Improvement of Flow Measurement Element for Air Cooler Branch Pipe of XX Power Plant No.3 Generator

Project Implementation Plan

• Overview and necessity of project (equipment)

The cooling method of XX power plant's generator is closed self circulating air cooling. The circulation of air is achieved through the radial airflow of the generator rotor. The airflow passes through the rotor ventilation duct, ventilation gap, air gap, stator iron core, and machine base and is introduced into the air cooler. The airflow cooled by the air cooler returns to the upper and lower ends of the rotor without the need for a separate fan on the rotor. Twelve water-cooled air coolers are symmetrically arranged around the stator frame of the generator to form a closed and self circulating air cooling system. The flow rate of the air cooler water supply main is1200~2100m³/hBefore the unit is started up, it is put into operation together with the technical water supply of the unit. As the cooling device of the generator, the flow rate and pressure of each branch pipe of the air cooler will directly affect the cooling effect of the generator during normal operation.

• Existing problems

At present, SW600 thermal conductivity flow meters are installed in the inlet pipes of the air coolers of generators 1-6 in XX power plant. The sensors are designed based on the principle of using probes to detect changes in medium temperature. The probes are equipped with heating sensors and thermal sensors, which are in contact with the medium. When the medium flows in the pipeline, the heat received by the thermal sensors will change with the flow rate of the medium. The thermal sensors will convert this temperature difference signal into an electrical signal and send it to monitoring. Due to the contact between its probe and the water medium in the air-cooled branch pipe, the probe surface adheres to sludge and rust after running for a period of time, directly affecting the accuracy of flow measurement in the air-cooled branch pipe. Since its commissioning in 2009, there have been multiple instances of inaccurate flow measurement in the air-cooled branch pipe caused by sensor failures. To ensure the accuracy of flow measurement in the air-cooled branch pipes, the operation and maintenance department of XX power plant carried out modifications and tests on the flow meters of the 4th and 5th air-cooled branch pipes of generator 2 and 12 air-cooled branch pipes of generator 6 during the maintenance period of 2015-2016; The flow measurement of the air-cooled branch pipe is accurate and the operation is stable. It is planned to renovate and replace the flow meter of the air-cooled branch pipe of Generator 3.

• Technical scheme demonstration

The renovation of the flow meter in the air cooling branch pipe and the renovation project of the air cooling branch pipe will be implemented simultaneously. The original air cooling branch pipe is divided into 5 sections and connected by 4 flanges. Now, the second and third sections of the air cooling supply and drainage branch pipes will be transformed and merged into one section of pipeline, and a model BR1158C series ultrasonic flowmeter will be installed on the newly merged water supply straight pipe. The effect diagram of the No.1 machine renovation test is as follows:

Before and after renovation

• Implementation of the plan and process requirements

1. Implementation of the plan

1. Transform the original air cooling branch pipe from five sections to four sections;
2. Use dismantled thermal conductivity flow meters;
3. The original sensor is a three wire sensor, and the new ultrasonic flowmeter is a four wire sensor. Find a spare core in the original signal cable and change the three wire wiring to a four wire wiring;
4. The thermal resistance and pressure gauge in the newly renovated straight pipe need to be re drilled and installed;
5. Power on and debug the newly installed ultrasonic flowmeter.

1. Process requirements

1. Before piping, the steel pipe must be polished with a groove, and any burrs on the inner wall of the steel pipe should be treated with a file;
2. useargon arc weldingWelding is carried out in a certain manner, and after welding, PT inspection of the weld seam shows no cracks;
3. Newly renovated straight pipe thermal resistance and pressure gauge openings should be located as close as possible to the back of the straight pipe to ensure that there are no holes between the ultrasonic flowmeter probes;
4. After welding, clean the inside of the pipeline to ensure that there is no welding slag or iron filings inside;
5. Before installing the ultrasonic flowmeter, the manufacturer needs to provide a product inspection certificate, and it cannot be used without inspection;
6. When installing the ultrasonic flowmeter probe, ensure that the probe is smooth. Set corresponding parameters such as pipe wall and diameter in the device according to the pipe diameter. When fixing the probe, ensure that its signal strength (UP, DN) is greater than 80, the signal quality (Q) is greater than 80, the probe coupling agent is evenly applied, and the sensor probe is reliably fixed.

• Debugging (testing) requirements

1. After all installation and wiring work is completed, power on the oil-water sensor and check the following items one by one:
2. The device displays normally without any abnormal alarm signals;
3. The parameter settings are correct and consistent with the on-site pipe wall parameter requirements;
4. The signal strength and quality of the probe are normal, and the flow measurement after starting the technical water supply of the unit is normal, stable, and without any jumping phenomenon.

• Quality acceptance and inspection

1. After the renovation of the air cooling supply and drainage branch pipes, there is no leakage phenomenon;
2. The electromagnetic flowmeter probe and device should be installed firmly, with standardized wiring, and the related cable wiring should be firm and aesthetically pleasing;
3. The measured value of the electromagnetic flowmeter is displayed normally, the parameter settings are correct, and the analog signal can be sent to the monitoring normally.

• Safety and environmental protection measures

1. Safety assurance measures

1. Random group maintenance of the project is carried out to ensure that the unit is in maintenance status for project implementation;
2. The maintenance process shall be strictly carried out in accordance with the "Safety Work Regulations" and on-site construction safety regulations;
3. Conduct analysis of hazardous points in project construction and develop preventive and control measures;
4. Qualified safety tools and electrical tools should be used after inspection;
5. The maintenance site should have sufficient and qualified construction power supply and lighting;
6. Drain the accumulated water in the air cooler branch pipe;
7. The generator flow meter cabinet has been powered off, and there is no voltage in the power and signal circuits of the air cooling branch flow meter measurement circuit;
8. When removing the original air cooling pipeline, the mechanical personnel shall first remove the original pressure gauge and thermal resistance, and it is forbidden to damage the anime components by rough construction;
9. Strictly implement wind tunnel management, register the brought in tools, materials, and other supplies, and verify them when taken out;
10. When cutting pipelines, a cutting machine should be used and gas cutting is prohibited;
11. Pay attention to fire prevention at the maintenance site, use fireproof cloth to protect the construction site, and place sufficient fire-fighting equipment on site;
12. New branch pipe openingAfterwards, toWill generateMetal debristimelyclean upAfter inspection and confirmation that there are no iron filings in the air cooling supply and drainage pipelines, they can be reinstalled;
13. The temporary power supply used during the construction process must be equipped with a leakage protector and pass inspection;
14. Welding operations must be carried out by certified personnel;
15. Adhere to civilized maintenance and construction, clean the site before the end of each day, ensure that the work is completed, the materials are clean, and the site is clean, and maintain a clean and orderly maintenance site.

Hazard analysis and pre control measures

serial number	hazard source	Pre control measures
1	slip and fall	Clean the bottom of the thrust oil basin thoroughly before starting work.
2	Iron filings in the air-cooled branch pipeline	After the drilling work is completed, check that there are no iron filings inside the pipe wall.
3	itemIn the wind tunnel	Personnel and items must be registered before entering and exiting the generator wind tunnel.
4	electric shock	usedThe shell of the argon arc welding machine needs to be reliably grounded,ifThe power cord is damagedDo not use.The power panel must be equipped with a qualified leakage protector.

（2） Environmental protection measures

1. Consumable materials used in construction and waste materials after maintenance must not be thrown around and must be recycled and disposed of.
2. Construction waste at the construction site should be promptly cleaned up and uniformly recycled for disposal.

• construction schedule

This project is carried out in conjunction with the maintenance of XX power plant units in 2016-2017.

• Arrangement of project implementation personnel

One person in charge of the work and five members of the work team.