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High-voltage cables of 110kV and above mainly use single-core cables, and their metal sheaths are generally interconnected and directly grounded at one end, and the other end is grounded through a sheath protector. These interconnections, sheath protectors, etc. are assembled in a box, which is a cable ground box.
Grounding boxes are divided into three types: direct grounding boxes, cross-interconnected grounding boxes and protective grounding boxes, which have been widely used.
The grounding box has the following problems during use:
Lack of circulating current detection and induced voltage monitoring functions.
The manual inspection cycle is long, problems cannot be discovered in time, and the best opportunity for emergency repair is missed.
There are many incidents of grounding wires being stolen and cut.
Once the ground wire is damaged or stolen, the voltage of the metal sheath will become a floating voltage, and its value may exceed the power frequency withstand voltage of the outer sheath of the cable, leading to breakdown. If the ground box is stolen, it will be difficult to detect it in a short time.
Lack of cable joint temperature cannot be predicted.
Due to reasons such as damage to the cable sheath, the cable temperature is too high, affecting line safety.
The cable trench environment is complex and there is a lack of real environmental data.
Garbage in cable trenches is easily decomposed by microorganisms to produce methane and other flammable gases, which brings great hidden dangers to the operation of high-voltage cables; cable trenches are prone to water accumulation, and running cables in a flooded state will seriously affect the cable insulation and service life.
According to the "Technical Standards for Grounding Boxes for Cable Lines" and on-site operation requirements, the design of the cable sheath intelligent grounding box was completed. The entire system consists of the following parts:
Cable sheath intelligent grounding box
• Solar panels and energy storage batteries
• Sheath protector
• Voltage, current, temperature sensors
• Audible alarm
• External sensor (optional)
• Gas sensors: oxygen, methane, etc.
• Access control, water immersion, human body sensing
Management platform
• Personnel management, equipment management
• Data collection, data
| Technical parameter name | Main technical parameters | Remark |
| Power supply | AC220V power supply | In this mode, the distribution box is equipped with a battery (12V/20AH). Solar panels can power batteries and smart terminals at the same time. |
| 12V solar power panel power supply | ||
| communication method | Wired: Ethernet、Modbus RTU(RS485) | |
| wireless：4G | ||
| 4-way loop current detection | AC 0~5mA ±0.5% | Access via CT, CT transformation ratio optional |
| 4-way induced voltage detection | AC 0~400V ±0.5% | Access via PT, PT transformation ratio optional |
| 4-way temperature detection | -55℃-125℃，±1℃ | |
| Ambient temperature and humidity | temperature：-40℃-80℃，±0.5℃ | |
| humidity：0-99%RH，0.2%RH | ||
| 4 analog inputs | examination range：4-20mA | General sensors can be connected, including oxygen sensors, harmful gas sensors, combustible gases, etc. |
| Detection accuracy：1% | ||
| 4 dry contact inputs | Dry contact input | Can be connected to general sensors, including access control, water immersion, motion monitoring sensors, etc. |
| 4 dry contact outputs | Dry contact output, rated load capacity 24V/1A | 1 channel is connected to sound and light alarm; the other 3 channels can be expanded |
Lithium battery + solar power supply, stable power supply
• Real-time monitoring of circulation, induced voltage, sheath temperature and other data
• Real-time monitoring of oxygen, harmful gases, flammable gases, etc.
• Real-time monitoring of access control, flooding, personnel and other status
• Over-limit alarms can be set for all states. If an alarm occurs, the person in charge will be notified immediately for handling.
• Alarm threshold configuration, SMS notification configuration
• Device information configuration (location,
• Cloud/IoT capabilities
Remote data monitoring and display
Metal sheath circulation monitoring system
Electromagnetic current transformers are installed in the A, B, C, and N phases of the direct grounding box and cross-interconnection box to monitor the current signals on the three-phase metal sheaths in real time and transmit them to the management platform through intelligent terminals. When the temperature value exceeds the set threshold, an alarm message is sent to the relevant person in charge.
Metal sheath induced voltage monitoring system
Electromagnetic voltage transformers are installed in the A, B, C, and N phases of the direct grounding box and cross-interconnection box to monitor the induced voltage signal on the three-phase metal sheath in real time and transmit it to the management platform through the intelligent terminal. When the induced voltage value exceeds the set threshold, an alarm message is sent to the relevant person in charge.
Metal sheath temperature monitoring system
By placing the temperature sensor close to the metal sheath, the temperature on the three-phase metal sheath can be monitored in real time and transmitted to the management platform through the smart terminal. When the temperature value exceeds the set threshold, an alarm message is sent to the relevant person in charge.
Gas condition monitoring system (optional)
For the operating environment of cable tunnels, the cable sheath intelligent terminal can be equipped with an optional gas sensor to monitor the gas environment of the cable tunnel. Such as oxygen, carbon monoxide and other harmful gases, methane and other flammable gases.
The contents of oxygen, harmful gases and toxic gases are monitored in real time through intelligent terminals and transmitted to the management platform in real time. When the gas content exceeds the set threshold range, the management platform automatically sends an alarm message to the relevant person in charge.
Additional scalable status monitoring (optional)
Smart terminals also provide a wealth of expansion interfaces to facilitate system function expansion.
access control sensor
water immersion sensor
Human body induction sensor
Alarm record
The system has predefined limit-limit alarms and displacement alarms. When an alarm occurs, the relevant person in charge will receive a text message reminder. At the same time, the management platform will save relevant records to facilitate viewing and alarm records and alarm processing.
Additional scalable status monitoring (optional)
The contents of oxygen, harmful gases and toxic gases are monitored in real time through intelligent terminals and transmitted to the management platform in real time. When the gas content exceeds the set threshold range, the management platform automatically sends an alarm message to the relevant person in charge.
