Discussion on Grounding Problem of High Voltage Cable
Number of page views:
High-voltage power cable copper shield and steel armor generally need to ground, both ends of the ground and one end of the ground What is the difference between the production of cable termination, steel armor and copper shield can be welded in a piece of cable production head, steel armor And copper shield can be welded in one?
35KV high-voltage cable for single-core cable, single-core cable in the power running, the shield will form the induced voltage, if the two ends of the shield at the same time ground, between the shield and the earth to form a loop, will produce induced current, Layer will heat, loss of a large number of electrical energy, affecting the normal operation of the line, in order to avoid the occurrence of this phenomenon, usually one end of the ground way, when the line is very long can also use the midpoint grounding and cross-connect and so on.
In the production of cable head, the steel armor and copper shield separate welding grounding, is to facilitate the detection of cable sheath is good or bad, in the detection of cable sheath, steel armor and copper shield between the voltage, if you can withstand a certain Of the voltage to prove that the inner layer is intact. If there is no such requirement, there is no need to detect the inner sheath of the cable, or the steel armor can be grounded together with the copper shield (we advocate the separation after grounding).
Why high-voltage single-core XLPE insulated power cable to use a special grounding?
Power safety regulations: 35kV and below the voltage level of the cable are used at both ends of the grounding method, which is because most of these cables are three-core cable, in normal operation, the current flow through the three core
And zero, there is no flux chain outside the aluminum package or metal shield, so that there is almost no induced voltage at both ends of the aluminum package or metal shield, so there is no induced current flowing through the aluminum package after grounding at both ends Or metal shields. But when the voltage exceeds 35kV, most of the single-core cable, single-core cable core and the relationship between metal shield, can be seen as a transformer primary winding. When the single-core cable core through the current when there will be magnetic lines linked to aluminum or metal shielding layer, so that both ends of the induced voltage. The size of the induced voltage is proportional to the length of the cable line and the current flowing through the conductor. When the cable is long, the induced voltage on the sheath is superimposed to the extent that it is endangering the safety of the person. A short circuit fault occurs on the line, Lightning shock, the shield will form a very high induction voltage, and may even breakdown jacket insulation. At this point, if the aluminum package or metal shield will be connected at both ends of the three, then the aluminum package or metal shield will be a great circulation, the value of wire current up to 50% - 95% Loss, so that aluminum or metal shield heat, which not only wastes a lot of power, but also reduces the cable carrying capacity, and accelerated the cable insulation aging, so single-core cable should not be grounded at both ends. [Individual cases (such as short cable or light load when running) before the aluminum package or metal shield at both ends of the three connected to each other. However, when the aluminum package or metal shield has one end is not grounded, then the following problems: When the lightning current or over-voltage wave along the core flow, the cable aluminum or metal shield does not appear at the ground side of the high impact Voltage; in the system short circuit occurs, the short circuit current flows through the core, the cable aluminum or metal shield does not appear on the ground side of the higher frequency induction voltage, insulation in the cable jacket can not withstand the role of this over-voltage And damage, will lead to multi-point grounding, the formation of circulation. Therefore, in the use of one end of the interconnection, you must take measures to limit the overvoltage on the protective layer, the installation should be based on the different circumstances of the line, in accordance with the principle of economic rationality in the aluminum or metal shield at a certain location using special connections and grounding Way, and at the same time install the protective layer to protect the cable sheath insulation breakdown. According to this, high-voltage cable line installation, should be in accordance with GB50217-1994 "power engineering cable design rules" requirements, single-core cable line metal jacket only a little ground, the metal sheath of any one of the induced voltage should not exceed 50- 100V (not taken when the safety measures can not be arbitrarily exposed to metal sheath is not greater than 50V; if taken effective measures, not more than 100V), and should be insulated. If the voltage is greater than this specified, the metal sheath shall be taken to be insulated or insulated and connected to a crossed interconnect. In order to reduce the single-core cable lines on the auxiliary cable and communication cable induction voltage, should be used as much as possible cross-connect wiring. For the cable length is not long, you can use a single point of grounding. To protect the cable sheath insulation, in the ungrounded end should be installed protective layer protection.
In order to strengthen the product quality supervision and safeguard the legitimate rights and interests of consumers, according to the "People's Republic of China Product Quality Law" and "product qu