Analysis of the situation in the field application

With the development of computer technology and power electronics technology, the application of low-voltage inverter has also developed rapidly. In recent years, low-voltage frequency converters have been widely used in various technologies of oil production in oil production plants. Frequency converter speed regulation can improve the control accuracy, production efficiency and product quality of machinery, reduce energy consumption, and achieve significant energy-saving effects in many production processes in Gudong oil production plant

I. energy saving principle of frequency converter

1. Energy saving of frequency converter

energy saving of frequency converter is mainly reflected in the application of fans and water pumps. In order to ensure the reliability of production, all kinds of production machinery have a certain margin when they are designed to be equipped with power drive. When the motor cannot run under full load, in addition to meeting the requirements of power drive, the excess torque increases the consumption of active power, resulting in a waste of electric energy. The traditional speed regulation method of fans, pumps and other equipment is to adjust the air and water supply volume by adjusting the opening of baffles and valves at the inlet or outlet. Its input power is large, and a large amount of energy is consumed in the closure process of baffles and valves. When using frequency conversion speed regulation, if the flow requirements are reduced, the requirements can be met by reducing the speed of the pump or fan

according to hydrodynamics, P (power) = q (flow) H (pressure), flow Q is directly proportional to the power of speed n, pressure h is directly proportional to the square of speed n, and power P is directly proportional to the cube of speed n. if the efficiency of the water pump is certain, when it is required to adjust the flow to decrease, speed n can decrease proportionally, and at this time, the shaft output power P is proportional to the cubic relationship we think. That is, the power consumption of the pump motor is approximately proportional to the speed. When the required flow Q is reduced, the output frequency of the frequency converter can be adjusted to reduce the motor speed n in proportion. At this time, the power P of the motor will be greatly reduced according to the cubic relationship, saving 40% to 50% energy than adjusting the baffle and valve, so as to achieve the purpose of power saving

for example, the power of a centrifugal pump motor is 55 kW. When the speed drops to 4/5 of the original speed, its power consumption is 28.16 kW, saving 48.8%. When the speed drops to 1/2 of the original speed, its power consumption is 6.875 kW, saving 87.5%

2. Power factor compensation energy saving

reactive power not only increases line loss and equipment heating, but also the reduction of power factor leads to the reduction of electric active power. Among a large number of reactive electric energy consumption circuits, the equipment is inefficient and wasteful. After using the frequency conversion and speed regulation device, due to the function of the internal filter capacitor of the frequency converter, the reactive loss is reduced and the electric active power is increased

3. Soft start energy saving

the hard start of the motor will cause serious impact on the electricity, and will also have too high requirements on the capacitance. The large current and vibration generated during start-up will cause great damage to the baffle and valve, and is extremely detrimental to the service life of equipment and pipelines. After using the frequency conversion energy-saving device, the soft start function of the frequency converter will make the starting current start from zero, and the maximum value will not exceed the rated current, reducing the impact on electricity and the requirements for power supply capacity, and extending the service life of equipment and valves. The maintenance cost of the equipment is saved

second, Gudong oil production plant in use of frequency converters

at present, Gudong oil production plant is using more than 480 various frequency converters, including more than 270 in the third production center, 45 in the first mine, 13 in the second mine, 22 in the third mine, 43 in the fourth mine, 57 in Xintan pilot mining, and 27 in the gathering and transportation team. Mainly abb and robinham in the United States, Fuji, Yaskawa, Sanken, Toshiba and Hitachi in Japan, and Siemens in Germany. At present, domestic frequency converters have achieved remarkable results in control technology and functions. The progress and achievements are expressed in pounds or kilograms. Therefore, the number of domestic frequency converters in oil plants is gradually increasing in the past two years, mainly including chunri, Senlan and Yantai Huifeng

III. main problems at present

the technical quality supervision station of Gudong oil production plant has carried out frequency converter maintenance since 2005, and has successively organized 150 on-site maintenance times, with a total power of 5800 kW

from the perspective of maintenance, the characteristics of frequency converter failure or damage can generally be divided into two categories: one is the frequent automatic shutdown phenomenon in operation, accompanied by a certain fault display code, and its treatment measures can be handled and solved according to the guidance methods provided in the random instructions. This kind of fault is generally a protective action phenomenon caused by the improper setting of the operating parameters of the frequency converter, or the external working conditions and conditions do not meet the use requirements of the frequency converter; The other is sudden faults such as insulation reduction or breakdown caused by short circuit and humidity caused by high temperature and conductive dust due to poor service environment (in serious cases, there will be abnormal phenomena such as ignition and explosion). The specific performance is:

1. The main control circuit of the frequency converter is faulty. It mainly includes the main board, power board, inverter, filter capacitor and other main control circuits are damaged

2. Inverter cooling DC fan failure. The fan is a vulnerable part with a service life of 25 years. However, due to the wide variety of frequency converters and different power levels, the rated current of internal DC fans is different and not universal. Some fans cannot be replaced in time due to the lack of spare parts after damage

3. The peripheral controller of the frequency converter is faulty. The frequency converter in the frequency conversion cabinet has no fault, but the external control circuit system has fault. Due to the long service life and complex control circuit, there are neither circuit diagrams nor wire numbers, and there are many and complex lines, which cause inconvenience to maintenance

4. The design of frequency conversion cabinet is unreasonable, the interior is too narrow, and the heat dissipation and ventilation effect is poor, resulting in poor heat dissipation. The working environment of some frequency converters is relatively poor, and there is a lot of wind, sand and dust, which seriously affects the normal operation of the frequency converter and even causes shutdown failure. The cooling and guide fan of the frequency conversion cabinet is a vulnerable part, and its service life is generally about 2 years. However, most of the cooling fans of the frequency conversion cabinet are not replaced in time after they are damaged, resulting in poor cooling, poor working stability of the frequency converter, increased aging, frequent overheating alarms and other phenomena

5. The daily maintenance of the frequency converter cannot keep up. The operator did not understand the basic operation of the frequency conversion circuit and some basic parameter settings, and could not find problems in time during use

6. The little horse pulls the cart. Due to the limitation of working conditions when it was put into production at that time, in order to save money during design and installation, many places have adopted variable frequency power less than the rated power of the motor. However, with the change of process production conditions, the problem of small horse pulling the cart occurred, resulting in the abnormal operation of the frequency converter. Such as No.1 combined water export, No.3 combined lifting and kdl8 station water injection

IV. main fault causes and preventive measures of the frequency converter

due to incorrect use methods or unreasonable setting environment, it is easy to cause malfunction and failure of the frequency converter, or it cannot meet the expected operation effect. In order to nip in the bud, it is particularly important to carefully analyze the cause of the failure in advance. After 60 years of normal use, the frequency converter has entered the high incidence period of faults, and there are often failures such as component burnout, failure and frequent action of protection functions, which seriously affect its normal operation

1. External electromagnetic induction interference is easy to cause faults

if there are interference sources around the frequency converter, they will invade the interior of the frequency converter through radiation or power lines, causing the control circuit to malfunction, causing abnormal operation or shutdown, and even damaging the frequency converter in serious cases. It is very necessary to take noise suppression measures outside to eliminate interference sources. The specific solutions are as follows: first, try to shorten the wiring distance of the control circuit and separate it from the main line; Second, the grounding terminal of the frequency converter should be carried out according to the regulations, and cannot be mixed with electric welding and power grounding; Third, the input end of the frequency converter is equipped with a noise filter to avoid interference from the incoming line of the power supply

2. Faults caused by environmental problems

the frequency converter is an electronic device, and there are detailed requirements for the installation and use environment in its specification. Vibration is the main cause of mechanical damage to electronic devices. For occasions with large vibration impact, rubber and other vibration avoidance measures should be adopted; Humidity, corrosive gas and dust will cause rust, poor contact and low insulation of electronic devices to form a short circuit; Temperature is an important factor affecting the life and reliability of electronic devices, especially semiconductor devices. Air conditioners should be installed according to the environmental conditions required by the device or direct sunlight should be avoided

it is very necessary to regularly check the air filter and cooling fan of the frequency converter. At present, the cooling fan of the frequency converter in use in the oil production plant is seriously damaged, and some frequency converters have a poor working environment, which seriously affects the heat dissipation and air circulation, resulting in the frequency converter easy to trip and overheat alarm in the high temperature season

3. Faults caused by parameter setting and equipment

the faults mainly occur in the low-voltage frequency converter used for polymer injection pump. The faults mainly show that it does not trip immediately when starting, but that the toughness and strength of such parts are strengthened during operation. Possible reasons are:

(1) the working state of the pump is unstable; (2) Pipeline pressure is too high; (3) The acceleration time setting is too short; (4) The deceleration time setting is too short; (5) The torque compensation setting is large; (6) Cause excessive current carrying at low speed; (7) The setting of electronic thermal relay is improper, and the action current is set too small, resulting in misoperation

4. Faults of main board and main circuit

due to long service life and some sudden reasons, the main board and main circuit are damaged. Such faults will inevitably cause damage and scrap of components and parts, which is the main consumption of frequency converter maintenance costs. Mainly:

(1) damage of rectifier block; (2) The charging resistance is damaged; (3) The inverter module is burnt out; (4) Damage of filter capacitor; (5) The main board and power board are damaged

5. Faults caused by improper maintenance

in addition to the damage of the cooling system fan, there is another main reason for most frequency converter overheat alarm faults, which is the lack of daily maintenance, and the serious accumulation of dust on the frequency converter radiator, which affects the heat dissipation

v. suggestions

l standardize the access channels of frequency conversion equipment and establish an access system

at present, Gudong oil production plant has a wide variety of frequency converters, and the devices between various frequency converters are not common, which makes it difficult to prepare materials and increase the difficulty of cost-effective maintenance. Therefore, it is suggested to standardize the frequency conversion equipment into different products, have a variety of material production channels, establish a market access system, reduce the brand types of frequency converters, and reduce the later maintenance and repair costs

(1) Limited brand range

Limited brand range, such as some brands with low failure rate and reliable operation in Gudong oil production plant in recent years. It is suggested that the specifications should be Fuji, abb, Senlan and other brands

(2) standardize the introduction channel

standardize the introduction channel, inspect the after-sales service of the manufacturer's technical force of the introduced equipment, and require complete data during the acceptance of the newly introduced frequency conversion equipment, including circuit diagrams, instructions, etc., so as to facilitate future maintenance in case of failure

2. Establish the daily maintenance system of frequency converter

standardize the management of frequency converter, and assign special personnel to be responsible for the daily maintenance of frequency conversion equipment. The specific contents of daily maintenance can be divided into:

(1) operation data record, fault record:

regularly measure the long-distance data of frequency converter and motor, including the output of frequency converter