Basler CBS 305 Current Boost System – Enhancing Fault Current Capability

The Basler Current Boost System Model CBS 305 is a specialized excitation booster that provides a temporary increase in generator field current during system faults. By boosting the excitation voltage, the generator can deliver higher short-circuit current, ensuring that protective devices such as fuses and circuit breakers operate within their designated time-current curves.

Need for Current Boosting

In many power systems, the fault current contribution from a generator may be insufficient to reliably trip downstream protection, especially when the generator is operating at reduced excitation or behind high-impedance transformers. The CBS 305 addresses this by sensing a voltage dip or a rate-of-change of current and rapidly increasing the field forcing voltage.

How It Works

The CBS 305 monitors the generator terminal voltage and/or current using internal transducers. When a fault is detected (e.g., voltage drops below 85% of nominal), the system activates a boost circuit that supplies additional DC voltage to the exciter field. This results in a 20–30% increase in short-circuit current for a duration up to 10 seconds, enough to clear most faults.

Key Features

• Solid-state design with fast response (< 5 ms)

• Adjustable boost threshold and duration

• Automatic reset after fault clearance

• Compatible with all Basler static exciters and AVRs

• Diagnostic LEDs for boost status and alarms

Technical Specifications

• Supply Voltage: 120/240 VAC or 24–48 VDC

• Boost Output: Up to 150% of nominal exciter field voltage

• Current Boost Magnitude: Adjustable 10%–50%

• Response Time: < 3 ms from fault detection to full boost

• Operating Temperature: -40°C to +70°C

• Enclosure: IP20, DIN rail mount

Installation and Integration

The CBS 305 is easily integrated into existing excitation systems. It connects to the AVR’s field circuit and receives trigger signals from the generator voltage transformer or current transformer. The unit includes isolation interfaces to prevent ground loops and ensures that the boost action does not interfere with normal AVR regulation.

Setting and Tuning

Using front-panel potentiometers, the boost threshold (voltage drop percentage), boost duration, and maximum boost current are adjustable. A test pushbutton allows simulation of a fault condition to verify system operation without actual faults.

Protection and Safety

The CBS 305 includes thermal protection to prevent overheating during extended boost cycles. It also has a timeout feature that limits the boost duration to prevent excessive field heating. An alarm relay provides annunciation of boost activation or system faults.

Applications

This system is particularly valuable in isolated power systems, marine applications, and standby generators where fault currents are inherently limited. It helps ensure that protective coordination is maintained, reducing the risk of arc flash and equipment damage.

Maintenance

Routine maintenance involves periodic function tests and visual checks of wiring and connectors. The unit is designed for long life with minimal degradation.

Conclusion

The Basler CBS 305 Current Boost System is an essential enhancement for generator protection, providing the necessary fault current to clear downstream faults quickly and safely.