Negative Sequence Voltage (47) and Current (46) setting on Main Switchgear 1

[rockman7892]

Does anyone have any recommended settings for negative sequence voltage (47) and current(46)relay elements located at 4.16kV Main Switchgear. It appears that these functions are strictly being used to detect voltage and current unbalance on the plant distribution system. Not sure if these functions are typically used on facility main breaker or if designer just blindly specified these settings to trip breaker simply because they are in the relay.

I have seen 5% pickup used for voltage unbalance and 10% used for current unbalance but not sure of delay settings to use on mains? Perhaps coordinate time delay with unbalance settings on downstream 4.16kV motor relays?

 

[davidbeach]

Determination of those settings would depend on:
[ul]
[li]What you want to accomplish with them; they are generally not used in that type of application.[/li]
[li]Do you really want to trip the main? It's great to trip motors, but lights?[/li]
[li]A system study to determine appropriate settings to accomplish the stated goals. The same goals applied to different systems will result in different settings.[/li]
[/ul]

 

[rockman7892]

davidbeach

[ul]
[li][/li]
[/ul]I am doing system study and protective device settings for new project. These particular settings were part of the project specification for the main relays on the main switchgear. Perhaps these were specified without much thought to their intent. It appears their only purpose would be to detect system voltage and current unbalance.

[ul]
[li][/li]
[/ul] Perhaps tripping the mains is not the best course of action like you mentioned. Maybe an alarm function is more appropriate? My understading is that only motors and generators are most adversely effected by these conditions. Large motors and generators typically have their own voltage/current unbalance protection at the motors or generators which is the case in this plant (although generators not operated in parallel with utility) My only though would then be these mains detecting unbalance and protecting LV (480V) motors from this condition.

[ul]
[li][/li]
[/ul]I have completed a SC and coordination study for this plant. What results from a system study are typically looked at to determine settings in order to accomplish stated goals?

Thanks!

 

[jghrist]

It would be best to ask whoever specified the relays for the intended purpose and the unbalance limits.