Directional Comparison Blocking (DCB) Scheme Basics | Transmission Line Pilot Scheme Protection

[@romeroengineering]

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[@SundayJoseph-i4i]

Thank you for this video. My question between POTT and DCB which one is more reliable and more secure?

[@davesmith9867]

Great video, clearly explains the concept and the excel sheet is a cool little tool. What is the philosophy behind blocking the Z2 when remote Z3 picks up? It is essentially covering 100% of the line but I guess by using relays at both ends of the line it provides extra security in comparison to using a Z2 with a reach of 100% of the line?

[@romeroengineering]

Typically, the Zone 2 element is set to overreach the transmission line with some margin to account for errors in measurement, line impedance data, etc. This is to make sure that it in fact covers 100% of the transmission line, even with some errors. A typical setting is 120%-125% of the transmission line's impedance, although it could be higher. If not used as part of a pilot scheme, such as a DCB scheme, it would trip with a time delay (usually around 30 cycles or 0.5 seconds) such that it coordinates with protection at the remote end. However, if it is used as part of a DCB scheme, it can trip much faster, since if the fault is beyond the end of the transmission line, it would be blocked by the remote Zone 3 element and therefore there is no need to coordinate with protection at the remote substation. We do need to account for some delay for the blocking signal to come in though, typically around 2-3 cycles.

[@davesmith9867]

@@romeroengineering Perfectly clear answer thank you.

[@hanial-shadadi9122]

How to perform such DCB between two autorecloser installed beside each other one feeding subtransmmesion line and the second one is feeding the other adjacent sub transmmesion line..? The distance between them is 3meters . The other case between two ACRs on the same subtranmession line the distance between them 30km ?! Hope getting answer from you . Thanks

[@romeroengineering]

Hi! We can discuss this on a one-on-one session, you can sign up here: www.romeroengineering.co/offers/ZEo7VkVz/checkout

[@ppopbha]

Thank you.

[@romeroengineering]

No problem Piyush!