How to observe a superimposed low frequency component on a power frequency signal?

I cannot find a way to observe the 27 Hz component in the Torque graphs of the "power_thermal" file for SSR simulation. The help section associated with this file describes the schematic and concludes that a 27 Hz sub-synchronous component is present and leads to torque amplification. However, there has been no mention of how this mode is to be observed. Please, help me with this problem. Thank you.