When the iron core of a power transformer is grounded at two or more points, circulating current will be generated inside the iron core, causing local overheating. In severe cases, it can cause local burning of the iron core, and even cause the grounding plate to melt, resulting in the suspension of the iron core potential and discharge faults, which seriously threaten the reliable operation of the transformer. Therefore, it is crucial to monitor the grounding current of the transformer iron core and clamps in real time during the operation of the transformer.

The traditional method of measuring ground current using a handheld clamp ammeter has the disadvantages of low accuracy, susceptibility to interference from power frequency magnetic fields, and inability to achieve real-time online monitoring of ground current. This monitoring scheme overcomes the above shortcomings and can real-time monitor the grounding current of transformer iron core and clamp grounding current. It has strong anti-interference ability and high accuracy. The monitoring data can be transmitted to the background through wireless communication, and combined with background analysis software, online monitoring and fault alarm can be achieved.

3.1 Purpose of System Implementation

⑴ Implement online monitoring of the grounding current of multiple transformer cores in the factory area, complete real-time collection, centralized management, unified processing, and convenient display of monitoring data.

⑵ Complete the automated operation process for monitoring, alerting, and handling potential grounding hazards in transformer cores, and build an intelligent power network.

⑶ Reduce the daily inspection and maintenance costs of staff, improve work efficiency, and strengthen risk prediction and assessment capabilities, truly achieving prevention before it happens.

3.2 System Implementation Content

This system mainly consists of three parts: upper computer software, data aggregation unit, and front-end acquisition unit.

For example, the grounding current of the iron cores of four transformers on site needs to be monitored, and the distribution range of on-site monitoring equipment is relatively wide. Considering the complexity and cost issues of on-site wiring construction, the system can choose wireless network relay communication method. The pre acquisition unit with built-in wireless communication module can automatically form a Mesh network while collecting on-site data. Each pre acquisition unit acts as a relay communication for each other, forming a topological wireless communication network. At the same time, the upper computer software in the central control room is connected to this wireless communication network through a data aggregation unit, and real-time reads the data collected by various collection units on site.

System Topology Diagram

3.3 System Features

(1) Real time online monitoring of the grounding current value of the transformer core, and automatic alarm when the grounding current value exceeds the set alarm value. The alarm stops after the fault disappears.

(2) Strong anti-interference ability and high measurement accuracy.

(3) The pre collection device has a high level of protection and is suitable for outdoor use.

(4) Adopting the standard MODBUS-RTU communication protocol, it can be easily converted to other communication protocols, thus facilitating interconnection with various communication interfaces.

(5) The system communication adopts wireless Mesh networking technology, and the topological network reflects the stability of the system communication. The communication distance of the system can reach up to two kilometers, and this communication terminal uses a free channel, which can be installed once without any communication usage fees.