Digitizing the Electric Substation
An electric substation has many functions, including the transfer of power from high-voltage feeder lines to lower-voltage distribution lines. Substation secondary systems protect, monitor, and control the flow of power through primary equipment like power lines, busbars, and switchgear.
Conventional substation designs rely on long runs of energized copper wire to connect primary equipment to relays and other secondary system devices in the control house.
Modern digital secondary systems can implement merging units in the substation yard to replace much of that copper wiring. Merging units digitize electrical signals from primary equipment and send those data to relays over fiber-optic cable, reducing the cost and physical footprint of field wiring. Data are transmitted over fiber-optic cable using pulses of light, making it much safer than electrified copper wire.
Protection schemes can even benefit from the additional logic in IEDs. Cabante says Davao Light is using “advanced features [that] protect the power line, especially in rural areas, where we need more sensitivity and reliability.” Nolasco Padillo, a system operations supervisor at Davao Light, also notes that high-resolution data collection and reporting improves system visibility at the control room level. Better visibility, in turn, means Davao Light can quickly identify problems and dispatch repair crews.
“Digitization aligns with our goal and mission to serve the customer better because we can restore—as early as possible—our substations that are down or in trouble.”
Cost, safety, and other factors make digitization a popular goal, but the network engineering required in many digital secondary systems creates a new challenge. Data have to move quickly—and without interruption—between merging units and relays to ensure fast tripping. Many approaches exist to solve this challenge, and Davao Light chose to adopt the international IEC 61850 technical standard to maximize ownership over their designs.
Innovating at Every Step
Davao Light wanted their digital secondary system to be reproducible and scalable, which would simplify substation design in the future. They also wanted to ensure that the design would meet the needs of different populations throughout their service area.
Davao Light Senior Protection Engineer Nesvelle Mae Pascua-Amper explained that “SEL devices are really customizable, so [when ordering a product] we can customize proposed relays or devices to meet our specific needs and preferences in every substation.” Standardizing on a set of devices but customizing each device’s details means engineers can create a single substation design but adjust device settings for each service area.
“In an urban area, we need a substation that will run even if the network is down,” Cabante says, while rural areas “need reliable, high-impedance fault detection because of overhead lines.”
They decided to use two intelligent merging units in their design: the SEL-401 Protection, Automation, and Control Merging Unit and the SEL-421 Protection, Automation, and Control System, each of which also acts as a backup protective relay in addition to creating Sampled Values data streams for other protective relays in the substation. This degree of redundancy is important in power system protection, particularly for high-impedance faults, where trip signals must be sent and processed in a fraction of a second to protect lives, property, and equipment.
Davao Light implemented a software-defined networking (SDN) solution, which pre-engineers all communication routes and ensures network availability. Gray had provided training in SDN using SEL-5056 Software-Defined Network Flow Controller software, and Davao Light’s engineers innovated from that foundation to create a solution that improved reliability for a system with primary and backup merging units.
Integrity. Teamwork. Innovation. Responsibility. Service Excellence.
Davao Light’s engineers knew their drive to innovate had to be moderated by their responsibility to continue serving the community. The team planned a series of successively more complex substation projects to keep reliability and safety as top priorities. Subsequent substations maintain or improve those standards while testing methods to decrease costs.
Engineers first retrofitted an older substation with modern IEDs and some IEC 61850 communication protocols as a test implementation, which gave them confidence in moving forward. Newly constructed substations were full IEC 61850 implementations, and substations currently under construction will test a wider variety of devices for interoperability.
Padillo explains that each successive design lets them improve without treating each new substation as a blank slate. “Because of our experience with the first substation, the succeeding substation was improved. We applied the lessons of those substations, and the third is even better. The fourth [substation] is expected to be better and more efficient.” He added optimistically, “We can continue to get better.”