The Megger Leakage Reactor Tester MLR10 is used to measure leakage reactance and other associated parameters in high voltage power transformers. Leakage reactance, or more generally leakage impedance, is measured at the transformer primary winding while the secondary winding is shorted. Ideally, a transformer’s primary and secondary windings should be 100% coupled by magnetic flux, but in real transformers there is always a small amount of leakage flux. Leakage inductance is a result of this leakage flux.