De-Energized testing using Motor Circuit Analysis

De-energized Testing in Place
De-energized Testing in Place

Motor Circuit Analysis (MCA) is a de-energized test method and the test can be initiated from the Motor Control Center (MCC) or directly at the motor. The advantage to testing from the MCC is the entire motor system, including the connections and cables between the test point and the motor, is evaluated.

ALL-TEST PRO MCA instruments apply a low voltage, non-destructive AC signal through the motor windings and measure the response to these signals. Winding faults are indicated by variances in the response to the applied signal through the windings. These variances cause unbalances in the measured response to the applied signal. Therefore, when testing 3-phase equipment such as motors, generators, or transformers the response of each phase is compared to the other two. When testing single phase devices or DC motors then the winding is compared to itself or compared to a like single phase device or a like DC motor.

ALL-TEST PRO MCA test instruments measure the phase angle (Fi), the current/frequency response (I/F), the impedance (Z) and depending upon the instrument, the resistance (R) and the inductance (L) of each winding. The unbalances of these measurements are compared and simple rules are used to determine the condition of the device under test. Moreover, each instrument will perform an insulation to ground test.

De-energized Bench Testing
De-energized Bench Testing

Computer software can be used to analyze the condition of the device under test and provide the user with a written report. Results can also be trended for identifying long term motor faults. I.e. used for Condition Based Maintenance or Predictive Maintenance purposes.

Additional investigation and analysis techniques are available to more thoroughly identify any of these variances in the winding so faults can be quickly and easily identified. These faults can be corrected or removed prior to energizing the winding preventing potential total destruction of the motor or other winding system.

For evaluation of the windings, whether a fault is developing between turns in a single coil, coils in the same phase, or coils across phases, the unbalance(s) between phases for the phase angle (Fi) and current/frequency response (I/F) measurements are evaluated.

The insulation to ground test is used to evaluate for conductor to ground issues.

Phase resistance is evaluated looking for connection issues, inductance is evaluated for possible rotor problems, and impedance and inductance matching are used to detect contamination or over-heating of the windings.

The de-energized test takes only a few minutes and if testing from the MCC, the connections, cables and the motor are evaluated.

Successful Applications using MCA

MCA Bench Testing
  • AC/DC Motors
  • Generators/Alternators
  • Machine Tool Motors
  • Servo Motors
  • AC/DC Traction Motors
  • Control Transformers
  • Transmission & Distribution Transformers
  • (Virtually Any Size)
  • For Commissioning Testing
  • For Troubleshooting
  • For Reliability Testing

Other De-Energized Testing Option Limitations

Meg-ohm Meter Insulation testing will only detect faults to ground. Since only about 17% of motor electrical winding failures begin as ground faults, these faults will go undetected using this method alone.

Surge testing requires the application of high voltages and while appropriate for testing new coils it can be destructive when testing a winding (or motor) where the condition of the insulation system is unknown. This aspect, combined with the size of surge testing equipment and the need for external power to operate the instrument makes it inappropriate for troubleshooting and predictive maintenance testing.

Resistance and inductance-only (RCL) test methods don’t provide enough information for reliable fault detection and troubleshooting.


Save Money, Make Money

Test Value Static Display

Just finding one of the faults mentioned above can save your organization countless hours of downtime and thousands of dollars in savings. 

Perform a simple Test Value Static (TVS™) in just a few minutes. Use this as an initial reference as a motor specific parameter value, and to confirm the health of an induction motor. Subsequent test results can be immediately compared to the reference TVS™ to instantly show developing problems or changes with the stator or squirrel-cage rotor.  A reference test can be established from the starter or motor drive, making it easy to detect changes with connections and cables, along with the motor. No need to access computer software while in the field!

Since TVS™ is a motor specific parameter it can be used as a Reference test for that particular motor.  The results can be stored.  Additionally, if you have multiples of the exact same motor (manufacturer/type) then the Reference test can be used for all of them. This makes incoming inspection of motors whether new or repaired very easy to perform as it only takes a few minutes per motor.