Distributed impedance injection module for mitigation of the Ferranti effect
Disclosed is a method for reducing the variation in voltage, due to Ferranti effect, using the impedance injection capability of distributed impedance injection modules. The Ferranti effect is an increase in voltage occurring at the receiving end of a long transmission line in comparison to the voltage at the sending end. This effect is more pronounced on longer lies and underground lines when the high-voltage power lines are energized with a very low load, when there is a change from a high load to a very light load, or the load is disconnected from the high-voltage power lines of the power grid. This effect creates a problem for voltage control at the distribution end of the power grid.
1. A method of reducing or eliminating a Ferranti effect in a high voltage transmission line comprising:
coupling impedance/voltage injection modules to the high voltage transmission line
at spaced apart locations along the high voltage transmission line, the impedance/voltage injection modules each being powered from the high voltage transmission line and having a high voltage transmission line current sensing capability, an impedance/voltage injection capability and a communication capability; and
using at least a subset of the impedance/voltage injection modules, sensing current in the high voltage transmission line; and
when the high voltage transmission line current indicates that a high voltage transmission line load at a receiving end of the high voltage transmission line is low or zero, injecting an impedance/voltage onto the high voltage transmission line at spaced apart locations along the high voltage transmission line to collectively reduce or cancel a voltage generated by a current charging a line capacitance passing through a line impedance.
2. The method of claim 1 wherein all impedance/voltage injection modules are used to inject the impedance/voltage onto the high voltage transmission line to reduce or cancel the voltage generated by the current charging the line capacitance passing through the line impedance when the high voltage transmission line current indicates that the high voltage transmission line load at a receiving end of the transmission line is low or zero.
3. The method of claim 1 wherein the at least a subset of the impedance/voltage injection modules sense the current in the high voltage transmission line and automatically inject the impedance/voltage onto the high voltage transmission line at spaced apart locations along the high voltage transmission line to collectively reduce or cancel the voltage generated by the current charging the line capacitance passing through the line impedance when the current in the high voltage transmission line indicates that the high voltage transmission line load at the receiving end of the high voltage transmission line is low or zero.
4. The method of claim 3 further comprising receiving information relative to the voltage on the high voltage transmission line at the receiving end of the high voltage transmission line and adjusting the injection of an impedance/voltage onto the high voltage transmission line at spaced apart locations along the high voltage transmission line to further control the voltage at the receiving end of the high voltage transmission line.
5. A method of reducing or eliminating a Ferranti effect in a high voltage transmission line comprising:
identifying a low current in the high voltage transmission line using a current sense device within at least a distributed impedance/voltage injection module coupled to the high voltage transmission line;
determining an increase in line voltage, due to the Ferranti effect, at a load or substation end due to the low current in the high voltage transmission line;
injecting a voltage using at least a selected number of distributed impedance/voltage injection modules to compensate for the increase in line voltage at the load or substation end;
thereby correcting the Ferranti effect on the high voltage transmission line.
6. The method of claim 5 , wherein the distributed impedance/voltage injection modules are powered from a power drawn from the high voltage transmission line.
7. The method of claim 5 , wherein the distributed impedance/voltage injection modules are suspended from the high voltage transmission line and are at a line potential of the transmission line.
8. The method of claim 5 , wherein the determined increase in line voltage at the load end of the line due to the Ferranti effect is corrected by a cumulative incremental distributed voltage injection by the distributed impedance/voltage injection modules coupled to the high voltage transmission line.
9. A system for controlling a voltage increase in a high voltage transmission line due to a Ferranti effect, the system comprising:
a plurality of distributed impedance/voltage injection modules coupled to the high voltage transmission line;
a line current sensing circuit associated with each impedance/voltage injection module;
an impedance/voltage injection circuit associated with each impedance/voltage injection module;
a voltage sensing and comparison capability at a load/substation end of the high voltage transmission line; and
a communication channel from the load/substation end of the high voltage transmission line to the distributed impedance/voltage injection modules for transferring information regarding a voltage sensed at the load/substation end of the high voltage transmission line;
wherein when a low current is sensed by the plurality of distributed impedance injection modules and an intimation of over voltage is received over the communication channel, each of the plurality of impedance/voltage injection modules generate and inject an incremental voltage on to the high voltage transmission line in a manner that a cumulative injected voltage from the plurality of impedance/voltage injection modules is sufficient to reduce or overcome the increase in voltage due to the Ferranti effect at the load/substation end of the high voltage transmission line.
10. The system of claim 9 , wherein a voltage correction is by equal distributed incremental voltage by each of the plurality of impedance/voltage injection modules.
11. The method of claim 1 , wherein the communication capability is any one of a wireless communication capability, a wire line communication capability or a power line communication capability.
12. A method of reducing or eliminating a Ferranti effect in a high voltage transmission line comprising:
coupling a plurality of impedance/voltage injection modules to the high voltage transmission line, the impedance/voltage injection modules each being powered from the high voltage transmission line and having an impedance/voltage injection capability and a communication capability; and
using at least a current sensing capability available on the high voltage transmission line, sensing a current in the high voltage transmission line; and
when the high voltage transmission line current indicates that a high voltage transmission line load at a receiving end of the high voltage transmission line is low or zero, injecting an impedance/voltage onto the high voltage transmission line using the impedance/voltage injection modules to collectively reduce or cancel a voltage generated by a current charging a line capacitance passing through a line impedance.
13. A system for controlling a voltage increase in a high voltage transmission line due to a Ferranti effect, the system comprising:
a plurality of distributed impedance/voltage injection modules coupled to the high voltage transmission line;
a line current sensing capability coupled to the high voltage transmission line and communicably linked to the impedance/voltage injection modules;
a voltage sensing and comparison capability at a load/substation end of the high voltage transmission line; and
a communication channel from the load/substation end of the high voltage transmission line to the distributed impedance/voltage injection modules for transferring information regarding a voltage sensed at the load/substation end of the high voltage transmission line;
wherein when a low current is sensed by the line current sensing capability and an intimation of over voltage is received over the communication channel, each of a subset of the plurality of impedance/voltage injection modules generate and inject an incremental voltage on to the high voltage transmission line in a manner that a cumulative injected voltage from the plurality of impedance/voltage injection modules is sufficient to reduce or overcome the increase in voltage due to the Ferranti effect at the load/substation end of the high voltage transmission line.