overall than AC locomotives. "Auxiliary Electric Motors" are mainly used for air cooling electric machinery such as traction motors. Electric locomotives concentrate high power electric machinery in a relatively small space and thus require a lot of cooling. Per the table below, a sizeable amount of energy (11–17%) is used for this, but when operating at nominal power only 2–4% is used. The fact that the cooling motors run at full speed (and power) all the time makes their power consumption constant, so when the locomotive motors are operating at low power (far below the nominal regime) the percent of this power used for cooling blowers becomes much higher. The result is that under actual operating conditions, the percent energy used for cooling is a few times higher than "nominal". Per the table below, AC locomotives used about 50% more energy for this purpose since in addition to cooling the motors, the blowers must cool the transformer, rectifiers and the smoothing reactor (inductors), which are mostly absent on DC locomotives. The 3-phase AC power for these blower motors is supplied from a rotary phase converter which converts single phase (from the catenary via the main transformer) to 3-phase (and this also takes energy). It's proposed to reduce blower speeds when less cooling is needed. Traction motor and gears efficiency While the above table shows that about 75% of the electric energy supplied to the rail substation actually reaches the electric traction motors of the locomotive, the question remains as to how much energy is lost in the traction motor and the simple gear transmission (only two gear wheels). Some in the USSR thought it was about 10% (90% efficient). But counter to this, it was claimed that the actual loss was significantly higher than this since the average power used by locomotive when "in motion" was only roughly 20% of nominal power, with lower efficiency at lower power levels. However, checking Russian books on the subject indicates that the supporters of 90% efficiency may not be too far off the mark. When calculating average efficiency over a period of time, one needs to take an average of efficiencies weighted by the product of power input and time (of that segment of power input): where is the power input and is the efficiency during time If efficiency is low at very low power, then this low efficiency has a low weighting