INJECTION UNIT LEVEL BYPASS
In an impedance injection module in which multiple converter units are placed in series to realize a high level of impedance injection, switches, preferably vacuum interrupters, are connected to short the input and the output terminals of each individual unit. Unlike the fault-protecting switch across the entire module, these switches at the individual converter unit level serve several purposes, overload and surge protection of a unit, insertion loss minimization of an idle unit when the required impedance injection is small, and electrically removing a defective injection unit from the power flow to increase the overall reliability of the impedance injection module in the face of the failure of one unit or a few units. For more rapid response, particularly in response to faults, the vacuum interrupter at the unit level may be accompanied by an SCR switch in parallel with it.
1 . A system for impedance injection into a power transmission line, comprising:
one or more impedance injection modules (IIMs), each IIM having a plurality of transformer-less flexible alternating current transmission system (TL-FACTS) based impedance injection units (IIUs) connected in series, to collectively inject impedance into the power transmission line, wherein each TL-FACTS based IIU comprises a switching device that, when closed, deactivates the TL-FACTS based IIU from the plurality of TL-FACTS based IIUs; and
a protection switch connected in series with the power transmission line and configured to bypass the plurality of TL-FACTS based IIUs when closed.
2 . The system of claim 1 , wherein each TL-FACTS based IIU further comprises electronic switches connected in parallel with the switching device to create a net switching speed faster than a switching speed of the switching device.
3 . The system of claim 2 , wherein each TL-FACTS based IIU further comprises:
a plurality of FACTS devices; and
a direct current (DC) power source connected to the FACTS devices;
wherein the DC power source provides energy to the power transmission line and is controlled by the FACTS devices to create an injected impedance.
4 . The system of claim 2 , wherein each TL-FACTS based IIU further comprises:
a plurality of FACTS devices; and
a direct current (DC) power source connected to the FACTS devices;
wherein the DC power source is charged by current flow through diodes protecting the FACTS devices when impedance injection is not required.
5 . The system of claim 4 , wherein each TL-FACTS based IIU further comprises a master controller configured to control the switching device, the electronic switches, the plurality of FACTS devices, and charging rate of the DC power source.
6 . The system of claim 5 , wherein to control the charging rate of the DC power source, the master controller is configured to change states of the electronic switches from open to conducting.
7 . The system of claim 1 , wherein to bypass the plurality of TL-FACTS based IIUs when closed, the protection switch is configured to short impedance injection terminals connected in series across the power transmission line.
8 . The system of claim 1 , wherein the switching device is a vacuum interrupter and the protection switch is a high-voltage vacuum interrupter.
9 . The system of claim 2 , wherein the electronic switches are back-to-back silicon-controlled rectifiers.
10 . The system of claim 1 , wherein the protection switch is rated for higher current and voltage than the switching device.
11 . An impedance injection module, comprising:
a plurality of transformer-less flexible alternating current transmission system (TL-FACTS) based impedance injection units (IIUs) connected in series, to collectively inject impedance into a power transmission line, wherein each TL-FACTS based IIU comprises a switching device that, when closed, deactivates the TL-FACTS based IIU from the plurality of TL-FACTS based IIUs;
wherein the plurality of TL-FACTS based IIUs are bypassed when a protection switch connected in series with the power transmission line is closed.
12 . The impedance injection module of claim 11 , wherein each TL-FACTS based IIU further comprises electronic switches connected in parallel with the switching device to create a net switching speed faster than a switching speed of the switching device.
13 . The impedance injection module of claim 12 , wherein each TL-FACTS based IIU further comprises:
a plurality of FACTS devices; and
a direct current (DC) power source connected to the FACTS devices;
wherein the DC power source provides energy to the power transmission line and is controlled by the FACTS devices to create an injected impedance.
14 . The impedance injection module of claim 12 , wherein each TL-FACTS based IIU further comprises:
a plurality of FACTS devices; and
a direct current (DC) power source connected to the FACTS devices;
wherein the DC power source is charged by current flow through diodes protecting the FACTS devices when impedance injection is not required.
15 . The impedance injection module of claim 14 , wherein each TL-FACTS based IIU further comprises a master controller configured to control the switching device, the electronic switches, the plurality of FACTS devices, and charging rate of the DC power source.
16 . The impedance injection module of claim 15 , wherein to control the charging rate of the DC power source, the master controller is configured to change states of the electronic switches from open to conducting.
17 . The impedance injection module of claim 11 , wherein to bypass the plurality of TL-FACTS based IIUs when closed, the protection switch is configured to short impedance injection terminals connected in series across the power transmission line.
18 . The impedance injection module of claim 11 , wherein the switching device is a vacuum interrupter and the protection switch is a high-voltage vacuum interrupter.
19 . The impedance injection module of claim 12 , wherein the electronic switches are back-to-back silicon-controlled rectifiers.
20 . The impedance injection module of claim 11 , wherein the protection switch is rated for higher current and voltage than the switching device.