At present, the main methods for measuring and monitoring AC residual current are manual inspection with handheld current clamp meters or separate testing of three-phase AC followed by calculation. Manual inspection measurements have certain subjective deviations to some extent, which are time-consuming and labor-intensive, and prone to omissions, while the method of separate three-phase AC testing lacks real-time performance. For the protection of residual current (leakage current), leakage current protectors are installed for protection according to set thresholds, and real-time continuous monitoring is also required to prevent accidents in advance. To this end, Wuhan Haomai has developed the MAC-3000 Residual Current Monitoring System for Substation AC Power Supply, which can monitor the status of residual current values in real time, issue early warnings, facilitate troubleshooting, and improve the work efficiency and accuracy of operation and maintenance personnel.

△ MAC-3000 Residual Current Monitoring System for Substation AC Power Supply

The MAC-3000 Residual Current Monitoring System for Substation AC Power Supply is developed based on standards such as GB/T13955-2017 Installation and Operation of Residual Current Operated Protective Devices. It is used to monitor the residual current and insulation status of the low-voltage power distribution system of station service electricity, effectively preventing personal electric shock and electrical fire accidents.

The device collects the residual current of each feeder in the panel cabinet and the grounding wire of the station service transformer in real time, realizing functions such as real-time monitoring of residual current values, threshold over-limit alarm, diagnosis, data recording, and human-computer interaction. It intuitively displays current monitoring and alarm information, reserves hard contact ports, and can be flexibly configured as required.

△ System Block Diagram

The system consists of three parts: residual current acquisition terminal, residual current concentrator, and residual current monitoring system host.

Residual Current Acquisition Terminal: It is used to obtain AC residual current values. Take measuring 1 channel of residual current as an example. The AC current transformer (CT) is installed on the low-voltage feeder of station service electricity (phase lines A, B, C and neutral line N) or the neutral line of the transformer to sense the residual current and convert the change of residual current into a proportional current, which is connected to the interface of the acquisition terminal. Each acquisition terminal supports simultaneous monitoring of up to 16 channels of residual current sampling values. The acquisition terminal performs signal processing and AD sampling on the received analog values, calculates the effective value of residual current, and stores it in the register of the acquisition terminal processor. It waits for a ModBus command response; upon receiving the ModBus command, it transmits the residual current value to the concentrator through the RS485 bus.

The residual current acquisition terminal can set the proportional coefficient of the sampling CT through the ModBus protocol, and CTs with different ratios can be installed, facilitating the on-site installation of various types of CTs to adapt to scenarios with different rated currents of feeders. The acquisition terminal supports the correction of measured values, improves sampling accuracy, facilitates on-site data verification and debugging, and ensures that the accuracy of the residual current acquisition instrument is not less than 1%.

Residual Current Concentrator: It collects data from the acquisition terminals connected via the on-site RS485 bus and forwards the data to the host through the RJ45 Ethernet port, realizing the conversion of different physical layers.

△ System Interface

Residual Current Monitoring System Host: It realizes intelligent management through the human-computer interaction interface. The host displays the real-time residual current values of each substation, conducts real-time monitoring of the installed lines, diagnoses the operating status of line equipment, and eliminates the need for manual on-site inspection. If the measured value exceeds the set alarm value, or there is an abnormality in the communication status or equipment working status, warning information will be displayed on the screen, and the alarm occurrence time will be recorded. The host system automatically records the monitoring data within 3 months and displays it in the form of data tables or graphs, providing a decision-making basis for the analysis of the change status of residual current values. The human-computer interface provides login management and permission differentiation functions, setting the viewing and operation permissions of personnel with different authorities for the equipment to prevent accidental tampering of equipment data.

The MAC-3000 Residual Current Monitoring System for Substation AC Power Supply conducts real-time monitoring of the residual current of each branch of the AC power supply and branch line selection, realizing real-time monitoring and intelligent diagnosis of the low-voltage AC power supply system of the substation, accurately reflecting the insulation status of the low-voltage power distribution system in a timely manner, and greatly improving the efficiency and accuracy of maintenance and inspection work.