Patent Publication Number: US-2022216689-A1

Title: System and method for cancelling parasite voltage of neutral electric line and lifting of voltage of phase line at a remote load

Description:
BACKGROUND OF THE INVENTION 
     Certain electric cabled systems provide power to remote active devices such as outdoor communication devices over long electric cables. For example, optical transmitters and receivers, street WIFI transmitters, LTE micro cell, and the like. In this regard, ‘long electric cable’ and ‘small cross section area’ relate to remote single phase powering systems where the current of the provided power through the cable over its entire length of Phase and Neutral wires during nominal operation causes a power line voltage drop (LVD) that exceeds a given allowed voltage drop threshold. As a result, active devices connected at the remote end of a long electric cable may receive power at a too-low voltage. Moreover, the voltage presented to the active device at the remote end of the cable may exhibit, with regard to a reference voltage such as the ground line, a too-low phase voltage and a too-high neutral line voltage due to neutral line stray voltage. CATV regulations forbid using a power supply that exceeds defined level, for example 60V/90 VAC for outdoor communication network or 120 VAC for indoor use, thereby solving the above-mentioned problem by increasing the supply voltage level is not allowed, for example, due to safety reasons. 
       FIG. 1A  shows a schematic illustration of a known system  10  used for providing power over long cable. System  10  comprises a single phase power source  100  connected via long cable  104  to active devices  114 . Power source  100  is connected to active device  114  via a phase line/lead, neutral line/lead and a ground line/lead. Active device  114  draws current  111  through a phase line/lead, and the return current through the neutral (AKA zero) line/lead is denoted  112 . Long cable  104  extends from line proximal end (LPE)  115  to line distal end (LDE)  117  with a midpoint LMP  116 . In the example of  FIG. 1A , the current drawn by active device  114  causes voltage drops that may be measured along the line, for example at LMP and at the distal end LDE. A simplified equivalent circuit  20  presents the internal resistance of the phase line as R PHASE LINE  and that of the neutral line as R NEUTRAL LINE , where the actual resistance of each of the lines depends on the physical characteristics of the line. 
       FIG. 1B  depicts graph  50  of voltage drops along line  104  (of  FIG. 1A ). In the example of  FIG. 1B , the drawn current causes a voltage drop of 30 VAC between the LPE (terminal  1002 ) and the LDE (terminal  1006 ). Assuming a homogeneous longitudinal resistance along the phase line and the neutral line, the voltage drop at midpoint LMP ( 1004 ) is 15 VAC. As a result, the phase-to-ground voltage at the active device&#39;s phase terminal  1006  is 120−30=90 VAC. Similarly, the parasite voltage on the neutral line between terminal  1003  and terminal  1007  is 30 VAC (assuming that the cross section of the two leads is substantially the same). The voltage drop over the phase line and the parasite voltage over the neutral line set the voltage between active device&#39;s  1009  terminals  1006  and  1007  at 90 VAC-30 VAC=60 VAC, that is half the source voltage, a difficulty which needs to be addressed. Further, the voltage between neutral terminal  1007  and the ground line, instead of being maintained as close as possible to zero, is, in the current example, 30 VAC, which presents another difficulty which must be addressed. 
     Known devices address the first problem of adjusting the voltage between the phase terminal and the neutral terminal of the remote active device back to nominal power voltage, yet, the parasite voltage developing on the neutral line is left untreated, thereby presenting a problem and especially where at least one unit at the remote end of the cable is referenced to ground voltage. This problem is intensified at known solutions because the correction of the phase voltage at the output without handling the parasite voltage of the neutral line not only leaves the output terminals at a voltage gap with respect to the ground line, but also may raise the output phase line to a risky level with respect to the ground because it may be equal to the nominal voltage plus the parasite neutral line voltage. Hence, phase voltage to the ground is higher than the nominal voltage allowed. Autotransformers have the advantages of often being smaller, lighter, and cheaper than typical dual-winding isolated transformers, Other advantages of autotransformers include lower resistance and lower energy losses, and increased VA rating for a given size and mass. The term ‘nominal voltage’ as used herein relates is a value assigned to a circuit or system to designate its voltage class conveniently (e.g., 120/240 volts, 300 volts, 480Y/277 volts). Thus, a nominal single AC phase power line voltage may be 240 VAC or 120 VAC, depending on the country discussed. 
     There is a need to enable providing of power voltage at a nominal level at the remote active device, thereby overcoming the disadvantages of the line voltage drop (LVD) and the Isolator transformer, and further to provide the AC power at the active device&#39;s terminals with voltage difference between the neutral terminal and the ground terminal close to zero. 
     SUMMARY OF THE INVENTION 
     A Phase and Neutral voltage Adjusting (PNVA) device is presented. The PNVA device comprises a phase AC input terminal, neutral line input terminal, ground line input terminal, phase AC output terminal, neutral line output terminal and ground output terminal. The device further comprises an autotransformer which comprises a plurality of taps each connected to a separate winding of the autotransformer and associated with at least one of an AC phase input terminal of the device and with an AC phase output of the device, and a plurality of taps each connected to a separate winding of the autotransformer and associated with at least one of an AC neutral line input terminal of the device and with an AC neutral line output of the device. The device further comprises at least one first single-port-to Multi-port (STMS) controllable selector switch associated with adjusting the AC phase output voltage, at least one second single-port-to multi-port (STMS) controllable selector switch associated with adjusting the neutral output voltage and a controller adapted to provide control signals for activating each of the at least one STMS of the AC phase output and the at least one STMS associated with the neutral output. Each of the at least one first STMS and at least one of the second STMS is adapted to connect the respective single port to a selected respective port of the multiple ports in response to a control signal from a controller. 
     In some embodiments, the controller is configured to respond to a signal indicative of the voltage between the AC phase input terminal and the neutral line input terminal and to respond to a signal indicative of the voltage between the neutral line input terminal and the ground output terminal. 
     In some embodiments, the controller is further configured to issue a first control signal to the at least one first STMS in response to the signal indicative of the voltage between the AC phase input terminal and the neutral line input terminal and to issue a second control signal to the at least one second STMS in response to the voltage between the neutral line input terminal and the ground output terminal. 
     In some embodiments, the first control signal is configured to select one of the multi ports of the at least one first STMS to be connected to the respective single port and the second control signal is configured to select one of the multi ports of the at least one second STMS to be connected to the respective single port. 
     In some embodiments, the single port of the one of the at least one first STMS is connected to the phase AC input terminal and the respective multi ports are each connected to one tap of the plurality of taps of the autotransformer, the single port of the one of the at least one second STMS is connected to the neutral line input terminal, and the respective multi ports are each connected to one tap of the plurality of taps of the autotransformer, and each of the taps connected to the second STMS is different from the taps connected to the first STMS. 
     In some embodiments, the one port of the multi ports of the at least one second STMS is selected to set the voltage between the neutral line output port and the ground output port to substantially zero, and the one port of the multi ports of the at least one first STMS is selected to set the voltage between the AC phase output port and the neutral line output port to a nominal line voltage. 
     A method for canceling parasite voltage on neutral electric line and lifting of voltage of phase line a remote load is presented, the method comprising providing a Phase and Neutral Voltage Adjusting (PNVA) device comprising a phase AC input terminal, a neutral line input terminal, a ground input terminal phase AC output terminal, a neutral line output terminal and a ground output terminal, the device further comprising: an autotransformer, at least one first single-port-to multi-port (STMS) controllable selector switch associated with adjusting the AC phase output voltage, at least one second single-port-to multi-port (STMS) controllable selector switch associated with adjusting the neutral output voltage and a controller adapted to provide control signals for activating each of the at least one STMS of the phase AC output and the at least one STMS associated with the neutral output. The method further comprises issuing a first control signal to the at least one first STMS in response to the signal indicative of the voltage between the phase AC input terminal and the neutral line input terminal and issuing a second control signal to the at least one second STMS in response to the voltage between the neutral line input terminal and the ground input terminal as long the ground is connected. 
     In some embodiments, the method further comprises selecting one of the multi ports of the at least one first STMS, in response to the first control signal, to be connected to the respective single port and selecting one of the multi ports of the at least one second STMS, in response to the second control signal, to be connected to the respective single port. 
     In some embodiments, the one port of the multi ports of the at least one second STMS is selected to set the voltage between the neutral line output port and the ground output port to substantially zero and the one port of the multi ports of the at least one first STMS is selected to set the voltage between the AC phase output port and the neutral line output port to a nominal line voltage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which: 
         FIG. 1A  is a schematic illustration of a known system providing power over long electric cable; 
         FIG. 1B  is a schematic voltage diagram depicting the voltage drop along an electric cable of a known system; 
         FIG. 2A  is a graph depicting the way a Phase and Neutral Voltage Adjusting (PNVA) device addresses voltage drops on a long phase line and the parasite voltage on long neutral line at a remote end of the line, according to embodiments of the present invention; 
         FIG. 2B  is a schematic illustration of a system for providing single phase AC regulated power via long line to a load separately to the phase line and the neutral line, according to embodiments of the invention; 
         FIG. 2C  which is a schematic high-level block diagram of a PNVA, according to embodiments of the present invention; 
         FIG. 2D  is a schematic high-level block diagram of a PNVA, according to embodiments of the present invention adapted to power two active devices; 
         FIG. 2E  is a schematic block diagram of a PNVA, comprising an autotransformer, according to embodiments of the present invention; 
         FIG. 3A  is a schematic illustration of a PNVA according to embodiments of the present invention; 
         FIG. 3B  is a schematic illustration of a the of  FIG. 3A  without a ground connection to the ground input terminal, according to embodiments of the present invention; 
         FIG. 3C  is a schematic illustration of a the of  FIG. 3A  with a local ground connection to the ground input terminal, according to embodiments of the present invention; 
         FIG. 4A  is a schematic illustration of another PNVA, according to embodiments of the present invention; 
         FIG. 4B  is a schematic block diagram of the PNVA of  FIG. 4A  without a ground connection to the input terminal, according to embodiments of the present invention; 
         FIG. 4C  is a schematic block diagram of the PNVA of  FIG. 4A  with an local ground connection to the input terminal, according to embodiments of the present invention; 
         FIG. 5A  is a schematic block diagram of an additional PNVA, according to embodiments of the present invention; 
         FIG. 5B  is a schematic block diagram of the PNVA of  FIG. 5A  without a ground connection to the input terminal, according to embodiments of the present invention; 
         FIG. 5C  is a schematic block diagram of the PNVA of  FIG. 5A  with a local ground connection connected to the input terminal, according to embodiments of the present invention; 
         FIG. 5D  is a schematic block diagram of the PNVA of  FIG. 5A  adapted to power two active devices, according to embodiments of the present invention; 
         FIG. 6A  is a schematic illustration of a chain of two serially connected single phase PNVAs according to embodiments of the present invention; and 
         FIG. 6B  is a graph depicting the source current during gradual connection of the active devices of serially connected PNVAs of  FIG. 6A , according to embodiments of the present invention. 
     
    
    
     It will be appreciated that, for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. 
     DETAILED DESCRIPTION OF THE PRESENT INVENTION 
     In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present invention. 
     According to embodiments of the present invention, a single controlled autotransformer may be used for adjusting the phase line voltage level and eliminating the parasite stray voltage over the neutral line simultaneously at the active device&#39;s input terminal connected at a remote end of a line so that the input AC phase and neutral levels conform with the required nominal voltages, and the voltage difference between the neutral terminal of the active device&#39;s device and a ground line is kept within a defined voltage difference, preferably that close to zero Vac. 
     Reference is made to  FIG. 2A , which is a graph  2000  depicting the way a phase and neutral voltage adjusting (PNVA) device  2008  addresses voltage drops on a long line at a remote end of the line, according to embodiments of the present invention. Section  2000 A of graph  2000  presents the schematic linear voltage drop along a 1000 feet line, similar to the description of the line voltage drop of  FIG. 1B . As seen in graph  2000 , due to the current drawn by active device  2011 , the voltage between PNVA  2008  input terminals  2006  and  2007  drops from 120 VAC to 60 VAC. Further, the voltage at terminal  2007 , is 30 VAC higher than the voltage at terminal  2003 , the neutral line terminal of the power source. As will be explained in detail hereinbelow, PNVA device  2008  provides means for correcting the voltage drops on the phase line and for eliminating the parasite voltage on the neutral by lifting the voltage of the phase line at terminal  2010  back to nominal voltage and by lowering the voltage of the neutral terminal  2009  down to close to 0 VAC. 
     Reference is made to  FIG. 2B , which is a schematic illustration of system  200  for providing single phase AC regulated power via long line  216  to active device  212 , separately to the phase line and the neutral line, according to embodiments of the invention. Single phase AC power source  202  provides AC source power over phase line  204 , neutral line  205  and ground line  206  and further provides continuous ground connection to remote active device  212 . As explained with respect to  FIG. 2A , due to load current  218  (in the phase line) and return load current  217  (in the neutral line), the distal phase voltage  208  to distal neutral AC voltage  209  measured is lower than the phase AC voltage  204  to the neutral AC voltage  205  measured next to the power source  202 . Similarly, the voltage between neutral line voltage  209  to ground AC voltage  210  at the distal terminal is higher than the voltage between the neutral line  205  to ground voltage  206  at the power source, and, therefore, it is higher than the voltage of the ground line at the terminals of the remote load. PNVA  215  may receive the AC voltage of the distal end ( 208 , 209 , 210 ) of line  216  and may be configured to regulate it so that the voltage output between phase port  213  and neutral output port  214  substantially equals the AC source voltage  202  and the voltage between the neutral output port  214  and the ground line (or another reference line, as the case may be) substantially close to zero level. PNVA  215  may equal PNVA  2008  of  FIG. 2A . 
     Reference is made now to  FIG. 2C , which is a schematic high-level block diagram of PNVA  2510 , according to embodiments of the present invention. PNVA  2510  may comprise a Single-port-To-Multiport Selector (STMS) switch  2520  and a control unit  2530 . STMS switch  2520  may be any known means for controllably connecting a single port to a selected one of several ports. STMS switch  2520  may be adapted to perform switching of the power provided by a long line (e.g., line  216  of  FIG. 2B ). For example, STMS switch  2520  may comprise a controllable rotary switch adapted to controllably connect its mid-port to one of the selectable other ports. Another optional embodiment may employ a dry-contact or a solid state switch for connecting/disconnecting one of the multiple ports to the single port. In the following exemplary embodiments hereinbelow, STMS switches will be depicted as an embodiment of multiple controllable switches with single in and single out ports. 
     Control unit  2530  may be any known controller, a programmable logic controller (PLC) or any other control unit that is adapted to provide switching signals to STMS switch  2520  in order to select one of the multiple ports for connection to the single port in response to one or more inputs received by control unit  2530 . Control unit  2530  may comprise a memory unit, data storage unit, input and output modules and the like, adapted to enable control unit  2530  to perform the functions described herein. In some embodiments, PNVA  2510  may comprise network connectivity capabilities, for example wireless connectivity to remote PNVAs and/or to a central control unit. In some embodiments, network connectivity may be performed over electric power wired line, e.g., line  216  (of  FIG. 2B ) as is known in the art. In some embodiments, control unit  2530  may be adapted to receive signals indicative of the voltage(s) along the line (such as line  216  of  FIG. 2B ). 
     Reference is made now to  FIG. 2D , which is a schematic high-level block diagram of PNVA  2560 , according to embodiments of the present invention. PNVA  2560  may have similar functionalities and may comprise similar units and modules as PNVA  2510 , with a capability to control the power voltage levels of more than a single active device. PNVA  2560  may regulate phase and neutral voltages of two or more active devices, such as active devices  2590 A and  2590 B, similarly to STMS  2510 . PNVA  2560  may comprise two or more STMS switch  2570  (the exact number is derived from the number of serviced active devices). Each of STMS  2570  may be built and function similar to STMS  2520  of  FIG. 2C . PNVA  2560  may further comprise control unit  2580  that may be built and may function similar to control unit  2530 , with the exception of being capable of controlling two or more PNVAs independently. 
     Reference is made now to  FIG. 2E , which is a schematic block diagram of PNVA device  2600 , comprising autotransformer  2605 , according to embodiments of the present invention. PNVA  2600  comprises autotransformer  2605  comprising n windings. 
     As is known in the art, an autotransformer is an electrical transformer with only one winding, where portions of the same winding act as both the primary winding and secondary winding sides of the transformer. The autotransformer winding has at least four switched taps, two switched taps (for connecting the preferred phase connection and two switched taps for connecting the preferred neutral connection) where electrical connections are made. Since an autotransformer has only one winding, it has the advantages of being more energy efficient, smaller, lighter, and cheaper than typical dual-winding and isolated transformers. Other advantages of autotransformers include lower leakage resistance, lower losses, lower excitation current, and increased VA rating for a given size and mass. In an autotransformer, the ratio of the secondary voltage to the primary voltage is determined as the relation between the number of secondary windings to the number of primary windings, where the primary and secondary may share at least some of the windings. The entire winding of the autotransformer may be considered as a ‘voltage distributor’ in which the voltage between any two taps of the transformer is expressed by the equation: 
     
       
         
           
             
               
                 
                   
                     V 
                     
                       
                         T 
                         ⁢ 
                         2 
                       
                       - 
                       
                         T 
                         ⁢ 
                         1 
                       
                     
                   
                   = 
                   
                     
                       V 
                       
                         
                           TIN 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                         - 
                         
                           TIN 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                       
                     
                     ⁡ 
                     
                       ( 
                       
                         
                           n 
                           
                             
                               T 
                               ⁢ 
                               2 
                             
                             - 
                             
                               T 
                               ⁢ 
                               1 
                             
                           
                         
                         
                           n 
                           
                             
                               TIN 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               1 
                             
                             - 
                             
                               TIN 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                             
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   Eq 
                   . 
                   
                       
                   
                   ⁢ 
                   1 
                 
               
             
           
         
       
         
         
           
             Where: 
             V T2-T1  is the voltage between the two output taps T1 and T2 
             V TIN1-TIN2  is the input voltage connected to input taps IN1 and IN2 
             n T2-T1  is the number of windings between the two output taps T1 and T2, and 
             n TIN1-TIN2  is the number of windings between the input taps IN1 and IN2 
           
         
       
    
     The voltage determined by Eq. 1 is a vector number, meaning that, if an output tap is connected to a winding that is closer to the first winding than winding of an input tape, then the voltage developing on the output tap will be lower than the voltage at the input tap. 
     PNVA  2600  may comprise at least two STMS, such as STMS  2601 ,  2602 ,  2603  and  2604 . At least two STMSs may be sufficient for regulating the output voltages  2600   PHOUT  and  2600   NUOUT  so as to bring these voltage to nominal levels, as described above, when AC voltage between the phase input port  2600   PHIN  and the neutral input  2600   NEIN  is lower than the preset nominal voltage and when the voltage between neutral input port  2600   NEIN  and the ground  2600   GRIN  is higher than the nominal voltage with respect to a reference voltage (e.g., ground line), as explained above. 
     Or, in case port  2600   GRIN  is not connected to the ground and the AC voltage between the input port  2600   PHIN  and the input  2600   NEIN  is lower than the nominal voltage by a measured voltage difference, STMS may be set to enable the voltage between Phase output port  2600   PHOUT  and Neutral output port  2600   PHOUT  to equal the preset nominal level, for example by raising the voltage of Phase output port  2600   PHOUT  by half the measured difference and by decreasing the voltage of Neutral output port  2600   NEOUT  by half the measured difference. 
     Each of the PNVAs may have a central port (single port), such as port  2601   CENT , for PNVA  2601  and multiple selectable ports, such as ports  2601   a - 2601   n  for PNVA  2601 . Each STMS may be configured to connect one selected port out of the multiple selectable ports (e.g., ports  2601   a - 2601   n ) to central port (e.g.,  2601   CENT ). Each of the multiple selectable ports (e.g., ports  2601   a - 2601   n ) may be connected to a selected winding of autotransformer  2605 . STMS, such as STMS  2600 , and may be controlled by a control signal provided at control port, such as port  2601 A. A control signal provided at control port  2601 A may cause STMS  2601  to connect a selected port of the plurality of selectable ports  2601   a - 2601   n  to central port  2601   CENT  and to thereby connect that selected port to the central port. 
     In embodiments using two STMSs, at least one STMS may be used to regulate the output phase voltage, and at least one STMS may be used to regulate the output neutral voltage. Each of the two STMSs may be connected as a selecting device at the primary side or at the secondary side of autotransformer  2605 . Since an autotransformer has only a single winding, to the taps of the autotransformer both the input terminals and the output terminals are connected. By convention, the windings connected between the input terminals are named ‘primary’, and the windings that are connected to the output terminals are named ‘secondary’. At least some of the primary windings may also be secondary windings. The input or output ports that are not connected via a STMS device are connected directly to a pre-selected winding of autotransformer  2605 . 
     Reference is made now to  FIG. 3A , which is a schematic illustration of PNVA  3000  according to embodiments of the present invention. PNVA  3000  may comprise autotransformer  3002 , control unit  3001 , and two STMSs  3007  and  3008 . The embodiment depicted in  FIG. 3A  demonstrates use of two STMSs connected to the primary side of autotransformer  3002 . PNVA  3000  may receive single phase AC power at the distal end of a long line ( 3030 ) at its input port  3029  via phase terminal  3026  and neutral terminal  3027 , and ground may further be connected to the terminal  3028 . Output port  3025  of PNVA  3000  comprises phase output terminal  3022 , neutral output terminal  3023  and the ground output terminal  3024 . Ground output terminal  3024  may be connected directly to the input ground terminal. Output phase terminal  3022  may be permanently connected to ‘high’ end winding  3019  of autotransformer  3002 , located at the distal end from winding  3020 , to which output neutral pin  3023  may permanently be connected. 
     STMS  3008  may be connected at its central port to input neutral line  3005  and may selectively be connected to one of its plurality of selectable ports  3008   a - 3008   n . Each of the selectable ports of STMS  3008  may be connected, via switches  3008 Si, to a predefined winding. All of the windings connectable via STMS  3008  are selected closer to first end winding  3020  than the windings connectable via STMS  3007 . 
     STMS  3007  may be connected at its central port to input phase line  3006  and may selectively be connected to one of its plurality of selectable ports  3007   a - 3007   n . Each of the selectable ports of STMS  3007  may be connected, via a respect switch  3007 Si, to a predefined winding. All of the windings connectable via STMS  3007  are selected closer to the second end winding  3020  than the windings connectable via STMS  3008 . 
     Each of switches  3007 Si and  3008 Si may be controlled to switch open or close via control bus  3009  or  3010 , respectively, which are connected to control unit  3001 . Control unit  3001  may receive input signals indicative of the voltage of input phase line  3001 P, input neutral line  3001 N and input ground  3001 G. Control unit  3001  may further be in operational communication with one or more other PNVAs and/or with a remote central control unit (not shown). 
     Reference is made now also to  FIG. 3B , which is a schematic illustration of PNVA  3000 ′, according to embodiments of the present invention. PNVA  3000 ′ may be similar or the same as PNVA  3000 , where the embodiment of  FIG. 3B  demonstrates use of a PNVA, such as PNVA  3000  when no ground line is connected at the input ground terminal  3028  or at output ground terminal  3024 . In such a case, controller  3001  may sense that the input ground terminal  3028  is floating (not connected). Absent a reference ground voltage, controller  3001  may act according to the assumption that the phase voltage drop magnitude equals the neutral parasitic voltage. Accordingly, controller  3001  may set STMS  3007  to raise output phase voltage at terminal  3022  by half the difference between nominal phase-to-neutral voltage level and the phase-to-neutral voltage measured at the input of PNVA  3000 , and may set STMS  3008  to be lowered by the same magnitude, thereby setting the output neutral voltage at terminal  3023  to as close as possible to a ground voltage level and setting the voltage difference between output phase terminal  3022  and output neutral terminal  3023  the nominal phase to neutral voltage level. For example, if the phase-to-neutral voltage measured at the input of PNVA  3000  is 90 VAC and the nominal phase-to-neutral voltage level is 120 VAC, STMS  3007  my raise output phase voltage at terminal  3022  by (120−90)/2=30 VAC. Similarly, STMS  3008  may lower the phase-to-neutral voltage by 30 VAC. 
     Reference is made now also to  FIG. 3C , which is a schematic illustration of PNVA  3000 ′, according to embodiments of the present invention. PNVA  3000 ′ may be similar or the same as PNVA  3000 , differing from PNVA  3000  by having local ground connection by ground line  3030 ′ connected at the ground input terminal  3028 . This embodiment is typical for power lines having only two wires, such as coaxial lines. 
     Reference is made now also to  FIG. 4A , which is a schematic illustration of PNVA  4000 , according to embodiments of the present invention. PNVA  4000  may comprise autotransformer  4002 , control unit  4001 , and two STMSs  4007  and  4008  connected to the primary side of autotransformer  4002 , similar to STMSs  3007  and  3008  of  FIG. 3A . PNVA  4000  further comprises STMSs  4029  and  4030  connected at the secondary side of autotransformer  4002 . STMSs  4007 ,  4008 ,  4029  and  4030  are controllable by control unit  4001  via control buses  4009 ,  4010 ,  4027 ,  4028 , respectively. 
     The embodiment depicted in  FIG. 4A  demonstrates the use of two STMSs connected on the primary side of autotransformer  4002 . Different from PNVA  3000 , PNVA  4000  demonstrates the use of four STMSs: STMS  4007  and  4008  connected at the primary side of autotransformer  4002 , and STMS  4029  and  4030  connected at the secondary side of autotransformer  4002 . The embodiment of  FIG. 4A  depicts optional connection of STMS  4029  via at least some of its selectable connections  4029   a ,  4029   b  to the windings having voltage higher than the voltage at winding  4007   a , which provides the highest voltage connectable to STMS  4007 . Similarly, STMS  4030  may optionally be connected to at least some winding via switches  4030   a ,  4030   b  having voltage lower than the voltage at winding  4008   a , which present the lowest voltage via STMS  4008 . PNVA  4000  may receive single phase AC power at the distal end of a long line (not shown) at its input port  4034  via phase terminal  4031  and neutral terminal  4032 , and may further be connected to the ground terminal  4033 . Output port  4025  of PNVA  4000  comprises phase output terminal  4022 , neutral output terminal  4023  and ground output terminal  4024 . Ground output terminal  4024  may be connected directly to the input ground terminal  4033 . Output phase terminal  4022  may be connected through STMS  4029  to one of several selectable windings tap of autotransformer  4002 . Output neutral pin  4023  may be connected through STMS  4030  to one of several selectable windings tap of autotransformer  4002 . The embodiment depicted in  FIG. 4A  presents a high level of flexibility in regulating the output phase and neutral voltages, by enabling multiple options composed of the number of selectable windings of all of the STMSs of PNVA  4000 . Control unit  4001  may receive an indication of the voltages between input phase terminal  4031  and input neutral terminal  4032  and of the voltage between neutral terminal  4032  and the ground terminal  4033  in order to determine the right selection of windings in at least some of STMSs  4007 ,  4008 ,  4029  and  4030 . In some embodiments, the control unit  4001  may also receive an indication of the output phase and neutral voltages in order to perform closed loop control of the voltage regulation. 
     Reference is made now also to  FIG. 4B , which is a schematic block diagram of PNVA  4000 ′, according to embodiments of the present invention. PNVA  4000 ′ may be similar or the same as PNVA  4000 , where the embodiment of  FIG. 4B  demonstrates use of a PNVA, such as PNVA  4000  when no ground line is connected at the ground input terminal  4033 . In such a case, controller  4001  may sense that the input ground connected is floating. Absent a reference ground voltage, controller  4001  may act according to the assumption that the phase voltage drop magnitude equals the neutral parasitic voltage. Accordingly, controller  4001  may set STMS  4007  and/or STMS  4029  to raise output phase voltage at terminal  4022  by half the difference between preset nominal voltage and the phase-to-neutral voltage measured at the input port  4034  between terminal  4031  and terminal  4032  of PNVA  4000 ′, and may set STMS  4008  and/or STMS  4030  to be lowered by the same magnitude, thereby setting the output neutral voltage at terminal  4023  to be as close as possible to a ground voltage level and setting the voltage difference between output phase terminal  4022  and output neutral terminal to nominal voltage. 
     Reference is made now also to  FIG. 4C , which is a schematic block diagram of PNVA  4000 ′, according to embodiments of the present invention. PNVA  4000 ′ may be similar or the same as PNVA  4000  of  FIG. 4A , differing by having a local ground connection via ground line  4036  connected at ground input terminal  4033 . This embodiment is typical for power lines having only two wires, such as coaxial lines. 
     Reference is made now to  FIG. 5A , which is a schematic block diagram of PNVA  5000 , according to embodiments of the present invention. PNVA  5000  may comprise autotransformer  5002 , control unit  5001  and two STMSs  5007  and  5008 . The embodiment depicted in  FIG. 5A  demonstrates the use of two DTMSs connected at the secondary side of autotransformer  5002 . PNVA  5000  may receive single phase AC power at the distal end of a long electric cable (not shown) at its input port  5029  via input phase terminal  5026  and neutral input terminal  5027 , and may further be connected to the ground input terminal  5028 . Output port  5025  of PNVA  5000  comprises phase output terminal  5022 , neutral output terminal  5023  and ground output terminal  5024 . Ground output terminal  5024  may be connected directly to the input ground line. Output phase pin  5022  may be connected to one selectable winding of autotransformer  5002  via STMS  5007 , and output neutral pin  5023  may be connected to one selectable winding of autotransformer  5002  via STMS  5008 . The input phase line may be permanently connected to winding  5003  of autotransformer  5002 , and neutral input line may be permanently connected to winding  5021  of autotransformer  5002 . The selection of winding between  5003  to  5019  and between  5020  to  5021  may consider providing sufficient dynamic range for the regulation of voltages of the phase and neutral outputs. 
     Reference is made now also to  FIG. 5B , which is a schematic block diagram of PNVA  5000 ′, according to embodiments of the present invention. PNVA  5000 ′ may be similar or the same as PNVA  5000 , where the embodiment of  FIG. 5B  demonstrates use of a PNVA, such as PNVA  5000  when no ground line is connected at the input port  5029 , terminal  5028 . In such a case, controller  5001  may sense that the input ground connection is floating. Absent a reference ground voltage, controller  5001  may act according to the assumption that the phase voltage drop magnitude equals the neutral parasitic voltage. Accordingly, controller  5001  may set STMS  5007  to raise output phase voltage at terminal  5022  by half the difference between preset nominal phase-neutral voltage and the phase-neutral voltage measured at the input port  5029 , terminal  5026  to  5027  of PNVA  5000 ′, and may set STMS  5008  to be lowered by the same magnitude, thereby setting the output neutral voltage at terminal  5023  to as close as possible to a ground voltage level and setting the voltage difference between output phase terminal  5022  and output neutral terminal  5023  to the nominal voltage. 
     Reference is made now also to  FIG. 5C , which is a schematic block diagram of PNVA  5000 ′, according to embodiments of the present invention. PNVA  5000 ′ may be similar or the same as PNVA  5000 , of  FIG. 5D , differing from PNVA  5000  by having a local ground connection connected by ground line  5031  to ground input terminal  5027 . This embodiment is typical for power lines having only two wires, such as coaxial lines. 
     Reference is made now also to  FIG. 5D , which is a schematic block diagram of PNVA  5000 ″, according to embodiments of the present invention. PNVA  5000 ″ may be similar or the same as PNVA  5000 , where the embodiment of  FIG. 5C  demonstrates providing output regulated phase and neutral voltages to two output ports  5025  and  5032 , which may be connected to the secondary side via STMSs  5007  and  5008 . The connection of each of output phase terminal  5022  and  5029  to STMS  5007  may controllably be timed by switches  5035  and  5034 , respectively, to avoid start up of both outputs simultaneously and thereby to avoid too high inrush current. The timing of connection may be controlled by output timing control unit  5033 . In some embodiments, output timing control unit may be embodied as a module in control unit  5001 . 
     Reference is made now to  FIG. 6A , which is a schematic illustration of chain power system  600  comprising a central AC powering source  601 , central powering switch  604  and two serially connected single phase PNVAs, according to embodiments of the present invention. Reference is also made to  FIG. 6B , which is a graph depicting the source current during gradual connection of the active devices of serially connected PNVA s of  FIG. 6A , according to embodiments of the present invention. Chain  600  comprising two serially connections, right and left to the central powering switch or splitter  604 , may receive electric power from central utility AC supply  601  supplying AC power to adjacent LTE transmitter  626  and may provide AC power to remote PNVA  603  and to PNVA  605 . PNVA  603  may provide power to PNVA  602 , and PNVA  605  may provide power to PNVA  606 . Each of PNVAs  602 ,  603 ,  605  and  606  may provide regulated phase voltage and about zero voltage level to the ground of the neutral line to the active devices, which are, in the embodiment of  FIG. 6A , wireless transmitters  624 ,  625 ,  626 ,  627  and  628 , respectively, such as LTE standard wireless transmitters. The lines connecting between the PNVAs are long lines. If all of the active devices will be connected at once to the power source, the inrush current may cause high voltage drops on the long electric lines  608 , 611 , 614 , 617 , which in turn may cause difficulties in stabilizing the network and regulating the voltage levels. According to embodiments of the invention, the connection of the various active devices to the AS power line may be done gradually, so as to gradually raise the provided current and thereby decreases the peak current, increase the max total continuous current at the power source and enable PNVA system  600  to gradually regulate the voltages.  FIG. 6B  depicts the AC source current levels during the power-up of system  600 . First transmitter  626  is connected to the local AC power supply  601  via AC splitter/switch  604 . Its inrush current is represented by peak point  6002 . After settling time, the current stabilizes and sets at point  6003 . After a determined (or predetermined) transmitter  625  of PNVA  603  is connected, that causes inrush current to rise to peak point  6005  and then to settle at level  6006 . This process may continue by gradually connecting transmitter  624  via PNVA  602 , and then transmitter  627  via PNVA  605 , and finally transmitter  628  via PNVA  606 . At the end of the power-up process, the stabilized current sets at level point  6015 . During the power-up process, all of the PNVAs that are providing AC power to their associated transmitter may be required to dynamically operate their STMSs, in order to ensure the output phase and neutral voltages at their output ports are kept within nominal boundaries, as explained hereinabove. 
     In some embodiments, the progress of the power-up process may depend on signals transmitted from each of the currently powered active device back to previous PNVA in serial, or to a remote central control unit (not shown) to indicate that the current has already stabilized and the next step of connecting additional active device may take place. 
     While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.