RelayHelper Spectrogram

I chose a motto for RelayHelper  - “You can just see”. So the spectrogram is the feature that proves one more time that motto. I wanted to have such frequency-time signal representation a long time ago and I can say that now I use it all the time just to satisfy my curiosity about what’s happening under the hood during short circuits and other events.

There are two ways to enable Spectrogram on the analog channel.

1 Switch the main window of the Comtrade page to the extended view.

Click on the Spectrogram button in the measurement section

2 In the Calculations menu select Spectorgram->Channel->(select analog channel from the list).

Spectrogram activated on 750 kV transmission line phase C voltage channel during single phase AR with default settings (Window size -  2 cycles, Noise threshold - 2%, Amplitude gain -  1).

Note that frequency scale is shown left to the measurement section. Frequency range depends on the file sampling frequency. High harmonics are usually very small so the spectrogram values are averaged using the RMS method across frequency bins.

Spectogram settings can be changed in the Calculations menu.

Increasing Window size, you increase frequency resolution but decreasing time precision. Frequency Resolution is calculated automatically based on file sampling frequency and window size. Noise threshold – removes all data below selected value (in percent of maximum value). Using Amplitude gain you can increase the brightness of visualization. 

The same phase C voltage channel with Window size -  4 cycles, and  Noise threshold - 0%.

The same with Amplitude gain -  4.

Now the third harmonic content can be seen after the CB phase was closed.

Close up look at the moment when the secondary arc extinguished.

Transformer inrush current. Window size -  4 cycles, Noise threshold - 0%, Amplitude gain -  1.

1GW generator neutral voltage during single phase short circuit in the 330 kV grid. 9 harmonic (450 Hz) can be noted. Window size -  4 cycles, Noise threshold - 0%, Amplitude gain -  1.

Spectrogram calculation requires a lot of power, so it can be enabled on one channel. Also there can be problems with files with high sampling frequency and big Window size settings.

I’ll be happy to see your thoughts. Have you tried it already?

RelayHelper