Hello,
I am involved in a project where a 3-phase 25 MVAr shunt reactor is to be installed at 50 kV line voltage. The connection would be star.
I have read that some manufacturers advice that shunt reactors below 72,5 kV should have isolated neutral and grounded neutral for voltages of 115 kV...
I have performed a number of noise recordings for a 20 MVA 132/50 kV transformer, ONAN.
As expected there is a 100 Hz component and multipla of this 100+n*100 Hz due to magnetostriction etc.
However I detect a very huge 500 Hz noise component in the noise frequency spectrum. I have cross...
Hello
I have performed measurements on a 50 kV, 3x1x1200 mm2 AL PEX cable with 96 mm2 CU screen.
The cable system has a length at 6700 m. At the midpoint the screens are earthed to reduce screen voltage the system has earthed screen at both ends. Cables are laid in flat formation.
A VLF test...
Hello
I need to calculate the necessary area (m2) of the inlet in a building where a heatloss of 24 kW is dissipated. There is a distance of 2,8 m between openings of inlet and outlet.
There are two scenarios:
- natural ventilation
- forced ventilation
I am looking for formulas or litterature...
Hello
At the utility grid at 10 kV I have made a model of this for simulating touch voltage. When experiencing a 2-pole short circuit to ground the touch voltage exceed 3 kV related to ground potential because of the high short circuit current and the resistance to ground. Maximum (worst case)...
Hi
Please refer to attached pdf. Can anyone tell me what is wrong considering my calculation of U2 potential when there is a single phase fault on HV in secondary substation. I am considering a TT-system with RE and RB not connected.
IEC 60364-4-442 table 44.A1 says U2=U0, however I reach the...
Hello everyone
IEC 61230 states to Apply a peak current factor of 2,5 for the peak sc. current. From grid study analysis of the utility grid the R/X short circuit ratio is close to zero. Thus the peak current factor theoretically reaches 2x sqrt(2)=2,83.
I am a little confused as why IEC tends...
Hello
At a horticulture with a lot of LED growth lamps we have made some measurements. See Fluke pictures below. I am not able to explain why L1 is dropping to 214 V and L3 is 8 V higher and 222 V. The load are approximately the same, 55-56 kW and 6-7 kVAr. Also the harmonics does not vary much...
Hello
One of our clients have multiple 10/0,4 kV substations at the industrial area with Dyn- transformers.
Now the client wishes to establish an earthing connection between the substations by mesns of 240 mm2 cable connection.
In my opinion this is an advantage regarding overall safety...
Hi all,
I am working at a electric utility company. We currently have complaints from a client claiming that the grid is subject to electrical disturbances.
The problem of the client is that a number of industrial PCs suddenly shut down (in some case only 3 in other cases all 16 PCs at the...
Hello
I am working in a utility company. One of our clients ives in one out of 20 townhouses. All houses have 6 kW PV´s 3-ph. installed. The problem is that the client is experiencing problems charging the electrical vehicle. From measurements we have concluded that the problem is caused by the...
Hello all
I need to parameterize a distance protection relay based on measurements of cable synchronous and zero sequence impedances on a 50 kV line.
However I am in doubt about the reference temperature to be used for the resistance values. We have measured them at 3°C, but I can´t find...
Hi
Here is a question which is bothering me.
In case one have a normal 3-phase installation with 3 lines and neutral it is well known that the line voltage increases from 230 V to 400 V in case the neutral connection is lost.
But I don´t see how this can be verified matematically. Can anyone...
Hi all,
Recently a local power plant suffered from an explosion initiated by a voltage transformer inside a closed room. This caused a double busbar fault on 132 kV. During the fault a steel door was blown out of the room. At the adjacent room a huge 500 kg steel door was blow 32 out in the...
Hi there.
In Cigré report TB347 p. 26 there is a modelling of EPR (Earth Potential Rise) in case of a single phase fault.
Refer to attached page 26: Can anyone explain me in detail how the formula for EPRr is derived. In the text it is mentioned that the expression can "easily" be derived ...
Hi all,
I have made some records on a single phase (132/27,5 kV,23 MVA) railway transformer.
Normally there are 2 earthing connection point situated on the tank of the transformer. We have removed one earthing connection, see phote and then one should expect to measure the sum of the...
I have some technical questions regarding single phase power transformers which I am not able to answer.
Please refer to attached PDF file. (Sorry for page 1 being up-side-down).
The electricity company of mine has installed two billing meters on a railway transformer. The main meter is...
Hi there
I am experiencing a quite strange problem which I am no yet able to explain. A single phase power line, 132 kV (solidly grounded) is feeding electrical trains rated 25 kV through a transformer 132/27,5 kV. The connection at 132 kV is between phase R and T. Current on T is measured from...
Hi out there
I am doing network studies on the LV distribution grid. According to prognosis we are facing a future with a huge amount of heat-pumps installed in the private house hold. I looked at a datasheet on a heat pump and it turned out that the starting current of the compressor is around...
