Background

In China, most of the medium voltage power distribution networks are either ungrounded or arc-suppression coil grounded. Accounting for about 80% of the total faults, the single-phase ground faults (also known as low current grounding) is very difficult to detect and locate. In the past years, the operation staff used traditional methods to locate line faults such as line patrol, which may cause unnecessary short-time power outages, increase workforce costs, and extend failure recovery time. 

Since 2007, InHand Networks has been providing cellular data terminal and gateway solutions for China State Gird. More than 150,000 cellular modems have been deployed to connect the FTU/TTU to the distribution data center. With years’ experience in industrial communication and distribution automation, InHand Networks has developed an innovative overhead line monitoring system for distribution power line fault detection and advanced analysis. Using intelligent sensor technology, signal processing, and artificial intelligence, the InHand Wireless Overhead-line Monitoring System (IWOS) is able to help China State Grid accurately identify fault types and quickly locate the faulty section on power lines, thus largely shortening response and processing periods of power line faults and improving power supply reliability.  

Solution

For each installation, there will be 3 Line Sensors installed on each phase of the power line and one Concentrator installed on the pole or power line. The IWOS Line Sensor harvests energy from current going through the power line and will be self-sufficient when there is more than 5 Amp. The Line Sensor captures waveforms of current and electric fields in the 4K Hz sampling range and 1% resolution, as well as measures the temperature of the power line. The Line Sensor sends data to the Concentrator via the mesh wireless sensor network. 

When a line fault occurs, the 3 line sensors will automatically triggers the waveform recording of current & electrical field and send to the concentrator. The concentrator will calculate the zero-sequence current by three-phase synthesis and send the waveform files to the IWOS analytics cloud platform for analysis and fault location. Combining the waveform files uploaded from different locations and the whole line topology, the cloud platform will conduct advanced analysis, complete fault location and notify the operation staff by alarms or SMS messages. The IWOS is efficient in fault detection & location, reducing power outages and costs.

Technology Breakthroughs

● High-precision Overhead Line Sensor

Advanced electronic current transformer, measurement precision of line current reaching ±1%.

● Three-phase synthesized zero sequence current

Innovative technology to acquire transient zero sequence current and electric field signal by high-precision three-phase time sync. This is the foundation of fault detection of low current grounding distribution network and single-phase ground system. 

● High efficient power supply and management

Uses solar panel as main power supply, and a maintenance-free long service life chargeable accumulator as backup.

●  Single-phase grounding fault location technology based on transient recording

When a grounding fault occurs, there will be a 5 to 20ms transient process as shown below. There is high-frequency transient signal on zero-sequence current i0. With high amplitude, the signal is bettor for single-phase grounding location. 

Easy Installation on Live Lines, Maintenance-free

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Achievements

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● The IWOS has been deployed in more than 20 cities in China with more than 5,000 installations by 2017 

● Detected more than 2,800 short faults and more than 10,000 grounding faults

● Accuracy rate of ground faults detection is close to 90% and faults location is 100%

● Adopted into the standard of Feeder Line Automation of China State Grid

● Obtained the certification of the Chinese Academy of Electrical Science

● Awarded Second place from Guangdong Power Grid Science and Technology company

● Awarded Third place from Science and Technology of Guangdong Province

● Awarded Science and Technology Innovation Achievement Award of Guangdong power industry