The Temelín nuclear power plant in the Czech Republic provides one-third of the country’s generation capacity. With the 30th year of plant operation approaching, ČEZ, the country's power system operator, launched an extensive program of upgrades and maintenance to equip it for the next 30-plus years.To minimize plant downtime, maintenance activities and upgrade projects take place during planned refueling outages, which occur every 10–16 months. The work demands meticulous planning and efficient execution.So when it came time to replace obsolete protective relays and upgrade the Temelín plant’s generator protection systems, ČEZ had already calculated the length of the necessary downtime precisely and carefully.I&C Energo, an integrator that has performed maintenance on the Temelín plant for 25 years, won the bid to manage the project; it would be responsible not only for executing the onsite work, but also for coordinating the work of other integrators and contractors.“The contract very strictly prescribes what to do and how much time you have,” says I&C Energo Division Director Jiří Kropáček. “You have to keep to the schedule. When the unit is out of operation, every hour has a cost.”
Obstacle and Opportunity
I&C Energo selected Montáže Čakovice, an integrator that specializes in power system design, installation, and commissioning, to perform the generation unit protection system upgrades. Montáže would be responsible for procuring new generator protective relays and related devices and designing a new protection system that included modern features like system monitoring, automated data collection, and event recording. But when the company solicited bids for the relay replacement, it hit an obstacle: each vendor stipulated that the generation units’ aging CTs would have to be replaced.“The current transformers could potentially saturate very fast during a fault,” explains Montáže engineer Zdeněk Tomáš. “They were working; there was no failure, but the power of the current transformer would potentially be too low for the proper operation of the relays."
ČEZ knew it would be necessary to replace the CTs at some point, but replacement would require expensive custom manufacturing, extend the nuclear plant’s downtime, and cause unacceptable operating losses. They needed the CTs to last as long as possible.Upon considering the CT replacement problem, Mr. Tomáš and the engineering team at Montáže realized they had something that might solve it: their partnership with SEL.Montáže Čakovice and SEL have been working together since 1998, when Montáže became one of the first integrators to partner with SEL in Europe. If there was a way to provide reliable protection while keeping the existing CTs in service, Mr. Tomáš and his team trusted that SEL, with its sophisticated power system modeling and testing capabilities, could find it.
Partnership and Problem Solving
Mr. Tomáš called his contacts at SEL, explained the challenge and the opportunity, and asked if it was something they wanted to take on. It was.Mr. Tomáš and his team worked with technicians at the Temelín plant to collect detailed data on the characteristics of the CTs and associated equipment, then communicated that information to the engineers at SEL headquarters in the United States.A team of SEL engineers quickly created a model of the generation system in their Real Time Digital Simulator (RTDS) testing facility and prepared to test the ability of SEL relays to respond to the output of the CTs.The RTDS system uses powerful computing to simulate the characteristics of electric power systems in accurate detail and produce the output signals used by relays in making protection and control decisions. This enables SEL to perform extensive hardware-in-the-loop (HIL) testing, in which protection and control devices are plugged into the RTDS racks and subjected to a multitude of fault conditions and operating scenarios. This process can provide data equivalent to years of operational history in only a few days, yielding rich data on how and why electric power systems and protective relays work the way they do.SEL would use this system to produce data on exactly how its relays responded to input from the Temelín nuclear plant CTs under a variety of fault conditions.
The HIL testing verified that, just as the other relay vendors had assumed, the CTs would saturate too quickly to provide a sufficient signal for the protective relays. However, because SEL relays collect data on the inputs they receive, the actions they take, and the system events they detect, the HIL tests revealed much more. A close examination of the relays’ response to the current inputs revealed the possibility that certain nonstandard settings could allow SEL generator protective relays to operate dependably with the ČEZ Temelín plant’s existing CTs.Unlike competitors' relays, SEL protective devices are designed with the flexibility to handle nonstandard inputs. And SEL not only had the ability to perform HIL testing in house, but could also provide testing data to the customer at no additional cost.So, SEL product development engineers calculated the specific settings, deployed them in an SEL-400G Advanced Generator Protection System relay, and ran the HIL tests again—testing, retesting, and meticulously documenting the results—to ensure a reliable response under all fault conditions. Montáže's team then presented the final test results to I&C Energo, demonstrating conclusively that SEL relays could save ČEZ the time and cost of replacing the CTs.Now SEL and Montáže Čakovice had to make it happen.
A Race Against the Clock
Device production, system design, relay commissioning, testing, installation—everything had to go smoothly to get the job done within the allotted schedule.As device production began at the SEL manufacturing plant, engineering teams from Montáže and SEL embarked on another collaboration designed to streamline the protection system upgrade. Technicians from Montáže gathered detailed information on the hardware at the Temelín plant, providing panel wiring diagrams and precise specifications on the legacy relays’ terminal block configurations.Engineers at SEL referenced that information to create prewired direct-replacement assemblies and construct new panels for the generator protection solution featuring the SEL-400G. These assemblies and panels would remove the need for the onsite installation teams to make complex wiring changes and dramatically reduce the time required for installation.
Montáže Čakovice partnered with SEL to provide a modern generator protection system for the ČEZ Temelín nuclear plant. Pictured are an SEL-400G, SEL-849 relays, monitoring stations with HMI screens, the nuclear plant’s cooling towers, and the substation outside the generation unit.
The SEL panels and direct-replacement assemblies reached the Czech Republic on schedule. Montáže then assembled the new panels and began the work of commissioning the relays and testing the system. With calibration values calculated by SEL engineers, configuring the relays went smoothly, and the Montáže team began testing the panels.
“We had all the time we needed to commission the relays and test them in our laboratory. When it was time for FAT tests, we were absolutely sure the system worked as designed.”
As the certified nuclear system integrator responsible for the final product, I&C Energo also needed to be absolutely sure of the system’s reliability. The generation plant and the Czech Republic’s electric power system depended on it. In testing the first set of panels, the I&C Energo team scrutinized every detail and inspected the panels down to each individual wire. Having verified that the work done by Montáže and SEL met their high standards, they were then able to streamline subsequent tests.
I&C Energo was also responsible for installing the new protection system at the ČEZ Temelín plant. Here, the work Montáže and SEL had put into the direct-replacement assemblies paid off; the process of removing the old panels and replacing them with the new proceeded with no delays or complications.
“It was our first cooperation with Montáže Čakovice. Our people were very satisfied with them. It is very, very difficult to do retrofits in such a strictly prescribed time, and there were no problems. Everything went well.”
Montáže Čakovice and SEL, working together, enabled I&C Energo to deliver for its biggest customer—saving the customer millions of dollars in the process.Since the generator protection upgrade in 2023, the system has performed reliably, as expected—and the advanced monitoring features of the SEL devices have enabled ČEZ Temelín technicians to maximize generation unit uptime by using detailed event reports to diagnose problems and prevent reoccurrences.
I&C Energo provides system integration services for large industrial plants and the power industry, where nuclear power is its principal sector. The company is able to assume full responsibility, from the projection stage through procurement, construction, and commissioning, as well as any subsequent service.
Montáže Čakovice offers engineering, supply, and assembly services with a focus on design, manufacturing, and installations for power systems. It is the authorized sales representative and system integrator for SEL in the Czech Republic and Slovakia.
More Highlights
Contact Us
For more information about this story’s featured solution or how SEL can engineer solutions to meet your needs, contact us below.