MAGNETIC FIELD MITIGATION OF POWER CABLE BY HIGH MAGNETIC COUPLING PASSIVE LOOP

Transcription

1 MAGNETIC FIELD MITIGATION OF POWER CABLE BY HIGH MAGNETIC COUPLING PASSIVE LOOP A. Canova, L. Giaccone Dept. of Electrical Engineering Politecnico di Torino Corso Duca degli Abruzzi 24, Torino (Italy) 1

2 Summary 1. Magnetic induction produced by cable power lines 2. HMC passive loop: unitary coupling factor multiple coupling factor 3. Advantages of the HMC Passive Loop 4. HMC performance Simulation results introduction of the phase splitting technique 5. First implementation of the HMC passive loop: high voltage power line (220 kv) comparison with other techniques further improvements 6. Conclusion 2

3 Magnetic induction produced by cable power lines Junction g zone Section S 1 and S 3 Section S 2 y S 1 S 2 S 3 z x d i=50 100cm Magnetic induction at the ground level on a plane over the HV power line (I=1000A, line depth= 1.5m) Magnetic Induction (μt) I = 1000 A (m) Trefoil Junction zone Magnetic induction at the ground level on a line orthogonal to the cables (trefoil and Junction zone) 3

4 HMC configuration with unitary coupling factor Magnetic core Principle scheme Shielding Cables Source cables Because of the coupling obtained by an appropriately sized magnetic core. The design step requires as input data the value of the rated current of the power line and the impedance of the shielding cables. With this system is possible to induce in the shield conductors a set of currents in opposition to the source ones. 4

5 HMC configuration with multiple coupling factor Shielding cables Principle scheme o' d 2 d 1 Windings Source cables o Although the base idea is very simple, due to technical reasons sometimes it is not possible to install the shield close to the power lines. An optimal design has to be done. In fact the geometrical displacement is no more simply defined (d 1 and d 2 ) and also the correct amplitude value of the shielding currents has to be determined (K sh =N 2 /N 1 I sh =I s /K sh ). 5

6 Advantages of the HMC Passive Loops It make use of common ferromagnetic and conductive materials (are not required, for example, materials with high magnetic permeability) The exploitation of the materials used can be maximized by a proper design of its components and therefore it is more lightweight compared to the other shield solutions considering the same performances (passive loops, closed ferromagnetic shields, flat or U-shaped conductive shields) The components of the shield can be assembled on site with a reduced number of operations and without having to perform complex welds It is adaptative. It adjust the shielding current by itself with relation to the source current No regulation components are required (differently from active loops) No compensation components are required (differently from passive loops) It is modular It can be adapted for several conductor layout configurations 6

7 HMC performance Simulation results Junction zone z y x S S 2 S 1 3 Line depth=1.5 m x=0m x=10m x=20m x=30m Magnetic flux density produced by the power line without shield (Ground level) Application of HMC: one shielding conductor per phase I s =1000A 7

8 HMC performance Simulation results- Phase splitting Junction zone z y x S S 2 S 1 3 Line depth=1.5m x=0m x=10m x=20m x=30m Magnetic flux density produced by the power line without shield (Ground level) Phase splitting Application of HMC: two shielding conductor per phase I s =1000A 8

9 First implementation of the HMC passive loop Shielding cable High voltage power line (220 kv) Phase splitting technique has been used 4 shielding cables per phase have been istalled HV cable HMC configuration 4 shielding cables Magnetic core 9

10 First implementation of the HMC passive loop High voltage power line (220 kv) Junction zone Shielding cables Magnetic core Joints Time for installation: less than one day 10

11 Comparison with Passive loops equispaziati Conduttori isolati MT sez. 185 mm2 Al 700 mm Elevato numero di conduttori da posare e giuntare 11

12 Comparison with Passive loop High voltage power line 220 kv length 2.3 km 3 jointing zone One jointing zone with HMC and 2 jointing zones with passive loop z y x Current value 250 A z y x Magnetic Induction (μt) Passive Loop HMC Magnetic Induction (μt) Passive Loop HMC Y axis (m) X axis (m) 12

13 Comparison with Passive loop Measurements have been normalized in order to evaluate the performance at the rated value 1400 A Shielding Factor = B o /B sh y y z x z x Magnetic Induction (μt) Magnetic induction at 0.5m from the gound level I = 1400A X axis (m) Source field Passive Loop HMC Shielding Factor X axis (m) Passive Loop HMC 13

14 Further improvements The magnetic cores realized for this application have been installed when the jointing zone installation was already finished Open Magnetic core Presence of an air gap (value of the shielding current lower than the theoretical one) Magnetic cores can be inserted (around the source cables) before the joints installation obtaining better performance Optimizing the magnetic core design and the exactly displacement of the shielding conductors with respect to the barycentre of the source conductor, by using commercial magnetic material, it is possible to achieve SF of about 30 Due to the three phase configuration of the power line it is possible sible to save one magnetic core installing just two of them. (I R + I S + I T = 0 I T = - I R - I S ) 14

15 HMC Passive loop Conclusion Closed ferromagnetic shield Flat/shaped shields SF Cost low mean high mean Complexity of Installation low mean high (in the junction zone) mean The life of the shield is dependent on the material, on the possible superficial treatment and on the goodness of the installation. The experimented system is, without any doubt, efficient. It has higher SF/cost ratio than the other solutions, moreover HMC passive loop has the advantage of a fast and easy installation 15