GDCO-301 Online Monitoring System of Circulating Current on Cable Sheath

GDCO-301 Online Monitoring System of Circulating Current on Cable Sheath

Cables above 35kV are mainly single-core cables with metal sheath. Since the metal sheath of the single-core cable is hinged with the magnetic field line generated by the AC current in the core wire, the two ends of the single-core cable have a high induced voltage. Therefore, appropriate grounding measures should be taken to keep the induced voltage within the safe voltage range (usually no more than 50V, but no more than 100V with safety measures). Usually, the metal sheath of short line single-core cable is grounded directly at one end and grounded through gap or protection resistor at the other end. The metal sheath of long line single - core cable is grounded by three - phase segmental cross - connection. No matter which kind of grounding method is adopted, good sheath insulation is necessary. When the insulation of the cable is damaged, the metal sheath will be grounded at multiple points, which will generate the circulating current, increase the loss of the sheath, affect the current carrying capacity of the cable, and even cause the cable to be burned due to overheat. At the same time, guarantee the high voltage cable metal sheath grounding directly connect site is also very important, if the ground point cannot effectively be grounded for various reasons, the cable metal sheath potential will rise sharply to several kilovolts even tens of thousands of volts, it is easy to lead to outer sheath breakdown and continuous discharge, causing the rise of the temperature of cable outer sheath or even burning.

GDCO-301 uses the circulating current method. When the single-core cable metal sheath is under normal conditions (i.e., one-point grounding), circulating current on the sheath, mainly capacitive current, is very small. Once multi-point earthing occurs on the metal sheath and forms a loop, circulating current will increase significantly and can reach more than 90% of the main current. Real-time monitoring of metal sheath circulation and its changes can realize on-line monitoring of multi-point earth fault of single-core cable metal sheath, so as to timely and accurately find the earth fault, fundamentally avoid the occurrence of cable accident and ensure the safe and reliable operation.

It uses GSM or RS485 as communication mode. It is suitable for multi-point ground fault monitoring of single core cables above 35kV.

RS485 port
● Baud rate: 2400bps, 9600bps and 19200bps can be set.
● Data length: 8 bit:
● Start bit: 1 bit;
● Stop bit: 1 bit;
● Calibration: no calibration;

GSM/GPRS port
● Working frequency: Quad-band, 850 MHz/900 MHz/1800 MHz/1900 MHz;
● GSM Chinese/English short mesages;
● GPRS class 10, Max. download speed 85.6 kbit/s, Max. upload speed 42.8 kbit/s, support TCP/IP, FTP and HTTP protocol.

Power supply
AC power supply
● Voltage: 85~264VAC;
● Frequency: 47~63Hz;
● Power: ≤8W

Battery
● Voltage: 6VDC
● Capacity: determined by continuous working time of battery
● Battery compatibility

Reference standard:
Q/GDW 11223-2014: Technical Specification for state detection for high voltage cable lines