Static Exciter Rotor Ground Fault Detector | AT-8100

Continuous Fault Resistance Monitoring for Brushed Exciters

AT-8100 Static Exciter Rotor Ground Fault DetectorThe Static Exciter Ground Fault Detector Model AT-8100 provides continuous wireless monitoring of insulation fault resistance and field voltage on brushed exciter generator and motor field windings, combining advanced ground fault measurement techniques with the latest innovations in digital telemetry. The system also provides users with condition monitoring data, allowing operators to monitor trends over time in order to make better informed operational and maintenance decisions.


  • Continuous on-line monitoring of faults while rotating or at standstill
  • Trending of fault severity resistance
  • Indication of fault location for ease of diagnosis and repair
  • Ongoing monitoring of field excitation voltage
  • Alarm relay contact outputs for multiple resistance limits
  • Built-in self-diagnostics and malfunction alarm


  • Rotor protection through condition-based maintenance
  • Predictive maintenance for large generators and motors
  • Early warning system of impending failure due to ground faults

Continuous Fault Resistance Trending for Predictive Maintenance

Accumetrics’ Static Exciter Rotor Ground Fault Detector Model AT-8100 provides statically excited field ground fault detection technology. Building on the success of the Accumetrics’ Earth Fault Resistance Monitoring Systems for brushless generator designs, the Rotor Ground Fault Detector system provides continuous on-line monitoring for brushed-style excitation generators and motors.

Conventional field ground detectors may detect the occurrence of faults but provide no advance warning or indication of the fault’s severity. In fact, the severity at the detection threshold may vary by several orders of magnitude, depending on fault location. Now, by combining 16-bit digital measurement technology with the most sophisticated technique available for generator ground fault measurements, Accumetrics overcomes these limitations with the Static Exciter Rotor Ground Fault Detector Model AT-8100.

Measurement of actual resistance allows users to monitor trends over time and track the progression of ground faults from their onset. This provides an early warning of impending failure and allows for predictive maintenance of a machine. Ground fault severity data can be used to make operational and maintenance decisions. In addition, the technique yields a location factor, which indicates where the fault occurs along the length of the field winding.

Rotor ConnectionsField Positive Terminal
Field Negative Terminal
Rotor Earth/Ground
Field Voltage
Measurement Range0 to 500 VDC (contact factory for other ranges)
Maximum Transient without Damage1000 V for 5 seconds
Resistance Measurement
Measurement Range0 to 80 MΩ
Accuracy±250 Ω ±0.5% of Reading 0 to 500 kΩ (exclusive of the effects of AC content and noise from the excitation system)
Ground/Earth Fault Location Factor
Range40 to 100% representing ratio of potential at fault to total field voltage (0 at negative terminal and 100% at positive terminal)
Accuracy±1% for a 10 kW fault and field excitation ≥25 V
Receiver Alarm Outputs
Ground/Earth FaultTwo independent alarm resistances, user selectable via computer interface from 500 W to 1 MΩ
MalfunctionActive upon detection of a malfunction in monitor operation or loss of receiver power
Alarm InterfacesForm C relay: 10 A / 24 VDC, 0.3 A / 240 VDC, 10 A / 250 VAC resistive
Receiver Analog Outputs
Analog OutputsDual analog output of Fault Location, Log Resistance (4-20 mA)
Receiver Digital Interface
Computer InterfacesRS232, Ethernet
Output DataGround/Earth Fault Resistance, Field Voltage, Location Factor when faults occur, Alarm and error conditions
User SettingsGround/Earth Fault Alarm Resistance Thresholds, Alarm Dwell Time, Network Settings
Ambient Temperature0 °C to 50 °C
System Power
85 VAC to 250 VAC 50/60 Hz, < 20 W