Downhole Cable Protector
Summary: large section power cables of 35kV and power cables of 66kV, 110kV and beyond 110kV are all single-core cables. One end of the cable metal shield is interconnected and grounding, the other end is ungrounding. When the lightning wave or internal voltage flows along the cable core, the high impulse induced over-voltage will appear at the ungrounding end of the cable metal shield. Or when the system is short circuited and the current flows through the cable core, there will be very high frequency over-voltage induced by its ungrounding ends. The above over-voltage may break through the insulation of the outer protective layer of the cable, which causes the multi-point grounding fault of the cable metal shield, which seriously affects the normal operation of the power cable and even greatly reduces the service life of the cable. Therefore, in accordance with the DL/T401-2002 standards of the electric power industry-----the guide for selecting high voltage power cable, the cable shield protector must be adopted to limit the induced voltage and over-voltage of the power cable metal shield or the metal shield.
Usually, in order to limit the induced voltage and fault over-voltage on the power cable metal shield and avoid forming a current circulation in the shield, one end of the cable metal shield is directly grounding and the other end must be grounded through a cable protector. If the wire line is long, the cable shield should be divided into three segments (or multiplier of three), and the cable protector at the subsection will be connected to the ground through the protector.
Features: the cable shield protector is installed between the cable metal shield and the ground in normal condition, the current of the protector is very small, it is the micro safety level. When the cable shield appears over-voltage, the protector is quickly put into operation, discharge the electric charges on the cable shield, and protect the safe operation of the cable.
The protector adopts ZnO varistors as protection component, no series gap, good protection and excellent nonlinear volt ampere curve. It not only has the advantages of the porcelain metal oxide lightning arrester, but also has the advantages of good electrical insulation, high dielectric strength, leakage resistance, corrosion resistance, heat resistance, cold resistance, aging resistance and explosion proof, and good chemical stability, water proof and air proof.
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