Isolines calculations electrical equipment::
Example of transformer station calculations::
What is needed for a calculation ?
• Disposition drawing, plans
- ground plan and cut of transformer station and the floors with OMEN
- plans in standard formats (dxf, pdf, paper)
• Used components
- Medium-voltage system (disposition, principle scheme)
- Transformers (technical data sheet, dimension drawing)
- Low voltage distribution (disposition, position of the busbars)
- Cable types
• Technical data
- operating voltage, operating currents
- operating state
• Description of the OMEN
- marking and description of the OMEN
The system is virtually passed with current and based on that the isolines are calculated and displayed.
As a result, the customer receives a report with location data and isolines images of the magnetic flux density. The isolines are represented below: XY (view from above), XZ (view from the front), YZ (view from the right) and documented as 3D display.
Example of substation calculation::
The entire system is drawn in 3D. The documents provided serve as basis. The compliance with the 26. BlmSchV. is checked in the example. The customer also wanted to know the distance between interference immunity norm EN 61000-4-8, for the future placement of electronic devices in new constructions of substations. The dimensions of the calculated substation are 200m x 80m.
Key figures: 11 cells free air system 11okV:
|110kV free air system||Extinguishing coils,
|Disposition of the substation|
The system is virtually passed with current and based on that the isolines are calculated and displayed. The isolines are represented below: XY (view from above), XZ (view from the front), YZ (view from the right) and documented as 3D display.
|Isolines calculation substation||
Cut through system
Comparison EFC400 with Copperfield®:
We use the simulation programs EFC400 (Winfield) and Copperfield® for the calculation of the spread of electrical and magnetic fields. It was interesting to check how the results of the two programs match each other.
Therefore, we have reproduced a variety of identical resources in both programs, set the currents identically and then compared the results.
Comparison of a MS-system
Basis for the calculation:
MS-system type Unisec
Field 1: Load disconnector input 630A
Field 2: Load disconnector outlet 630A
|EFC400 view from above||EFC400 view from the front|
|Copperfield view from above||Copperfield view from the front|
Comparison of NS-distribution
Basis for the calculation:
Field 1: 1200mm Sefag outlet strips
Field 2: 500mm Sirco connected from below
Field 3: 1200mm Sefac outlet strips
In: 833 A
|View from above 1m from floor TS EFC-400||View from the front EFC-400|
|View from above 1m from floor TS Copperfield||View from the front Copperfield|
What should it be?::
The isoline calculation tools have a variety of class libraries implemented. What to do if a required component is missing? Redraw or simply use a similar component? The following example shows calculated isolines with a similar component:
|Available/similar: 20kV transformer:||Required: 21.6kV Transformator:||Formula:|
Voltage OS 20 kV
Voltage US 0.40 kV
In(os) 28,857 A (28.87)
In(us) 1442,856 A (1443.38)
In(inductor_seg) 72,698 A (86.603)
(calculated values are in red)
Voltage OS 21.6 kV
Voltage US 0.42 kV
In(os) 26,73 A
In(us) 1374,64 A
In(inductor_seg) 82,478 A
|I(us) = S / √3x U (us)
I(os) = S / √3x U (os)
In(inductor) = In*uk /s
In(inductor_seg) = In(spule) x 2.5
(s = Shielding effect boiler 2.5)
|The comparison of the already in the library available/similar and the precisely required transformer.|
|Left: The vavailable/similar transformer||Right: The exact required transformer|
Conclusion: The calculation error is approximately 5%. On a first glance, the difference is not overly large. However, if only similar types are being used for all components, or the integration of switches and crossings is waived, the result can be heavily distorted, in or against the favor of the operator of the station. For this reason we suggest that only library components are being used, which comply with the manufacturer. Otherwise, the components have to be reproduced.
Caution: The components available in the libraries often don’t comply with the actual information of the manufacturers and thus lead to incorrect results.
Worst case or best case?::
The following example is a comparison of a low-voltage distribution with different connection of the outflows. Here we have a clear difference between the "worst-case" and "best-case":
|Left: “Best case”: Total power is evenly distributed on all outflows||Right: “Worst case”: Total power is used at the end of the busbar|
Conclusion: The deviation of the isolines calculation is ~15%. It is essential to reproduce the outflows in the simulation according to how they are actually arranged. Otherwise the results of the calculation are inaccurate
Unbalance and magnetic fields::How does an unbalanced load of the rail of a NS-distribution affect the magnetic field strengths? Here are the results of calculations with different unbalanced loads on a low-voltage distribution:
I: L1=866A, L2=866A, L3=866A
I: L1=866A, L2=844A, L3=822A
I: L1=866A, L2=822A, L3=779A
I: L1=866A, L2=801A, L3=736A
Conclustion: Asymmetries have a very negative effect on the field strengths. The 1µT line spreads, in the calculated example with an unbalanced load, from 15% around 1.2m of just 6m to over 7m.
If the neutral conductor current at an unbalanced, similar load is considered too (112A at 15% asymmetry), the field strengths are even further negatively influenced..