The Impact on Low Voltage Motor Performance with Zeus PEEK Insulation Products

This article discusses the evaluation of a small 0.75 hp, 4-pole, 460 V, AC induction motor. The original insulation system of the motor was a typical Class 155C (Class F) material with a Class F lead wire and light varnish coating.

Initial testing was followed by the replacement of the original wiring and insulation system in the motor with Zeus-manufactured products. The Zeus-manufactured products used were PEEK lead wire, PEEK magnet wire, and PEEK Lay Flat^® tubing used as phase insulation and as the slot liners.

Figure 1. Original stator prior to head removal and stripping.

A Class 180C (Class H) material impregnated with polyester resin trickle varnish was used as the new insulation system (Figure 2).

The evaluation was carried out before and after motor rebuild, as well as before and after trickle varnish impregnation with respect to the Zeus insulation system. An ALL-TEST PRO 5™, Electrom iTIG 12D, ALL-TEST PRO OL™, and an Amprobe^® AMB55 high voltage insulation resistance tester were used to test the motor before and after rebuild.

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Figure 2. New insulation system cut-away.

The testing revealed variations in the capacitance and insulation resistance curve before and after the application of trickle varnish for the Zeus-rebuilt motor. All other evaluation results were within the expected limits.

However, the electrical signature analysis revealed that the motor experienced a severe imbalance, misalignment, and eccentricity of the rotor in the air gap between the stator and the rotor. These were not issues when the insulation system alone was considered.

Evaluation with ALL-TEST PRO 5

The low voltage motor circuit analyzer ALL-TEST PRO 5 (ATP5) performs measurements on circuit and insulation-to-ground capacitance to determine insulation defects before the motor failure.

In this evaluation, the ATP5 was used to test the motor with the initial insulation system and then the motor was rebuilt with Zeus products for low ohm resistance, impedance, inductance, capacitive phase angle, insulation to ground, current/frequency (I/F) response, and capacitance to ground (Table 1).

Table 1. Test results for original motor and motor rebuilt with Zeus-manufactured products

The test results revealed that the motor with Zeus products showed nearly identical outputs as the motor with the original insulation system relating to the tested parameters.

Slight electrical variations are typical during the comparison of multiple motors of the same design. In addition, each phase was balanced in the original as well as in the Zeus motor, suggesting that the motor rebuilt with Zeus products will electrically run as designed.

Evaluation with the AMPROBE^® AMB55

Insulation resistance curves were generated using the AMB55 high-voltage industrial insulation tester to evaluate the variations between the original motor and the Zeus-rebuilt motor.

The measurement of resistance curves was performed following the procedure outlined in the IEEE Std 43-2013 Annex D for insulation resistance profile (IRP) testing.

The original motor generated an as-expected polarization index curve, revealing the drop in the insulation system absorption current to zero when performing the ten-minute test (Figure 3).

Figure 3. Original insulation system polarization index.

The Zeus-rebuilt motor was then tested before and after the application of trickle varnish insulation resin for IRPs. The insulation polarized to 1 TΩ within 12 and 5 seconds before and after the application of the trickle varnish, respectively (Figures 4 and 5).

These values reveal that the Zeus-rebuilt motor polarized quickly, providing a small absorption current. The leakage current observed for the Zeus-rebuilt motor, measured at 1 TΩ, was much lower than the original motor, where the value was >10 GΩ.

Figure 4. Insulation resistance curve before the addition of trickle varnish showing that the insulation polarizes to 1TΩ in 12 seconds.

Figure 5. Insulation resistance curve after the addition of trickle varnish impregnation showing that the insulation polarizes to 1 TΩ in 5 seconds.

Electrom iTIG D12 Low and High Voltage Testing

The Electrom iTIG D12 performs a set of low and high voltage motor winding tests to identify the condition of an insulation system. The tests performed by the Electrom iTIG D12 are surge comparison, high potential test, polarization index, dielectric absorption, insulation resistance, and resistance. Voids in the insulation system that could lead to insulation failure in variable frequency drive (VFD) applications can be detected by performing surge partial discharge tests.

Low voltage tests are dissipation (D) factor, capacitance (C), inductance (L), phase angle (Ø), impedance, and quality (Q) factor. Initial evaluation with the iTIG D12 showed the original motor was prone to winding failure in VFD applications. As can be seen in Figure 6, the original motor showed a significant partial discharge of 668,070 pC.

Figure 6. Original insulation system showing partial discharge of 668,070 pC at 1316V test voltage.

Conversely, in the case of the motor rebuilt with Zeus components the partial discharge was 703 pC, which was almost three orders of magnitude lower than the partial discharge shown in the original motor (Figure 7). A slight increase in the partial discharge was observed in the Zeus-rebuilt motor following the addition of the trickle varnish impregnation (results are not shown).

The low partial discharge was also measured at higher voltages, revealing the superior operating condition of the Zeus motor compared to the original motor. The data also suggests that the Zeus motor was less prone to winding failure when subjected to VFD applications.

Figure 7. Zeus-rebuilt insulation system showing partial discharge of 703 pC at 1920 V test voltage.

The test results also revealed that although windings were similar for the original motor and for the Zeus-rebuilt motor, the Zeus motor showed better capacitance, D factor, and Q factor than the original motor for each of the three lead configurations (Table 2). For the Zeus motor, the capacitance was improved by 0.01, or ~7.3%, and the D factor was decreased by 0.001, or ~8.3%, when compared to the original insulation system motor.

Table 2. Test results

Low Voltage C/LIZ Test Data

Low Voltage C/L/Z Test Data

Electrical Signature Analysis with ALL-TEST PRO OL

The motor was then tested for efficiency at specific values and to identify significant mechanical or electrical conditions of interest by placing it on a dynamometer. The motor was initially evaluated with the original insulation system and then later with Zeus components.

At 80% load, the speed was 1715 rpm for the original motor, which was below the 1725 rpm mentioned on the nameplate of the motor. However, the Zeus motor displayed 79.8% efficiency at the same load, but the speed was 1746 rpm. Oak Ridge Motor Efficiency and Load software (ORMEL ''96) was used to measure the efficiency.

Secondly, voltage and current harmonics measurements revealed 3.8% of current total harmonic distortion (THDC) and 2.4% of voltage total harmonic distortion (THDV) for the Zeus motor. The THDC and THDV for the original motor insulation system were 2.4% and 1.3%, respectively.

The increased voltage and current harmonics observed for the Zeus-rebuilt motor suggest a negative effect on efficiency. However, due to the higher RPM (1746rpm) of the Zeus motor compared to the original motor (1715 rpm) at the same load, the new Zeus insulation system motor appeared to have higher efficiency than the original motor.

Conclusion

The performance of the Zeus products was superior to the original OEM installed insulation and winding material in various areas. The Zeus system showed improvements with respect to D factor, Q factor, partial discharge, capacitance, and stiffness of the windings over the original motor insulating system.

These partial discharge results suggest that the Zeus motor is less likely to fail when used in an inverter application compared to the original motor. Further evaluation at different conditions and temperatures would be needed to confirm this advantage.

The very low leakage current and absorption times observed in the Zeus motor were better than the original motor and insulation materials. Also, the Zeus-rebuilt motor seemed to operate with higher machine efficiency due to reduced insulation system related losses.

This information has been sourced, reviewed and adapted from materials provided by Zeus Industrial Products, Inc.

For more information on this source, please visit Zeus Industrial Products, Inc.