Hi everyone,
I am working on a project that has a 1.5 km of transmission line feeding a 230kV substation with a disconnect switch, breaker and a 230kV/35kV transformer. I understand we need to install a surge arrestor in front of the transformer to protect it, but would there be one needed in...
Thanks for the pdf 7anoter4
Yes, this is real case scenario where the motor is slipping poles when the clutch is engaged and trips the motor. The clutching time is about 5-6 sec and they do allow the clutch to slip @ first and hopefully they are maintained properly.
Electricalpete: I am...
Thank you all for the response.
The sync motor is reactor started and drives a high inertia load such as a ball mill. Since the load is cascading inside the mill, the mechanical torque experienced by the motor is consistently changing and hence the machine angle. Damping in the system and motor...
Hi,
I have a question about the machine(torque)angles in synchronous motors with exciters.The sync motor is a 6500hp 36 pole motor @ 4.16kV, which is started as an induction machine.The load is a high inertia load which gets engaged when the moor reaches sync speed.
When the motor is running...
Hi,
In Waross explanation, I believe we can assume the transformer impedance to have minimal effect on the fault currents ( 240 ohm NGR is the most dominant impedance). As we decrease the NGR resistance ( 240 ohm to 24 ohms), the SLG fault currents increases to 100A and so do the losses due to...
Thanks for the info.
But would the current seen on the primary depend on the turns ratio of the XFMR ( or would it be very close to 5.2)
Also wouldn't the primary single phase see only 58% of the secondary L-G fault currents ( IEEE Std C37.91)
Hi,
I have a 12.47kV/4.16kV 5MVA delta-wye(10A,10s resistive grounded system) feeding a 5kV switchgear. The NGR is rated for 10A, 10s and I am using SEL-751A protection relays.
1) A ground fault on the secondary of the transformer would be seen by the primary as L-L fault?
2) How would this...
Thank you all for your inputs. This design has been passed down to me and I am trying to figure out the design details to program the relays. So sorry for any incomplete data.
I have confirmed that the SEL710 would provide back up 51 protection only, although the VFD would also be able to...
Thanks for the reply.
I believe the SEL 710 might be providing a back up protection for the motor incase the VFD has to be taken out of service. Also, may be they dont want to rely on the VFD to provide overload protection. The CTs for the relay are located ahead of the VFD and isolation...
Hi,
I have a SEL 710 protection relay that protects a VFD (with an isolation transformer) and 700HP motor. There are fuses on the line side of the VFD for short circuit protection and contactors( controlled by SEL 710)for opening/closing the circuit. I am not an expert, so please correct me...
Thank you all very much for the details. I had an additional question:
What would happen if before energizing T2( assuming T1 is already energized with load), a tie-in disconnect switch between secondary of T1 & T2 is closed first. These back charging currents from T1 to T2 - would these be the...
A couple of things to take into account during fault calculation
1) Fault contribution from the Utility( Ultimate vs present day)
2) Any synchronous motors attached on 4.16KV bus
3) 31.5KA is the short circuit interrupting rating, and not the bracing rating of the equipment.
Please correct...
Thanks for the response.
Just so that I am clear, can the cables cause a heating effect on the rungs( 12 inch apart) of a ladder cable tray( 24 inch width). Should this be of concern. I have noted about non ferrous terminations & clamps and have specified it to the electrical contractor.
Hi,
This has been a very good learning forum and I hope to learn a lot from you guys. Thus my first post & the question
I am installing 4 X single conductor 600V 750MCM teck cables in a cable tray( hot dipped galvanized steel) which would be bonded at every 15m. These cables would be installed...
