Care should be taken when following the steps mentioned here especially when it is across transformer. There are points which are important are not considered in the setting calculation.
When it is based on ANSI 37 standard, bus bracing will be based on momentary network. For HV & MV switchgears, the corresponding asymmetrical RMS and asymmetrical peak short circuit currents have to be considered. Whilst, for LV switchgears, it's symmetrical RMS and asymmetrical RMS are being considered. All these information have to be clearly specified in a dedicated table once we prepared a power system study report. In my previous experience, we normally indicate in the drawing the asymmetrical RMS rating of the bus (for MV/HV SWGR) only and symmetrical RMS rating of the bus (for LV SWGR). For HV/MV SWGRS, the standard values for assymetrical RMS raring are 25kA, 31.5kA & 40kA in 3 seconds. But my last project ( nuclear power plant project), we used 50kA 3 seconds (which is rarely used in other facilities). The assymetrical crest rating of the SWGR will be considered/verified by the manufacturer once they start production of the SWGRS. Meanwhile, for LV SWGRS, the standard values in the market for symmetrical RMS rating are 25kA, 31.5kA, 40kA, 50kA, 65kA in 1 second. 80kA or 100kA is seldom used. One of my projects, a GOSP ( gas oil separation plant) we used the latter ratings. The assymetrical RMS will also be considered based on the actual short circuit study (maximum) that has to be provided to the SWGR manufacturer as well.
@@juliussalutan8006 Thank you for your response. But how they choose the 3sec for MV/HV and 1 sec for LV applications? why only 1 sec and 3 sec? Why not 2sec, 4sec or 5 sec at most?
@@PhilsChannel as we know energy is directly proportional to the square of the current multiply by time. So the 3-second rated time has a higher short circuit withstand capability against rated 1 second. MV/HV has been rated in 3 seconds to facilitate the coordination time interval (CTI) in which upstream protection device time delay becomes longer as it requires to coordinate downstream protective devices. We need to consider also the relay operation time, lock out relay operation time, circuit breaking interrupting time, etc.. Thus, upstream HV/MV switchgears are being designated with a higher rated time i e. 3-sec but it could be 1 second as well. From your question why not use 2s, 4s or 5s? Im not sure how it was agreed by the industry practitioners or by any standard ( i havent seen yet). Its has been an industry practice to use 1 second or 3 seconds for switchgears and 2 seconds for transformers.
Why for 51P, you are using 1.5 pu ? why you are not using 1.1 or 1.2 since if exceed the 1 pu, I think it transformer will slowly damage ? and For 50P, what it 2,5 pu ? It is consider through fault current refer to IEEE 242 and or it has consider transformer inrush instead of 2nd harmonic block ?
Excellent explanation. Thanks
Excellent lecture. Thanks 🙏🙏🙏🙏
Great explanation sir..
Thanks Engineer
Thank you ❤
Thanks 🙏
Care should be taken when following the steps mentioned here especially when it is across transformer. There are points which are important are not considered in the setting calculation.
Very nice appreciate you sir g
Nice
thank you po sir
Welcome sir
Why was 35430A used instead of 1288A as 11KV fault current in the computation of 11KVside pickup current?
I have same question.. why the 35430 is used instead of the 1288
Same question here
It is to be taken 1288A. As you can't divide LV current by HT ct ratio. Needs correction.
I have seen your bus bracing rating, How do we select bus bracing? And when do we use 1sec against 3 secs?
When it is based on ANSI 37 standard, bus bracing will be based on momentary network. For HV & MV switchgears, the corresponding asymmetrical RMS and asymmetrical peak short circuit currents have to be considered. Whilst, for LV switchgears, it's symmetrical RMS and asymmetrical RMS are being considered. All these information have to be clearly specified in a dedicated table once we prepared a power system study report. In my previous experience, we normally indicate in the drawing the asymmetrical RMS rating of the bus (for MV/HV SWGR) only and symmetrical RMS rating of the bus (for LV SWGR). For HV/MV SWGRS, the standard values for assymetrical RMS raring are 25kA, 31.5kA & 40kA in 3 seconds. But my last project ( nuclear power plant project), we used 50kA 3 seconds (which is rarely used in other facilities). The assymetrical crest rating of the SWGR will be considered/verified by the manufacturer once they start production of the SWGRS. Meanwhile, for LV SWGRS, the standard values in the market for symmetrical RMS rating are 25kA, 31.5kA, 40kA, 50kA, 65kA in 1 second. 80kA or 100kA is seldom used. One of my projects, a GOSP ( gas oil separation plant) we used the latter ratings. The assymetrical RMS will also be considered based on the actual short circuit study (maximum) that has to be provided to the SWGR manufacturer as well.
@@juliussalutan8006 Thank you for your response. But how they choose the 3sec for MV/HV and 1 sec for LV applications? why only 1 sec and 3 sec? Why not 2sec, 4sec or 5 sec at most?
@@PhilsChannel as we know energy is directly proportional to the square of the current multiply by time. So the 3-second rated time has a higher short circuit withstand capability against rated 1 second. MV/HV has been rated in 3 seconds to facilitate the coordination time interval (CTI) in which upstream protection device time delay becomes longer as it requires to coordinate downstream protective devices. We need to consider also the relay operation time, lock out relay operation time, circuit breaking interrupting time, etc.. Thus, upstream HV/MV switchgears are being designated with a higher rated time i e. 3-sec but it could be 1 second as well. From your question why not use 2s, 4s or 5s? Im not sure how it was agreed by the industry practitioners or by any standard ( i havent seen yet). Its has been an industry practice to use 1 second or 3 seconds for switchgears and 2 seconds for transformers.
@@juliussalutan8006 Great response.
Thank you for your sharing.
Why for 51P, you are using 1.5 pu ? why you are not using 1.1 or 1.2 since if exceed the 1 pu, I think it transformer will slowly damage ? and For 50P, what it 2,5 pu ? It is consider through fault current refer to IEEE 242 and or it has consider transformer inrush instead of 2nd harmonic block ?
Thanks sir.........
welcome sir
@@juliussalutan8006 Tacloban din ako sir....
@@gerryboypanot7344 LIT graduate ako sir we back 1997
Supply the equations
How to get po yung 4330A @ 0.4kV thank you
reference book pls