Hello all
I am modelling a VCB for transient studies and am a little confused. IEC62271 prescribes TRV tests on a 36kV breaker at a TRV rate of rise of 0,57kV/us, however the literature suggests that when modelling the VCB withstand a value of between 20-30V/us should be used. This is very...
Please can you help me understand something.
In the 4x4 world we often install a second battery in a vehicle to power fridges etc. This is normally connected to the charging circuit via an solenoid when the engine runs. If the second battery is very flat a very high charging current could flow...
Haven't been on the forum for a long time. Hoping I can get some advice.
A client is designing a network for a mine. The supply transformers are 2 x 80MVA 132/33kV Yd earthed via a NECR.
The 33kV is required due to the heavy load and can be considered as an intermediate voltage.
The mine and...
Thanks guys.
There are undervoltage relays currently installed on the winders. Problem is that they are tripping spuriously due to dips. Relays are set to 80%Un instantaneous and I was wondering if it would be good practice to recommend a time delay to offer better dip ride through. Question is...
I am trying to find 'typical' undervoltage settings for a SCIM. I have very few details on the machines (they are pretty old) apart from 4MW, 6,6kV and application ward leonard mine winder.
I don't want to pre-empt but would imagine an UV level of 80%Un would be acceptable (yes/no? lower?) but...
Sorry I am late in on this one, haven't been in the forum for some time.
POW switching would be for energising transients on a cap bank/filter bank.
The initial voltage collapse is given by dV=Ls/(Ls+Lf); where Ls = source inductance and Lf = filter inductance.
For a large bank such as b4l's...
Here’s the problem :
Network :
- 132/6,6kV 20MVA 10% Yd (earthed via NECR) supply transformer, giving LV fault level of 192MVA.
- 6x6,6kV 150mm^2 400m PILC feeders to Mill Substation. Mill SS feeds 2 x 5,5MW mills.
- Speed control is achieved by slip recovery via Alstom PWM drive in rotor...
In answer to your question regarding the 30kA for 3s.
This is simply the rated short time current of the of the board (busbars etc.). The amount of current that the board can handle depends on the duration of the fault i.e. k=I^2t = 2700kA^2s. If the max. fault duration was 2s then rated short...
Client has been having irregular 11kV VT failures on an submerged arc furnace installation. System details as follows:
- 2 x VTs per furnace 11/28/75kV connected phase to phase upstream of the furnace breaker.
- Supply transformer 88/11kV 75MVA.
- 4,8 MVAr plain capacitor bank switched with the...
We generally set the pickup on the HV at 200-250% full load to avoid nuisance tripping due to inrush and the LV at 125% to provide some overload protection.
However, as Bung alluded to above, we find that one generally runs out of time when doing grading. Protection across transformers and...
From the above I must conclude that the risk of ferroresonance is acceptably low, for the following reasons:
- Earthed system.
- 3 phase switching (no grading capacitors).
- Capacitors not switched with transformer (although they could obviously be tripped with the transformer).
Must sound like...
Is it possible for ferroresonance to occur in the following scenario :
22/11kV 2MVA Dyn transformer, resistance earthed, no load on transformer. 1,1 MVAr plain capacitor bank connected at 11kV.
My understanding is that for ferrorresonance to occur there must be either an unearthed system or...
Sorry to come into the discussion so late.
With one 10 MVA transformer in circuit resonance occurs near to 11th/13th which may be a problem depending on the harmonic sources on the network (you do mention traction nearby) especially as there is often no damping load. However if the transformers...
