AZP-A2

AZP-A2 protection unit for aircraft DC networks

The AZP-A2 is an automatic overvoltage protection unit used in aircraft DC electrical systems. It protects the onboard network and connected equipment if generator voltage rises above the permitted level. This situation usually appears when the voltage regulation circuit fails, for example when a regulator of the R-27 type stops holding the generator output within the normal range. The AZP-A2 is not a voltage regulator. It is a protection device that disconnects the faulty source before overvoltage can damage onboard consumers.

Generator protection logic through AZP-A2

In operation, the unit monitors generator voltage in the DC power system. If the voltage exceeds the protection threshold and remains in the dangerous zone long enough to confirm a fault, the AZP-A2 sends a command to disconnect the generator. The trip delay is needed so the unit does not react to every short transient in the network. This is important in aircraft power systems, where short voltage jumps may appear during switching, load changes, or generator transition modes. The unit acts only when the condition matches the protection logic.

Aircraft power system operation with AZP-A2

The AZP-A2 works together with the generator, voltage regulator, excitation circuit, contactor equipment, DC busbars, warning circuits, and cockpit controls. When the protection operates, the generator excitation circuit is interrupted and the generator is removed from the onboard network. From the cockpit this may look like a generator failure, but the reason can be different: regulator fault, wiring issue, contactor malfunction, generator problem, or incorrect network behavior. Maintenance checks should therefore follow the aircraft electrical diagram, not only the protection unit itself.

Manual reset and testing of AZP-A2

The AZP-A2 is a single-action protection device in the sense that after operation it needs to be returned manually. The reset is made by pressing the button on the unit cover. On many aircraft, a ground test button is also provided to check the serviceability of the protection circuit. This test is useful because the protection must trip reliably, but it also must avoid false operation during normal short voltage changes. The measuring part of the unit is electronic and uses a time delay for more selective operation.

Identification and ordering checks for AZP-A2

The AZP-A2 is used in aircraft and helicopter DC power systems, including applications associated with Mi-8 / Mi-17 / Mi-171 and An-24 type electrical systems where this equipment is specified by documentation. Before ordering, the installed unit marking should be checked against the aircraft parts catalog, wiring diagram, or maintenance documentation. The designation may be written as AZP-A2 in export requests and as АЗП-А2 in Russian documentation. The product is also known under alternative designation АЗП-А2.

Product Type: Aircraft overvoltage protection unit
Function: Automatic protection of DC generator network against overvoltage
Application / Where Used: Aircraft and helicopter DC electrical systems
System / Installation Area: Generator protection circuit / DC onboard network
Compatible Aircraft / Equipment: Aircraft and helicopters with applicable 27 V DC generator systems, including Mi-17, Mi-171, Mi-8 and An-24 type installations when confirmed by documentation
Associated Equipment: DC generator, voltage regulator including R-27 type, excitation circuit, generator contactor, DC busbar
Operating Mode: Single-action protection with manual reset after operation
Measuring Element Type: Static electronic measuring element with time delay
Protection Action: Disconnects generator by interrupting excitation circuit / removes generator from onboard DC network
Reset Method: Manual reset button on unit cover
Ground Test: Supported where provided by aircraft wiring
Technical Documentation: Aircraft electrical system documentation / AZP-A2 maintenance documentation

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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.