ESS Grounding System Concept Fundamentals and Requirements Carlos

ESS Grounding System Concept Fundamentals and Requirements Carlos A. Martins RF Electrical Power Systems www. europeanspallationsource. se December 11 th, 2013

Grounding Fundamentals Principles of “equipotentiality” Radiated noise Conducted noise

EMC grounding mesh size • Rule based on radiated noise (RN): An ideal grounding plane can be fairly approximated to a meshed plane, if: M[m] ≤ λ [m]/50, with λ wavelength Most typical RN • Rule based on conducted noise (CN): Considering the self inductor of a mesh conductor to be 1µH/m, the mesh size (M) allowing for less than 10 V between racks depends only on the noise current level and on its frequency according to Most the following rule: typical M[m] ≤ 1. 6 / ( f[MHz] x I[A] ) CN Assuming I = 1 A (10 MW power supply with good internal EMC compliancy) Main noise frequency Mesh size, M 1 MHz 6 x 6 m 2 2 MHz 3 x 3 m 2 4 MHz 1. 5 x 1. 5 m 2 6 MHz 1 x 1 m 2 Good match Main noise frequency (MHz) Mesh size (m 2) 0. 25 MHz 6 x 6 m 2 0. 5 MHz 3. 2 x 3. 2 m 2 1 MHz 1. 6 x 1. 6 m 2 2 MHz 0. 8 x 0. 8 m 2

Grounding Fundamentals Interconnection of electrical equipment in view of EMC compliancy From a renowned EMC consultant ( French guru in EMC) In “Schneider Electric – EMC Guidelines, Chapter Q”

Grounding Fundamentals Using cable trays for improving the effectiveness of the grounding system - All these cable trays are interconnected at each possible point, including at each cabinet in both extremities, creating therefore a unique grounding network, economical, in 3 D, using all existing conductor paths

Safety earth (Lightning Protection) according to IEC 62305 8 µs 20 µs The principles of lightning protection are in line and very close to those of EMC protection Coarse grounding mesh embedded into the building structure, in 3 D (typical mesh sizes: 10 x 10 m 2 or 20 x 20 m 2)

Safety earth (lightning protection) according to IEC 62305

Safety earth (Lightning Protection) according to IEC 62305

EMC grounding based on a mesh system No specific EMC standards available Terminal pad MEBB EMC grounding mesh

Total grounding concept of a surface building at XFEL (DESY) Skizze ebenerdiges Gebäude zum XFEL-Gesamterdungskonzept 17 = Sketch flat-ended building for XFEL total grounding concept (Google translate) 16 18 24 3 20 21 22 4 25 8 8 Legend: 1 - Diaphragm wall with steel-reinforced 2 - Underwater sole 3 - Shaft wall with shielding ( flat bars in the grid 5 x 5 m with welded junction points ) 4 - Base plate with shielding ( flat bars in the grid 5 x 5 m with welded junction points ) 5 - Foundation Earth 6 - Foundation earth connector to the reinforcement of the diaphragm walls 7 - Connection wall shield with fixed earthing point 8 - Connection ground shield 9 - Potential equalization bar in the lowest floor 10 - Connection to Foundation Earth potential equalization rail 11 - Equipotential bonding rail for equipment ground 5 10 26 12 - Equipotential bonding rail to the wall shield 13 – First floor with shielding ( flat bars in the grid 5 x 5 m with welded junction points ) 14 - Connecting the ceiling shield to the wall shielding 15 - Connection of the tunnel to the earth wall shielding 16 - Lightning rod 17 - Fishing rod 18 - Roof constructions, such as air conditioning with exhaust air tower 19 - Ring earth to control the potential 20 - Connecting the wall shielding with fixed earthing point 21 - Potential equalization bar on the ground floor 22 - Lightning rod connection 23 - Connection earther 24 - Facade 25 - Facade connection 26 - Connection to other buildings (Google Translate) 27 - Floor ceiling without shielding

Total grounding concept of a shaft building at XFEL (DESY) = Sketch shaft building for XFEL total grounding concept (Google translate) Legend: 1 - Diaphragm wall with steel-reinforced 2 - Underwater sole 3 - Shaft wall with shielding ( flat bars in the grid 5 x 5 m with welded junction points ) 4 - Base plate with shielding ( flat bars in the grid 5 x 5 m with welded junction points ) 5 - Foundation Earth 6 - Foundation earth connector to the reinforcement of the diaphragm walls 7 - Connection wall shield with fixed earthing point 8 - Connection ground shield 9 - Potential equalization bar in the lowest floor 10 - Connection to Foundation Earth potential equalization rail 11 - Equipotential bonding rail for equipment ground 12 - Equipotential bonding rail to the wall shield 13 – First floor with shielding ( flat bars in the grid 5 x 5 m with welded junction points ) 14 - Connecting the ceiling shield to the wall shielding 15 - Connection of the tunnel to the earth wall shielding 16 - Lightning rod 17 - Fishing rod 18 - Roof constructions, such as air conditioning with exhaust air tower 19 - Ring earth to control the potential 20 - Connecting the wall shielding with fixed earthing point 21 - Potential equalization bar on the ground floor 22 - Lightning rod connection 23 - Connection earther 24 - Facade 25 - Facade connection 26 - Connection to other buildings (Google Translate) 27 - Floor ceiling without shielding (Google Translate)

Grounding concept at FRIB […] the FRIB facility has a low-impedance facility-wide ground mesh, the FGM, embedded in the floors (and some facility walls) interconnected to the building steel and perimeter grounds. Access to this multi-point, quasi-equipotential-surface ground system mesh is provided through a combination of low-impedance perimeter ground busses and grounding plates located throughout the facility.

Grounding concept at ESS Terminal pad Welded joint EMC grounding mesh

EMC Grounding Mesh 1 Stub section of the RF Gallery (view from top) Grounding rail - MEBB ≤ 2 m Mesh welding Fixed earthing terminal point or clamp for EBB Galvanized steel flat bar (3 x 30 mm)

Materials requirements & tentative cost estimate (RF Gallery) Material needs Per stub: - 25 feed-through pads; - ~ 350 m galvanized steel flat bars; - ~ 130 mesh welding points; Tentative materials cost estimate ≤ 2 m Labor might be the driving cost !!! Per stub: - feed-through pads: 25 * 20€ = ~ 0. 5 k€ - galvanized steel bars: 350 m * 3 € /m = ~ 1 k€ - mesh welding solder: 130 * 2 € = ~ 0. 26 k€ - Total (materials): < 2 k€ RF Gallery (30 stubs ? ): - feed-through pads: 30 * 0. 5 k€ = ~ 15 k€ - galvanized steel bars: 30 * 1 k€ = ~ 30 k€ - mesh welding solder: 30 * 0. 26 k€ = ~ 7. 8 k€ - Total (materials): < 60 k€

Tunnel Ground interconnection rods or cables (could be cable pipes, if metallic) RF Gallery Cable chutes (lightning and safety ground, as per IEC 62305) Waveguide sluts Grounding rails – MEBB’s Cable chutes Extension to the Tunnel

Global EMC grounding mesh Cable chutes Tunnel ≤ 2 m RF Gallery

Conclusion • A safety earth system for lightning protection shall be implemented, following IEC 62305 : - in the RF Gallery and - in the Tunnel • The safety earth system (lightning protection) may require a foundation electrode, embedded into the foundation concrete, and will require grounding rails (MEBB’s – Main Equipotential Bonding Bar) made available all along the RF gallery and tunnel in both lateral walls: - Terminal pads will be permanently fixed into the lateral walls (internal side) in order to allow fixation of the external grounding rails (MEBB’s); - These terminal pads will be connected to the foundation electrode via connection rods embedded into the concrete; • Furthermore, an EMC grounding system shall be implemented both in the RF Gallery and in the Tunnel: - Mesh size: 2 x 2 m 2 in all the surface of the Gallery and all surface of the Tunnel; - The mesh of the EMC grounding system will be embedded into the finishing layer of the concrete (basement floor). It shall be no further deep than 15 cm from the finished floor surface; • Both these grounding systems shall be functionally independent from the reinforcement metallic structure, however electrically connected to it at several points; • Both grounding systems shall be interconnected at the grounding rails MEBB’s (RF gallery or tunnel), every 8 m all along the accelerator building;

Conclusion (cont. ) • Grounding rods may be used in the cable chutes to interconnect the RF gallery grounding rail to the tunnel grounding rail. 2 rods per chute are suggested. Such grounding rods can be also part of the safety ground (lightning protection). Alternatively, if the cable pipes are metallic they could be used for these interconnects; • The EMC grounding mesh can be made of galvanized steel flat bars (3 x 30 mm 2), welded at the junction points. Alternatively, it may be made of the same materials as the lightning protection safety ground, if this one is already based on a meshed system; • The EMC grounding mesh shall be made accessible to surface terminal pads, as illustrated in the pictures (yellow dots), in order to allow for short connection to all electrical equipment (racks, modulators, klystrons, etc. ). The location of these terminal pads should be so that the maximal external connection length to the electrical equipment should be less than 2 m; • The methodology to connect the EMC grounding mesh to the floor surface terminal pads (RF gallery and tunnel) is still not totally defined and shall be defined with the support of Conventional Facilities;