Arcteq delivered an AQ-2000 medium-voltage arc quenching system to Stora Enso’s Anjala paper mill. The 6-kV switchgear retrofit project used the AQ 100 series arc protection system.
The main goals were twofold: cost savings and extending the lifetime of the switchgear originally installed in 1976. Both were achieved: five million euros were saved, while the switchgear gained a couple of decades to its life.
Extending the Life of a 40-Year-Old Switchgear
The project got its start in 2017 with the installation of the plant’s second Motor Commander unit for one of its 8-MVA motors. Power quality issues had forced the removal of the current limiter, which then caused the circuit breakers to exceed their short circuit capacity. Luckily, this did not adversely affect the withstand ratings of the busbar and the disconnectors. The current limiter also caused an unacceptable voltage drop during motor starting, which was another reason to remove the limiter from the system.
The 6-kV switchgear retrofit project was implemented using the AQ 100 series arc protection system. The system detects an arc flash, which triggers the arc quenching device. Next, the AQ-2000 system (based on the patented and dependable Thompson coil technology) extinguishes the starting arc fault by creating a controlled low-impedance path for the arc fault current to flow through. The implemented system provides a total arc elimination time of as fast as 5 milliseconds, and the level of arc flash incident energy is less than 1.2 cal/cm2.
“We were especially impressed by the re-usability of Arcteq’s quenching device,” says Harri Mörsäri, Engineering Manager at Stora Enso.
Arcteq’s scope of supply in the project also included an AQ-M215 motor protection relay and an AQ-V211 voltage protection relay. However, as arc flash protection is the most sensitive and critical protection for the plant and keeping the system within the dedicated arc flash protection is crucial for the plant’s continued operation, these other protection relays were kept separate from the arc protection system. We also provided commissioning services and training for Stora Enso specialists. The project was completed and commissioned in August 2017, and it extended the life of the switchgear for another couple of decades.
How to Save Five Million Euros
As well as extending the life of the switchgear, Stora Enso looked to save costs. Stora Enso had two alternative investment models: they could retrofit the breakers and relays and improve on safety by installing an arc quenching device, or they could replace the entire switchgear lineup with a new one.
“The cost of implementing a circuit breaker retrofit and adding arc quenching technology was significantly less than the cost of a brand-new switchgear lineup. Also, the required shutdown was shorter,” says Mr. Mörsäri.
Installing new switchgear would have cost almost 5.2 million euros more than the retrofit option. The bulk of the costs of installing whole new switchgear came from the ten additional days that the plant would have had to be shut down for the installation of the new switchgear, amounting up to five million Euro. The retrofitting, on the other hand, could be done during a normally planned maintenance outage, therefore not causing additional costs for extra outages.
A Continuing Partnership in Protection
Stora Enso’s very first acquaintance with Arcteq was the installation of Arcteq’s revolutionary Motor Commander, for protecting and controlling two of Stora Enso’s 8-MVA synchronous motors.
“We were the first ones to buy and apply the Motor Commanders. The very first one was commissioned in December 2016,” Mr. Mörsäri adds.
In Phase 2 of the retrofit project, Arcteq supplied 2-winding and 3-winding transformer protections for the facility. This phase of the project was completed and commissioned in May 2018. The third Motor Commander installation was completed and commissioned in the fall of 2018.
The Anjalankoski paper mills, colloquially known as Anjala, were founded in 1938 and are located in Southeastern Finland in Inkeroinen. The thermomechanical plants produce book and magazine paper and folding boxboards. With Europe as the main market and 500 employees, the mills’ annual turnover is over 450 million Euro. The plant has seven main transformers, two 110-kV switching stations, and approximately 300 bays, and its active power consumption is 140 MW.