Basler CBS377 Current Boost System
The Basler CBS377 Current Boost System (P/N 9109600102) is an advanced auxiliary device designed to amplify current signals from current transformers (CTs) in generator protection and control circuits. It compensates for CT burden and extends the effective range of protection relays, ensuring accurate operation under all fault conditions.
Purpose and Need
In large generator installations, the distance between CTs and protection relays can introduce significant burden, reducing the available secondary current. The CBS377 boosts the CT output, providing a clean, amplified signal to the relay, thereby improving sensitivity and reliability. It is especially beneficial when the original CTs are undersized or when additional loads are added to the CT circuit.
System Components
High‑gain amplifier module with differential inputs.
Built‑in power supply derived from the CT circuit.
Adjustable gain settings to match CT ratio and required output.
Status LEDs for power, saturation, and fault.
Compact DIN‑rail or panel‑mount enclosure.
Key Features
Wide input current range (0.1–10 A AC).
Gain adjustable from 1× to 10×.
Low phase shift (< 2°) for accurate relay timing.
Fast transient response (< 1 ms).
Isolated output to prevent ground loops.
Thermal and overcurrent protection.
Technical Specifications
The CBS377 operates from the CT secondary current itself, requiring no external auxiliary power. Input impedance is less than 0.1 Ω to minimise burden. The output current is proportional to the input with the selected gain, capable of driving standard relay inputs up to 20 A. The system is rated for continuous operation at 150 % of nominal current and withstood short‑time overloads up to 40 A for 1 second.
Installation and Wiring
Mount the CBS377 near the protection panel to minimise lead length. Connect the CT secondary leads to the input terminals, and the output terminals to the relay inputs. Ensure proper polarity: a reverse connection will cause a 180° phase shift. Ground the system at a single point to avoid circulating currents.
Setting the Gain
Determine the required gain by dividing the relay input requirement by the available CT secondary current. For example, if the relay needs 5 A but the CT supplies only 1 A at rated load, set the gain to 5×. The internal DIP switches allow stepwise gain adjustment. Verify the output with a current clamp meter during commissioning.
Applications
Common uses include generator differential protection, distance protection, and overcurrent schemes where CT performance is marginal. It is also used in retrofitting projects where existing CTs cannot be replaced, providing a cost‑effective solution to improve protection performance.
Testing and Commissioning
After installation, perform a primary or secondary injection test to verify the gain and phase shift. Inject a known current into the CT primary and measure the output at the relay. Check the LEDs for saturation indication; if the saturation LED lights, reduce the gain or increase the CT size.
Maintenance
Routine maintenance consists of visual inspection of terminals and cleaning. Re‑test the gain settings annually or after any modification to the CT circuit. The solid‑state design ensures high reliability with no moving parts.
Benefits Over Traditional Methods
Compared to using burden resistors or auxiliary CTs, the CBS377 provides active amplification with minimal phase error and higher dynamic range. It reduces engineering effort and improves overall protection coordination.
Conclusion
The Basler CBS377 Current Boost System is an essential tool for optimising CT performance in generator protection. Its flexibility, ease of installation, and robust design make it a valuable addition to modern power system protection schemes.
