Product Introduction

The ABB UNS4881b,V4 3BHE009949R0004 is a complete digital automatic voltage regulator (AVR) unit from ABB UNITROL 5000 series, dedicated for synchronous generator excitation control. It adopts high-speed digital control algorithm to perform precise terminal voltage regulation, excitation current control and reactive power management. With integrated multi-protection logic and abundant communication interfaces, this unit supports automatic and manual control mode switching, delivering stable and safe operation for large generators in thermal power, hydropower and industrial captive power plants.

Content Details

ABB UNS4881b,V4 3BHE009949R0004 is a fully integrated excitation control unit for ABB UNITROL 5000 static excitation system. This digital AVR continuously samples generator voltage and current signals from VT and CT loops in real time, calculates control outputs dynamically and sends firing commands to thyristor rectifier bridges to adjust generator rotor excitation current. It maintains generator output voltage within tight tolerance under variable load conditions and stabilizes reactive power flow during grid fluctuation. The controller supports seamless switching between automatic voltage regulation mode and manual field current control mode, ensuring uninterrupted operation when faults occur.

It is built with comprehensive protection and limiting functions including V/Hz limitation, excitation overcurrent protection, underexcitation protection, overvoltage protection and loss-of-field protection. These protection functions prevent generators from running outside safe operating boundaries and reduce the risk of generator damage during grid faults. Multiple communication interfaces such as PROFIBUS DP and Modbus are available, supporting data connection with SCADA and upper monitoring system for remote parameter configuration, real-time data viewing and fault event recording.

Equipped with powerful self-diagnosis and watchdog monitoring functions, the unit continuously checks input signal loops, internal processor status, power supply and communication links. If signal loss, power abnormality or hardware failure is identified, the controller will trigger local alarms and store fault records for post-fault analysis. Constructed with industrial-grade electronic components and conformal coating, the AVR unit has outstanding shock resistance, vibration resistance and strong EMC performance. It can work steadily in control cabinets with high electromagnetic interference, wide temperature variation and humid environment in various power generation sites.

The compact enclosure design simplifies installation and wiring work. Front panel LED indicators and local operation keys allow field engineers to view running parameters and read fault codes directly without extra configuration tools. Widely used in large synchronous generator excitation control and grid-connected power generation projects. Before shipment, each ABB UNS4881b,V4 unit passes full function test, closed-loop simulation test and aging inspection to eliminate hidden hardware defects and guarantee reliable 24-hour continuous operation of generator sets.

Tags: UNS4881b V4 3BHE009949R0004 ABB UNITROL 5000 AVR

ABB CI546 3BSE012545R1 S100 I/

ABB UCD240A101 3BHE022287R0101

ABB UCD224A103 3BHE023681R0103

ABB DSSR122 48990001-NK DC-DC