In power distribution system design, the automatic transfer switch function can be regarded as the "final line of defense" for ensuring the continuity of power supply.
However, when dealing with complex power-distribution scenarios—such as a configuration comprising two utility power feeds, one bus tie switch, and two diesel generators—traditional automatic transfer switching solutions often require multiple dedicated ATS units to operate in coordination, and may even require an additional PLC for logic implementation. This not only results in complex wiring but also leads to persistently high commissioning and maintenance costs.
However, the ABB 615 series relay protection devices provide a completely different answer: all of this can be achieved with just one REF615.
How is this achieved? Today, we will take an in-depth look at the distinctive capabilities of the ABB 615 series in complex automatic transfer switching scenarios.
I. The Strength Behind ABB's Relay Protection: Programmable Logic Transforms Relay Protection into a "Universal Controller"
First, we need to understand a key concept: the ABB 615 series does not inherently include a backup automatic transfer function.
This may sound somewhat unexpected, but the ABB REF615 product protection function list does not include a ready-made function option called "standby automatic transfer."
So, how does it implement automatic transfer protection across various types of projects? The answer lies in its powerful programmable logic (PLC Logic).
The ABB 615 series incorporates a comprehensive logic library and supports graphical programming via the PCM600 engineering tool. By utilizing a variety of logic elements—including timers, flip-flops, AND gates, OR gates, NOT gates, RS flip-flops, and monostable flip-flops—users can implement multi-layered logic functions and flexibly combine protection functions with logic function blocks, enabling device configurations to be perfectly tailored to specific application requirements.
Here, "programmability" also has an additional prerequisite: compatibility with the hardware configuration.
Taking the REF615 as an example, it offers 12 different standard configurations, each differing in its combination of protection functions and IO channels. For instance, configurations A and B include non-directional overcurrent protection and directional ground-fault protection; configurations C and D include non-directional overcurrent protection and non-directional ground-fault protection; while the standard configuration H additionally provides frequency protection and other features. The implementation of the backup automatic transfer function relies on the device's own voltage detection module to sense the busbar voltage status. As noted in relevant case studies, if the REF615 is to be used for functions requiring voltage signal acquisition—such as incoming-line backup automatic transfer—it is necessary to select a version equipped with voltage detection capabilities (e.g., the REF615K). Although the REF615D does not include a voltage module, it can still be used for busbar interconnection backup automatic transfer; in this application, the busbar interconnection device is responsible only for signal acquisition and logic processing: it receives status signals from the two incoming lines via the I/O interface and then issues opening and closing commands to those lines through logical operations. Therefore, when planning a solution, selecting the appropriate hardware configuration based on the actual application scenario is critical.
Therefore, an automatic backup power supply is not something that can be "purchased and used immediately"; rather, it is "implemented through programming." The distinctive feature of this design philosophy lies in the fact that it does not confine users to a fixed backup power supply template; instead, it places full control over the logic design in the hands of the engineer, enabling each backup power supply solution to be precisely "customized" according to site-specific requirements.
In terms of logical sophistication, ABB products possess a unique advantage: thanks to its comprehensive logic library and full support for logic gates, even the most stringent and complex functional requirements can be implemented through the logic architecture built into the device, thereby providing a perfect replacement for traditional PLC-based solutions. As industry insiders put it: ABB's automatic transfer switch is not a device; it is a methodology.
More importantly, ABB's automatic transfer switching implementation offers a highly flexible approach: signals can be transmitted via hard-wired connections between devices, or through IEC 61850 GOOSE network communication; the two methods can even be combined to meet the specific requirements of different projects.
II. Typical configuration: two utility power feeds + bus tie + two diesel generators
To provide a more intuitive demonstration of the robust capabilities of the ABB 615 series in complex automatic transfer switching applications, we use a typical industrial power distribution scenario as a case study:
-Two 10 kV utility power feed-in lines (QF1 and QF2), each supplying Busbar Section I and Busbar Section II, respectively
-A section of the busbar circuit breaker (QF3), used for interconnecting the two busbar sections and switching between the diesel generator and the main power supply
-Two diesel generators (QF4 and QF5), connected respectively to Busbars Section I and Section II
-All circuit breakers support electric opening and closing
In this type of scenario, the automatic backup power supply logic we need to implement must at least cover the following operating conditions:
Logic 1: Main power backup automatic transfer — when a single main power supply fails, the bus tie switch automatically transfers.
During normal operation: both utility power supplies are functioning normally; QF1 and QF2 are closed, while the busbar transfer switch QF3 is open, resulting in the two busbar sections operating separately. The automatic transfer switch is in the "charging" state, continuously monitoring the power supply status.
When the primary mains power supply is lost: after a delay-based confirmation, the automatic transfer switch logic executes the first step—issuing a trip command to open the primary incoming circuit breaker QF1. Once it is confirmed that QF1 has opened (based on the dual criteria of circuit-breaker position feedback and the absence of line current), a short delay is used to issue a close command, closing the bus tie breaker QF3; the entire load is then supplied by the secondary mains power supply.
Self-feeding and self-restoring logic: Once the Section I mains power is restored and remains normal for a specified period (typically 10–15 seconds), the system automatically opens the section interconnection QF3, then closes the Section I incoming line QF1, thereby restoring the separate operation mode.
The same logic applies to the loss-of-power condition in Section II.
Logic 2: Dual mains power failure — diesel generator automatic start-up
Trigger condition: When both mains power supplies are lost and the mains backup automatic transfer switch fails to operate (because there is also no power on the other side of the bus tie), the diesel generator transfer logic should be activated.
Diesel generator start-up and switching: When the automatic transfer switch logic detects that both utility power circuits have lost voltage and carry no current, it issues a diesel generator start-up signal. Once the diesel generator voltage has been established and stabilized, the corresponding diesel generator incoming-line switch is closed according to the priority strategy (for example, first close diesel generator QF4 with Section I; if diesel generator QF4 fails, close diesel generator QF5 with Section II).
Self-power restoration logic: When any one of the utility power lines is restored and remains operational normally for a specified period, the system automatically disconnects the diesel generator supply line, shuts down the diesel generator, then closes the utility power supply line switch to restore utility power supply.
Logic 3: Diesel generator side-by-side automatic transfer — mutual backup between diesel and AC generators
Trigger condition: Assume that柴发 QF4 is currently operating independently under full load; if柴发 QF4 fails and trips.
Chiller–generator backup logic: When the backup automatic switching logic detects that the chiller QF4 has tripped and the busbar has lost voltage, it automatically issues a closing command to chiller QF5, allowing the other chiller to take over power supply.
Self-feeding and self-restoration logic: Once the faulty diesel generator (QF4) returns to normal operation, the system automatically switches back to diesel generator QF4, disconnects diesel generator QF5, and restores the original operating mode.
III. "Single-Unit Integrated Management": One REF615 with fully integrated logic
In the aforementioned complex standby-auto transfer scenarios, the distinctive advantage of the ABB 615 series lies in the fact that all standby-auto transfer functions—mains power standby-auto transfer, auto transfer with automatic reconnection, diesel generator interlocking switching, and diesel generator mutual backup—can be programmed and operated within "a single protection device."
This means that no additional PLC configuration is required, no coordination among multiple backup automatic transfer devices is needed, and there is no need to worry about logical conflicts between different devices. A single REF615, leveraging its built-in programmable logic capabilities, can collect data on the status of circuit breakers throughout the entire system, perform logical operations, and issue commands, thereby providing unified dispatching for the opening and closing of the utility power incoming lines, bus tie lines, and diesel generator incoming lines.
The benefits of this integrated solution are evident:
-Simplify the system architecture: reduce the number of devices and minimize failure points
-Unified logical management: All logic is centralized in a single unit, making commissioning and maintenance more intuitive
-Reduce project costs: eliminate the need for dedicated automatic backup power supply devices and PLCs
IV. Communication or hardwired connection: two options available for flexible selection
The ABB 615 series automatic transfer switch solution also offers a significant advantage: highly flexible signal interaction. Depending on the specific requirements of the project, users can choose to transmit signals between devices via IEC 61850 GOOSE communication or through conventional hard-wired connections.
Option 1: GOOSE communication (recommended for digital substations)
For newly constructed projects or retrofit projects that meet the requirements for digitalization, the adoption of a GOOSE communication solution is strongly recommended.
-Principle: The REF615 containing the automatic transfer switch logic serves as the GOOSE publisher, transmitting control signals such as opening commands and closing commands to the various incoming-line protection devices (e.g., other REF615 units) via the station control layer network; each incoming-line protection device acts as a GOOSE subscriber, receives the commands, and executes the corresponding operations. Simultaneously, the incoming-line protection devices feed back circuit breaker status, voltage/current signals, and other data to the automatic transfer switch device via GOOSE.
-superiority:
-Significantly reduce the number of secondary cables and simplify wiring
-Signal transmission speeds can reach the millisecond level, meeting the requirements for rapid switching.
-Facilitates system scalability and remote maintenance
-Align with the development trends of digital substations
Option 2: Hard-wired solution (suitable for conventional substations)
For traditional substations or retrofit projects that do not have the conditions required for GOOSE communication, all functions can also be implemented using conventional hard-wired configurations.
-Principle: The automatic transfer switch device issues opening and closing commands directly via its DO (digital output) terminals, which are connected by cable to the opening and closing circuits of each incoming-line circuit breaker; the incoming-line protection devices, in turn, feed back the circuit breaker position, line voltage/current status, and protection operation signals to the automatic transfer switch device via their DI (digital input) terminals.
-superiority:
-Technically mature, with high familiarity among field engineers
-Independent of the network; physical isolation provides stronger resistance to interference
Special note: Both solutions support the scenario in which the diesel generator is started after both of the city power feed-in lines have lost power. In the GOOSE solution, the start signal is issued via MMS or GOOSE; in the hard-wired solution, a dry contact signal is directly output through the DO terminals to the diesel generator controller.
V. Field Validation: A Case Study on the 10 kV Power Distribution Upgrade in an Industrial Park
Beyond theory, we have also seen endorsement from real-world projects.
In a data center project at a domestic bank, users replaced legacy electromagnetic relays with REF615 devices. This not only reduced the fault isolation time from 300 ms to just 40 ms, but also enabled millisecond-level coordination for the automatic transfer of bus tie backup through IEC 61850 GOOSE, thereby significantly improving power supply reliability.
This case fully demonstrates the practical value and reliability of the ABB 615 series relay protection devices in the application of automatic transfer switching.
Partial display of logical content
VI. Complex automatic backup power supplies can actually be made very simple.
In complex power-distribution scenarios involving incoming utility power lines, bus tie circuits, and multiple diesel generator sets, traditional solutions often fall into the predicament of "a mere accumulation of multiple devices, logically independent systems, and significantly increased commissioning difficulty."
The ABB 615 series, with its open programmable logic architecture and extensive logic library, enables users to use a single device to centrally program, centrally manage, and flexibly deploy all automatic transfer logic.
Regardless of whether the communication approach is a future-oriented GOOSE networking solution or a mature and reliable hard-wired solution, the most suitable path for the project can always be identified.
If you are interested in the solution presented in this article, or if you are seeking a self-feeding solution for a similar project, please feel free to contact us for further technical details and a customized solution. The ABB 615 series makes your power distribution automation projects smarter and more efficient.
