Diagnostic testing of hermetic and dry-type transformers – examples

Artur Polak
ENERGOPOMIAR-ELEKTRYKA Sp. z o.o.
Tadeusz Glinka
Łukasiewicz – Górnośląski Instytut Technologiczny

This article presents a method for diagnosing the main insulation of transformer windings: hermetic and dry-type oil-immersed, using a direct voltage U₀, and the turn-to-turn insulation using a direct current I₀. The main insulation resistances R_g15 and R_g60 are identified using a direct voltage U₀, and a polarization test is performed: charging the insulation system to voltage U₀, short-circuiting it at time and partially discharging it, then opening it and recording the voltage recovery curve. The turn-to-turn insulation parameters: capacitance C_z and resistance R_z are measured using a direct current I₀. Using the energy balance equation 0,5LI₀² = 0,5C_zU_max², at the instant of a step-like interruption of the current I₀, the parameters C_z and R_z are calculated. The measurement procedure is illustrated with an example. The test object was a 160 kVA dry-type transformer.

Więcej w numerze: 7/2026 Energetyki.

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