Reservoir water diversion project, the design scale is 900km3/d.The water delivery pipeline is 176km long and the diameter of the pipeline is DN2200. The real-time flow and cumulative flow data of water delivery are measured by super-large-diameter electromagnetic flowmeters.
1 Principle and advantages of electromagnetic flowmeter
1.1 Principle of electromagnetic flowmeter The sensor is composed of measuring tube, excitation coil and measuring electrode and other components.The measuring principle is based on Faraday's law of electromagnetic induction.The excitation winding supplies power to generate a magnetic field. When the conductive water transfer medium passes through the magnetic field of the measuring tube, it cuts the magnetic force line and generates an induced potential U in the direction perpendicular to the magnetic field and flow velocity.
Its expression is as follows:
(1) In the formula: K is the instrument structure constant; B is the magnetic induction intensity; V is the average flow velocity; D is the inner diameter of the measuring tube.In the electromagnetic flowmeter sensor, the original voltage signal of the induced potential is a linear function of the average flow velocity, which has nothing to do with the flow velocity distribution and other characteristics of the medium.
The induced potential (millivolt electrical signal) is transmitted to the intelligent converter through the cable for digital processing to calculate real-time flow and cumulative flow.And converted to standard signal output [1].1.2 Advantages of electromagnetic flowmeter measurement Water delivery measurement using electromagnetic flowmeter measurement has the following advantages.① There is no shrinkage or protruding parts in the water pipeline, and the pressure loss is almost zero; ② The induced electrical signal is related to the average value of the pipe section, and only a short straight pipe section before and after is required, which reduces the size of the flowmeter well and reduces the The engineering cost is particularly important; ③The water transmission medium contains a certain amount of sediment, while the electromagnetic flowmeter sensor only has the lining and electrodes in contact with the water, and is anti-corrosion, wear-resistant, and the instrument has a long service life[2]; ④The ultra-large-caliber electromagnetic flowmeter passes through the interface Connected with the real-time computer monitoring system, it can carry out data communication on the water delivery flow information.
2 Anti-jamming control for sensor installation
2.1 Grounding measures for sensor installation The grounding of sensor installation directly affects the anti-interference performance of the system, and the grounding wire used must prevent any other interference voltage from being induced.Therefore, the grounding wire cannot be connected with the grounding wire of other live electrical equipment; the grounding construction adopts the method of grounding the ground electrode on the spot.Install the grounding electrode outside the flowmeter well, and use flat steel to introduce the grounding point of the flowmeter.The grounding resistance value is not greater than 10,
2.2 Grounding ring installation measures
The water pipeline adopts a metal pipeline with an insulating coating inside, and a grounding ring must be installed to improve the anti-interference performance, otherwise the instrument will work unstable.The installation method of the grounding ring is shown in Figure 2.
In Figure 2: V1 and V2 are ground wires, provided by the manufacturer; PE is a functional ground wire, and the construction site is made of flat steel.D1 and D2 are sealing gaskets; E is the grounding ring; F1 is the pipe flange; F is the sensor flange; Y is the sensor signal output.2.3 Cable laying and shielding measures The power of the excitation winding of the ultra-large-diameter electromagnetic flowmeter is relatively large, and an amplifier NB900F must be added between the sensor IFS4000F of the flowmeter well and the intelligent converter IFC110F to meet the excitation requirements.
Pay attention to the following points when wiring and shielding the electromagnetic flowmeter.
① The connecting cable between the electromagnetic flowmeter sensor and the converter shall be the cable supplied by the manufacturer.Do not introduce outside interference.The laying of cables is protected by steel pipes.
②Excitation power supply and signal cables are required to be laid separately through pipes in order to prevent being crushed by machinery and bitten by incisors (rats).
③The cables in the junction box are not allowed to cross or coil.
④The protective ground wire PE must be connected to the separate U-shaped clamp terminal in the junction box.
⑤ During construction, do not loosen the protective connecting conductor between the yellow-green line U-shaped clamp terminal and terminal 10 in the signal converter.
3 key process control points
During on-site installation, in order not to affect the detection accuracy of the metering system, the following process requirements must be strictly met.
① Keep the electrode axis horizontal.When the electromagnetic flowmeter sensor is installed, the axes of the two electrodes must be in the horizontal direction.
② The measured medium is filled with the measuring tube.The measuring tube must be filled with water, and there must be no phenomenon that the tube is not full or bubbles gather in the measuring tube.
③Meet the requirements of flow direction and straight pipe section.The direction indicated by the arrow on the sensor is the positive direction of medium flow; the ultra-large-diameter electromagnetic flowmeter (sensor and converter installed separately) is designed to be installed in the flowmeter well of the pipeline.In order to ensure accurate measurement, it is necessary to ensure that the flowmeter *D/requires the last 2D straight pipe section (D is the nominal diameter).
4 Installation of super large diameter electromagnetic flowmeter
4.1 Assembly of sensor and expansion joint
Install the grounding ring and expansion joint on the downstream side of the flowmeter according to the arrow on the sensor, and pre-adjust the expansion joint to a short state.
4.2 Well fracture of flowmeter
The flowmeter well fracture steps are as follows:
①Confirm the fracture position of the installed sensor, and measure the size of the broken pipe (according to the size after the expansion joint is stretched).
②The skylight is opened in the fracture area of the pipe, and the M-shaped steel support is made into the pipe to ensure the roundness of the pipe and prevent the deformation of the pipe end after the fracture and affect the flange installation.
③ After the fracture, the grooves are mechanically processed at the pipe ends on both sides to meet the requirements of welding flanges [4].
4.3 Hoisting
The assembled sensor plus expansion joints has a total weight of about 6t, and is hoisted in place by a 25t truck crane on site.After hoisting in place, adjust and release the expansion joint, install a grounding ring and a gasket between the upstream flange and the sensor, and align and tighten the penetration bolts; also install a gasket, Insert the bolts and tighten.
4.4 Flange welding
Adjust the positions of the upstream and downstream flanges, grounding rings and gaskets of the pipeline, tighten the bolts, and fix them by spot welding.Remove the pre-tightening bolts of the upstream and downstream flanges, adjust the contraction expansion joints, so that the upstream and downstream flanges are separated from the flow meter and expansion joints, and leave a welding space inside the flanges.The inside and outside of the flange adopt fillet weld to weld the upstream and downstream two flanges.
4.5 Non-destructive testing and anti-corrosion treatment of welding joints
①Testing standards and qualified grades
All flange interface fillet welds need to be non-destructively tested, using electromagnetic flaw detection, and the inspection ratio is *.The quality should meet the secondary requirements of the standard JB4730-2005 [5].If the welding seam of the pipe flange is found to have excessive defects, it should be dealt with in time to make the re-inspection pass.Any weld can only be repaired once.
②Outside the inner anti-corrosion flange weld
The internal and external anti-corrosion of the steel pipe fittings of the flange is treated in the same way as the steel pipe body. The external anti-corrosion of the flange welds is painted with modified chlorosulfonated polyethylene anti-corrosion coating; the internal anti-corrosion coating of the flange is drinking water grade * epoxy coating.Both inner and outer sides are coated with two bottoms and two sides.
4.6 The overall fastening and positioning of the sensor expansion joint
After the welds of the upstream and downstream flanges pass the flaw detection, they enter the overall fastening and positioning process of the sensor expansion joint.
①Adjust and release the expansion joint, install a grounding ring and a gasket between the upstream flange and the sensor, insert the bolts and tighten them.
②Add a gasket between the downstream flange and the expansion joint, insert the bolts and tighten them.
③In a symmetrical manner, fasten all flange bolts and install positioning sensors and expansion joints.
4.7 System hydraulic test
After the overall installation of the sensor and the expansion joint is completed, the hydraulic test should be carried out together with the water pipeline.The test pressure is 1.5 times the working pressure.After passing the hydrostatic test, it can be put into operation [6].
5 System debugging and commissioning
According to the instrument parameters, process parameters and operation control mode, set the main menu, subroutine function and data configuration of the intelligent transmitter; when the pipeline is filled with process fluid (water), perform impedance and insulation for sensor cables and electrodes Performance test; use the GS8A simulator to simulate the test of the intelligent transmitter.
6 System check and put into operation
6.1 Checking the sensors
①Preparation
The measuring pipe is filled with process fluid (water) and is at rest.Power must be cut off before opening the case (box).Measuring instruments and tools required for the inspection include an ohmmeter or an AC voltage/resistance bridge.The (signal and excitation) plug must be pulled out before inspection, taking care not to remove the connection inside the signal converter terminal box (yellow-green wire between the U-shaped clip and terminal 10).
② Check content
Measure the resistance between 7 and 8 wires (excitation winding), it should be 20~170Ω normally.Measure the insulation resistance between 1 pair of 7 circuits (excitation and signal circuits), the normal value should be >20MΩ.For the measurement of the electrode circuit, use an AC voltage/resistance bridge to measure the resistance between the 1-2 and 1-3 circuits respectively. The two values are normally 1kΩ~1MΩ and should be approximately equal. The detected impedance is mainly determined by the conductivity of the water. [7].③ Electrode circuit inspection results analysis If there is a huge difference, it indicates that the electrode wiring is broken or the electrode is polluted; if it is less than this range, discharge the fluid in the tube and measure again; if it is still too low, the electrode circuit is short-circuited.
6.2 Check Smart Converter with GS8A Simulator
①Check wiring
Disconnect all wires 1, 2, 3, 7, 8 to the sensor from the terminal box and record where each cable terminal is wired.Connect the mA meter to the terminal I+/I-, the precision is 0.1, the internal resistance Ri=15~500Ω, the measuring range is 0~20mA, the pulse range is 0~10kHz; the time base is at least 1s.
② Inspection steps and methods
According to Ftc1.011.051.063.02 program data setting, calculate and check zero point, mA output range and pulse output value.The GS8A simulator sends a zero-point analog signal to verify the zero-point value of the transmitter; the mA value of the current output set point of the GS8A simulator should be within the tolerance range; the hourly pulse value of the pulse output set point of the GS8A simulator should be within the allowable within range.
6.3 System commissioning
After the calibration is over, remove the calibration wiring after the power failure, and restore the sensor cable wiring.After the system checks and checks are correct, the power is sent again, and the system can be officially put into operation.
7 Conclusion
During the installation process of the ultra-large-caliber electromagnetic flowmeter in the water pipeline of the urban water diversion project, the anti-interference measures of the sensor must be strictly controlled; several key process points that affect the measurement accuracy must be strictly controlled; assembly, hoisting, welding, and non-destructive testing in the field installation process must be controlled , anti-corrosion and other aspects of the quality; according to the instrument parameters, process parameters, control parameters, correctly set the function and data of the menu program to ensure the expected system indicators.The practice of the Harbin water diversion project shows that, using the above-mentioned engineering methods, the instrument system has been in operation for one year, and the accuracy of measurement and reliability of operation all meet the design requirements.
