#REALFLOW WATER BLAST TUTORIAL MANUAL#

РІР‚вЂњ Actually, there was an existing 13800/240V. In your Case for the Transformer Protection, u didnРІР‚в„ўt have Differential Protection in Any new transformer or Running Transformer if u Energize for the first time or you Energize after Shutdown the windings will conduct a minimum current that we called as Inrush current at the time we need some protection to block this inrush so in ur case u didnРІР‚в„ўt have differential protection only u have Earth fault so what they recommend for 6s is ok but After energized it should return to 5s.

#REALFLOW WATER BLAST TUTORIAL MANUAL#

РІР‚вЂњ see As per the manual they assumed their secondary is 500V but over NGT is 240V so according to that u need to use a resistor to 0.2 ohms to get the stable and accurate measurement for the earth fault. РІР‚вЂњ In which conditions NGT secondary voltage should be increased above 500 V instead of 240 V?

Even if it is not the case they can increase the pickup of the relay momentarily using the inrush detection function instead of increasing the TOP is what I feel.

РІР‚вЂњ I presume here they have SEF means they must be connected to the neutral of the transformer. To protect the transformer winding which is not converted by the residual connection we will go for SEF at neutral and keep pickup sensitive. My understanding is for a residual connection we generally go with a 10-30% of CT ratio as a pickup. РІР‚вЂњ But SEF will be used at the neutral of the transformer, right? Do we still have to consider CT dynamic characteristics if ALF is ok?Р”В«ut in this case, they have not used neutral CT. U have to be pretty sure about your CT dynamic response before giving a low setting to a residual connected earth fault relay. РІР‚вЂњ If any low setting can be given to a residual connected earth fault relay, then y do u think we use CBCT? There is a very interesting section in NPAG that explains this. To give a sensitive setting to relay, u need to consider the error n CT dynamic characteristics into account. РІР‚вЂњ The main idea behind using SBEF is that, in the DY transformer, there is no backup protection available for the Y side earth fault relay. РІР‚вЂњ To detect fault close to the neutral point.that too for impedance grounded system Stand by earth fault is not sensitive earth fault.

Generally NGR fault current withstand time is 10s, But, by the name itself donРІР‚в„ўt u think that must be kept sensitive to residual connection pickup setting? If NGR is present, you need to check the NGR current withstand time and make sure that the delay is less than this. SEF is the last level of tripping for an uncleared earth fault and hence this time delay is ok. Had it been a SEF connected to neutral CT 6s delay is ok. I am never in favor of giving 10% pickup to a residual connected earth fault relay. What is the difference between normal earth fault and SEF if u connect it to a residual connection of phase CT? Stand by earth fault by definition and philosophy should be connected to neutral CT. You can block SEF for the first 5 sec from transformer charging then you can unblock to avoid nuisance tripping due to unbalance inrush current, making 6 sec is not correct as you are permanently increasing the operating time of SEF By SEF u mean to stand by earth fault or sensitive earth fault? РІР‚вЂњ SEF connected in the residual connection? Also, ask them to block inrush current. Therefore recommendation was to increase the timing of SEF to 6 sec. Since there was a residual connection of SEF (Io setting was 10% FLC) so unbalanced current flow is neutral. When DR files were investigated, there was a huge unbalance current flowing during the charging of the transformer for 5 sec. The problem was whenever the transformer was charged Relay SEF protection operated. РІР‚вЂњ There was a 5 MVA newly installed isolation transformer having ABB make REF615 relay connected to it. Join the problem-solving WhatsApp group to get your answer:

Realflow water blast tutorial