Fast and stable at the same timeThe extremely short operate time of RED 521 is typically 10-15ms at all internal faults, regardless of the number of connectedfeeders. At the same time, the terminal maintains completestability for external faults, even when heavy CT saturationoccurs. This unique combination of speed and stability is essentialfor effective busbar protection. RED 521 has very low CTrequirements compared to other numerical differential protectiondevices due to its unique measuring principle. This also allowssharing of CT circuits with other relays to save costs.
Easy to useRED 521 offers a compact solution that can be easily adaptedto different busbar configurations. Up to 18 current transformerscan be connected directly to the terminal. It is simple to engineerfor any application since only two operational settings and nointerposing auxiliary CTs are needed. The CT ratios are enteredas primary values from the front mounted HMI. This significantlyreduces both commissioning and installation time. RED 521 isthe ideal solution for your retrofits and new installations sinceit can be connected to the same CT cores as protection relayswithout auxiliary CTs.