Mr Cuky2000,
That's what I intended to achieve at the beginning.But the lead engineer didn't agree and he insisted on tripping the fuse first.
You mentioned the fuse opens before contactor. But to me, motor relay will trip the contactor first under the fault current unless the relay is set...
I am doing a dynamic motor starting study for 5000HP motor using ETAP.
Based on motor data,load data, motor innertia(1130),coupling inertia(25), load inertia(78), the starting time is only 3seconds. Based on my experience, it should be at least 5s. is there something wrong with my inputs? Or...
Mr Swgmfg,
Soory for the late response.In 1/4 cycle, we have a large current to blow the fuse. The contactor can withstand peak current up to 85kA. I think the fuse sould be able to trip the circuit within the peak period so that the contactor wouldn't withstand longer high current.
I am dealing with TOSHIBA international on a project. They have already purchased fuses for their switchgears. The problem is, their fuses can't ideally protect their contactors from short circuit faults. I understand that it is a common practce to allow fuses to blow rather to trip the...
What about eletronic solid state relay 50/51? Does 1.25 factor stil apply? I assumed solid state relays should act faster than traditional induction relays so 1.25 sholud still apply.
I niticed on IEEE buff book-P298 that overload relays- 49/50 should be set at 100% cable capacity and induction relays should be set at125% cable capacity. Is this the common practice here in North America?
Thank you for you guys. Now I understand more the common practice here in North America. Fuse is good for short circuit protection but can provide the backup protection for overload relay.Our Motor circuit overload is protected by SR469. The main overlaod can be protected by SR750. I believe it...
Mike,
Thank you for the quick response.The problem is, 57X fuse is used for the backup protection of SR469( Overlaod and short circuit). The switchgear company did their co-orination study and decided to use the 57R, which i think can only provide backup protection for short circuit fault.The...
I have a prolem here. The switchgear company has purchased all the fuses for their use based on the co-ordinaation study they did inside their switchgear, but the 57X curve is way above our upstream overcurrent protection curves. Even above the transfirmer curve. This means, this fuse is...
I just checked SR469 Manual. It doesn't have DC filter so we might have to delay Inst setting in order to avoid tripping while starting. Total clearing time for CB is 0.25s.Asymetrical inrush current lasts only 1 cycle. That should work.
Actually it is the recommended time by GE Multilin, it might be accurate,
CB opening time: 0.08s
Relay overtravel: 0.10s
Safety factor for CT saturation: 0.22s
I am doing a MV motor protection setting. But the Asymetrical inrush current is overlapped with SR469 Inst. setting, if if shift Inst a bit above, like 0.06s, which is still below Cirucir breaker openning time.Then they would be co-ordinated.Is it reliable to do so?
As I mentioned before, The motor is VFD controlled(running and starting)and VFD should have overload protection itself, the fuse is used for short circuit protection.
It is a common problem. Actually our breakers are controlled by SR750 relays at upstream and downstream respectively. Altough I am trying to set downstream CB trip faster by lower current setting, and to set upstream CB slower by higher setting. Hopefully, this will work.
Hi, Folks,
Inst. settings are very sensitive. Sometimes I try to avoid it for the main and branches. Per code, CEC or NEC, we are not allowed to disable them. So what I normally do is to set Inst on Main higher than the branch fault currents(Max.available), which is reduced by impedance in...
It is Ferraz Shawmut fuse 3barrels. 900E fuse overlapped with upstream overload protection portion of feeder curve.
I studied this system again. 900E fuse is used to protect VFD bus, which feeds VFD controlled motors( 2 motors, one starting one running). I am assuming VFD should have over load...
I am doing a coordination study for a ficility by using ETAP and SKM.
What is confusing me is, the same type of fuse was showing on SKM and ETAP TCC differently. on SKM,there is almost no overlap, because the top left portion of 900E was cut off, which was showing on ETAP. the top left portion...
