Cathodic protection of ground grid

I. Brief introduction to the project

In the phase I project of Xx power plant, ground grid adopts sacrificial anode protection to apply cathodic protection. In order to make the service life of ground grid not less than 30 years, mug-3 magnesium alloy sacrificial anode is used according to calculation, the specification is 700×(90+110)×90mm, and the quantity is 785, each weighing 11kg. Reference electrodes are made of copper/copper sulfate reference electrodes. There are 8 McT-2 type electrodes, 8 test piles, 16 groups of inspection plates and 785 cloth bags with the specification of φ 250×1200mm.

2. Compilation basis

1, "Electrical Installation engineering grounding Device construction and acceptance Code" GB50169-92

2, "electrical equipment installation engineering electrical equipment handover test standard" GB50150-81 chapter 25

3, "Thermal Power Construction Quality Inspection and Assessment standards fifth Electrical Equipment"

4, "Electric Power Construction Safety Construction Management Regulations"

5, "Electric Power Construction safety Work Regulations"

Cathodic protection 37-F19519-D1305

3. Construction tools

One electric welding machine, 50 meters of copper electric welding belt, a set of welding tools, a movable plate

Iv. Process flow, technical requirements and standards

Technical requirements and standards of process flow

One, material inspection

1, anode inspection: before the sacrifice anode is used, according to the relevant standards and specifications, the appearance of the size and weight of the inspection.

2, cable inspection: check the cable specifications, size, insulation, and anode joint.

3, bag inspection: verify the size and integrity of the bag.

The anode has no warping, no burrs, cracks, pores, inclusions and attachments on the surface, and the size and weight meet the requirements.

The specification, model and size of the cable should be correct, the insulation skin should not be damaged, and the connection with the anode should be firm.

Correct size and no damage.

2. Fabrication and installation of bagged anode

1, anode surface cleaning

2. Stir the packing material

3, bagged anode assembly.

4. Excavation of anode pit.

5. Placement of bagged anode.

Remove the oxide film and oil on the surface.

Ensure that the packing material is dry and without agglomeration. Stir the packing material evenly and do not mix it with rocks, plastic tape, soil, weeds and other sundries. (Filling material formula ratio: copper sulfate: gypsum powder: bentonite =1:1:2)

First fill the bag with packing material about 10cm high, then put the anode in the middle of the bag, and surround the anode with packing material to ensure that the thickness of the packing material around the anode is consistent (not less than 50mm) and uniform compaction. Finally, bind the anode cable and the bag mouth firmly with thin rope to prevent loose mouth.

The size and depth of the pit should ensure that the anode can be placed horizontally, and the anode and the ground grid are on the same horizontal plane. The location of the pit should ensure that the distance between the anode and the ground grid is within the range of 1.0 ~ 1.5 meters.

Place the anode horizontally in the pit.

3. Connection of anode and ground grid

1. Connection of anode cable and ground grid

2, the buried cable

Weld the reinforcing plate at one end of the anode cable together with the ground grid. The weld length is not less than 100mm. The welding joint must be firm to ensure electrical conductivity. In the location of the test pile, the anode cable should be introduced into the test pile and connected to the grounding network through the measurement cable.

The buried depth of the anode cable should not be less than 0.7m. There should be no stones, soil, weeds and other debris in the backfill to avoid damage to the insulation layer of the cable. A certain amount of allowance should be left during cable laying to prevent ground damage caused by soil settlement and deformation.

Four, backfill soil to confirm that the solder joints, joints meet the requirements, backfill the soil. In dry areas, after the anode bag is buried by the backfill, water is poured into the anode pit, so that the anode packing material is filled with water and the backfill is tamped down.

V. Installation of the test system

1. Installation of long-term saturated copper/copper sulfate reference electrode

2. Installation of test pile

3. Check the tablet Settings

The surface of the reference electrode is ceramic products, which should be handled with care in the installation process to prevent breakage. The burying method of the reference electrode is the same as that of the anode, and the burying depth is the same as that of the grounding network. The reference electrode should be buried as close as possible to the grounding grid, close to the measuring ground point, and a certain distance from the anode, not more than 2 meters away from the anode.

Remove reference electrode in the copper sulfate solution with distilled water or fresh water allocation in advance for 4 hours, open a back to packing packing belt, with water electrode copper sulfate solution will turn stuffing mix into a paste, then soaked electrodes placed back into packing, good packaging, the reference electrode buried along with the packing back to dig a pit, again after backfill to pit irrigation, To ensure that the electrode is tightly combined with the surrounding soil; Lead the reference electrode cable into the test pile and connect it to the binding post.

According to the design requirements, determine the installation position of the test pile; A measuring cable is welded on the grounding network, and the measuring cable, anode cable and reference electrode cable are introduced into the test pile together, respectively connected to the three terminals (the terminals of the measuring cable and anode cable are electrically connected through a copper sheet), and then the pile leg is implanted into the ground and backfilled.

Two groups of inspection sheets are set at each test pile. One is connected to the grounding grid (for cathodic protection) and the other is not connected and is in a natural state of corrosion.

5. Security risk analysis

No. Engineering flow program safety risk analysis, preventive measures responsible person

1 with electric welding construction personnel burn sleeve welder gloves Wang Xia

2 Soak the reference electrode in the copper sulfate solution. The copper sulfate solution corrodes the hand. Try not to splash the solution on the hand

3 reference electrode installation Ceramics are fragile and should be handled with care during installation

Six, safety precautions

1. When entering the construction site, you must wear the safety helmet correctly.

2, the use of welding machine must wear a mask and welder gloves.

3. It is strictly prohibited to carry out open-air welding in rainy days.

4, the welding machine must be checked before use its insulation is strictly prohibited leakage.

5, the filling material should be set to ensure that there is no gap around the anode, backfilling should pay attention to prevent damage to the anode and cable.

6. The welding piece of the sacrificial anode is welded to the ground network system. The joint must be strong mechanically and conductive electrically.

7. All cables should be kept loose enough to prevent cable deformation. The filler material around the cable should be free of stones and other debris, which may cause insulation damage when the cable is placed in the trench.

8. The sacrificial anode shall be tested to ensure that the size of the anode material, the length of the cable, the connector of the anode conductor and the integrity of the seal comply with the technical specifications. Attention should be paid to preventing crack and damage during loading, unloading and installation. All cables should be carefully examined for defects in insulation. Pay attention to prevent cable insulation damage. The damage to the cable insulation must be repaired.

Seven, environmental protection matters needing attention

1. After the construction of electric welding, the skin should be cleaned in time.

2. Preventive measures should be taken when rinsing the paint. It is strictly prohibited to splash on the ground.