Medium voltage inrush current regulation and interconnection control system and method
A medium voltage inrush current (MVIC) regulator and interconnection control system for interposing between a distributed power generation facility and a utility grid. The facility has a designated generator step-up (GSU) transformer and is connected to the utility grid at a point of interconnect. The system includes a pre-insertion impedance injection transformer, a low voltage first switch connected between the pre-insertion transformer and secondary coils of the designated GSU transformer, a medium voltage second switch connected inline between the pre-insertion transformer and primary coils of the designated GSU transformer, and a controller. In response to restoration of the utility grid following a loss-of-grid event, the controller opens and closes the first and second switches according to an automated pre-energization switching sequence such that magnetic flux in the designated GSU transformer occurs at a reduced rate, thereby reducing inrush of current and undesirable power quality phenomena.
1. A method of reducing inrush current using a medium voltage inrush current regulator and interconnection control system interposed between a distributed power generation facility, having a designated generator step-up transformer, and a utility grid, the distributed power generation facility being connected to the utility grid at a point of interconnect, the regulator and interconnection control system having a pre-insertion impedance injection transformer, a low voltage first switch connected between the pre-insertion impedance injection transformer and secondary coils of the designated generator step-up transformer, and a medium voltage second switch connected inline between the pre-insertion impedance injection transformer and primary coils of the designated generator step-up transformer, the method comprising the steps of:
(a) opening and closing the first and second switches according to an automated pre-energization switching sequence in response to restoration of the utility grid following a loss-of-grid event such that magnetic flux in the designated generator step-up transformer occurs at a reduced rate, thereby reducing inrush of current and undesirable power quality phenomena;
(c) wherein the automated pre-energization switching sequence comprises:
(i) closing the low voltage switch, starting at a first predetermined period of time after initial energization of the utility grid at the point of interconnect, to energize the secondary coil of the designated transformer;
(ii) then, after a second predetermined period of time, closing the medium voltage switch to cause the designated transformer to be connected in parallel to the pre-insertion impedance injection transformer to provide full distribution voltage to the designated transformer; and
(iii) then, after a third predetermined period of time, opening the low voltage switch to remove the pre-insertion impedance injection transformer from the parallel circuit.
2. The method of claim 1 , wherein ensuring that the first and second switches are open includes opening the first and second switches before the initial energization of the utility grid at the point of interconnect.
3. The method of claim 2 , wherein the regulator and interconnection control system includes one or more metering relay, and wherein execution of the automated pre-energization switching sequence is contingent upon input received from the one or more metering relay.
4. The method of claim 2 , wherein the regulator and interconnection control system includes one or more protective relay, and wherein execution of the automated pre-energization switching sequence is contingent upon input received from the one or more protective relay.
5. The method of claim 2 , wherein the regulator and interconnection control system includes an uninterruptible power supply and a battery, and wherein the automated pre-energization switching sequence is carried out using power provided by the uninterruptible power supply and battery.
6. The method of claim 5 , wherein execution of the automated pre-energization switching sequence is contingent upon input received from the uninterruptible power supply and battery.
7. The method of claim 1 , wherein the first predetermined period of time has a magnitude designed to ensure that the grid is stable and the designated transformer and the elements of the system are available to operate.
8. The method of claim 7 , wherein the first predetermined period of time is in the range of 3-15 seconds, inclusive.
9. The method of claim 8 , wherein the first predetermined period of time is in the range of 5-10 seconds, inclusive.
10. The method of claim 1 , wherein the second predetermined period of time has a magnitude designed to ensure that oscillation is reduced sufficiently relative to steady state.
11. The method of claim 10 , wherein the second predetermined period of time is in the range of 5-15 seconds, inclusive.
12. The method of claim 11 , wherein the second predetermined period of time is in the range of 10-12 seconds, inclusive.
13. The method of claim 10 , wherein the magnitude is designed to ensure that oscillation is reduced to within 2% of steady state.
14. The method of claim 1 , wherein the third predetermined period of time has a magnitude designed to ensure that the voltage grid is stable and the designated transformer and the elements of the system are available to operate.
15. The method of claim 14 , wherein the third predetermined period of time is in the range of 1-5 seconds, inclusive.
16. The method of claim 15 , wherein the third predetermined period of time is in the range of 1.0-2.5 seconds, inclusive.
17. The method of claim 1 , further comprising a step of customizing a magnitude of one or more of the first, second, and third predetermined periods of time based on specific characteristics of the photovoltaic power station where the system is installed.
18. The method of claim 1 , further comprising a step of displaying, via a user interface, real-time status information during, and based upon, the automated pre-energization switching sequence.
19. A method of reducing inrush current using a medium voltage inrush current regulator and interconnection control system interposed between a distributed power generation facility, having a designated generator step-up transformer, and a utility grid, the distributed power generation facility being connected to the utility grid at a point of interconnect, the regulator and interconnection control system having a pre-insertion impedance injection transformer, a low voltage first switch connected between the pre-insertion impedance injection transformer and secondary coils of the designated generator step-up transformer, and a medium voltage second switch connected inline between the pre-insertion impedance injection transformer and primary coils of the designated generator step-up transformer, the method comprising the steps of:
(a) following a loss-of-grid event, ensuring that the first and second switches are open;
(b) in response to restoration of the utility grid following the loss-of-grid event, opening and closing the first and second switches according to an automated pre-energization switching sequence such that magnetic flux in the designated generator step-up transformer occurs at a reduced rate, thereby reducing inrush of current and undesirable power quality phenomena;
(c) communicating, via a wireless communication link, with real-time operator interface software; and
(d) providing, via the real-time operator interface software, a remote operator with the capability to adjust parameters and timing sequence settings without physically going on site, including providing the remote operator with the ability to remotely issue a command to trigger the automated pre-energization switching sequence or to clear a trip event prior to initiating the automated pre-energization switching sequence.
20. A method of reducing inrush current using a medium voltage inrush current regulator and interconnection control system interposed between a distributed power generation facility, having a designated generator step-up transformer, and a utility grid, the distributed power generation facility being connected to the utility grid at a point of interconnect, the regulator and interconnection control system having a pre-insertion impedance injection transformer, a low voltage first switch connected between the pre-insertion impedance injection transformer and secondary coils of the designated generator step-up transformer, and a medium voltage second switch connected inline between the pre-insertion impedance injection transformer and primary coils of the designated generator step-up transformer, the method comprising the steps of:
(a) following a loss-of-grid event, ensuring that the first and second switches are open;
(b) in response to restoration of the utility grid following the loss-of-grid event, opening and closing the first and second switches according to an automated pre-energization switching sequence such that magnetic flux in the designated generator step-up transformer occurs at a reduced rate, thereby reducing inrush of current and undesirable power quality phenomena;
(c) housing the pre-insertion impedance injection transformer, the first and second switches, and a user interface in a primary voltage cabinet, wherein the pre-insertion impedance injection transformer, the first and second switches, and the user interface are part of a self-contained assembly; and
(d) housing the user interface is housed in a side compartment, of the primary voltage cabinet, that is separated from the rest of an interior of the primary voltage cabinet but is accessible by an exterior door.