The AREVA MICOM P391 Rotor Earth Fault Detector is a dedicated protection accessory designed for generator rotor insulation monitoring applications. It is part of the MiCOM P34x generator protection family and provides rotor earth fault detection by injecting a low-frequency signal into the generator field circuit and measuring insulation resistance changes.

The P391 works together with MiCOM P342, P343, P344, and P345 generator protection relays through a current loop interface. It provides continuous monitoring of rotor winding insulation condition and helps detect field winding earth faults before they can cause serious generator damage.

This module is widely used in power plants, turbine generator systems, and industrial generator protection applications where reliable rotor insulation supervision is required. The P391 is commonly supplied as a replacement spare for existing AREVA/ALSTOM MiCOM protection installations.

🔹 Product Parameters

🔹 Common Questions & Answers (Q&A)

Q: What is the main function of AREVA MICOM P391?
A: The P391 detects insulation resistance changes between the generator rotor field winding and earth, providing rotor earth fault monitoring for generator protection systems.

Q: Which relays work with the P391?
A: The P391 is designed to operate with MiCOM P342, P343, P344, and P345 generator protection relays equipped with the required current loop interface option.

Q: How does the P391 detect rotor earth faults?
A: It injects a low-frequency square wave signal into the rotor circuit and measures changes in the electrical characteristics caused by insulation faults.

Q: What are common problems with a faulty P391?
A: Typical issues include incorrect rotor insulation readings, loss of current loop communication, injection signal failure, diagnostic alarms, and unstable protection measurements.

Q: Can the P391 replace another rotor earth fault module directly?
A: Replacement requires checking the MiCOM relay model, CLIO/current loop configuration, wiring, firmware compatibility, and generator excitation system requirements.

Q: What protection function does the P391 support?
A: It supports 64R rotor earth fault protection by providing rotor resistance measurement data to the connected generator protection relay.

🔹 Recommended AREVA / MiCOM Models

1. AREVA MiCOM P391 – Rotor Earth Fault Detector
2. AREVA MiCOM P342 – Generator Protection Relay
3. AREVA MiCOM P343 – Generator Protection Relay
4. AREVA MiCOM P344 – Generator Protection Relay
5. AREVA MiCOM P345 – Generator Protection Relay
6. AREVA MiCOM P346 – Generator Protection Relay
7. AREVA MiCOM P341 – Generator Protection Relay
8. AREVA MiCOM P741 – Transformer Differential Protection Relay
9. AREVA MiCOM P742 – Transformer Protection Relay
10. AREVA MiCOM P921 – Voltage Protection Relay
11. AREVA MiCOM P922 – Frequency Protection Relay
12. AREVA MiCOM P122 – Motor Protection Relay
13. AREVA MiCOM P123 – Motor Protection Relay
14. AREVA MiCOM P127 – Feeder Protection Relay
15. AREVA MiCOM P632 – Transformer Differential Relay