Design of the most popular low voltage frequency c

2022-08-09
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The design of common low-voltage frequency conversion control cabinet

the problem is raised

as we all know, frequency converters have been widely used in all walks of life. However, many electrical engineers and manufacturers and customers want to know how to design the frequency conversion control system and the specific requirements of the design and manufacture of the frequency conversion control cabinet for practical applications. This chapter summarizes the design points from the actual design and application cases, and writes my humble opinions for peer reference

design according to the actual situation and customer requirements

before designing the frequency conversion control system, you must understand the system configuration, working mode, environment, control mode, and customer specific requirements

the specific system is divided into new design system or equipment transformation system

bci1680l 193 for the transformation of old equipment, electrical engineers should know the following technical parameters and requirements accurately

1. specific parameters of the motor, 2. factory date, 3. manufacturer (domestic, 4. imported)

5. rated voltage of the motor, 6. Rated current, 7. number of phases

8. Load characteristic type of motor, 9. Working system

10. motor starting mode

11. working environment. Such as site temperature, 12. Protection level, 13. Electromagnetic radiation level, 14. Explosion proof level

15. specific parameters of power distribution

16. The actual distance from the installation position of the frequency conversion cabinet to the motor position. (the distance from the frequency conversion cabinet to the motor is a very important parameter)

17. The number and mode of the motor driven by the frequency conversion cabinet

18. Switching between frequency conversion cabinet and old electrical system 19. Replacement relationship. Generally Δ- Y startup and frequency conversion work are mutually standby. 20. For use, 21. For switching, 22. For protection

10. Selection parameters and sampling location of the peripheral sensor transmitter of the frequency conversion cabinet

10. The control mode of the frequency conversion control cabinet, such as manual/automatic, local/remote, and the range of the control signal. Whether distribution group

11. Isolation of strong current circuit and weak current circuit. Isolation of acquisition and control signals

12. Power supply quality in the workplace, such as lightning protection, surge, electromagnetic radiation

for the new frequency conversion system, the electrical engineer should have a deep understanding of the load characteristics of the transmission machinery with the mechanical engineer, so as to determine the motor type and capacity. According to the mechanical load characteristics and capacity of the sample slipping motor during the experiment, the type and capacity of the frequency converter are selected

at present, there are many kinds of mechanical load and motor torque characteristics, three of which are commonly used

1. constant torque load. For example, conveyor belts, elevators, etc.

the formula is p=t*n/975 p-power of motor t-motor torque n-motor speed

for constant torque, the system design should pay attention to:

(1) the motor should be a special motor for frequency converter

(2) the frequency conversion cabinet should be equipped with a special cooling fan

(3) increase the motor capacity, (make both ends of the power battery enterprise under pressure 4) reduce the load characteristics

(5) increase the capacity of the frequency converter

(6) the relationship between the capacity of the frequency converter and the capacity of the motor should be based on the brand, (7) generally the capacity of 1.1~1.5 motors

2. Square torque load. For example, the formula of fan and water pump is t=k1*n2, p=k2*n3 p-power of motor t-torque of motor n-speed of motor

generally, fan and water pump adopt frequency conversion to save energy, which is proved by theory and practice to be about 40~50%, and such applications account for about 30~40% of inverter applications

for square torque load, the system design should pay attention to:

(1) asynchronous AC motor is usually selected as the motor. According to the environmental needs, (2) select the motor protection grade and mode

(3) if the frequency conversion cabinet is greater than 7.5kW, ventilation and heat dissipation facilities should be installed

(4) motor, (5) frequency converter capacity relationship

relationship coefficient foreign frequency converter capacity domestic frequency converter capacity

foreign motor capacity is equal to motor capacity 1 5 motor capacity

domestic motor 1.2 motor capacity 1 Motor capacity

3. Constant power load. Such as windlass, machine tool spindle

formula: p=t*n/975=cont

generally, when it reaches a specific speed range, it operates according to constant torque, and when it exceeds a specific speed, it operates according to constant power

constant power mechanical characteristics are complex

for each frequency conversion control cabinet, the design is the focus of the whole system, which can best reflect the key link of product quality. For the frequency conversion control cabinet, the electrical design engineer should start with the following design aspects

1. Schematic design of variable frequency control system

2 Main circuit design

3. Circuit control circuit design. Including conventional control circuit, 4 PLC control interface circuit, 5 Frequency converter, etc

6. Process design of frequency conversion control cabinet. Including electrical process design, 7 Cabinet sheet metal process design

schematic design

according to the above principle rules, refer to the schematic diagram of the frequency conversion control cabinet, and draw the schematic diagram according to the actual needs

main circuit design. Select the electrical components of the main circuit in the following order

(1) determine the mechanical load characteristics, (2) power, (3) torque, (4) speed

(5) determine the motor characteristics, (6) rated voltage, (7) rated power, (8) rated current, (9)

(10) according to the above conditions, (11) and the needs of actual customers, (12) choose the following electrical components (13)

tr transformer is optional and selected according to the voltage level standard

fu fuse, generally, 2 Times the rated converter current. Pay attention to the fast melting type of fuse

qa- air switch, generally, 1.2 times the rated frequency converter current

km- will significantly improve its mechanical properties. It is necessary to select the rated frequency converter current

ly- lightning surge arrester, preferably, especially in Thunderstorm prone areas and AC power surge prone areas, to protect the frequency conversion system from accidental damage. Generally equipped with 40KVA surge arrester

dk reactor

the function of reactor is to suppress the adverse effects caused by the heavy higher harmonic components of the input and output current of the frequency converter, while the function of filter

is to suppress the radio wave interference caused by the frequency converter, that is, radio wave noise

some frequency converters have built-in reactors, and in some cases, reactors may not be installed. Generally, the frequency converter manufacturer provides parameters for how much power frequency converter is equipped with how much reactor. Select the parameters of reactor, which can be calculated by the following formula

l= (2%~5%) v/6.18*f*i

v-rated voltage v

i-rated current a

f-maximum frequency hz

lbi/LBO input and output filter. Generally, it should be configured according to frequency

r-braking resistance calculation is complex, and it should be configured under the guidance of the inverter cabinet manufacturer

the circuit control circuit is designed according to the knowledge of electrical engineers and the requirements of frequency converters. However, attention should be paid to

(1) input/output weak current signal, (2) with PLC, (3) instrument, (4) sensor transmitter, (5) signal isolation must be adopted, (6) otherwise, (7) control system signal is chaotic, (8) system is abnormal (9) normal

(10) interface with PLC, (11) conventional control system, (12) surge absorber must be installed

(13) the control power supply should adopt isolation transformer, (14) for electrical isolation

process design of frequency conversion control cabinet

(1) electrical process design

electrical engineers have designed the frequency conversion circuit. The next step is electrical process design, including:

1 How much power frequency converter, 2 What type of cable is provided, 3 What is the wire diameter, 4 How far is it. Generally, you can check the table or calculate

5. Grounding wiring

6. Anti interference wiring. Is very important. Shielded cable for general strong current cable, 7 The cable and shielding layer are fixed on the base plate with metal clips, 8 Some also install shielding metal rings, 9 Anti interference

10. Configuration of cable duct connectors for incoming and outgoing lines

cabinet sheet metal process design

should be designed according to the following principles

1. The environmental

temperature of the frequency converter: the environmental temperature of the frequency converter is -10 degrees -50 degrees, so ventilation and heat dissipation must be considered

humidity:

vibration:

gas: whether there is explosion, corrosive gas

2. Cabinet bearing weight

3. Transportation convenience. Install lifting hooks, 4. Safe handling

5. Nameplate of cabinet, 6. CI mark of manufacturer, 7. Identification

conclusion: a high-quality frequency conversion control cabinet, from design, process, manufacturing, transportation, packaging, is a product with higher actual requirements. It requires quality assurance in all links in order to make a high-quality and level control cabinet

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