Transformer losses are broadly classified as no-load and load losses. No-load losses occur when the transformer is energized with its rated voltage at one set of terminals, but the other sets of terminals are open circuited so that no through or load current flows. Load losses occur when the output is connected to a load so that current flows through the transformer from input to output terminals. When measuring load losses, the output terminals are shorted to ground and only a small impedance-related voltage is necessary to produce the desired full load current. In this case, the core losses are small because of the small core flux and do not significantly add to the measured losses. In operation, both types of losses are present and must be taken into account for cooling considerations. Voltage is produced in coils surrounding the magnetic core by rotating the saturated flux vector so that the component linking the coil is sinusoidal.