I. Industry Requirements and Current Situation Analysis

According to Article 18 of the “Detailed Rules for Installation, Maintenance, and Overhaul of Underground Leakage Protection Devices—2022 Edition,” “at least one remote leakage test shall be conducted on the feeder switch every month.” The number of personnel required for the test is 3 to 5. During the test, first disconnect and lock out the vacuum magnetic starter. Then, open the housing of the magnetic starter, connect one end of the test resistor (a 11 kΩ 10 W resistor for 660 V systems, and a 20 kΩ 10 W resistor for 1140 V systems) to a phase bolt below the contactor inside the electromagnetic starter, and connect the other end to the grounding bolt on the body of the magnetic starter. After reassembling the starter housing, confirm with personnel near the feeder switch before restoring power. Once the electromagnetic starter is activated, observe whether the feeder switch trips promptly. This will determine whether the feeder switch’s operation is reliable. After completing the test, remove the test resistor and restore the system to its original configuration.

According to the relevant provisions of the "Detailed Rules for the Three-Stage Protection of Underground Power Supply in Coal Mines," the leakage protection device operating underground in coal mines shall undergo a remote, manual leakage trip test at least once per month.

During testing, it was necessary to manually connect a test resistor, involving cumbersome operational steps, prolonged power outages, and a high risk of electric shock for operators—posing significant safety hazards. The installation and use of this device fundamentally address these issues.

When conducting the test according to the above-mentioned test specifications, 3 to 5 workers are required to enter the well for operation. It is necessary to disassemble and reassemble the electromagnetic starter housing twice, and also to connect and disconnect the test resistor. The operation is complex and poses a risk of electric shock.

During this test, since it was impossible to measure the operating time of the feeder switch or to determine the leakage current, it was not possible to accurately and reliably assess the reliability of the feeder switch.

Current situation underground: Under normal circumstances, leakage current tests are rarely conducted—or even completely skipped—because they are overly cumbersome and require cooperation among multiple work teams. Moreover, there are seldom complete records of these tests.

Conclusion: The remote insulation leakage test underground is extremely important, yet the current testing situation is not optimistic. There is a need for a remote insulation leakage testing device that is safe, convenient, labor-saving, eliminates the need to enter the well, and can record data.

II. Product Overview

The explosion-proof and intrinsically safe leakage current testing device for mining applications is an intelligent, automated device designed specifically for conducting remote leakage tests on feeder switches in underground low-voltage power networks.

This device employs carrier-wave communication, using power cables in place of dedicated communication lines. It’s simple and convenient to install—no need to lay additional communication cables—to enable remote communication and control. Operators can not only use a remote control to operate the resistance box remotely, but also leverage backend software to perform remote leakage tests from afar. “Previously, conducting remote leakage tests was an important yet tedious monthly task that required the coordination of multiple people. Now, performing these tests is as easy as pressing a button on the remote control—it’s safe, convenient, and all done with just one device.”

This testing method is safe and efficient. Throughout the entire testing process, personnel do not need to come into contact with any part of the switch, fundamentally eliminating the risk of electric shock and providing a robust technical safety foundation for the safe operation of testing personnel.

The explosion-proof and intrinsically safe leakage current testing device for mining applications is suitable for use in underground coal mines and other environments where the surrounding medium contains methane and coal dust—explosive gases. It is designed for remote leakage current testing of vacuum feeder switches in three-phase power grids with a frequency of 50 Hz and rated voltages of 1140 V (660 V, 127 V), where the neutral point is ungrounded. The device features a remote closing function and can store historical test data for easy retrieval and documentation. Additionally, it supports remote operation via an industrial network (MODBUS-TCP), enabling testing to be performed from the surface without the need to enter the mine. This product also boasts a compact size, light weight, and ease of installation.

III. Technical Parameters

Rated voltage: 1140V (660V/127V)

Overall power consumption: <5W

Operating voltage inside the test chamber: 5V

Carrier module dynamic power consumption: 1.5W

Carrier module transmission distance: 2 km

1140V test resistance/power: 20k/10W

660V test resistance/power: 11k/10W

127V test resistance/power: 2k/10W

IV. Product Features

This device is an automated testing apparatus designed to address the current situation of remote leakage tests in underground wells. The device features the following characteristics:

Safety insurance: This device is designed for long-term, one-time installation. During testing, there’s no need to open any enclosures, perform wiring operations, or even touch any downhole equipment—testing can be completed entirely without entering the well. Additionally, with the communication cable connected, testing can be carried out from the surface without requiring a trip downhole.

Convenient and fast: This device is easy to install and requires few connections. The testing process is simple and straightforward, and the test can be completed with just a few simple operations.

Accurate and reliable: This device features leakage current detection and leakage time detection functions, and it also has recording capabilities for convenient access at any time.

Flexible compatibility: This device is suitable for various underground voltage environments, including 1140V, 660V, and 127V. It is also applicable to scenarios where a single feeder switch controls multiple remote electromagnetic starters. Each host unit can support up to 8 remote test boxes.

Reduce headcount, increase efficiency: This device requires only one person to complete the entire testing procedure, which takes about 5 minutes. When connecting the communication cable, the test can be performed from the ground (requiring a computer on the ground for support).

Network information: This device is equipped with a corresponding ground-based monitoring system. Through an industrial network (MODBUS-TCP), all test devices installed underground can be connected and communicated with the ground-based network backend, enabling test operations to be carried out from the surface without the need to enter the mine. At the same time, data collected from each underground test device can be uploaded to the ground network platform and stored for subsequent retrieval and query.

V. Conditions of Use

1. Altitude not exceeding 2000 m;

2. The ambient temperature is from -5°C to +40°C;

3. Air humidity shall not exceed 95% (+25°C);

4. In an environment free of gases or vapors that could corrode metals or damage insulation;

5. In environments containing explosive mixtures of gas and coal dust;

6. In places free of rain, snow, and dripping water;

7. The installation inclination relative to the horizontal plane shall not exceed 15°.

8. Pollution Level: Grade 3.

VI. Working Principle

The leakage current test is primarily conducted within a remote leakage testing cabinet. Inside the remote leakage testing cabinet, there is a leakage resistor that matches the system’s power grid. After the feeder switch is closed, the operator issues a leakage test command. The internal control system then activates the high-voltage relay in the remote testing cabinet, causing the grid voltage to be connected to ground through the leakage resistor, thereby generating a leakage current. Once the feeder switch detects this leakage current, the leakage protection mechanism is activated, cutting off the power supply and successfully completing the remote leakage test. Subsequently, the operator issues a reset or closing command to restore the power grid to its normal state.

7. Implementation Standards

GB/T 3836.1-2021 Explosive Atmospheres – Part 1: Equipment – General Requirements

GB/T 3836.2-2021 Explosive Atmospheres – Part 2: Equipment protected by flameproof enclosures “d”

GB/T 3836.4-2021 Explosive Atmospheres – Part 4: Equipment protected by intrinsically safe “i” type

Q/DT 01-2022 “Explosion-proof and Intrinsically Safe Leakage Current Test Resistance Box for Mining Use”

8. External Dimensions and Weight

Length × Width × Height mm: 507mm × 192mm × 413mm

Weight kg: <50kg

9. Equipment Installation Diagram