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Appendix
years later. Leakage reactance testing is performed by short-circuiting the low-
voltage winding, and applying a test voltage to the high-voltage winding
(Figure 12-24).
Figure 12-24 Short-circuit impedance test
Changes in leakage reactance and observed in capacitance tests (explained
later) serve as an excellent indicator of winding movement and structural
problems (displaced wedging, buckling, etc.). This test does not replace
excitation current tests or capacitance tests, but complements them and they
are often used together. The excitation current test relies on the magnetic
resistance of the core while the leakage reactance test relies on the magnetic
resistance of the leakage channel between the windings (Figure 12-24).
Using the test system, the leakage reactance can also be measured over the
frequency range from 15 to 400 Hz. Intact windings show a nearly constant
reactance value in this frequency range.
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