Whether the type selection of frequency converter is scientific or not is very important to the normal operation of frequency conversion system.
Many beginners do not know enough about the method of general frequency converter selection, or even if they know the method, they are not sure whether the selected frequency converter model is the correct solution. The following Xiaobian will solve the riddle for you.
Inverter selection depends on the type of load. Inverter selection should first look at the AC motor.
Because the frequency conversion system generally determine the motor first, and then select the frequency converter.
In principle, the type of frequency converter should be determined according to the actual current of the AC pilot during the long working time, rather than the power on the nameplate of the motor.
Load equipment driven by frequency conversion systems can be roughly divided into three types
Constant torque load
Constant power load
Fan, pump type load
Different load types choose different models of frequency converters.
>>>Constant power load<<<
During the operation of the load equipment, the power remains constant. Such as machine tools, cutting machines, paper machines and so on.
For example: machine tool frequency converter system, is constant power load, load inertia is very large, frequency converter selection configuration VFT with the same power model, plus brake unit and brake resistance.
>>>Constant torque load<<<
Constant torque load equipment requires high frequency torque and fast dynamic response. WinMovFT inverter at 0Hz vector state, reach 150% torque, can meet the needs of various working conditions.
For example: a dredging ship owner bucket converter system, is constant torque load, double motor, and load overload time is long, so the selection of frequency converter configuration VFT amplifier two gear model, at the same time the power supply of the equipment is mostly generator power supply, frequency converter needs to be configured input AC reactor.
>>>Constant fan, pump type load<<<
This is more suitable for the use of frequency conversion speed regulation of the field environment, the frequency converter function technology is not too high requirements, the use of frequency converter after the energy saving effect is remarkable.
For example, in the frequency conversion system of a large central heating equipment in Northeast China, the blower and induced draft fan (centrifugal fan) frequency converter are selected and configured with VFTP models with the same power. Supplementary pump (centrifugal pump) frequency converter selection configuration of the same power VFTP model; Circulating pump frequency converter selection and configuration of the same power machine VFT model; Belt conveyor (coal conveyor) frequency converter selection configuration amplification first gear VFT model; Cleaning machine frequency converter selection configuration amplification first gear VFT model; The selection and configuration of the frequency converter of the crusher (coal crusher) is to enlarge the VFT model of one or two grades.
Now Xiao An has summed up two misunderstandings in frequency converter selection, please take warning:
1, in order to save power and choose the frequency converter
Many manufacturers and salesmen boast about how high the power saving rate of frequency converters, and users also believe it. They choose frequency converters at high cost simply to save power, but they are disappointed.
After the use of frequency converter can save electricity, is determined by the type of load it drives. For fan and pump load, the energy saving effect is remarkable after choosing frequency converter, while for constant power load and constant torque load, the energy saving effect is much worse, or even can not save electricity.
2. The frequency converter selection is determined by the rated power of the motor nameplate
There is a certain theoretical basis for choosing the frequency converter according to the rated power of the motor. However, in many field practical situations, the rich amount of the motor operation is too large, or the motor runs under overload. In this way, the selection of frequency converter is either too large, resulting in economic waste, or the selection of frequency converter is too small, resulting in motor damage or the frequency converter explosion.
The more simple method of estimation is that the selection of frequency converter is based on 1.1 times of the maximum working current when the motor is running steadily. If the mechanical equipment is of heavy load type, the frequency converter also needs to be amplified to use a first gear.
Notes for frequency converter selection
Inverter selection is mainly determined by the driving load characteristics and the actual working current of the motor. In addition, there are also the following matters needing attention:
1 The environment
For some high temperature (more than 50 degrees), high altitude (more than 1000 meters) applications, the selection of frequency converter should be appropriate to leave a certain margin, to ensure the service life of the frequency converter and motor.
2 distance
The distance between the installation site of the frequency converter and the drive motor is more than 50 meters, and the selection of the frequency converter should be combined with the reactor to reduce the carrier frequency.
3 Yituo many
When a frequency converter drives multiple motors, if the cable connected in the middle is too long, the general frequency converter selection should be amplified to use a first gear, and the fuse should be installed behind each motor.
4 High speed motor
A large number of harmonics will be generated during the operation of high-speed motor, which will enhance the output current of frequency converter and generate a large amount of heat. Therefore, the selection of frequency converter is also larger than the ordinary motor.
5 Explosion-proof motor
In some mines and oil mining environments, when the frequency conversion system is explosion-proof motor, the frequency converter should be selected with explosion-proof function of the frequency converter, and the frequency converter should be placed in a safer place.
6 Protection grade
For dusty and humid applications, attention should be paid to the protection level of frequency converter when selecting the type.
7 Single phase motor
Converters are useless when single-phase motors are used in the field.
8 Variable mechanical and electrical machine
When the pole changing motor is used on site, the maximum working current of the frequency converter should not exceed the rated current of the frequency converter, and idling should be prevented from damaging the frequency converter when the number of motor poles is converted.
Inverter selection principles and steps
Inverter selection is a technical work, if the choice is not appropriate, may make the frequency converter blasting machine damage, serious will affect the normal production of the factory, so scientific and reasonable selection of frequency converter is of vital importance. The following is a list of the frequency converter modeling principles for the reference of end users.
1. Professionals do professional things
Inverter selection is determined by the technical engineers of the manufacturer according to the actual situation of the site, which is not only accurate, but also conducive to the later debugging, installation and after-sales service.
2. Function requirements of load equipment
According to the actual working conditions (starting torque, response speed, speed regulation accuracy, etc.), consider whether to choose general frequency converter, vector frequency converter or special frequency converter, and whether to choose heavy load or light load.
3, AC motor working current
Inverter selection depends on the actual working current of the motor to determine the power. In general, for fan and pump loads, the rated current of the motor can also be used as the basis for frequency converter selection. For the situation that the motor may run under overload, the selection of frequency converter usually requires the amplification of one gear.
4. Site installation environment
For metal conductive dust on site, or when the working environment temperature is too high, the selection of frequency converter needs to be careful. At this time, we need to have a special space to place the frequency converter, and the cooling function of the fan is better, so as to determine the selection of frequency converter is a hanging machine, cabinet machine or industrial frequency conversion integrated machine.
Peripheral equipment for frequency converter selection
After the selection of frequency converter is completed, it is necessary to consider whether to configure other peripheral equipment according to the actual situation on site. The peripheral equipment of frequency converter selection mainly includes circuit breaker, reactor, contactor, brake resistor and so on.
1、 The circuit breaker
The circuit breaker can easily control the power off and closing of the circuit. It is mainly used to automatically disconnect the power supply when the frequency conversion system is out of reverse current, overcurrent, short circuit and undervoltage, so as to isolate and protect the power supply.
2、 The electric one
Reactor is often used in frequency conversion selection peripheral equipment. When the distance between the frequency converter and the motor is too long, or the distance between the frequency converter and the power supply is too close, in order to improve the power factor, so that the inrush current in the input to the minimum, in the process of frequency converter selection must add DC reactor or AC reactor.
3、 Contactor
The contactor is divided into input contactor and output contactor. When a component of the frequency conversion system fails, the power supply will be automatically cut off to prevent the equipment from being burned out by connecting remotely.
4、 Braking resistor
When universal frequency converter is applied to inertial loads such as CNC machine tools and elevators, brake resistors are needed for frequency converter selection to consume the excess energy generated in the frequency conversion system.
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