System And Method For Deicing Of Power Line Cables

Abstract

A system and method for deicing power transmission cables divides the cable into sections. Switches are provided at each end of a section for coupling the conductors together in parallel in a normal mode, and at least some of the conductors in series in an anti-icing mode. When the switches couple the conductors in series, an electrical resistance of the cable section is effectively increased allowing self-heating of the cable by power-line current to deice the cable; the switches couple the conductors in parallel for less loss during normal operation. In an alternative embodiment, the system provides current through a steel strength core of each cable to provide deicing, while during normal operation current flows through low resistance conductor layers. Backup hardware is provided to return the system to low resistance operation should a cable overtemperature state occur.

1 . A system for deicing and anti-icing operations of AC and DC power transmission lines comprises:
 at least one section of cable for transmission of power in the transmission line comprising at least a first, a second, and a third conductor; wherein the first, second, and third conductor are mutually electrically insulated along the length of the section but are connected at ends of the section to form a series serpentine path of at least three conductors connected in series; and   at least a first switch at a first end of the section of cable, and at least a second switch at a second end of the section of cable, the first and second switches operable such that the first, second, and third conductor are connected in parallel in a normal mode and operate in series in an anti-icing mode.   
   
   
       2 . The system of  claim 1  wherein connections for power transmission through the section of cable are made to the first conductor at the first switch, and to the third conductor at the second switch. 
   
   
       3 . The system of  claim 1  wherein at least one switch further comprises a switching device and a switch controller, wherein the switching device and controller are electrically isolated from ground, and wherein the switch is controlled by control signals from a anti-icing system controller at another location. 
   
   
       4 . The system of  claim 1 , wherein the section of cable further comprises a fourth and a fifth conductor, and wherein there is a third switch at the first end of the section of cable for coupling the fourth and fifth conductors to the first conductor, and a fourth switch at the second end of the section of cable for coupling the third and fourth conductors to the fifth conductor, and wherein the third and fourth conductors are electrically coupled near the fourth switch, and the fourth and fifth conductors are electrically coupled near the third switch. 
   
   
       5 . The system of  claim 4  wherein connections for power transmission through the section of cable are made to the first conductor at the first switch, and to the fifth conductor at the second switch. 
   
   
       6 . The system of  claim 4  wherein the system further comprises a controller for monitoring current in the transmission line and determining when anti-icing is required, and for determining a switch configuration for anti-icing operation based upon the current in the transmission line. 
   
   
       7 . The system of  claim 4  wherein a conductor selected from the group consisting of the second conductor, the third conductor, the fourth conductor and the fifth conductor has a resistance substantially greater than a resistance of the first conductor. 
   
   
       8 . The system of  claim 4  wherein at least one switch further comprises a switching device and a controller, wherein the switching device and controller are electrically isolated from ground, wherein the switch is controlled by control signals from a system controller, and wherein the system controller is located at a location remote from the at least one switch. 
   
   
       9 . A system for anti-icing operation of power transmission lines comprises:
 at least one cable having at least two sections, wherein each section comprises:
 at least a first, a second, and a third conductor; wherein the first, second, and third conductor are mutually insulated; 
 a first switch for coupling the second and third conductors to the first conductor at a first end of the cable, the second and third conductors being electrically coupled near the first switch; 
 a second switch for coupling the first and second conductors to the third conductor at a second end of the cable, the first and second conductors being electrically coupled near the second switch; and 
   wherein the third conductor of the first section is connected to the first conductor of the second section; and   a system controller for simultaneously opening the first and second switches of each section to increase resistance of the at least one cable by placing the first, second, and third conductors in series for anti-icing operation of the cable of that section, and wherein the system controller is capable of sequentially opening switches of sections.   
   
   
       10 . The system of  claim 1  further comprising apparatus for sensing overheating of at least one conductor of the cable, and for placing the first, second, and third conductors in parallel to reduce resistance of the cable upon sensing overheating. 
   
   
       11 . A switchbox for switching conductors of a transmission line cable between a parallel configuration and a series configuration, the switchbox comprising:
 an energy storage device for providing power to the switchbox;   apparatus for charging the energy storage device;   a control signal receiver for receiving switch operation commands, the control signal receiver powered from the energy storage device;   at least one switch for determining current flow through at least one conductor of the cable, the switch electrically actuated under control of the control signal receiver; and   apparatus for overriding the control signal receiver and placing the cable conductors in a parallel configuration if a high temperature is detected on a conductor of the cable.   
   
   
       12 . A system for deicing of a cable of a power transmission line, the cable comprising N conductors, where N is an odd integer larger than one, where each of the N conductors are electrically insulated from the other conductors the system comprising:
 a first and a second switchbox, wherein the first switchbox is coupled to a first end of the cable and the second switchbox is coupled to a second end of the cable;   wherein each switchbox has at least (N−1)/2 switches;   wherein in a first mode the switches of the switchboxes connect all N conductors of the cable in parallel, and in a second mode the switches of the switchboxes connect all N conductors in series to increase cable resistance for effective deicing operations; and   a system controller for placing the switchboxes in the first mode for normal operation and in the second mode for deicing the cable.   
   
   
       13 . A system for anti-icing operation of a cable of a power transmission line, the cable comprising a resistive strength core and at least one conductor, the strength core being electrically insulated from the at least one conductor the system further comprising:
 a switchbox for diverting sufficient current from the conductor through the resistive strength core for anti-icing operation of the cable in a first operating mode, and wherein a majority of the current passes through the conductor in a second operating mode.   
   
   
       14 . The system of  claim 13  wherein the switchbox places an inductance electrically in series with the conductor during the first operating mode, the strength core being electrically in parallel with the series combination of inductor and conductor. 
   
   
       15 . The system of  claim 14  wherein the switchbox places an inductance electrically in series with the conductor during the first operating mode by inserting a magnetic core material into a coil, and wherein the magnetic core material is removed from the coil during the second operating mode. 
   
   
       16 . The system of  claim 13 , wherein the switchbox further comprises apparatus for switching between the first and the second operating mode under command of an external system controller, apparatus for sensing an overheat condition of the cable, and apparatus for reducing current in the resistive strength core when an overheat condition is detected. 
   
   
       17 . The system of  claim 16  wherein the switchbox comprises a transformer, the transformer having a secondary coupled to the strength core during deicing. 
   
   
       18 . The system of  claim 12 , wherein the cable has a strength-reinforcement conductor of higher electrical resistance and mechanical strength than the N conductors of the cable; wherein
 the strength-reinforcement conductor is electrically insulated from other conductors along the length of a section, but is connected at the first section end to a first conductor of the N conductors and at the second end of the section to an Nth conductor of the N conductors; and   wherein opening of switches in the switchboxes increases the effective electrical resistance of the N conductors between the switchboxes such that a larger current is diverted into the strength-reinforcement conductor to deice it.   
   
   
       19 . A system for anti-icing of power transmission lines comprises:
 at least one section of cable for transmission of power in the transmission line comprising at least a first, a second, and a third conductor; wherein the first, second, and third conductor are mutually electrically insulated;   at least a first switch at a first end of the section of cable, and at least a second switch at a second end of the section of cable, the first and second switches operable such that the first, second, and third conductor are capable of being connected in at least a low resistance configuration, an intermediate resistance configuration, and a high resistance configuration; and   a system controller for determining when anti-icing operation is required, for selecting an appropriate anti-icing configuration from the intermediate and high resistance configurations, and for setting the switches into the anti-icing configuration when anti-icing operation is required, and into the low resistance configuration when anti-icing operation is not required.   
   
   
       20 . A method for deicing a section of a cable of a power transmission line, the cable comprising a plurality of conductors extending between a first switchbox and a second switchbox, the section of cable having a normal operating mode wherein the plurality of conductors are electrically in parallel, the method comprising:
 detecting ice accumulation on the section of the cable;   configuring switches of the switchboxes to couple a plurality of the conductors of the cable electrically in series thereby placing the section of cable in a deicing mode having a deicing mode resistance greater than a resistance of the section of cable in the normal operating mode;   allowing a current flowing in the section of cable to resistively heat the section of cable to deice the section of cable; and   reconfiguring the switches of the switchboxes to return the section of cable to the normal operating mode.   
   
   
       21 . The method of  claim 20  wherein the switches in the switchboxes have at least a first configuration corresponding to the normal operating mode, a second configuration corresponding to the deicing mode having a first resistance between switchboxes, and a third configuration corresponding to a second deicing mode having a second resistance between switchboxes; the method further comprising:
 monitoring the current flowing in the section of cable to determine a deicing mode appropriate for the current.   
   
   
       22 . The method of  claim 21  further comprising transmitting a message to request an increase in the current flowing in the section of cable when current in the cable is insufficient for deicing. 
   
   
       23 . The method of  claim 21  wherein a first conductor of the plurality of cables has a resistance substantially different from a resistance of a second conductor of the plurality of cables. 
   
   
       24 . The method of  claim 20  wherein the transmission line is configured to transmit power to electric vehicles.