36 / 2018-08-21 20:39:17

Calculation and Restraining Method for Circulating Current of Single Core High Voltage Cable

Power Cable,Circulating Current,Numerical calculation,Restraining Method

Power cable has many advantages of more stable transmission of electrical energy, higher reliability, being less affected by climatic and environmental factors and less land occupation. Therefore, the single-core high-voltage power cables have been used more and more widely in the process of urban power grid construction. On the basis of Faraday law of electromagnetic induction, it is an inherent phenomenon to generate the induced voltage on the metal sheath of single-core high-voltage power cable. Excessive induced voltage on the metal sheath not only affects the insulation of the sheath and personal safety, but also creates the grounding circulating current on the sheath when the induced voltage is unbalanced. The excessive grounding circulating current on the metal sheath will cause massive additional loss, lead to the increase of cable temperature, reduce cable transmission efficiency, and reduce safe operation lifetime of cable. Therefore, it is important to calculate the grounding circulating current on the cable metal sheath and study the circulating-current restraining methods to ensure the normal operation of the cable.
When the cable adopts cross-grounding mode, the induced voltage on the metal sheath can be effectively reduced (especially for the long-distance high-voltage cable transmission lines), and then the grounding circulating current is controlled within a certain range, so the cross-bonding grounding mode is widely used by high-voltage power cables. In this paper, aiming at the single-core high-voltage power cables in cross-bonding grounding mode, by expounding the calculation theory of the induced voltage and current of the cable metal sheath, a mathematical model of grounding circulating current was established. And then, mathematical models of metal sheath circulating-current restraining methods were also established. Meanwhile, a corresponding calculation program by MATLAB software was developed. Combined with the actual cable line, the accuracy and reliability of the calculation model and calculation program can be verified. Furthermore, further analysis on the effectiveness and applicability of the circulating-current restraining methods and the combined circulating-current restraining methods by the calculation program were conducted.
The main conclusions can be obtained as follows.
(1)The program was competent to reflect the actual grounding circulating current;
(2)Appropriate resistance in series before grounding of cable metal sheath has reinforcing effect on the grounding current. However, it can significantly reduce the grounding circulating current on metal sheath. With increasing the resistance, the grounding circulating current on metal sheath shows the decreasing tendency;
(3)Suitable grounding resistance can significantly reduce the grounding current. As the resistance increases, the grounding current decreases, but it has little effect on the grounding circulating current on metal sheath;
(4)Appropriate inductance before grounding of cable metal sheath has reinforcing effect on the grounding current. However, it can significantly reduce grounding circulating current on metal sheath. With increasing the inductance, the grounding circulating current on metal sheath shows the decreasing tendency;
(5)Proper compensating inductance at the end of cable metal sheath can reduce the grounding circulating current on metal sheath, and there is an optimal compensation inductance value.
Finally, when the four circulating-current restraining methods are used in combination, the suppression effect on the grounding circulating current on metal sheath is more significant.