SEL 351S Relay 67 versus 32 Element 3

[tmaly1]

Folks,

SEL 351S Relay Settings started to confuse me, they use the 67 Directional Overcurrent element and the 32 Reverse Power element backward, in my opinion.

Have any of you worked or dealt with setting this kind of relay. My application is for dual-feed industrial substation and I want to set the Directional Element for that purpose but it is confusing me!!

If I only want to monitor the Direction of the current (not power) flow and trip in a pre-determined direction. Which one should I use and what about all these Reverse and Forward Impedance values they require?!
Any Insight, please.

 

[jghrist]

The SEL-351 does not use 32 as a designation for reverse power. E32 enables directional control for the overcurrent elements. Directional control is not simple because there are various methods of determining direction for phase and ground overcurrent applications. Some of the settings can be made automatically by the relay by setting E32=AUTO.

I'm not sure what you mean by the reverse and forward impedance values. Are you trying to set the load encroachment logic? This introduces a whole other set of complications.

Power elements (with Firmware Version 7) are designated with PWR and can be used for reverse power protection.

 

[tmaly1]

In the directional overcurrent relay settings, they ask you for values for Z1F (relay forward impedance) and Z2F (relay reverse impedance)!! What is really strange is that the 67 elements (67P,N,G,Q) are listed under non-directional overcurrent element and only 50Q/G elements are listed under the directional element supervision!!!

The whole thing is very, very confusing!!

 

[cranky108]

In the 351 relay, or other flavors, the 67 elements can be either directional or non-directional depending on your settings.
The directional can be derived in several ways, Negative sequence, zero sequence current, or zero sequence voltage. You should choose on or more and make the settings that match (the relay won't ask for settings on things you turn off).

Z1F, and Z2F are thresholds which should not overlap. The book should have a recommend setting, or call SEL for help.

 

[davidbeach]

SEL has lots of application engineers available to support users. They also offer classes to help new users in understanding the relays.

 

[dpc]

SEL 351S Relay Settings started to confuse me

If it's any consolation, you're not alone. The SEL-351 is one of more difficult relays to work with - due to the odd SEL terminology used, the "rich feature set", and inconsistencies when compared with other SEL products.

It's a very capable relay and we use them quite a bit, but it is not easy to work with.



"An 'expert' is someone who has made every possible mistake in a very narrow field of study." -- Edward Teller

 

[stevenal]

Z2F is not the reverse impedance, it is the negative sequence forward impedance. Unless you have a good understanding of these values as well as a good reason to set them differently, I suggest setting E32 to AUTO so the relay will calculate the values.

The 67 elements are directional when E32 is enabled, and non-directional when not. The difference between a 67 element and the corresponding 50 element can be found in the logic diagram in the instruction manual. Make sure you note how LOP plays in.

Also, please understand that the directional logic is intended for looking at the direction of a fault (primarily reactive). Reverse real power flow under un-faulted conditions is a whole different matter entirely, and the directional elements may not be suitable.

 

[tmaly1]

Thank you all for your insight, your input and willingness to help. I will continue my struggle with the SEL 351S -;o)). Please keep me posted and in your thoughts if you find any helpful thoughts on the 351S.

Thanks again and best regards to all

 

[stevenal]

I set a 351A to trip on reverse real power. Since the directional elements use line impedance, I used the load encroachment function instead since the impedances can be set independently. ZLIN starts a timer, timer output is ORed with TRIP at the output. The timer also sets a latch which in turn triggers a display reading "REVERSE POWER." TRGTR resets the latch. Seems to work, has been secure, and keeps the boss happy.