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Core Materials and Components
The ultimate properties, performance, and cost of any electric machine are largely determined by its construction materials. From magnetic compounds to specialized dielectric insulators, selecting the right materials is crucial for optimal thermal and electrical performance.
Mechanical Dimensions & Electrical Parameters
Geometric Dimensioning and Tolerancing (GD&T) is a system for defining and communicating engineering tolerances.Â
It uses a symbolic language on engineering drawings and computer-generated 3D models to explicitly describe nominal geometry and its allowable variation. This ensures manufacturing staff know the exact degree of accuracy and precision required on every feature.
For electrical parameters, Resistance (measured in ohms, Ω) is the opposition to the passage of an electric current, sharing conceptual parallels with mechanical friction.Â
Inductance (measured in Henrys, H) is the property of a conductor that opposes a change in current.
Example Testing Protocol: Measure and record A-B, B-C, and C-A line-line resistances and inductances. Hipot and surge test the stator after varnish at 1800VAC (max current leakage 5mA). Before and after varnish, perform a corona test (partial discharge) with a pulse up to 3000V.
High Potential (Hipot) Testing
Three types of High Potential tests are commonly used, differing in the amount of voltage applied and the acceptable current flow:
- Insulation Resistance Test: Measures the resistance of the electrical insulation between the copper conductors and the stator core. Ideally infinite, a lower resistance usually indicates an insulation problem. (Reference: IEEE Std 43-2000)

- Dielectric Breakdown Test: Voltage is increased until the dielectric fails (breaks down). This destructive test is used on a random sample basis to help designers estimate breakdown voltage and identify failure points.

- Dielectric Withstand Test: A standard test voltage is applied (below the Breakdown Voltage limit), and leakage current is monitored. If leakage exceeds a preset limit, the test fails. This is a non-destructive safety test usually performed on 100% of products before they leave the factory.
Partial Discharge (PD) Testing
The measurement of partial discharges (IEC TS 60034-27) is a highly sensitive means of assessing new insulation quality and detecting localized sources of PD in used electrical winding insulation caused by operational stress.Â
Unlike standard dissipation factor or insulation resistance tests, PD testing identifies highly localized weak points. It provides valuable information on system weakness, aging processes, and required intervals between overhauls.