DMR-200D

DMR-200D differential relay for DC generator control

The DMR-200D is a differential minimum relay used in aircraft DC power supply systems. It controls the connection of a DC generator to the onboard electrical network and disconnects it when the generator can no longer supply the system correctly. This is not a voltage regulator. Its job is closer to generator switching and protection. The relay monitors the voltage relationship between the generator and the aircraft bus, then allows or blocks generator connection according to the operating condition.

Generator connection logic through DMR-200D

In normal operation, the DMR-200D connects the generator to the onboard network only when the generator voltage is slightly higher than the bus voltage. This prevents unstable or premature connection. If the generator voltage falls below the network level and reverse current appears, the relay disconnects the generator. That protection is important in DC systems, because a weak or failed generator should not be driven by the aircraft electrical network as a motor.

Protection functions of the DMR-200D unit

The relay also protects the system against incorrect polarity connection. If the generator polarity is wrong, the unit blocks connection to the network. Depending on the aircraft electrical layout, the DMR-200D may also take part in remote generator switching and indication circuits. In practice, the relay is checked together with the generator, contactor circuits, wiring, generator control panel, and bus voltage. A generator fault and a relay fault can look similar from the cockpit, so troubleshooting usually follows the aircraft electrical diagram.

Aircraft electrical system with relay DMR-200D

The DMR-200D is used in DC generator circuits of aircraft and helicopters. It is known from Soviet and Russian aircraft electrical systems, including helicopter applications such as Mi-2 and other platforms using comparable DC generator architecture. The exact installation depends on the aircraft type and the generator set fitted to the aircraft. The relay works in the power supply chain together with the generator, voltage regulation equipment, contactors, switches, busbars, and warning circuits.

Identification and ordering checks for DMR-200D

Before ordering, the installed relay marking should be checked against the aircraft parts catalog, acceptance label, or maintenance documentation. In English requests, the designation is usually written as DMR-200D. In Russian documentation it appears as ДМР-200Д. The relay rating and installation variant should be confirmed by the aircraft electrical system documentation, not only by the general name. The product is also known under alternative designation ДМР-200Д.

Product Type: Differential minimum relay for aircraft DC generator systems
Function: Automatic generator connection, reverse current protection, polarity protection, remote switching support
Application / Where Used: Aircraft DC electrical power supply systems
System / Installation Area: Generator control and onboard DC network protection circuit
Compatible Aircraft / Equipment: Aircraft and helicopters equipped with applicable DC generator systems
Operating Voltage: 25–30 V DC
Generator-to-Bus Voltage Difference for Connection: 0.2–1.0 V
Reverse Current for Disconnection: Not more than 10 A
Nominal Current: 200 A
Weight: Not more than 1.6 kg
Technical Documentation: DMR-200D acceptance label / technical documentation

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