150 is shown as a single element, in some implementations, each switch device 230_1, 230_2, 230_3, 230_4 has a dedicated local controller that controls the operations of that switch device. In these implementations, the spot network 201 includes four instances of the controller 150, and each instance of the controller is associated with one switch device. Each switch device 230_1, 230_2, 230_3, 230_4 may be, for example, a network protector. In implementations in which the switch devices 230_1, 230_2, 230_3, 230_4 are network protectors, each network protector may have a dedicated local controller.

FIG. 3 is a block diagram of a power system 300 that includes an area network 301. The area network 301 includes redundant feeders 304 (only one of which is labeled), switch devices 130 (each of which may be a network protector), and transformers 342 that provide power to the loads 103. The area network 301 may include tens of redundant feeders 304 and switch devices 130, and the loads 103 may include tens, hundreds, or thousands of loads. The switch devices 130 are controlled by the controller 150. Although the controller 150 is shown as a single element, in some implementations, each switch device 130 has a dedicated local controller.

FIGS. 1, 2, and 3 are provided as examples, and the controller 150 may be used with distribution networks having other configurations. For example, the distribution network 201 may have fewer or more than four parallel low-voltage feeders.

FIG. 4 is a block diagram of a controller 450 in a power system 400 that includes a distribution network 401. The controller 450 is an example of an implementation of the controller 150. The distribution network 401 may be a medium-voltage distribution network or a low-voltage secondary distribution network. The distribution network 401 includes a plurality of feeders. In the example of FIG. 4, two feeders are shown and one is labeled as feeder 404. A switch device 430 is coupled to the feeder 404. The distribution network 401 includes additional switch devices 430 coupled to the other feeders. In the example of FIG. 4, an additional switch device is labeled as 430_1.

The switch device 430 may be a single-phase or multi-phase switch device. The switch device 430 includes a resettable switching apparatus 432 and a sensing system 434. The switch device 430 is coupled to the controller 450. The controller 450 is shown as being separate from the switch device 430. However, in some implementations, the controller 450 is included in the switch device 430. For example, the controller 450 and the switch device 430 may be contained together in the same housing. The switch device 430 is electrically connected to the feeder 404.

The resettable switching apparatus 432 is any type of switch that is capable of opening and closing the feeder 404. The resettable switching apparatus 432 is configured for repeated operation. For example, after the resettable switching apparatus 432 opens the feeder 404 to stop or prevent current flow, the resettable switching apparatus 432 is able to close the feeder 404 such that current flow in the feeder 404 resumes. The resettable switching apparatus 432 also may include additional components and systems such as actuators, motors, springs, levers, and/or driving electronics that facilitate the operation of the switching apparatus 432.

In some implementations, the feeder 404 is a high-voltage or medium-voltage feeder, and the switch device 430 is configured to open and close such a feeder. For example, the switch device 430 may be a switchgear or a recloser. In these implementations, the resettable switching apparatus 432 may be a plurality of electrically conductive contacts that are joined to close the feeder 404 and separated to open the feeder 404. For example, the resettable switching apparatus 432 may include a first electrical contact and a second electrical contact configured to move relative to the first electrical contact to open and close the feeder 404. The resettable switching apparatus 432 may be a vacuum interrupter or a high-voltage or medium voltage circuit breaker.

In some implementations, the feeder 404 is a low-voltage feeder that is in a secondary electrical distribution network. In these implementations, the switch device 430 may be, for example, a network protector or other switch device configured for low-voltage use. In implementations in which the switch device 430 is a network protector, the resettable switching apparatus 432 may be an air circuit breaker operated by relay that monitors the voltage across the open contacts and the current through the closed contacts. An air circuit breaker includes two electrical contacts that operate in air at atmospheric pressure. When the electrical contacts are joined, current can flow in the feeder 404. When the electrical contacts are separated, current cannot flow in the feeder 404.

The switch device 430 also includes a sensing system 434. The sensing system 434 includes one or more detectors or sensors, each of which is configured to sense one or more properties of the electrical current in the feeder 404. The sensing system 434 may include any type of current sensor, such as, for example, a current transformer (CT) or a Rogowski coil. Alternately or additionally, the sensing system 434 may include one or more voltage sensors and/or one or more power sensors. The sensing system 434 may include a relay.

The switch device 430 also includes a controller 450. The controller 450 is coupled to the switch device 430 and to a test generation device 440 via a communication path 455. The communication path 455 may be any type of wired and/or wireless path capable of transporting signals, information, and/or data. For example, the communication path 455 may be a control cable, a wire, and/or an Ethernet or other network cable.

The test generation device 440 may be, for example, a device capable of injecting reactive power, such as the reactive power generation apparatus 644 of FIGS. 6A and 6B, or a device capable of changing the amount of voltage on the feeder 404, such as the distribution transformer 542_1 of FIG. 5A, a voltage regulator, or any other device or apparatus that includes a tap changer. The power generation apparatus 644 may be, for example, a capacitor bank, power electronic switches, a power converter, and/or an inverter. The test generation device 440 is electrically connected to the feeder 404, however, the test generation device 440 is not necessarily connected between the switch device 430 and the loads 103 as shown in FIG. 4. Moreover, although the test generation device 440 is shown as being distinct from the switch device 430, in some implementations, the test generation device 440 is integrated with the switch device 430. For example, the test generation device 440 may be housed within a unit or container that also houses the resettable switching apparatus 432.

The controller 450 is an electronic controller that includes an electronic processing module 452, an electronic storage 454, and an input/output (I/O) interface 456. The electronic processing module 452 includes one or more electronic processors, each of which may be any type of electronic processor and may or may not include a general purpose central processing unit (CPU), a graphics processing unit (GPU), a microcontroller, a field-programmable gate array (FPGA), Complex Programmable Logic Device (CPLD), and/or an application-specific integrated circuit (ASIC).

The electronic storage 454 may be any type of electronic memory that is capable of storing data and instructions in the form of computer programs or software, and the electronic storage 454 may include volatile and/or non-volatile components. The electronic storage 454 and the processing module 452 are coupled such that the processing module 452 can access or read data from and write data to the electronic storage 454.

The electronic storage 454 stores executable instructions, for example, as a computer program, logic, or software, that cause the processing module 452 to perform various operations. For example, the electronic storage 454 stores executable instructions that cause the processing module 452 to determine the structure of the distribution network 401 using the process 700 of FIG. 7. To provide another example, the electronic storage may store instructions that cause readings from the sensing system 434 to be stored on the electronic storage 454. The instructions also may include instructions that compare the readings obtained by the sensing system 434 at different times to determine whether one or more properties of the electrical power in the feeder 404 change over time. The properties include, for example, the direction of current flow on the feeder 404, magnitude of voltage on the feeder 404, phase angle of voltage on the feeder 404, magnitude of current on the feeder 404, phase angle of current on the feeder 404, active power on the feeder 404, reactive power on the feeder 404, or impedance at a known point on the feeder 404.

The electronic storage 454 also may store information about the switch device 430 and/or the feeder 404, such as one or more threshold values used for determining whether a change has occurred in one or more measured properties. For example, as discussed above, the electronic storage 454 may store instructions that determine whether one or more measured properties on the feeder 404 changes over time. In this example, if the magnitude of the measured voltage on the feeder 404 changes by at least the voltage change threshold over the associated time, the controller 450 produces an indication that the voltage magnitude has changed. Thresholds for other properties also may be stored on the electronic storage 454. Moreover, the threshold may be expressed as a percentage change that is stored on the electronic storage 454. The same percentage change may be used as a threshold for all measured properties, or each measured property may have a different threshold. In some implementations, threshold values or threshold percentage changes may be entered into the controller 450 via the I/O interface 456.

Furthermore, the electronic storage 454 may store instructions that, when executed, cause the electronic processing module 452 to send the test generation device 440 a command signal that causes the test generation device 440 to generate a test signal 445 and provide the test signal 445 to the feeder 404. The electronic storage 454 also may store instructions that cause the electronic processing module 452 to analyze values of one or more properties of electrical power on the feeder 404 and/or in a power system that includes the feeder 404 after controlling the test generation device 440.

Furthermore, the electronic storage 454 may include instructions that implement techniques for filtering and/or preparing the data produced by the sensing system 434. For example, the electronic storage 454 may include instructions that implement an analog-to-digital (A/D) converter that digitizes analog data from the sensing system 434.

Additionally, the electronic storage 454 may store instructions related to the operation of the switch device 430. For example, the electronic storage 454 may store instructions, that when executed by the processing module 452, cause the controller 450 to issue a command to the switch device 430 such that the switch device 430 opens or closes. Moreover, the electronic storage 454 may store information related to the conditions under which the switch device 430 is to be opened or closed. For example, the electronic storage 454 may store a threshold value that represents a maximum acceptable difference between the network-side and source-side voltage vectors to allow the switch device 430 to transition from the open state to the closed state, as discussed with respect to FIG. 8.

The I/O interface 456 may be any interface that allows a human operator and/or an autonomous process to interact with the controller 450. The I/O interface 456 may include, for example, a display (such as a liquid crystal display (LCD)), a keyboard, audio input and/or output (such as speakers and/or a microphone), visual output (such as lights, light emitting diodes (LED)) that are in addition to or instead of the display, serial or parallel port, a Universal Serial Bus (USB) connection, and/or any type of network interface, such as, for example, Ethernet. The I/O interface 456 also may allow communication without physical contact through, for example, an IEEE 802.11, Bluetooth, or a near-field communication (NFC) connection. The controller 450 may be, for example, operated, configured, modified, or updated through the I/O interface 456.

The I/O interface 456 also may allow the controller 450 to communicate with systems external to and remote from the switch device 430. For example, the I/O interface 456 may include a communications interface that allows communication between the controller 450 and a remote station (not shown), or between the controller 450 and a separate electrical apparatus in the power system 100 (FIG. 1) using, for example, the Supervisory Control and Data Acquisition (SCADA) protocol or another services protocol, such as Secure Shell (SSH) or the Hypertext Transfer Protocol (HTTP). The remote station may be any type of station through which an operator is able to communicate with the controller 450 without making physical contact with the switch device 430 or the controller 450. For example, the remote station may be a computer-based work station, a smart phone, tablet, or a laptop computer that connects to the controller 450 via a services protocol, or a remote control that connects to the controller 450 via a radio-frequency signal. The controller 450 may communicate information such as the determined tap position through the I/O interface 456 to the remote station or to a separate device in the power system 400.

As discussed above, the test generation device 440 may be a reactive power generation apparatus or a distribution transformer. FIG. 5A shows an example that includes distribution transformers 542_1 and 542_2. FIGS. 6A and 6B shows an example that includes a reactive power generation apparatus 644.

FIG. 5A is a block diagram of a power system 500. The power system 500 includes distribution network 501. In the example of FIG. 5A, the distribution network 501 is a low-voltage secondary distribution network that includes low-voltage feeders 504_1 and 504_2. The distribution network 501 includes a first medium-voltage feeder 506_1 and a second medium-voltage feeder 506 2 that are feed by the source 102. The first and second medium-voltage feeders 506_1 and 506_2 include respective circuit breakers 105_1 and 105_2. The system 500 also includes medium-voltage loads 518_1 and 518_2, which are respectively connected to the medium-voltage feeders 506_1 and 506_2.

The power system 500 also includes network protectors 530_1 and 530_2. The network protector 530 1 controls an electrical connection between the low-voltage feeder 504_1 and the loads 103. The network protector 530_2 controls an electrical connection between the low-voltage feeder 504_2 and the loads 103. Each network protector 530_1 and 530_2 includes an instance of the controller 450.

FIG. 5C is a block diagram of the network protector 530_1. The network protector 530_1 includes a resettable switching apparatus 532, a sensor system 534, and a relay or switch control 535. The resettable switching apparatus 532 may be, for example, an air circuit breaker.

The sensing system 534 is configured to measure voltage and/or current in the respective low-voltage feeder 504_1. The sensing system 534 may include, for example, a current sensor that measures current in the low-voltage feeder 504_1, a first voltage sensor that measures voltage between the source side of the network protector 530_1 and the load side of the network protector 530_1, and a second voltage sensor that measures voltage between the low-voltage feeder 504_1 and ground or other reference potential. The relay 535 controls the state of the switching apparatus 532 based on measurements from the sensing system 534. The network protector 530_2 is configured in the same manner. Any type of sensor capable of measuring voltage and/or current may be used in the sensing system 534. The current sensor may be, for example, a current transformer (CT) or Rogowski coil. The voltage sensor may be, for example, a potential transformer (PT).

The system 500 also includes distribution transformers 542_1 and 542_2, which are substantially identical to each other. FIG. 5B shows the distribution transformer 542_1 in greater detail. The transformer 542_1 includes a primary winding 543a and a secondary winding 543b that are magnetically coupled by a core 541. The primary winding 543a and the secondary winding 543b are made of an electrically conductive material such as, a metal or a metal alloy, for example, copper or a copper alloy. The primary winding 543a is on a primary or source side of the transformer 542_1, and the secondary winding 543b is on a secondary side of the transformer 542_1.

The core 541 is made of a ferromagnetic material, such as, for example, iron or steel. The core 541 may be a gapped core or an un-gapped core. In implementations in which the core 541 is an un-gapped core, the core 541 is a contiguous segment of ferromagnetic material. A gapped core includes a gap that is not ferromagnetic material. The gap may be, for example, air, nylon, or any other material that is not ferromagnetic. Thus, in implementations in which the core 541 is a gapped core, the core includes at least one segment of a ferromagnetic material and at least one segment of a material that is not a ferromagnetic material.

Referring also to FIG. 5B, the primary winding 543a includes T taps 546, where T is an integer number that is greater than one. The taps 546 are made of an electrically conductive material (such as, for example, metal), and the taps 546 are electrically connected to the primary winding 543a. Each tap is separated from the nearest other tap, with at least one turn being between any two adjacent taps. During operational use of the distribution transformer 542_1, there is a potential difference V_T between any two adjacent taps 546.

The medium-voltage feeder 506_1 is electrically connected to a tap selector 547. The tap selector 547 is made from an electrically conductive material and is configured to electrically connect the medium-voltage feeder 506_1 to one of the taps 546. The amount of voltage provided to the low-voltage feeder 504_1 depends on which of the taps 546 the tap selector 547 is connected to, thus, the controller 450 is able to change the voltage on the low-voltage distribution feeder 504_1 by a known amount by moving the tap selector 547 from one of the taps 546 to another one of the taps 546.

The controller 450 in each network protector 530_1 and 530_2 receives data from respective source-side monitors 534_1 and 534_2. The source-side monitors 534_1 and 534_2 may be sensors that are configured to measure, for example, the voltage and/or other electrical properties on the primary side of the transformers 542_1 and 542_2. In some implementations, the source-side monitors 534_1 and 534_2 are part of the respective transformers 542_1 and 542 2.

During normal operation of the power system 500, the medium-voltage circuit breakers 105_1 and 105_2 are closed, and the feeders 504_1 and 504_2 of the secondary distribution network 501 form a mesh or loop structure. The voltage at the primary side of the transformers 542_1 and 542_2 is dictated by the sources 102_1 and 102_2, respectively. Performing a tap change operation by moving the tap selector 547 to another tap does not change the voltage at the primary side of the transformers 542_1 and 542_2.

During abnormal operating conditions, the circuit breaker 105_1 or 105_2 opens, for example, due to a fault or scheduled maintenance, and the secondary distribution network 501 has a radial structure. When the secondary distribution network 501 has a radial structure, the voltage at the primary side of the transformers 542_1 and 542_2 depends on the voltage drop due to the loading on the secondary side. Thus, under an abnormal condition, a tap change operation changes the voltage on the primary side of the transformers 542_1 and 542_2. In the implementation shown in FIG. 5A, the source-side monitors 534_1 and 534_2 are used to monitor the voltage on the primary side of the respective transformers 542_1 and 542_2.

By performing a tap change operation and then monitoring the response to that tap change operation, the controller 450 is able to determine whether or not an abnormal condition exists in the distribution network 501. Moreover, the controller 450 may determine that the distribution network 501 is operating in an expected or normal condition even if there is reverse power flow on the feeder 504_1 and/or the feeder 504_2.

In some implementations, the controller 450 monitors one or more properties or parameters of electrical power in the feeder 504_1. A significant change in one or more of the monitored properties or parameters triggers the controller 450 to issue a tap change test command to the distribution transformer 542_1 to perform a tap change operation to generate a test signal 545. The voltage at the primary side of the distribution transformer 542_1 is analyzed based on data from the source-side monitor 534_1. If the voltage at the primary side of the distribution transformer 542_1 changes, the controller 450 determines that the feeder 504_1 has a radial structure and thus is in an abnormal condition. The controller 450 issues a command that causes the network protector 530_1 to open such that the feeder 504_1 is disconnected from the loads 103. If the voltage at the primary side of the distribution transformer 542_2 does not change, the feeder 504_1 has a mesh structure and is in a normal or expected operating condition. The network protector 530_1 remains closed.

The feeder 504_2 (and any other feeders in the distribution network 501) may be monitored and analyzed in the same manner. Moreover, in some implementations, the controllers 450 also control the reclosing, or closing after opening, of the network protector 530_1 and 530_2 using, for example, the process 800 discussed with respect to FIG. 8.

FIG. 6A is a block diagram of a power system 600. The power system 600 is similar to the power system 500 (FIG. 5A), except the power system 600 also includes a reactive power generation apparatus 644. The reactive power generation apparatus 644 may be any device or system that is capable of producing a test signal 645 that has a known amount of reactive power (Qc). Reactive power is the product of the voltage and current that is out-of-phase with each other. For example, the reactive power generation apparatus 644 may be a capacitor bank, an inductor bank, a bank of devices that includes inductors and capacitors, a power converter, or an inverter. The reactive power generation apparatus 644 is coupled to the controller 450 and is configured to be controlled by the controller 450. For example, the controller 450 may be configured to generate command signals that cause the reactive power generation apparatus 644 to inject the test signal 645 into the distribution network 601.

In the example shown in FIG. 6A, the reactive power generation apparatus 644 is electrically connected to the low-voltage feeder 504_2 between the loads 103 and the network protector 530_2. However, other implementations are possible. For example, the reactive power generation apparatus 644 may be between the distribution transformer 542_1 and the network protector 530_1. In another example, the reactive power generation apparatus 644 may be integrated with the network protector 530_2. Furthermore, the system 600 also may include an additional reactive power generation apparatus connected to the low-voltage feeder 504_1.

As discussed below, the test signal 645 is observed on a first side 644a and/or a second side 644b of the reactive power generation apparatus 644 to determine the structure of the distribution network 601.

FIG. 6A shows the power system 600 during normal or expected operating conditions. During normal and expected operation of the power system 600, the circuit breakers 105_1 and 105_2 are closed, the feeders 504_1 and 504_2 of the secondary distribution network 601 form a mesh or loop structure and, based on Kirchoff s Current Law (KCL), the reactive power (Qc) in the test signal 645 is divided into a first reactive power 648 that flows toward the loads 103 and a second reactive power 649 that flows toward the transformer 542_2. Under normal or expected operating conditions, the amount of reactive power in 648 and 649 depends on the impedance of the path toward the loads 103 and the path toward the transformer 542_2, respectively.

FIG. 6B shows the power system 600 during an abnormal condition after the circuit breaker 105_2 has opened due to, for example, a fault or scheduled maintenance. In FIG. 6B, the circuit breaker 105_2 is in grey shading to indicate that it is open. The circuit breaker 105_1 remains closed, and the source 102 remains connected to the feeder 506_1. During abnormal conditions, the network 601 has a radial structure. According to Kirchoff s Current Law (KCL), in a radial structure, the injected reactive power Qc becomes the source of reactive power on the second side 644b of the reactive power generation apparatus 644. Therefore, during abnormal conditions, the reactive power flow 649 on the second side 644b of the reactive power generation apparatus 644 remains constant before and after the injection of the test signal 645, while the reactive power flow 648 on the source side of the reactive power generation apparatus 644 (the first side 644a in the example of FIG. 6B) changes by Qc, which is the amount of reactive power in the test signal 645.

Thus, to determine the structure of the distribution network 601, the reactive power is observed on the first side 644a and/or the second side 644b of the reactive power generation apparatus 644 before and after injection of the test signal 645. For example, if the reactive power 648 on the source side of the reactive power generation apparatus 644 (the first side 644a in the example of FIG. 6B) changes by Qc after injection of the test signal 645, the distribution network 601 has a radial structure. If the reactive power 648 on the source side of the reactive power generation apparatus 644 does not change by Qc after the injection of the test signal 645, the distribution network 601 has a mesh or loop structure. Alternatively or additionally, the reactive power 649 on the second side 644b of the reactive power generation apparatus 644 may be observed before and after the injection of the test signal 645. If the reactive power 649 does not change, the distribution network 601 has a radial structure. If the reactive power 649 changes, the distribution network 601 has a mesh or loop structure. The reactive power on either side 644a, 644b of the reactive power generation apparatus 644 may be measured by the sensing system 534 or by a separate sensor (not shown).

In some implementations, the controller 450 monitors one or more properties or parameters of the electrical power in the feeder 504_1. A significant change in at least one of the monitored properties or parameters triggers the controller 450 to issue a command to the reactive power generation apparatus 644, and the test signal 645 is generated and injected into the feeder 504_2. Furthermore, if the controller 450 determines that the network 601 has a radial structure, the controller 450 opens the network protector 530_2. Such an implementation is discussed below with respect to FIG. 7. Moreover, in some implementations, the controllers 450 also control the reclosing, or closing after opening, of the network protectors 530_1 and 530_2 using a process such as the process 800 discussed with respect to FIG. 8.

FIG. 7 is a flow chart of a process 700. The process 700 is an example of a process for determining the structure of a distribution network. The process 700 may be used to determine the structure of any of the distribution networks 101, 201, 301, 401, 501, and 601 discussed above. Moreover, the process 700 may be used to determine the structure of other distribution networks. The process 700 may be performed by the controller 150 or the controller 450. The process 700 is discussed with respect to FIG. 4 for the purposes of providing an example.

The distribution network 401 is monitored (710). For example, and referring to FIG. 4, the sensing system 434 continuously monitors properties and parameters of the voltage and/or current on the feeder 404 and the measured data is stored on the electronic storage 454.

Whether or not a change in one or more monitored properties of the electricity in the network 401 is determined (715). The electronic storage 454 includes executable instructions that compare the measured data over time to determine whether one or more properties of the power flow in the feeder 404 has changed over a particular time period. The time period may be, for example, 1 millisecond (ms) to 10 seconds (s). The properties may be any measured or derived property and include, without limitation, amplitude and/or phase angle of voltage and/or current, reactive power, impedance, active power, impedance, and/or current flow direction.

To provide a specific example, the sensing system 434 may be configured to measure the magnitude of current flow in the feeder 404 every 5 ms, and the controller 450 may be configured to determine the amount of change between each measurement or between every other measurement. In this way, the controller 450 determines the amount of change in the measured current magnitude over a specified time period. The controller 450 compares the determined amount of change to a threshold related to that property. Continuing the example of current magnitude, the controller 450 is configured to compare the change in the current magnitude to a pre-determined current magnitude threshold.

To provide another example, the property may be the direction of current flow on the feeder 404. A change in direction is considered a change in a property, but is not assumed by the controller 450 to necessarily indicate the presence of an abnormal condition. Moreover, the electronic storage 454 may store a threshold or a specification related to the current direction property. For example, the threshold may specify a period of time over which the direction is reverse (toward the source) before the direction of current flow is determined to have changed.

If none of the changes exceed a threshold, there has not been a change in one or more properties at (715), the process 700 returns to (710) and continues to monitor the feeder 404.

If the change exceeds the threshold, then the controller 450 determines that there has been a change in an electrical property, and the process 700 moves to (720). In some implementations, the controller 450 only detects that a change in an electrical property has occurred if the amount of change of more than one property exceeds the appropriate threshold for that property.

The controller 450 causes the test generation device 440 to generate the test signal 445, which is provided to the feeder 404 (720). In implementations in which the test generation device 440 is a distribution transformer (such as shown in FIG. 5A), the controller 450 causes the tap selector 547 to move to a different one of the taps 546. In implementations in which the test generation device 440 is a reactive power generation apparatus (such as shown in FIGS. 6A and 6B), the controller 450 causes the reactive power generation apparatus 644 to generate the test signal 645 by providing a known amount of reactive power to the feeder 404.

In some implementations, the controller 450 causes the test signal to be produced without performing (710) and (715). For example, an operator of the system 400 may manually trigger the generation of the test signal 445 by communicating with the controller 450 through the I/O interface 456. In other words, the process 700 may be performed without performing (710) and (720), and the generation of the test signal 445 may be triggered by events other than a change in a monitored electrical property.

After providing the test signal 445 to the feeder 404, the controller 450 analyzes the response to the test signal 445 (730). For example, if the test signal is the reactive power test signal 645 (FIGS. 6A and 6B), the controller 450 determines whether the reactive power on a side of the reactive power generation apparatus 644 changes after the reactive power test signal 645 is injected. In another example, if the test signal is the tap change voltage 545, the controller 450 determines whether the voltage on the primary side of the transformer 542_1 changes after the tap change occurs.