High pressure trigger pulse closing device with capability to estimate critical reclosing time

Abstract

A system and method for determining an optimal time to perform a pulse test to determine whether a fault exists after a switch is opened to remove the fault so as not to destabilize the generator is provided. The method includes detecting a fault, opening a switch to remove the fault, determining an optimal time to perform a pulse test to determine whether a fault continues to exist after the switch is opened based on predetermined system data and parameters such that the pulse test is not performed too early that it may destabilize the generator, and performing the pulse test at the optimal time to determine whether the fault exists. Available system data and information, such as a priori knowledge or real-time dynamics, may be used to determine the optimal time. The method also determines a desired time to perform a reclosing operation if the fault does not exist.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 253,359, filed October 7, 2021, the entire disclosure of which is expressly incorporated by reference herein for all purposes.

[0002] The present invention relates generally to a system and method for determining the optimum time to perform a pulse test to determine if a fault is present in a circuit after a switch has been opened to remove the fault, to prevent generator destabilization, and to determine the optimum time to re-energize the circuit if no fault is present. [Background technology]

[0003] Electricity networks, often referred to as power systems, typically include a number of power plants with many generators, such as gas turbines, nuclear reactors, coal-fired generators, and hydroelectric dams. The power plants provide electricity at various medium voltages, which are stepped up by transformers to a high voltage AC signal and connected to a number of high voltage transmission lines that feed power to a number of substations, usually located in a geographical area, where the power is stepped down to medium voltages by transformers for distribution. The substations provide medium voltage power to a number of three-phase feeders, including three single-phase feeders that provide medium voltage to various distribution transformers and siding connections. A number of three-phase and single-phase sidings branch off from the feeders that provide medium voltage to various distribution transformers, where the voltage is stepped down to a lower voltage for distribution to loads, such as homes and businesses. The above types of power networks typically include switching devices, breakers, reclosers, interrupters, etc., that control the flow of power through the network.

[0004] Periodically, faults occur in power networks due to various factors, such as animals touching wires, lightning strikes, falling branches on power lines, vehicles hitting utility poles, etc. If such faults cause short circuits and increase the load on the network, the current flow from the substation can increase significantly along the fault path, e.g. many times higher than normal. This amount of current can significantly heat up and possibly melt the wires, and even cause mechanical damage to various components in the substation and the network. In many cases, such faults are not permanent or bolted faults, but temporary or intermittent faults, and the cause of the fault, e.g. a lightning strike, is removed shortly after the fault occurs and the distribution network starts working normally almost immediately.

[0005] Rapid fault clearing is widely accepted as one of the most effective techniques to improve or maintain the transient stability of a power system while at the same time limiting the let-through current that can damage equipment. Reclosing as soon as possible after the fault is initially cleared is effective in maintaining or restoring network stability by returning the circuit to its pre-fault configuration. Conventional reclosing is most effective only if the fault is cleared, otherwise the full fault current is reapplied every time a hard-reclose is attempted. Reclosing a permanent fault can cause or exacerbate network instability, especially in high-voltage networks where the available fault current can be tens of thousands of amperes. Such large available fault currents can also cause immediate or potential damage to power system equipment. The characteristically low network impedance of high-voltage networks can also cause the available fault current to increase rapidly, meaning that it can quickly reach damaging levels unless the fault current is interrupted very quickly.

[0006] To clear faults very quickly, fault interrupters such as reclosers are often provided with a switch that allows or prevents power flow downstream. Reclosers monitor current flow by detecting current and voltage in the feeder to look for problems in the network circuit, such as detecting faults. If a fault current is detected, the recloser opens accordingly and then closes after a short delay in the process of determining if the fault still exists. If a fault current flows while the recloser is in the closed state, the recloser opens immediately, and if a fault current is detected again or more than once during the subsequent switching operation, the recloser remains open, which may result in longer intervals between inspections.

[0007] Reclosing devices are known that use pulse testing techniques in which the switch contacts are opened and closed in a pulsed manner, the pulses typically being less than a current cycle so that the full fault current is not applied to the network while the recloser is testing to determine if the fault is still present. Pulse closing technologies have been successful in significantly reducing the fault current stress on the network equipment during recloser testing. However, the switching devices required to generate such short pulse durations are relatively complex and expensive. For example, those skilled in the art will appreciate that vacuum interrupters used to generate the pulse often use two magnetic actuators, one to close the contacts together and one to use the moving mass of the opening actuator to quickly open the contacts and reverse the direction of the closing actuator.

[0008] A triggered vacuum gap (TVG) device has been proposed as a no-moving-parts switching mechanism for pulse testing. A typical TVG device includes two stationary main electrodes disposed within a vacuum chamber, with a main vacuum gap defined between them. The TVG device also includes a trigger element, such as a trigger electrode, with a vacuum trigger gap between the trigger electrode and the corresponding main electrode. The trigger gap is designed with a length much shorter than the main vacuum gap so that its breakdown voltage is much lower than that of the main vacuum gap. To further reduce the breakdown voltage of the trigger gap, it can be bridged with an insulator, such as a ceramic. When a sufficiently high trigger voltage impulse is applied across the trigger gap to the main and trigger electrodes, the trigger gap breaks down. This breakdown across the trigger gap creates a plasma cloud that propagates into the main vacuum gap in a fraction of a millionth of a second, causing breakdown of the main vacuum gap. This state of the TVG device is the closed switch state. When current begins to flow through the TVG device, it continues to flow until the AC current signal on the electrodes passes through a zero crossing, at which point the plasma is quenched by the vacuum and the arc is extinguished. Because the plasma can be ignited in this vacuum chamber, the timing of when the TVG device conducts can be precisely controlled, i.e., on the order of microseconds. Furthermore, because there are no moving electrodes, precise mechanical actuation is not required.

[0009] TVG devices can be easily and accurately triggered at relatively low voltages of only a few kV across the main vacuum gap, so that the delay associated with the creation of the plasma cloud that effectively closes the switch can be tightly controlled to within a few microseconds of the desired point of pulse testing. Once the trigger gap conducts current, it can interrupt even large currents at the first line-frequency zero-crossing, resulting in a high withstand voltage between the main electrodes immediately after current interruption. Although this function is powerful, it is generally only used for pulsed power applications and not for power systems in synchronous closing applications. More specifically, TVG devices have the excellent ability to interrupt not only high frequency currents, but also line frequency currents at high frequency current zero-crossings. This function is important because high frequency currents are generated by the charging and discharging of stray capacitances and inductances during switching operations in power systems. Such high frequency transient currents usually decay very quickly and in most cases are not even noticed when a mechanical switch is performing a closing operation. However, in the case of TVG devices, the high frequency current zero-crossing can have the undesirable effect of premature extinguishing of the plasma arc during pulse testing. A TVG device is likely to interrupt one of several high frequency current zeros that occur within 100 microseconds of the device pulsing the current. Current interruption is a statistical event that depends on physical processes such as the vacuum arc, di / dt, and contact materials. If the plasma arc is extinguished by a high frequency current zero crossing, the TVG device must be re-triggered, but a high frequency current transient may occur again, causing a current zero crossing in the TVG current and interrupting the TVG current again.

[0010] If the TVG device can maintain current conduction through the plasma arc and the zero crossing of the high frequency current in a controlled manner, the TVG device will not cease conduction. A few hundred microseconds after triggering, the line frequency current in the TVG device will be high enough and the high frequency current will decay sufficiently to effectively eliminate the "early" current zero crossing. In other words, if the TVG device can maintain conduction through the zero crossing of the high frequency current for about 300 microseconds after triggering, then successful TVG device closure in a distribution or transmission system will be achieved.

[0011] After a transient fault in a high-voltage electrical network, a reclosing attempt that is too early or too late can impair the network's ability to return to a stable state, and the reclosing event itself is a system disturbance, so the timing and severity of the reclosing event can improve or harm the network dynamics. Reclosing restores the system to the pre-fault topology, but the post-fault topology (active lines, voltage magnitudes, generator angles, power flows) may differ from the pre-fault topology and may not be compatible. Trigger pulse closures are effective in reducing the severity of pre-reclosing fault testing and the reclosing itself, and they provide accurate point-on-wave testing and switching actions over a relatively short period of time, such as milliseconds or cycles. However, the optimal timing of the reclosing event in terms of its potential impact on network stability is typically over a long period of time, such as several seconds or tens of seconds, and is a unique characteristic of each network. Therefore, reclosing requires situational sensing of both the inherent dynamics of the network and the network operator's operations or protection to estimate the critical reclosing time and make trigger pulse checks and reclosing decisions accordingly.

[0012] Reclosing as soon as possible after the fault is initially cleared helps maintain or restore network stability by returning circuits to the pre-fault topology before spinning generators lose synchronization, before voltage and frequency variations affect loads, such as warm-load pick-up versus cold-load pick-up, and before the fault condition is picked up by other devices, such as protective relays. Rapid reclosing also reduces the risk that a secondary circuit outage may occur while the original faulted circuit is unavailable, and reduces the time that equipment may become overloaded after power flow is rerouted, both of which can lead to cascading trips. Summary of the Invention [Problem to be solved by the invention]

[0013] In some cases, however, unless special attention is paid to the timing of the reclosing scheme relative to the response of other network elements, rapid reclosing can destabilize a network that would otherwise move toward a new stable point. Also, timing the reclosing too early can result in the fault re-occurring after reclosing because the ionized air may not have enough time to clear from around the conductors. These possibilities are examples of critical components of the critical reclosing time. Just as the critical clearing time defines the time interval during which a fault must be cleared to prevent network instability, the critical reclosing time defines the time interval during which a reclosing can occur after a fault has been cleared (including ionization around the conductors) without the system becoming unstable. [Means for solving the problem]

[0014] A system and method are disclosed and described below for determining an optimal time to perform a pulse test to determine whether a fault exists after opening a switch to remove the fault so as not to destabilize the generator. The method includes the steps of detecting a fault, opening a switch to remove the fault, determining an optimal time to perform a pulse test to determine whether a fault continues to exist after opening the switch based on predetermined system data and parameters such that the pulse test is not performed too early that may destabilize the generator, and performing the pulse test at the optimal time to determine whether the fault exists. The determination of the optimal time can utilize available system data and information, such as a priori knowledge or real-time dynamics, including predetermined system parameters and their associated estimations of rotor angle, bus voltage angle, active and reactive power flows, and frequency of a remote generator. The method also determines a desired time to perform a reclosing operation if the fault does not exist.

[0015] Further features of the present disclosure will become apparent from the following description and claims, taken in conjunction with the accompanying drawings. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a block diagram of a pulse closing system including a pulse closing / reclosing device of a high voltage transmission network. [Diagram 2] FIG. 2 is a cross-sectional view of a TVG device that can be used in the pulse closing / reclosing device shown in FIG. [Diagram 3] 1 is a graph showing the effect of generator rotor angle on loss of network capacity due to a permanent fault without reclosing, with generator rotor angle on the horizontal axis and power on the vertical axis; [Figure 4] 1 is a graph showing the effect on generator rotor angle of a loss of network capacity due to a temporary fault, with the horizontal axis showing generator rotor angle and the vertical axis showing power, when the network capacity is fully restored as a result of reclosing the circuit. [Diagram 5]1 is a graph showing generator power on the vertical axis versus time on the horizontal axis, illustrating that a pulse check was performed too early, causing system instability. [Figure 6] 1 is a graph showing time on the horizontal axis and generator power on the vertical axis, illustrating that the system was stabilized by a pulse test. [Figure 7] 1 is a graph showing time on the horizontal axis and energy on the vertical axis, illustrating that a pulse check was performed too early, causing system instability. [Figure 8] 1 is a graph showing time on the horizontal axis and energy on the vertical axis, illustrating that the system was stabilized by a pulse test. [Figure 9] 1 is a graph showing the effect of reclosing on a transient fault, with time on the horizontal axis and energy on the vertical axis. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The following descriptions of disclosed embodiments of a system and method for determining an optimal time to perform a pulse test to determine whether a fault is present in a circuit after a switch is opened to remove the fault without causing the generator to become unstable, and for determining a desired time to re-energize the circuit if no fault is present, are merely exemplary in nature and are not intended to limit the disclosure, its application, or uses.

[0018] This disclosure proposes a system and method for determining the optimal time to perform a pulse check in anticipation of reclosing an opened switch to clear a fault based on the real-time dynamics of other network elements such as loads, generators, protection schemes, etc. The method enables pulse checks to prevent reignition of fault arcs due to the presence of persistent fault-causing elements such as tree branches or ionized air near a faulted conductor, prevent destabilization of rotating generators, minimize automatic load shedding, and keep distributed generation online.

[0019] The system employs pulse closing / reclosing devices that see the current and past dynamics of the local network circuits in which they are installed and are situationally aware of their own participation in clearing or switching events. However, the critical pulse check time may depend on the operating conditions of a network larger than the pulse closing / recloser can see with its own local sensors and controls. Thus, the critical pulse check time estimator must either pre-configure the pulse switchgear with a priori data on the larger system behavior under various contingencies, or how those contingencies are reflected in the dynamics of the pulse closing / recloser's local circuits (which the pulse closing / recloser itself monitors), and / or, to a lesser extent, rely on high-speed communication of system parameters from a wide area, such as generator rotor angles, phase shifters, active and reactive power flows (magnitude and direction), and frequency, unless the network stability is dependent on non-rotating generation. The rate of change or trajectory of these system parameters also provides a predictive timer for the critical pulse check interval estimator to calculate the time remaining before a reclosing attempt will be effective in preventing instability. The following assumes that the substation communications equipment has sufficient bandwidth and data rates to exchange system-wide measurement and control / status information to each recloser.

[0020] When a pulse closing / reclosing device is pre-configured to determine the timing of pulse checks based on its own local sensors and a priori knowledge of the larger system behavior, it monitors the local network and infers stability considerations for its local area: it estimates remote generator rotor angles, bus voltage angles, real and reactive power flows (magnitude and direction), and frequency based on the dynamics of its local network and pre-calculated relationships between local areas.

[0021] When real-time system data is available both locally and remotely, the pulse closure / recloser can be configured to rely on the rapid exchange of remote system parameters such as generator rotor angle, bus voltage angle, real and reactive power flows (magnitude and direction), and frequency, available, for example, from phase measurement devices already widely deployed in power networks. The rate of change of these measured system parameters initiates a countdown timer to estimate the time remaining before a pulse check attempt will have an effect in preventing instability. The minimum value of this timer, updated in real time, sets the critical pulse check interval time.

[0022] If the pulse check during the critical pulse check interval indicates sufficient conditions for reclosure, then reclosure may occur within the critical interval. Other permissive conditions may also be applied to enforce or disable the reclosure action depending on the desired system operation apart from stability issues. Sufficient conditions for reclosure after a pulse check include that no fault is present, that the critical reclosure interval time has not been exceeded, and that the observed real-time system parameter (local and / or remote) response to the previous pulse check indicates that restoring the system to its pre-fault condition by reclosure will not compromise stability.

[0023] 1 is a block diagram of a pulse closure system 10 for a high voltage transmission network, illustrating components that may be used to determine the optimal time to perform a pulse test to determine whether a fault is present in the circuit after a switch is opened to clear the fault, as described above, without destabilizing the generator. The system 10 includes three high voltage transmission lines 12, 14, 16, each on phase A, B, and C, receiving high voltage power from a generator 18, such as a turbine. A pulse closure / recloser 20 of the type described above is coupled to the high voltage transmission lines 12, 14, 16 and includes a switch assembly 22 having a reclosing switch 24, such as a vacuum circuit breaker, and a pulse check TVG device 26 on the high voltage transmission line 12, a switch assembly 28 having a reclosing switch 30 and a pulse check TVG device 32 on the high voltage transmission line 14, and a switch assembly 34 having a reclosing switch 36 and a pulse check TVG device 38 on the high voltage transmission line 16. The pulse closure / recloser system 20 also includes an actuator control 40 that opens and closes the reclose switches 24, 30, 36 during fault clearing and reclosing operations, and a trigger control 42 that generates plasma arcs in the TVG devices 26, 32, 38.

[0024] A voltage sensor 48 is coupled to the high voltage transmission lines 12, 14 on the transmission side of the pulse closing / reclosing device 20, and a voltage sensor 50 is coupled to the high voltage transmission lines 14, 16 on the transmission side of the pulse closing / reclosing device 20 to provide voltage measurements on the high voltage transmission lines. A voltage monitor 52 receives voltage measurements from the voltage sensors 48 and 50. A current sensor 54 provides a current measurement on the high voltage transmission line 12, a current sensor 56 provides a current measurement on the high voltage transmission line 14, and a current sensor 58 provides a current measurement on the high voltage transmission line 16. A current monitor 60 receives current measurements from the current sensors 54, 56, 58. Voltage monitoring in this configuration uses line voltage measurements from the voltage sensors 48 and 50. In an alternative embodiment, the voltage measurements may be line-to-ground voltage measurements requiring three voltage sensors. The signal processor 62 receives voltage and current signals from the monitors 52 and 60, processes the signals, and provides the processed signals to a fault detection and response logic controller 64. The fault detection and response logic controller 64 commands the actuator control 40 and trigger control 42 to control the reclose switches 24, 30, 36 and TVG devices 26, 32, 38 consistent with the description herein. The signal processor 62 communicates with a communication device 66 to receive voltage and current signals, status signals, etc. from other components in the network.

[0025] While the TVG devices 26, 32, 38 may be any TVG device suitable for the purposes described herein, one representative example is shown in FIG. 2, which is a cross-sectional view of an exemplary embodiment of an electrically triggered TVG device 70. The TVG device 70 includes a vacuum enclosure 72 having a cylindrical insulator 74 and conductive end plates 76, 78. In the exemplary embodiment, the vacuum enclosure 72 is 10 -6 mbar or more, 10 -3The TVG device 70 is sealed at a vacuum pressure of less than mbar. The TVG device 70 also includes a pair of opposing conductive electrodes 82, 84 defining a trigger gap 86 therebetween. Electrode 82 is connected to a stem 88 that extends through a sealed hole in the end plate 76, and electrode 84 is connected to a stem 90 that extends through a sealed hole in the end plate 78, by which the TVG device 70 is connected to other switching elements. The inner surface of the insulator 74 is protected from conductive deposits by a cylindrical metal vapor shield 92.

[0026] The pulse trigger circuit 94 generates a sufficient high voltage / low current pulse across the trigger gap 86 to initiate the plasma arc, which is then maintained for hundreds of microseconds by a low voltage / high current pulse. In an exemplary embodiment, the duration of the initial high voltage / low current pulse is a few microseconds, and the duration of the low voltage / high current pulse is a few hundred microseconds. The geometry of the arrangement between the trigger electrode and its target surface focuses the initial pulse to an extremely small area of ​​the electrode 82, expanding the power density of the trigger pulse on the electrode surface, and the electrical trigger energy transferred to the electrode results in near instantaneous vaporization of the electrode material and transition of the vapor into a high density plasma cloud 96 that expands as a plasma plume toward the electrode 74, resulting in electrical breakdown of the gap 86 and the creation of a vacuum arc between the electrodes 82 and 84. The breakdown of the gap occurs based on the magnitude of the voltage difference between the electrodes 82 and 84 after the plasma cloud 96 is created. The electrode material can be selected based on its triggering capability, i.e., ablation capability under the laser pulse, along with its vacuum arc interruption capability and dielectric strength in vacuum.

[0027] Below is further analysis to determine the optimal time to perform fast pulse testing without destabilizing the generator.

[0028] Figure 3 is a graph showing the effect of generator rotor angle on loss of network capacity due to a permanent fault, with generator rotor angle on the horizontal axis and power on the vertical axis. Graph line 100 is the generator rotor angle before the fault, graph line 102 is the generator rotor angle during the fault, and graph line 104 is the generator rotor angle after the fault. The generator rotor angle is calculated using the equal area method and is obtained from the oscillation equation:

[0029]

number

[0030] Here, M is the angular momentum of the generator, δ is the phase difference angle between the rotor and stator of the generator, and ΔP is the change in power transmission capacity after a fault occurs. When a fault occurs, the generator 18 rotates at a steady-state angle δ 0 from angle δ 1 until the fault is cleared. The generator 18 rotates at an angle δ where the energy gained in the area 106 is absorbed in the area 108 and the areas 106 and 108 are equal. 2 Further analysis reveals that the angle δ can be reduced to a value that can be cancelled by the reconstructed system without destabilizing it. 1 A critical clearance time is obtained that maintains the maximum clearance time. As the clearance time can be extended to a maximum, the generator rotor angle fluctuations are maximized, just as as the clearance time is shortened below the critical value, the generator fluctuations decrease.

[0031] FIG. 4 is a graph for the case of a temporary fault shown in FIG. 3. In this case, the fault occurs at an angle δ 1 The fault is cleared at an angle of δ 2’ The system operates in a time-limited post-fault mode until the capacity is restored at δ. 3 , the areas 106, 108, 110 are equal, and the angle δ 1 from angle δ 3 The total displacement up to is the angle δ 1 from angle δ 2It becomes smaller than the total displacement up to that point. Intuitively, when the removal time becomes shorter (the area 106 becomes smaller) and the capacity before the fault recovers earlier (when the area 108 becomes smaller), the impact of the fault transient event is further mitigated (the area 110 becomes smaller).

[0032] When the system inertia decreases, it can be deduced from the swing equation that the critical clearing time should also decrease. However, by reviewing the protection and control implementation methods to forcibly shorten the clearing time, it may be possible to suppress the impact of the fault, and by restoring the non-faulty wires earlier, the system can recover itself more quickly.

[0033] Figure 5 is a graph showing time on the horizontal axis and generator power on the vertical axis, indicating that the system became unstable in the pulse test at 1.31 seconds. Figure 6 is the same graph showing that the system did not become unstable in the pulse test at 1.38 seconds. Here, the graph line 112 is Pelec (power), the graph line 114 is Pmech (mechanical power), and the fault occurs at the 1-second mark. In Figure 5, the pulse test gives sufficient perturbation to generator 18 and finally operates it offline (trips). In Figure 6, the timing of the pulse test is adjusted so that a fault occurs in the network without generator 18 becoming unstable due to the pulse test. According to the swing equation, generator 18 is decelerating when Pelec > Pmech, and when Pelec < Pmech, generator 18 is accelerating by accessing the local generator parameters sufficiently. Through the swing equation, the response of generator 18 to faults and reclosing is predictable.

[0034] FIG. 7 shows a graph with time on the horizontal axis and energy on the vertical axis, which shows that the system was destabilized at the pulse test at 1.31 seconds, and FIG. 8 shows the same graph with the pulse test at 1.38 seconds, which shows that the system was not destabilized. Here, the graph line 120 is the cumulative imbalance (Pmech-Pelec), the areas 122, 124, 126 show the acceleration energy, and the areas 128, 130 show the deceleration energy. If the predicted generator characteristics give an overall energy balance (equal area criterion), the generator will remain online, otherwise it will not be online. This is evident from FIGS. 7 and 8, which show the black energy balance with the acceleration areas 122, 124, 126 and the deceleration areas 128, 130. In the stabilized case, the final net unbalance energy in the system becomes zero at time t about 2.1 seconds, after which the system remains stable, albeit with some fluctuations around the new operating point, and the generator 18 remains online. In the destabilized case, the energy balance continues to accumulate in the acceleration direction. After the time t inflection at approximately 1.7 seconds, the generator becomes unable to recover.

[0035] Figure 9 shows the effect of reclosing after pulsing the line to ensure that the fault is temporary. This scenario is obviously less disruptive to the system than a reclosing operation, but the question is whether the balance of the region shown in Figure 4 can be achieved. The line is inspected at time t = 1.3 s and reenergized immediately after being found to be fault-free. The restoration of the line causes a gradual increase in deceleration energy, consistent with the predictions of Figure 4, and the system has recovered by time t = 1.4 s. Fluctuations continue, but eventually settle down. It should be noted that inspecting and reenergizing the line, although effective in recovering the system more quickly, still changes the system dynamics, which may cause local voltage excursions, which themselves may cause the generator 18 to trip offline. Therefore, the reenergization must be determined with this possibility in mind, either by choosing the reclose tie appropriately or by adjusting the protection parameters to prevent their exceedance.

[0036] The foregoing disclosure discloses and describes merely exemplary embodiments of the present invention. Those skilled in the art will readily recognize from the above description and the accompanying drawings and claims that various changes, modifications, and variations can be made without departing from the spirit and scope of the present disclosure, as defined in the following claims. [Explanation of symbols]

[0037] 10 Pulse Closure System 12, 14, 16 High voltage power lines 18. Generator 20 Pulse Closing / Reclosing Device 22, 28, 34 Switch Assembly 24, 30, 36 Reclosing switch 26, 32, 38 Pulse inspection TVG equipment 40 Actuator Control 42 Trigger Control 48, 50 Voltage sensor 52 Voltage Monitor 54, 56, 58 Current sensors 60 Current Monitor 62 Signal Processor 64 Fault detection and response logic controller 66 Communication Equipment 70 TVG equipment 72 Vacuum enclosure 74 Cylindrical Insulator 76, 78 Conductive end plate 82, 84 conductive electrode 86 Trigger Gap 88, 90 stem 92 Metal Vapor Shield 94 Pulse Trigger Circuit 96 Plasma Cloud 100, 102, 104, 112, 114, 120 Graph lines 106, 108, 110 areas 122, 124, 126 (acceleration) area 128, 130 (deceleration) area

Claims

1. 1. A method for testing for the continued presence of a fault in an electric power system and preventing generator instability, comprising: detecting the fault; opening a switch to clear the fault; determining an optimal time to perform a pulse test to determine whether the fault continues to exist after the switch is opened based on predetermined system data and parameters, such that the pulse test is not performed early enough that the generator may become unstable; performing the pulse test at the optimal time to determine whether or not the fault exists; performing a reclosing operation at a desired time if the fault is not present; wherein determining the optimal time to perform the pulse test comprises determining the time for the pulse test based on a priori knowledge of system behavior and based on estimating electrical characteristics from predetermined system parameters and their relationships.

2. The method described in claim 1, wherein the electrical characteristics include a rotor angle of a remote generator, a bus voltage angle, active and reactive power flows, and frequency.

3. The method of claim 1 , wherein determining the optimal time to perform the pulse test comprises determining the time of the pulse test in real time.

4. 4. The method of claim 3, wherein determining the optimal time to perform the pulse check includes detecting a remote generator rotor angle, a bus voltage angle, active and reactive power flows, and frequency.

5. 2. The method of claim 1, further comprising the step of preventing reclosing by the switch if the pulse test indicates that the fault still exists.

6. The method of claim 1 , wherein the pulse testing is performed in a vacuum trigger gap (TVG) device.

7. The method of claim 1 , wherein the power system is a high voltage transmission system.

8. 1. A method for testing for the continued presence of a fault in a high voltage electrical power transmission system and preventing generator instability, comprising: detecting the fault; opening a switch to clear the fault; determining an optimal time to perform a pulse test to determine whether the fault continues to exist after the switch is opened based on predetermined system data and parameters, such that the pulse test is not performed early enough that the generator may become unstable; conducting said pulse test using a vacuum trigger gap (TVG) device at said optimum time to determine whether said fault exists; preventing reclosing by the switch if the pulse test indicates that the fault is still present, and allowing reclosing by the switch if the pulse test indicates that the fault is not present. wherein determining the optimal time to perform the pulse test comprises determining the time of the pulse test based on a priori knowledge of system behavior including estimating electrical characteristics from predetermined system parameters and their relationships.

9. The method described in claim 8, wherein the electrical characteristics include a rotor angle of a remote generator, a bus voltage angle, active and reactive power flows, and frequency.

10. 9. The method of claim 8, wherein determining the optimal time to perform the pulse check includes detecting a rotor angle, a bus voltage angle, active and reactive power flows, and frequency of a remote generator, and determining the time for the pulse check in real time.

11. 1. A system for detecting the continued presence of a fault in an electric power system and preventing generator instability, comprising: means for detecting said fault; means for opening a switch to clear said fault; means for determining an optimum time to perform a pulse test to determine whether the fault continues to exist after the switch is opened based on predetermined system data and parameters, such that the pulse test is not performed too early that the generator may become unstable; means for performing the pulse test at the optimum time and determining whether or not the fault exists; means for reclosing the circuit at a desired time if said fault does not exist; wherein the means for determining the optimum time for performing the pulse test estimates electrical characteristics from predetermined system parameters and their relationships.

12. 12. The system of claim 11, wherein the means for determining an optimal time to perform the pulse check determines the time of the pulse check based on a priori knowledge of system behavior.

13. The system of claim 11, wherein the electrical characteristics include a remote generator rotor angle, a bus voltage angle, active and reactive power flows, and frequency.

14. 12. The system of claim 11, wherein the means for determining an optimal time to perform the pulse test determines the time for the pulse test in real time.

15. 12. The system of claim 11, wherein the means for determining the optimum time to perform the pulse check detects a remote generator rotor angle, a bus voltage angle, active and reactive power flows, and frequency.

16. 12. The system of claim 11, further comprising means for preventing reclosing by said switch if said pulse check indicates that said fault still exists.

17. The system of claim 11 , wherein the pulse testing is performed in a vacuum trigger gap (TVG) device.

18. The system of claim 11 , wherein the power system is a high voltage transmission system.

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