MAGNETIC FLUX MONITORING

Description

Magnetic flux monitoring is a proven, non-invasive diagnostic technique used to detect rotor faults in synchronous machines, such as hydrogenerators and salient pole motors.
It is particularly effective for identifying inter-turn short circuits, which develop gradually as the insulation between rotor winding turns deteriorates due to thermal cycling, mechanical vibration, and the presence of contaminants such as oil, dust, or moisture.

In many cases, these faults do not immediately affect field current or machine output, making them difficult to detect during routine operation.
Traditionally, detection relied on offline methods like rotor drop testing or impedance comparison. While useful, these tests require rotor removal and machine shutdown, and they provide only a static snapshot of the machine's condition — often missing faults that develop under actual load and temperature conditions.

Magnetic flux monitoring overcomes these limitations by continuously measuring the magnetic flux density in the air gap during normal operation, providing real-time insights into rotor health without interrupting production or opening the machine.

Benefits of Magnetic Flux Monitoring

Early Detection of Rotor Faults
Identify shorted turns and other rotor anomalies before they escalate into severe damage.
Non-Invasive Installation
Sensors are mounted on the stator wall, requiring no rotor removal or disassembly.
Real-Time Monitoring
Analyze magnetic flux behavior under real operating conditions, including load and temperature effects.
Avoid Rotor Drop Testing
Eliminate the need for offline testing and manual inspection to assess winding condition.
Enable Predictive Maintenance
Plan maintenance based on measured trends rather than fixed intervals, optimizing uptime.
Support Root Cause Analysis
Use waveform deviations and pole-specific analysis to understand fault origin and severity.

Issues Addressed by Magnetic Flux Monitoring

The primary application of magnetic flux monitoring is the detection of inter-turn short circuits in the rotor winding. These faults occur when insulation fails between turns, causing current to bypass part of the winding and disrupting the magnetic field generated by the affected pole.

Beyond classic shorted turns, magnetic flux monitoring also helps reveal other rotor-related anomalies, including short circuits localized within a pole, magnetic unbalance, or mechanical instability (such as a loose pole piece or winding movement under stress). These issues manifest in the form of localized reductions in flux amplitude, distortion of the flux waveform, or pole-to-pole asymmetries — all of which can be tracked and analyzed in real time through flux monitoring.

Because these faults often do not impact field current directly, they can go undetected without dedicated flux analysis. Magnetic flux monitoring provides the sensitivity and resolution needed to catch these changes early and intervene before major failures occur.

Monitoring parameters

Magnetic flux monitoring systems measure the magnetic flux density in the air gap of synchronous machines — the key indicator of rotor excitation behavior.
This value, expressed in Tesla (T), reflects the magnetic field strength generated by each rotor pole.

At MC-monitoring, this measurement is performed using the MFT-100 Magnetic Field Transducer, a Hall-effect based sensor specifically designed for harsh environments and narrow air gaps, with a linear range of ±2 Tesla.

By continuously analyzing this flux density over time and across all poles, maintenance teams gain early visibility into rotor health and the ability to act before performance is compromised.