Long term equivalent circuit of power cable accessories
with the rapid development of China's power grid, power cable construction project continues to increase, the power cable accessories line is associated with increases rapidly, the equivalent circuit of power cable accessories long-term also is widely used, the power supply reliability by the power sector and power users more and more attention. In the following paragraphs we learn about the together:
( 1) Long term and short term
power cable is a kind of power transmission line, the transmission line itself geometric length L is greater than its transmission wavelength into the waves ( Wavelength into = V/f) radio frequency transmission speed , or both to compare to, according to the transmission line for the long term, or for the short term. When waves of transmission for the pulse wave, the wavelength is equal to the pulse width. Visible, long term or short term is relative to the wavelength meng waves or pulse width r relative concept.
in microwave technology, the wavelength of the measuring unit is meters or cm. Therefore, the geometry of a long length doesn't have to be very long, sometimes only a few centimeters or meters will be enough. For power transmission lines, even if the line length of km above, it compared with the power frequency signal wavelength ( 6000公里) A much smaller, so can't call it for the long term.
when the road on the cable fault diagnosis using pulse reflection test technology, the situation will change. Visible, when the length of cable line in dozens of meters can be equivalent to the long term.
( 2) Long term equivalent circuit
power cable is seen as a long term, it is no longer a simple conductor ( Wire core) An insulating - On the ground ( Outer sheath) Loop, but by lots of equivalent resistance, conductivity, inductance and capacitance, these parameters along the cable line evenly distributed, so called distribution parameters.
when current flows through the signal of the resistance and inductance per unit length of cable, the voltage drop can be generated and will return by conductance and capacitance shunting the way. When high frequency waves cable transmission, you can ignore the wastage of the resistance and conductance, that ro = go = 0, the circuit is called lossless circuit. If no special instructions, the cable equivalent circuit are discussed refers to the lossless circuit.
our country is increasing investment in construction of uhv, now uhv transmission is given priority to with overhead lines, exist such as the covers an area of more, transmission security vulnerable to climate condition the influence, transmission quality is not high, will affect the safety of the power grid stability, therefore, USES the ultra high voltage cable, will become the developing trend of associated with ultra-high pressure and ultra-high voltage cross-linking cables and cable accessories research and development will be the important direction of future development.