Dynamic simulation relative voltage angle

asked 2021-05-07 05:23:57 -0500

electrical_t
3 ●1 ●1 ●2

I am retrieving the voltage angle of the buses in my network via psspy.voltageandanglechannel() however the overall angle of the network seems to be decreasing over time. As all bus voltage angles decrease at the same rate and the angle relative to each other remains the same the load flow is not affected. I have tried using psspy.setrelang() to instruct the simulation to calculate the angles relative to a specific machine however this seems to only apply to the machine angles and not the bus voltage angles. Does anyone know how to do this for the bus voltage angles? Or what may be the cause of this drift in the angles?

answered 2021-05-08 03:55:06 -0500

perolofl

2947 ●1 ●8 ●16

Bus voltage angles in PSSE are always in absolute angles and are not affected by set_relang option.

The reason for the drift in voltage angles are frequencies deviating from nominal frequency (50 or 60 Hz). At underfrequency all bus voltage angles are decreasing and vice versa at overfrequency.

Below there is an example of two bus voltage angles after simulation of a trip of a generator.

image description

The bus bus voltage angles are constantly decreasing due to the underfrequency in the system. Any oscillatons in the angles are not seen here.

However, when plotting the difference between the two channels the oscillations are seen clearly, as shown below. Here channel 12 minus channel 2 is plotted:

image description

So, by choosing one of the bus angles as reference and plotting the other against that channel, the relative bus voltage angles can be plotted!!!

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Thanks perolofl for your reply, much appreciated. I am able to confirm that the voltage angles relative to the swing bus are not changing using your suggestion. PSSE should calculate the bus angles relative to the swing bus though as this is causing me trouble when connecting my simulation to PSCAD.