BZU-4A-2S

BZU-4A-2S in aircraft AC power systems

The BZU-4A-2S is an aircraft generator protection and control unit used in three-phase AC power supply systems. It is installed where the aircraft electrical network must work with generators connected to the onboard AC bus and where automatic switching, monitoring and protection are required. The unit controls the generator channel, checks the main electrical parameters and prevents unsafe operation of the onboard power system. In helicopter applications, this block is associated with AC power systems operating at aircraft standard frequency and voltage.

Generator control through BZU-4A-2S

The main task of the BZU-4A-2S is to manage generator connection and disconnection according to system conditions. When the generator reaches the required operating parameters, the block allows it to be connected to the aircraft network. When the engine or generator stops, or when the electrical parameters move outside the permitted range, the unit removes the generator from the bus. This automatic logic is important because the crew should not have to manually control every transient process in the power system during start, shutdown or abnormal operation.

BZU-4A-2S protection of the onboard network

The BZU-4A-2S protects the aircraft AC network from dangerous operating conditions. It monitors voltage, frequency, phase condition and load-related faults, including overload and short-circuit situations. If the controlled parameters become unsafe, the unit disconnects the faulty generator channel or prevents connection to the network. This protects consumers connected to the aircraft AC bus and helps avoid damage to wiring, generators, regulators and onboard equipment. In practice, the block works as a gatekeeper between the generator and the aircraft electrical system.

Parallel generator operation with BZU-4A-2S

The unit is designed for systems where two three-phase generators can operate in parallel from a common drive arrangement. In such systems, control is more demanding than in a simple single-generator circuit. The block must take into account not only voltage and frequency, but also phase symmetry, correct phase sequence and safe connection timing. Incorrect connection of a generator to the bus can create high current loads or disturb the whole electrical system. The BZU-4A-2S helps keep parallel operation within the required limits.

BZU-4A-2S with GT40PCh and BRN-208M equipment

The BZU-4A-2S may work together with aircraft AC generators such as GT40PCh-type generators and voltage regulation units such as BRN-208M, depending on the aircraft power system configuration. The generator produces the three-phase AC supply, the regulator stabilizes the voltage, and the protection / control unit supervises switching and fault response. A problem in the electrical system should therefore not be assigned to the BZU block automatically. During troubleshooting, the generator, regulator, wiring, sensors, contactors and protection unit all need to be checked as one system.

Aircraft application of BZU-4A-2S

The BZU-4A-2S is associated with helicopter AC power systems, including Mi-24 and Mi-26 applications and related modifications depending on equipment configuration. In these aircraft, the unit is installed as part of the electrical power generation and distribution system rather than as a cockpit control device. Its exact location and connection depend on the aircraft version and the installed equipment rack layout. Before replacement, the unit should be checked against the aircraft parts catalog, wiring diagram and power system documentation.

Construction and supply of BZU-4A-2S

The BZU-4A-2S is made as a plug-in aircraft electronic block in a metal housing. It is intended for continuous operation in aviation conditions, including vibration, temperature variation and mechanical loads typical of helicopter service. For procurement, the exact designation BZU-4A-2S Series 2 should be stated clearly. The block may be supplied as new, stored, repaired or overhauled depending on availability. For aircraft use, the passport, repair status, test documentation, completeness and compatibility with the target power system should be verified before shipment.

Product Type: Aircraft generator protection and control unit
Designation: BZU-4A-2S / BZU-4A-2S Series 2
Function: Generator control, protection and monitoring in aircraft AC power systems
Application / Where Used: Three-phase AC aircraft electrical power supply systems
System / Installation Area: Generator control and protection channel; aircraft AC power generation and distribution system
Compatible Aircraft / Equipment: Mi-24, Mi-26 and related helicopter modifications depending on electrical system configuration
Associated Generators: GT40PCh-type aircraft AC generators, depending on installation
Associated Regulation Equipment: BRN-208M-type voltage regulation units, depending on system configuration
Control Power Supply: 27 V DC
Permissible DC Supply Range: 27 V ±2.7 V, up to 30 V according to system data
Controlled AC Network: Three-phase AC
Controlled AC Voltage Range: 201.8–210 V
Nominal Controlled Frequency: 400 Hz
Additional High-Frequency AC Supply: 35–53 V AC, 800 Hz
Operating Mode: Continuous operation
System Function: Support of parallel operation of two generators from a common drive arrangement
Protection Functions: Overvoltage, undervoltage, frequency deviation, overload, short circuit, phase imbalance and incorrect phase sequence control
Time Delay Logic: Built-in time relay thresholds to reduce false trips during short transient deviations
Construction Type: Plug-in block-type unit in metal housing
Dimensions: 302 × 208 × 128 mm
Weight: Not more than 6.2 kg
Manufacturer: Sarapul Electric Generator Plant / SEGZ, according to supplied technical description
Technical Documentation: Product passport, test documentation, repair / overhaul documentation and aircraft maintenance documentation as applicable

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Warranty
All products are covered by a standard 6-month warranty.
Extended warranty is available upon request and is agreed individually; it may affect the final product price.