Testing a power swing or out-of-step scenario on modern protective relays can be a tricky task. Past methods of testing power swing and out of step conditions have often involved imprecise methods of applying voltages and currents to simulate impedances seen by the relay. By manually ramping the impedance trajectory, or playing several vector states where a specific impedance was applied, it was possible to initiate a power swing block or out-of-step trip in a protective device. However, with more advanced algorithms implemented into modern protective relays, previous methods of testing might not work.
One method that has proven to work is applying a simulation of the power system, complete with all of the necessary sources and impedances of the elements under study. The output of the simulation can then be stored in a format suitable for field testing such as COMTRADE. This format can be played to the protective relays and the response measured. Although this method is effective, it can be daunting to personnel who may be required to test these schemes, but who may not have a background in power system protection or simulation. It is for this reason that a simplified method of testing power swing and out of step conditions without the use of complex simulations is desired.
This paper will talk about a non-traditional method of that utilizes the superposition of two waveforms of dissimilar frequencies to achieve a power swing and out-of-step condition. The rate of change of impedance can be controlled as well as the minimum and maximum impedances, the number of pole slips, as well as the starting phase angle relationships. These parameters can be manipulated via basic formulas suitable for beginning field personnel.