Primary-switch-mode power supplies provide very-fast response to overcurrent conditions on the output side, promoting extended operating life.
A downside is that selective protection of individual current paths on the secondary side via standard circuit breakers often is ineffective when a Top Boost function, providing excess current for a short time, is not available for high-speed magnetic tripping.
To help solve this problem, Wago announced three new electronic circuit breakers for its line of 787 Series power supplies that will provide selective protection for power supplies without a Top Boost feature.
"The short-circuit current is limited using an active current-limiting circuit breaker, preventing voltage drop across adjacent current paths," says Michelle Goeman, product manager. "In addition to parameter setting, the display and serial interface control both the integrated fault memory and the instantaneous values of the output current and voltage. So, it can perform not only proactive monitoring and fault diagnostics, but also energy monitoring."
Such monitoring capabilities are ideal, says Goeman, in applications for which events must be logged, such as those in food, medical or process industries, where loads are separated over long distances, or if remote access is required.
Goeman says the DIN-rail mounted 787-860, 787-861 and 787-862 electronic circuit breakers each separately protect up to four current paths (up to 10 A at 24 Vdc max each), while offering independent programming of appropriate channel- or circuit-specific ratings and trip times via 759-860 Configuration software included free of charge with the hardware.
"In the event of a fault or short circuit, the electronic circuit breakers can shut down the tripped channel within 10 msec," says Goeman. "Rather than halting the entire system, power is maintained to other loads, for example, to a PLC on one path and HMI on another. This prevents a systemwide shutdown, as well as possible data loss. Afterward, the tripped load may be remotely reset via a control input or from the display."
With the free visualization software or an on-unit LCD, the 787 series breakers provide independent channel-monitoring of voltage, current, fault diagnostics and energy consumption. "Some additional features include four current channels with delayed switching-in of channels at 250 msec/channel, a rugged metal housing, LED status indication, signal outputs and Cage Clamp, spring-pressure, connection technology for vibration and maintenance-free terminations," states Goeman.
The 787-861 electronic circuit breaker features an integrated short-circuit current limitation, which avoids overload of upstream power supply units. This guarantees definite shutdown selectivity. "The 787-860 and 787-862 don't have short-circuit current limitation," says Goeman. "However, they have adjustable trip times for quicker responses.”
Goeman adds that the electronic circuit breaker modules are optimized for advanced applications or those distributed over great distances. "The devices can be used behind primary switch mode power supply units with any overload or short circuit behavior," she states. "If the output of the power supply unit is divided into several circuit paths, the electronic circuit breaker will protect the circuit paths separately. This makes the electronic circuit breakers ideal for control panels or machines powered by a single, larger power supply."
All three models are 40x127x163 mm and weigh 800 g. The devices conform to UL 1077, UL 2367 (for 787-861), EN 60959, EN 61000-6.2 and EN 61000-6.3, and UL 508 is pending.
