tripping is achieved. This requires a detection of the fault by an independent tripping zone 1.To avoid sequential tripping as described, and when zone 1 is not available, weak-end infeedtripping logic is used. The weak end infeed function only works together with permissiveoverreach communication schemes as the carrier send signal must cover the hole line length.The WEI function sends back (echoes) the received signal under the condition that no fault hasbeen detected on the weak-end by different fault detection elements (distance protection inforward and reverse direction).The WEI function can be extended to trip also the breaker in the weak side. The trip is achievedwhen one or more phase voltages are low during an echo function.In case of single-pole tripping, the phase voltages are used as phase selectors together withthe received signal CRLn.Together with the blocking teleprotection scheme some limitations apply:• Only the trip part of the function can be used together with the blocking scheme. It is notpossible to use the echo function to send the echo signal to the remote line IED. The echosignal would block the operation of the distance protection at the remote line end and inthis way prevents the correct operation of a complete protection scheme.• A separate direct intertrip channel must be arranged from remote end when a trip oraccelerated trip is given there. The intertrip receive signal is connect to input CRL.• The WEI function shall be set toWEI=Echo&Trip. The WEI function block will then givephase selection and trip the local breaker.Avoid using WEI function at both line ends. It shall only be activated at the weak-end.14.2.3 Setting guidelines IP15024-1 v1M13856-4 v5The parameters for the current reversal logic and the weak-end infeed logic (WEI) function areset via the local HMI or PCM600.Common base IED values for primary current (IBase), primary voltage (UBase) and primarypower (SBase) are set in a Global base values for settings function GBASVAL.GlobalBaseSel: It is used to select a GBASVAL function for reference of base values.14.2.3.1 Current reversal logic M13856-6 v5SetCurrRev toOn to activate the function.SettDelayRev timer at the maximum reset time for the communication equipment that givesthe carrier receive (CRL) signal plus 30 ms. A minimum setting of 40 ms is recommended,typical 60 ms.A longtDelayRev setting increases security against unwanted tripping, but delay the faultclearing in case of a fault developing from one line that evolves to the other one. Theprobability of this type of fault is small. Therefore settDelayRev with a good margin.Set the pick-up delaytPickUpRev to <80% of the breaker operate time, but with a minimum of20 ms.14.2.3.2 Weak-end infeed logic M13856-10 v6SetWEI toEcho, to activate the weak-end infeed function with only echo function.SetWEI toEcho&Trip to obtain echo with trip.1MRK 511 358-UEN A Section 14Scheme communication349Application manual
