BZUNP355G

Control functions of the BZUNP355G unit

The BZUNP355G controls generator connection and disconnection logic and monitors abnormal operating conditions in the aircraft AC system. Its protection functions cover short circuit conditions, overvoltage, undervoltage, frequency deviation, and incorrect phase sequence. These are not separate manual functions for the crew. The unit processes the relevant signals inside the electrical protection chain and acts through the connected switching and control circuits. In service, a fault in this area may involve the BZUNP355G itself, but it can also be related to wiring, current transformers, voltage regulation equipment, or generator output condition.

BZUNP355G with voltage regulator and transformer blocks

The unit works with the BRN120T5A-3C voltage regulator, current transformer blocks, and phase sequence control equipment. These connected units form the working protection loop around the AC generator. The voltage regulator controls generator output, the current transformer block provides current-related signals, and the phase control equipment monitors correct phase order. The BZUNP355G ties this information into the control and protection logic. During troubleshooting, this matters: replacing only one block without checking the rest of the circuit may not remove the fault, especially on helicopters after overhaul or partial electrical system repair.

Aircraft application of BZUNP355G

The BZUNP355G is used on Mi-8, Mi-17, Mi-171, Mi-172, Mi-26, and Ka-32 helicopters fitted with compatible three-phase AC power supply systems. Installation details may vary by helicopter type, production batch, and modification standard. On Mi-8 / Mi-17 family helicopters, the unit is associated with the onboard AC generator system and electrical compartment equipment. On Mi-26 and Ka-32 installations, the operating role is similar, but wiring, panel layout, generator configuration, and connected protection equipment may differ. For replacement, the aircraft type alone is not enough; the unit marking and aircraft electrical documentation should be checked.

Identification and ordering of BZUNP355G

Before ordering a BZUNP355G unit, compare the marking on the housing with the aircraft parts catalog, product passport, or repair documentation. The designation may appear as BZUNP355G, BZUNP-355G, БЗУНП355Г, or БЗУНП-355Г depending on the document language and formatting. For mixed fleets, repaired helicopters, or machines with updated electrical panels, it is better to provide a photo of the data plate and the relevant electrical system reference. The unit may also be checked using the BZUNP355G NVKV.301433.006 diagnostic panel. The product is also known under alternative designations BZUNP355G and BZUNP-355G.