Distribution Automation Networks — Application & Testing

Abel Gonzalez, Megger Features, Summer 2023 Features

Reclosers play an important role in distribution networks, where their primary role is to automatically reclose following a trip operation due to a fault. This ensures that power restoration causes only a momentary disruption to customers, rather than an extended outage. 

Over the years, distribution networks have been automated to enhance system performance. Network automation involves communication between the devices in the network to exchange information and make decisions for better performance of the system. In a distribution network, strategic placement of sectionalizers and switches in conjunction with reclosers and substation breakers constitutes a loop scheme.

Distribution feeder loop schemes are considerably more reliable compared to radial schemes. The loop scheme minimizes system downtime during a fault condition by quickly isolating the faulty portion of the network and restoring service to the unfaulted portion.  Proper protection coordination between multiple protective relays, feeder breakers, and sectionalizers present in the loop scheme should be tested and validated to ensure reliable and efficient operation. 

This article discusses the operation of distribution feeder schemes. Applications, protection settings, test methods, test connections, and challenges are addressed in detail. End-to-end testing, which is used to validate such schemes, is explained.


Reclosing is a protective function used to automatically restore power after a fault without human intervention. It is used in distribution as well as transmission systems and is based on the fact that a high percentage of faults are temporary in nature.

Even in the analog version without the benefit of microprocessor relays, reclosers are a form of intelligence applied to the protection and control of power systems.

Distribution Feeder Reconfiguration Schemes

A distribution feeder reconfiguration scheme can be applied when several feeders, each with multiple reclosers, can be connected so that there are multiple ways to provide power to each of the feeders. In the example shown in Figure 1, Recloser 4 operates as a normally open tie to provide an extra path of connection to either feeder in the presence of a fault.

Figure 1: Two feeders provide an extra path of connection.

When a permanent fault occurs, e.g., between Recloser 2 and Recloser 3, Recloser 2 goes through its operation cycle and opens, leaving all customers between Recloser 2 and Recloser 3 without power as can be seen in Figure 2.

Figure 2: Recloser 2 opens following its cycle.

Since the fault happened between Recloser 2 and Recloser 3, only customers connected between those two reclosers should remain without power. An obvious solution is to open Recloser 3 and close Recloser 4 as can be seen in Figure 3.

Figure 3: The line between Recloser 2 and Recloser 3 is isolated.

In this example, after the fault between Recloser 2 and Recloser 3, the line section between Recloser 3 and Recloser 4 is now back in service. This can be done manually from a central control station but can be achieved without any human intervention if the proper algorithms are used. 

Because of the reconfiguration operation presented in the example, Recloser 5, Recloser 6, and Recloser 7 now see a higher load than before the fault. This happens because they now see the additional load that corresponds to the line section between Recloser 3 and Recloser 4 that was previously fed from Feeder 1. Recloser 1 also sees a different albeit reduced load. Designing such systems also means making sure that both feeders can carry all the additional load from adjacent feeders.

Even the direction of the power flow at the recloser may be affected. For instance, if the fault occurred between Recloser 1 and Recloser 2, they will remain open at the end of the operation cycle and Recloser 3 will see an inversion in power flow as can be seen in Figure 4.

Figure 4: Power flows in the opposite direction for Recloser 3.

Also notice that for the TIE (Recloser 4), the direction of power flow depends on whether the fault happened on Feeder 1 or Feeder 2 as can be seen by comparing Figure 4 and Figure 5.

Figure 5: The direction of power flow for Recloser 4, which acts as the TIE, depends on fault location.

During regular operation, when no change has occurred on the network, a given recloser controller will maintain a fixed settings group. However, as soon as the network changes because of a reconfiguration operation, the protection and control settings on the controller must change to allow it to adapt to the new conditions. This means the settings group of the recloser will probably need to change owing to the new network conditions, and more than two settings groups may be required. 

From the testing perspective, this means that all of the settings groups used in the automation will need to be tested for all reclosers that are affected by changes in the network.


Reconfiguration schemes can be implemented with or without any communication channels between the various reclosers. 

In some algorithms that use a scheme without communications, the reclosers rely on the fact that whenever a recloser operates on a radial feeder, all other reclosers downstream suffer a momentary loss of voltage. In these cases, reclosers will count the number of times a loss of potential is detected and how long each loss of potential event lasts and use this information along with the direction of power flow at the time of the loss for their operation. When configuring and testing these schemes, it is important to adequately estimate and evaluate the limits — in magnitude as well as time — for a loss of potential.

In a scheme with communications, each recloser has a communications channel that is used to send status and permissive information to a remote terminal unit as well as to other reclosers on the network as shown in Figure 6. 

Figure 6: Communications-Assisted Scheme

For security purposes, these communication-assisted schemes are preferred whenever communications channels are available.

The communication medium can be radio, leased lines, fiber optics, etc. Some of these networks can use Ethernet, and the implementation of the algorithm can be done using proprietary communication protocols or standard protocols such as the distributed network protocol (DNP) or IEC 61850.


Testing the recloser itself is relatively well-known and is not the focus of this article. A typical recloser evaluation will include tests for insulation resistance, breaker contact resistance, operation sequence, minimum pickup, time current curves, operating time, single shot to lockout, reclosing time, total clearing time, and others. These types of tests are done on individual reclosers and should be performed as part of any commissioning or maintenance program. Methods for testing the recloser can be classified by the mode of signal injection: primary injection or secondary injection method. 

Primary injection. During primary injection, current is injected into the primary side of the recloser. This has the advantage of testing the functionality of the current sensors, and it can be considered a whole-system test for the recloser itself. However, this kind of testing requires the use of relatively large primary injection test sets capable of producing the high fault currents usually required to test this equipment. Additionally, when dealing with distribution automation schemes, it is often necessary for the tests to include the voltage inputs of the reclosers since they are part of the reconfiguration algorithms. This complicates testing using primary injection on these systems.

Secondary injection.Secondary injection, as the name implies, injects secondary values into the recloser controller’s current and voltage inputs. It has the advantage of using smaller, more flexible equipment with lower power requirements. These types of tests lend themselves to a high degree of automation. One challenge in testing reclosers with secondary injection is accessing the analog inputs and the digital inputs and outputs of the controller without significant rewiring. Modern test equipment exists that allows the user to connect directly to the controller’s connector and inject analog signals into the controller’s analog inputs while at the same time sending trip and reclose signals to the breaker and receiving breaker status information from the breaker. The breaker can also be bypassed altogether by simulating the 52a/b contacts directly from the secondary injection test set. Such a connection diagram can be seen in Figure 7.

Figure 7: Testing a Recloser Controller Using Secondary Injection

To test the recloser, a state sequencer is typically used to simulate a sequence of power system conditions like faults (trips) and idle (reclose) states as well as the operation of binary inputs and outputs. Figure 8 shows the changes in the root mean square (RMS) values of voltages and currents during the test as well as the expected operation of binary inputs and outputs. Binary Output 1 in this case is being used to simulate the 52a/b contacts. Binary Input 1 is being used for the trip signal.

Figure 8: Sequence of States to Test a Recloser

End-to-end testing. The purpose of testing distribution automation schemes goes beyond testing the individual elements of the scheme and should aim for verification of the whole system. For this purpose, end-to-end testing is used. During this type of test, the distribution automation scheme can be evaluated by simulating fault conditions simultaneously at different points of the feeders. 

The relays inside the controllers receive currents and voltages from their own terminals and, in communications-assisted schemes, status and permissive data from relays on other parts of the scheme. For this reason, it is important to be able to synchronize the test systems on each end so that test quantities can be injected simultaneously into all the controllers involved. 

A time signal from a global positioning system (GPS) clock can be used to synchronize multiple test systems. Time signals are available in various standards such as 1 pulse per second (PPS), precision time protocol (PTP), IRIG-B, etc. Using IRIG-B time synchronization for end-to-end testing requires multiple relay test sets able to decode the IRIG-B signal. This signal is used to trigger the simultaneous injection of analog values. In some cases, the IRIG-B signal that is obtained from a GPS receiver can also be provided to the relays under test. During testing, the test sets can be synchronized independently of the timing mechanism used by the relays on the network.

In general, during an end-to-end test, the connections will be as shown in Figure 9.

Figure 9: End-to-End Connections

As you can see, the typical setup consists of test sets and their operators on each of the terminals to be included in the test. A means of synchronization must be provided, in this case in the form of GPS clocks. Each operator must be able to communicate with its own test equipment, the relay under test, and the clock, as well as with the operators on the other end.

The sequence of tests to be injected into the reclosers on each end can be produced using a sequencer as was mentioned previously or, if dynamic testing is preferred, COMTRADE files containing transient waveform information from actual or simulated faults can be injected to perform the testing. 

The test sets used on both ends will ideally have the same characteristics, i.e., the same brand, model, and firmware versions. When that is not the case, the synchronization procedure must include a means to compensate for the different injection delays caused by having dissimilar test sets. The measurement of such time delay can be done using the setup shown in Figure 10.

Figure 10: Setup for Measuring Injection Delay Difference between Two Test Sets

In the setup shown in Figure 10, simultaneous injection is triggered from both test sets, and the resulting waveforms are recorded in a digital fault recorder. The desired measurement will be the time difference between the injected signals from each test set as can be seen in Figure 11.

Figure 11: Time Delay Measurement

In Figure 9, only two terminals were shown for simplicity. A real-world test could consist of many terminals as can be seen in Figure 12. 

Figure 12: End-to-End Testing with Multiple Terminals


Reclosers are the brain and the muscle of the distribution system and must be tested thoroughly before being put into operation and again during every maintenance cycle.

Testing the recloser can be accomplished using a combination of primary and secondary injection methods. Modern test equipment allows for secondary injection testing of the recloser without any rewiring of the analog and digital inputs and outputs of the controller.

Reclosers are used in distribution automation schemes to provide higher reliability for customers. These schemes can be implemented using a variety of techniques. The most popular techniques involve means of communication between the reclosers in the field as well as the use of multiple settings groups on the recloser controllers.

Testing these schemes can be accomplished using end-to-end tests. Using tools that allow for synchronized injection of signals at different locations is extremely important. 


[1] IEEE. IEEE Std. C37.104-2012, IEEE Guide for Automatic Reclosing of Circuit Breakers for AC Distribution and Transmission Lines.

[2] Robert E. Goodin; Timothy S. Fahey, PE; and Andrew Hanson, PE. Distribution Reliability Using Reclosers and Sectionalizers. ABB. Available at https://library.e.abb.com/public/9a7bdfb0769f75c885256e2f004e7cd8/Reliability%20Using%20Reclosers%20and%20switches.pdf. 

[3] James Ariza, G. Ibarra.“Application Case of the End-to-End Relay Testing Using GPS-Synchronized Secondary Injection in Communication-Based Protection Schemes,” NETA PowerTest 2023.  

[4] Sughosh Kuber. “End-to-End Testing for Line Differential Protection,” NETA World, Winter 2019. Available at https://netaworldjournal.org/end-to-end-testing-for-line-differential-protection/.

Abel Gonzalez is a Senior Relay Applications Engineer with Megger LTD in Markham, Ontario. He previously worked as a Design Engineer for Arteche Medición y Tecnología in Zapopan and Jalisco, Mexico, and Curitiba, Brazil. Abel’s research areas are the analysis operation, control, and protection of electric power systems. Earlier in his career, he worked as a Tele-traffic Engineer, Control Engineer, and head of the Marketing Department for the Cuban Telecommunications Company. Abel is a member of IEEE-PSRC. He received his BS and MSc in electrical engineering from the Universidad Central de Las Villas, Cuba, and was later an Assistant Professor for the Faculty of Electrical Engineering at the Universidad Central de Las Villas, Cuba, where he taught courses in electrical drives and power electronics.