Technology Overview
Why Test Motors?
Because motors fail. Based on statistical data compiled by the Electric Power Research Institute (EPRI), 47% of motor failures are due to electrical faults/failures. The 47% can be further broken down into rotor problems (10%) and winding problems (37%). The other 53% of failures will be mechanical faults.
Winding defects can occur due to insulation age, contamination, power surges, thermal overload, damaged wire/materials, vibration, and other causes. They begin as energy crossing an insulation fault (such as moisture or contamination), which isolates at least one turn. This generates additional stress and heat across the defect, which progresses until an arc is drawn and the winding fails.
About Winding Faults
There are four basic types of winding faults.
- Between turns in a coil
- Between coils in a phase
- Between coils in different phases
- Between a coil or phase and ground
Only about 17% of electrical faults begin as a conductor to ground fault. The other three fault types may or may not propagate into a ground fault as the failure becomes advanced. The short-term result of these faults is reduced efficiency (and higher operating costs). Symptoms include higher operating temperatures, perhaps nuisance tripping, and reduced motor life. As faults advance, the ability of the motor to drive the load may decrease. The longer-term result is always motor failure.
More facts about winding faults:
- Usually start in the end turns of windings
- Greatest stresses
- Insulation is weakest
- They start small and escalate over time
- They always end in failure
- Contributing factors to failure
- Overloading
- Frequent start/stop cycling
- Vibration
- Contamination
- Age, Heat, & Motor Drives
Off-Line Testing Options
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.
ALL-TEST PRO® instruments are your best choice for fault detection and troubleshooting.
Off-Line testing using Motor Circuit Analysis
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.
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 off-line test takes only a few minutes and if testing from the MCC, the connections, cables and the motor are evaluated.
Successful Applications using MCA
- 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
On-Line Testing using Electrical Signature Analysis
Electrical Signature Analysis (ESA) is an energized test method where voltage and current waveforms are captured while the motor system is running and then, via a Fast Fourier Transform (FFT), a spectral analysis is done by the provided software. From this FFT, faults related to incoming power, the control circuit, the motor itself, and the driven load are detected and can then be trended for Condition Based Maintenance/Predictive Maintenance purposes.
All ESA analysis systems require motor nameplate information of voltage, running speed, full load current, and horsepower (or kW). Additionally, optional information such as rotor bar and stator slot count, bearing numbers, and information for driven load components, such as blade count for a pump or tooth count for a gear box application can be entered for a more detailed and accurate analysis.
Energized on-line testing will provide valuable information for AC induction and DC motors, generators, wound rotor motors, synchronous motors, machine tool motors, etc.
ALL-TEST PRO ESA instrument is actually two instruments in one- a complete Power Quality Analyzer (PQ) and complete Motor Analyzer (ESA). When in PQ mode it can be used for energy data logging, harmonic analysis, voltage and current charting, view waveforms, waveform capture of sags and swells, transient capture, and event capture.
When in ESA mode, it will provide the analyst with information about incoming power, mechanical and electrical health of the stator, rotor analysis, air gap analysis, and analysis of the driven load (gear boxes, belted applications, bearing, etc).
The key difference between Motor Current Signature Analysis (MCSA) and Electrical Signature Analysis (ESA) is with MCSA the FFT is done on the current waveform only and not the voltage. This makes it more difficult to easily and quickly distinguish incoming power related problems from motor and driven load problems. With ESA you have both the current and the voltage FFT to see on the same screen. So it is just a matter of comparing the Voltage and Current FFT spectra to determine the source of the fault.
Successful Applications using ESA
- AC/DC Motors
- VFD Applications
- Generators
- Traction Motors
- Machine Tool Motors
- Gearboxes
- Pumps and Fans
- For Reliability Testing
- For Commissioning Testing
- For Troubleshooting Testing
- For Energy Evaluation
MCA & ESA System Evaluation
| Power | Controls | Connections | Cables | Stator Elec | Stator Mech | Rotor | Air Gap | Insulation | Bearings | Alignment | Load | Drive | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| MCA | - | X | X | X | X | X | X | X | X | - | - | - | - |
| ESA | X | X | L | - | L | X | X | X | - | X | X | X | L |
| MCA ESA |
X | X | X | X | X | X | X | X | X | X | X | X | L |
Green indicates that a developing fault can be both detected and trended for Condition Based Monitoring or Predictive Maintenance purposes. Yellow indicates a fault can be detected, but is difficult to trend or cannot be detected at an early state.
Product Overview
AT31
The hand-held ALL-TEST PRO® 31 (AT31) is an excellent trouble-shooting tool that will test a wide variety of motors and transformers. The AT31 will find winding faults such as turn to turn and coil to coil, along with grounded windings. The rotor test helps you detect rotor problems such as broken rotor bars and eccentricity.
The AT31 will measure impedance (Z), phase angle (Fi), current/frequency response (I/F), insulation to ground resistance (500V or 1000V and measure to 500 meg-ohm), will perform a quick pass/fail rotor test (by turning the motor shaft), and will measure EMI.
Measurement results can be entered into our optional Condition Calculator (CC) software. The CC software will perform an unbalance calculation and report back on the condition of the winding, plus will allow the results to be stored and printed. However, Condition Calculator software does not perform data trending.
AT31 testing range is dependent upon motor, transformer, or generator design, but the AT31 has successfully tested AC motors of hundreds of horsepower in size.
ATIV
The handheld ALL-TEST IV PRO 2000 (ATIV) is an excellent analytical instrument for detecting and trending potential winding faults in AC and DC motors, transformers (distribution and transmission), generators, alternators, and other devices with windings. The ATIV is also used for off-line rotor testing for issues such as eccentricity, broken/fractured rotor bars, and casting voids.
The ATIV makes the following 5 measurements plus an insulation to ground test:
Resistance (R), phase angle (Fi), current/frequency response (I/F), the impedance (Z) and inductance (L).
The ATIV will store up to 500 motor tests and test results can be sent to the provided computer software via the PC interface. The provided TREND software offers analysis, trending and reporting for single and three phase AC induction motors.
Optional EMCAT PROTM software is available for analysis of DC motors and transformers.
The ATIV will test fractional horsepower motors to large synchronous machines and test measurement rules are well established and are easy to understand.
ATPOL II
On-Line testing using the handheld ALL-TEST PRO® On-Line II instrument (ATPOL II) has never been safer due to its small size and wireless Bluetooth* communications to your computer. Bluetooth means operating the instrument from up to 10 meters** away, potentially allowing the operator to be at a safe distance from the energized equipment.
ATPOL II is actually two instruments in one- a complete Power Quality Analyzer (PQ) and complete Motor Analyzer (ESA). When in PQ mode it can be used for energy data logging, harmonic analysis, voltage and current charting, view waveforms, waveform capture of sags and swells, transient capture and event capture. In ESA mode it evaluates the condition of incoming power, the control circuit, the motor itself, and the driven load and results can be trended for Condition Based Maintenance/Predictive Maintenance purposes.
The ATPOL II will provide valuable information for AC induction and DC motors, generators, wound rotor motors, synchronous motors, machine tool motors, etc.
For even greater operator safety our optional ALL-SAFE PROTM connection boxes can be installed so the electrical panel need not be opened for data collection purposes. Besides better operator safety during data collection, this will also allow the user to test potentially a hundred motors each day.
*Bluetooth® is a registered trade mark of Bluetooth SIG, Inc.
** Bluetooth operation range is dependent upon hardware used and potential local RF interference.
