Fault Current Limiters

See what a fault current limiter does ↓

A Cost-Effective Alternative for Distribution Utilities

Hyper Tech is developing a superconducting fault current limiter (FCL) for the distribution grid, designed to ride through qualifying momentary faults without the first recloser interruption. The design is intended to be cost-effective compared with an air-core reactor or a high-impedance transformer while consuming very little electricity during normal operation, when no fault current is present.

Why the First Recloser Opening Matters

Automatic reclosers open a faulted feeder and then reclose after a programmed interval. If the fault has cleared, service continues after the first reclose. If it remains, further trip-and-reclose attempts may occur before lockout. Even a brief loss of supply can stop a manufacturing line or transfer a data center onto backup power; sensitive equipment may shut down if its ride-through capability is exceeded.

Around 90 Percent Are Temporary on Many Overhead Feeders

Eaton's recloser guidance reports that approximately 80–95% of overhead-distribution faults are temporary, lasting from a few cycles to a few seconds. This is the context for the often-used figure of around 90%. Actual fault mix and recloser timing vary by feeder. Temporary faults are not necessarily able to clear while the line remains energized.

Design Goal Avoid the First Opening for Qualifying Momentary Faults

Hyper Tech's superconducting inductive FCL is intended to limit qualifying momentary fault currents before they cause the first recloser opening. The FCL and protection settings must be coordinated so the limited current and fault duration remain below the applicable first-trip time-current characteristic, while customer voltage stays within the equipment's ride-through limits. If the fault extinguishes under those conditions, the recloser can remain closed and the customer avoids a loss-of-supply interruption.

The goal is continuous operation through qualifying transient events, with very low electricity use during normal operation. Around 90% temporary faults does not establish a 90% interruption-avoidance result: the achievable percentage must be demonstrated for the feeder, fault types, clearing behavior, protection settings, and customer voltage tolerance.

Limit Fault Current Without Continuous High Losses

Distribution utilities must keep fault currents within equipment ratings while avoiding unnecessary customer interruptions. The superconducting FCL is designed to carry normal load current with very low losses and introduce current-limiting impedance during a fault. For qualifying self-clearing events, the coordinated system aims to avoid the first recloser opening. Persistent faults, faults requiring de-energization, and other conditions outside the ride-through envelope must still be isolated by the protection system.

Comparison with Conventional Equipment

Air-core reactors and high-impedance transformers are established ways to reduce fault current on distribution systems. Their purchase and installation costs, normal operating losses, and effect on voltage regulation all contribute to utility economics. Hyper Tech's superconducting FCL is being developed as an alternative that combines competitive installed cost with very low electricity consumption when no fault is present.

Superconducting FCL Operation

In normal operation, the superconducting circuit is designed for very low resistance and low insertion impedance. During a qualifying momentary fault, the inductive FCL limits current long enough for the fault to clear without the recloser opening, provided the customer voltage remains acceptable. For sustained or non-qualifying faults, coordinated protection must trip and isolate the affected circuit. Total normal operating electricity use includes cooling and auxiliary equipment as well as electrical circuit losses.

Lower Electricity Use and Competitive Lifecycle Cost

The central goal is to reduce the ongoing electricity cost of fault-current protection while maintaining a cost-effective alternative to an air-core reactor or a high-impedance transformer. Utility comparisons will consider installed cost, total normal operating electricity consumption, maintenance, fault-limiting performance, and recovery requirements over the service life.

Development Focus

Hyper Tech's development program focuses on distribution substations and feeders serving customers such as manufacturing facilities and data centers. Testing will assess first-trip avoidance, residual customer voltage, fault extinction, recovery, and protection coordination, alongside installed cost and total normal operating electricity use. The interruption-avoidance percentage is a result to be demonstrated, not an established product rating.