Is-Limiter: Fault current limiter

The I_S-limiter is a fast current limiting device designed to protect electrical systems from the damaging effects of short-circuit currents. It detects rising fault currents almost instantaneously and interrupts them before they reach dangerous levels -within  few milliseconds.

By limiting the short-circuit current, the IS-limiter protects critical equipment infrastructure such as medium voltage and low voltage switchgear and transformer.  It is widely used in industrial facilities, power distribution networks, and data centers where continuity of service and equipment protection are essential.

The I_S-limiter works by detecting and interrupting high short-circuit currents within less than 1 millisecond. It continuously monitors the current flowing through the system. It detects rising fault currents based on at least two criteria almost instantaneously and interrupts them within milliseconds.

 The I_S-limiter consists of two parallel paths: The main current path carries the high rated normal current, while the fuses for limitation are connected in parallel.  The control unit is constantly monitoring the current and sends in case of a fault - under the assumption that the specific tripping criteria are met- a tripping signal to the charge element within main current path, which results in a disconnection. The parallel current path with fuse limits the short-circuit current during the first current rise (less than 1 ms). This design ensures that the short-circuit current within the system can be limited to the withstand capability of the weakest component.

 This combination of fast detection and mechanical action drastically reduces the peak fault current seen, and energy released into the system, effectively protecting the equipment.

ABB’s I_S-limiter offers a range of advantages that enhance system protection, reliability, and operational efficiency:

• Rapid fault current limitation: It detects, and interrupts short-circuit currents within milliseconds, significantly reducing peak current and energy let-through to protect downstream equipment
• Improved system uptime and redundancy: By enabling safer interconnection of networks or transformers, it increases operational flexibility and continuity of service – ideal for mission-critical environments
• Energy-efficient system performance: Limiting fault current levels allows for optimized load flow and can reduce overall energy losses in the distribution network
• Simple and flexible installation: The I_S-limiter is designed for easy integration into both indoor and outdoor environments with a compact, plug-and-play design
• Accelerating project timelines: It solves short-circuit design challenges in both new (greenfield) and existing (brownfield) installations
• Proven global reliability: With successful applications in over 80 countries, the I_S-limiter is a trusted solution across a wide range of industries and power systems worldwide

The I_S-limiter is designed for simplicity in both operation and maintenance. Once installed, it functions automatically and requires no operator intervention during normal system conditions. Its control unit continuously monitors current flow and automatically triggers the limiting function when a short-circuit event is detected – ensuring protection without the need for manual action.

From a maintenance perspective, the I_S-limiter has a modular design with easily replaceable components. After a fault event, the Is-limiter insert can be quickly and safely replaced, minimizing system downtime. Moreover, the tripped insert can be refurbished by ABB. 

The I_S-limiter is fast fault current limiting device. It detects rapidly rising fault currents and operates within less than a millisecond – much faster than a circuit breaker. Rather than waiting for the full fault current to build, the I_S-limiter limits the peak current during the initial rise of the fault current before it reaches damaging levels. This makes it valuable in systems where fault currents could exceed the ratings of the installed equipment.

 Furthermore, the I_S-limiter is designed to work in coordination with existing protection devices like circuit breakers and relays. It handles the immediate, fast response during a fault, while the circuit breaker follows with a full isolation of the faulted section. This layered protection approach enhances both system safety and equipment lifespan, without requiring major changes to the existing equipment and protection scheme.