QHow to select Marine Cable?ASelection steps and principles of Marine Cable
1. According to the application, laying location, and working conditions of marine cable to select the appropriate marine cable.
2. According to the duty, power type, cable core and load current of electrical equipment to select the appropriate cable cross-section.
3. According to system short-circuit current calculations, determine whether the cable short-circuit capacity to meet the requirements.
4. According to ambient temperature to amend the rated ampacity, and then determine whether the cable allowable current is greater than the load current.
5. According to bunched laying correction factor to amend the rated ampacity, and then determine whether the cable allowable current is greater than the load current.
6. Check line voltage drop, and determine whether the line voltage drop is less than the predetermined value.
7. According to the setting value of the protection device to determine whether the cable is coordinate with protection device; if uncoordinated, determine whether you can change the appropriate protective devices or setting value, or you should re-select the appropriate cable cross-section.
Marine cable type selection should consider the following factors:
1. Application of the marine cable-- for power, lighting or radio communications.
2. Cabling position of marine cable --- dry, wet, cold, or whether requiring shielding.
3. Working conditions of marine cable --- fixed laying, pipe wear or portable
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QHow to choose suited cross-linked polyethylene(XLPE) insulating power cable?ABasic requirements of choosing cross-linked polyethylene (XLPE) insulating power cable
1. Cable core temperature maximum operating current is applied, shall not exceed the allowable value of the continuous operating current loop cable core temperature must not exceed the permissible values listed in section 2.4 of Schedule that cross-linked polyethylene (XLPE) insulating power cable core maximum rated temperature is 90 ℃.
2. The maximum short-circuit current thermal effects produced by the role of time, should not undermine the continued use of the cable characteristics. For non-fuse protection circuit, according to the short-circuit current core temperature does not exceed a Linear Section 2.4 of the Schedule are allowable values, namely cross-linked polyethylene (XLPE) insulating power cable cores maximum temperature of 250 ℃.
3. Circuit connection is very long, the limits for voltage drop should not exceed the allowable value.
4. For longer distances large current loop or more than 35kV high-voltage cable, to meet the three requirements under the premise of economic current density law should press the selection line core cross section, namely the cable core cross section can be determined as follows
Wherein Y • max-- normal working hours maximum continuous operating current, A; J-- economic current density, A / mm2.
QWhat is the difference between THHN and THWN electric wire?ATHHN and THWN are all nylon sheath electric wire, one type of American Standard electric wires, they are according to UL62 and UL83 Standard.
THHN is short for thermoplastic high-heat resistant nylon-coated wire; it is with better electrical properties and physical properties than common PVC insulation electric wires, which are with better features of heat resistance, rotproofness, self-lubrication and oil resistance. THHN nylon electric wire is used to connect branch circuit and various kinds of electronics.
THWN is short for thermoplastic heat- and waterproofness nylon-coated wire, it is with features of thermoplasticity and water-resistant. The application of THWN is same as THHN, it is known as THWN is evolution of THHN.
In conclusion, the basic difference between THHN and THWN is the waterproofness.
QWhy there are so many layers in power cable?APower cables outermost layer is generally rubber or synthetic rubber sleeve, this layer is not only insulation layer, but also play a role to protect cable from harm.
High voltage power cables with a layer of resin-like filler which mainly play the role of insulation, low voltage power cables without this stuff. Power cables are with some similar ribbons wrapped around, which are to secure the each cable core, filled the middle of the gap.
Shield layer, there are two cases, the power cable shield has two effects: first, because the current through the power cable is relatively large, the current creates a magnetic field around, in order not to affect other elements, so add that to shield electromagnetic fields shield in the cable; the second is to play a role ground protection, if damaged, leaked current can occur within the cable core role shield along the outflow, played security protection.
Power cable is made of a conductive core, an insulating layer, a protective layer. Detailed: conductive core, an inner semiconducting layer, an insulating layer and an outer semiconductive layer, copper shield, filler, inner liner, double steel protective layer, the outer sheath. Above the main structure is for 10kV power cable.
QSelecting and wining principle of control cables in the inverter control cabinetA1. For class Ⅰ signal cables must be shielded cables, class Ⅰ signal millivolt signal, the strain signal should be shielded twisted pair cable, but also to ensure that the shield is only a little ground, and to a good grounding. This can greatly reduce the electromagnetic interference and electrostatic interference.2. For Class Ⅱ signals should be shielded, Class Ⅱ signal for controlling, interlocking signal into the mold, open into the signal, it must be shielded cable, preferably shielded twisted-pair cable. Prohibiting the use of more than one core cable in the portion of the core wire for the transmission of class Ⅰ or Ⅱ class signal, the other part of the core lines for transmitting signals Ⅳ Ⅲ class or classes.3. For Ⅳ class signal is strictly prohibited and Ⅰ, Ⅱ class tied together signal traces should be treated as a 220V power line, class Ⅳ signal and power cables together with traces should be shielded twisted-pair cable. The absolute prohibition of high-power switch output signal lines, power lines, power lines, cable and Frequency Control System Ⅰ, Ⅱ class signal cables parallel bundle.
4. For Ⅲ class signal, allowing the 220V power line traces together (ie the same class Ⅳ signal), but also with Ⅰ, Ⅱ class together with the signal traces. But class Ⅲ signals must be shielded cable, preferably shielded twisted pair cable, and with Ⅰ, Ⅱ class signal cables more than 15cm apart. It prohibited the same signal several wires are distributed in different several cables (such as the three-wire RTD)
In the field cabling must be effectively separated from easy to produce interference cables Ⅲ, type Ⅳ signal cable, power lines, etc., so that it Ⅰ, Ⅱ class signal cables laid site is maintained at a safe distance (eg 15cm above).
Signal and power cables should be different trunking alignment, when entering the inverter cabinet, should also be away from each other as possible. When these two cables can not be routed separately to meet the requirements, they must be shielded cable (shielded or twisted pair cable), and shall meet the following requirements:
1. If the spacing between the signal and power cables is less than 15cm, it must set the shielding metal separator between the signal and power cables, and grounding separator.
2. When the signal and power cables vertically or horizontally when installed separately, the spacing between the signal and power cables should be more than 15cm. For some disturbances particularly large applications, such as contact voltage is AC 220V power supply cable, the current in the inductive load 10A above, but when the power cable is not shielded, so it requires a direction perpendicular to the signal cable spacing must more than 60cm.
3. When two cables perpendicular, if the power cable is not shielded, in 1. 6mm in thickness is more than covered the iron cross section.
In order to reduce interference from analog converters and other equipment, should control the drive signal line and power circuits (main circuit and sequence circuit) traces separately. Distance should be more than 30cm. Even in the control cabinet, also have to maintain this connection specification. The signal cable is no longer than 50m, signal line protection metal pipe or a metal hose has to be extended to the control terminal of the inverter to ensure complete separation of signal lines and power lines. Analog control signal lines should use shielded twisted pair cable, wire gauge is 0.5 ~ 2mm2. When wiring cable stripping it as short as possible (5 ~ 7mm), while the subsequent stripping shield wrap with insulation tape to prevent contact with the shield and other equipment and the introduction of interference.
Q10kV high tension power cables test notesA1. DC voltage cable insulation volume resistivity of the electric field distribution depends on the material, and the electric field distribution depends on the Ac voltage of each of the dielectric constant of the medium, especially in the DC cable terminal head, connector boxes and other cable accessories in alternating electric field intensity distribution and the distribution of the field strength is completely different, and the mechanism and the mechanism of aging DC voltage AC voltage insulation aging is not the same. Therefore the DC voltage test can not simulate high voltage cable operating conditions.
2. 10kV High tension power cable in the DC voltage will have a"memory"effect, unipolar accumulation of residual charge storage. Once you have the test because the DC voltage caused by "memory, that will take a long to release the DC bias If the DC cable before the release of residual charge is not fully operational, it will be superimposed on the DC bias power frequency voltage peak, the cable so that the voltage value far exceeds its rated voltage, which may cause the cable insulation breakdown.
3. DC voltage test, there will be injected into the polymer inside the electronic media, the formation of space charge, so reducing the electric field strength of the premises, making it difficult to breakdown occurs. Semiconductor contamination and projections at the point of high-voltage cables, etc. prone to space charge. However, if the cable terminal head occurs when the surface flashover test cable attachment or breakdown will cause the cable core line generated wave oscillation, has been the accumulation of space charge of the place, since the oscillation voltage polarity is rapidly changing different polarity, so that the at a field strength significantly increased, it may damage the insulation, resulting in more clicks to wear.
4. The 10kV high tension power cable fatal weakness is easy to produce water tree inside insulation, once the water branch. in the DC voltage will be rapidly converted the formation of discharge and accelerated the deterioration of insulation, so after running frequency voltage is formed converted into electrical trees, and the formation of discharge and accelerated the deterioration of insulation, so after running frequency voltage is formed under the action breakdown. And pure water trees in the AC operating voltage can remain fairly voltage value, and can be maintained for a period of time.