching is mainly ensured by manual inspections of press plate positions conducted by operation and maintenance personnel. With the continuous expansion of the power grid scale, the workload of press plate inspections has increased significantly, and the contradiction between the workload of operation teams and their carrying capacity has become increasingly prominent.

When the power supply company planned to carry out the renovation of online press plate monitoring, it evaluated multiple schemes and finally decided to adopt the method of installing intelligent wireless sensors for press plates to achieve online monitoring. For blade-type press plates, micro-switches are used to detect the switching status of the plates; for wire-spring press plates, gyroscope sensors are used to monitor the rotation angle of the rotating components of the plates in real time to sense their switching status. This scheme adopts the ISM (433MHz) communication frequency band, is powered by batteries, operates in periodic sleep mode, and supports timed/status-change reporting. It has a reliable service life of 5–6 years, and can be quickly deployed without power outage, without any modifications to the existing protection panel cabinets, press plates, and circuits.

For the press plate renovation project of this 220kV substation, the intelligent press plate management system independently developed by Wuhan Haomai was selected for online press plate monitoring. The system mainly consists of an intelligent press plate management platform, an intelligent management host, press plate controllers, press plate detectors, and press plate detector accessories. During the construction period, comprehensive installation and commissioning of the intelligent press plate management system were carried out.

The main installation scope of the press plate detection system covers: protection panels and measurement & control panels in the protection room of the main control building, as well as the front panels of switch cabinets in the 10kV high-voltage room.

Scheme Implementation

A power supply circuit is drawn from the UPS uninterruptible power supply panel in the protection room to supply power to the entire system.

Intelligent press plate detectors and intelligent press plate controllers are installed on each protection panel, measurement & control panel with press plates, and switch cabinet front panels with press plates in the 10kV high-voltage room.

The intelligent press plate detector can collect the status of single-row press plates on the panel, and upload the press plate status to the intelligent press plate controller of the same panel through dedicated cables.

One controller is installed on each panel cabinet with press plates. The controller uses a DC 12V power supply (converted from AC 220V through a power module). One air switch and one power module are configured for every 10 controllers, which are installed on the guide rail at the rear of the first panel cabinet. The controllers are connected in series via cables for power supply.

An intelligent management host is added in the protection room to aggregate data from all intelligent press plate controllers in the area. After processing, the collected press plate signals are uniformly uploaded to the online press plate monitoring system through a switch for centralized management and display.

The press plate monitoring system is deployed in the Zone I or Zone II network, while the press plate inspection and verification system is deployed in the Zone IV network. The press plate monitoring system sends press plate monitoring data based on the IEC 104 protocol unidirectionally to the press plate inspection and verification system through an isolation device. (It is necessary to confirm with the dispatching or automation team whether on-site network security devices such as Zone II switches, Zone IV switches, and unidirectional isolation devices are deployed in the substation.)

The entire construction period took less than two weeks, completing the construction plan ahead of schedule and passing the acceptance inspection. The system has greatly saved labor costs, enabling operation and maintenance personnel to detect and eliminate hidden dangers in a timely manner, and avoid relay protection device misoperations caused by incorrect or missing switching of press plates, winning unanimous praise from the user unit.