The MLS 7100 transformer loss measuring bridge was especially designed to greatly simplify the determination of transformer core and copper losses – an ideal choice when working on site. The measuring bridge features open circuit as well as short circuit measuring. Many transformers can be directly connected to the
MLS 7100 without needing further transducers.

Core losses are an importanttransformer quantity when talking about electrical efficiency, operating expenses and the overall transformer value. Core losses mainly emerge from steel losses (eddy currents and hysteresis losses) and also from the core losses.

Steel losses are typically determined using open circuit measurement, as a relatively small magnetizing current is flowing. Using this technique, the copper losses are minimized due to the square correlation of power and current.

Copper losses are determined using short circuit measurement, as the magnetizing modulation of the steel core should be minimized. In addition the short circuit voltage is determined this way, which is also an important quantity. In practice, the test voltage is inputted at the h.v. side (l. v. side shortened), as at least many mid power transformers reach their nominal current in between the voltages that are easily available in industrial power networks (e. g. 3 x 400 V → 4 % of 10 kV).

During open circuit measurements, the steel core has to be fully modulated to reach the nominal transformer voltage. Using the h. v. side, the voltage would be quite too high, so the test voltage is typically inputted at the l. v. side (e. g. 3 x 400 V) and the results are recalculated accordingly.