The supplier of frequency converter braking unit reminds you that with the promotion and development of industrial automation, the application of frequency converters is becoming more and more widespread. Frequency conversion speed regulation has been recognized as one of the ideal and promising speed regulation methods. The main purpose of using a universal frequency converter to form a frequency conversion speed regulation transmission system is to improve productivity and product quality; The second is to save energy and reduce production costs. In this process, the usage skills of frequency converters are particularly important.
Shielded wires should be used for signal and control lines to prevent interference. When the line is short, such as when the distance jumps by 100 meters, the cross-sectional area of the wire should be enlarged. Signal and control lines should not be placed in the same cable trench or bridge as power lines to avoid mutual interference. It is better to place them in conduit for better suitability.
02 Transmission signals are mainly based on current signals, as current signals are not easily attenuated or interfered with. In practical applications, the signal output by sensors is a voltage signal, which can be converted into a current signal through a converter.
03 Frequency converter closed-loop control is generally positive, meaning that the input signal is large and the output is also large (such as during central air conditioning cooling operation and general pressure, flow, temperature control, etc.). But there is also a reverse effect, that is, when the input signal is large, the output is relatively small (such as when the central air conditioning is working on heating and the heating hot water pump in the heating station).
When using pressure signals in closed-loop control, do not use flow signals. This is because pressure signal sensors have low prices, easy installation, low workload, and convenient debugging. However, if there are flow ratio requirements in the process and precision is required, a flow controller must be selected, and appropriate flow meters (such as electromagnetic, target, vortex, orifice, etc.) must be selected based on actual pressure, flow rate, temperature, medium, velocity, etc.
The built-in PLC and PID functions of the 05 frequency converter are suitable for systems with small and stable signal fluctuations. However, due to the built-in PLC and PID functions only adjusting the time constant during operation, it is difficult to obtain satisfactory transition process requirements, and debugging is time-consuming.
In addition, this type of regulation is not intelligent, so it is generally not used frequently. Instead, an external intelligent PID regulator is selected. When in use, simply set the SV (upper limit value), and there is a PV (operating value) indicator during operation. It is also intelligent, ensuring the best transition process conditions, making it ideal for use. Regarding PLC, various brands of external PLCs can be selected according to the nature, number of points, digital quantity, analog quantity, signal processing and other requirements of the control quantity.
The 06 signal converter is also frequently used in the peripheral circuits of frequency converters, usually consisting of Hall elements and electronic circuits. According to signal transformation and processing methods, it can be divided into various converters such as voltage to current, current to voltage, DC to AC, AC to DC, voltage to frequency, current to frequency, one in multiple out, multiple in one out, signal superposition, signal splitting, etc. For example, the Saint Seil CE-T series electric isolation sensors/transmitters in Shenzhen are very convenient to apply. There are many similar products in China, and users can choose their own applications according to their needs.
When using a 07 frequency converter, it is often necessary to equip it with peripheral circuits, which can be done in the following ways:
(1) A logic functional circuit composed of self-made relays and other control components;
(2) Buy ready-made unit external circuits;
(3) Choose a simple programmable controller logo;
(4) When using different functions of the frequency converter, function cards can be selected;
(5) Select small and medium-sized programmable controllers.
There are two common frequency conversion technology transformation schemes for parallel and constant pressure water supply with multiple water pumps (such as clean water pumps in urban water plants, medium and large water pump stations, hot water supply center stations, etc.):
(1) Save initial investment, but the energy-saving effect is poor. When starting, first start the frequency converter to 50 Hz, then start the power frequency, and then switch to energy-saving control. In the water supply system, only the water pump driven by a frequency converter has slightly lower pressure, and there is turbulence and loss in the system
(2) The investment is relatively large, but it saves 20% more energy than Plan (1). The pressure of the Yuantai pump is consistent, there is no turbulence loss, and the effect is better.
When multiple water pumps are connected in parallel for constant pressure water supply, a signal series connection method is used with only one sensor, which has the following advantages:
(1) Save costs. Just one set of sensors and PID.
(2) Since there is only one control signal, the output frequency is consistent, that is, the same frequency, so the pressure is also consistent, and there is no turbulence loss.
(3) When supplying water at constant pressure, the number of pumps in operation is controlled by PLC as the flow rate changes. At least 1 unit is required, 2 units are required for moderate quantities, and 3 units are required for larger quantities. When the frequency converter is not working and stopped, the circuit (current) signal is on the path (there is a signal flowing in, but no output voltage or frequency).
(4) More advantageous is that because the system only has one control signal, even if the three pumps are put into different inputs, the operating frequency is the same (i.e. synchronized) and the pressure is also the same, so the turbulence loss is zero, that is, the loss is minimized, so the energy-saving effect is the best.
Reducing the base frequency is the most effective way to increase the starting torque
This is due to the significant increase in starting torque, so some difficult to start equipment such as extruders, cleaning machines, spin dryers, mixers, coating machines, mixers, large fans, water pumps, Roots blowers, etc. can all be started smoothly. This is more effective than usually increasing the starting frequency for starting. By using this method and combining it with the measures of changing from heavy load to light load, the current protection can be increased to the maximum value, and almost all equipment can be started. Therefore, reducing the base frequency to increase the starting torque is an effective and convenient method.
When applying this condition, the base frequency does not necessarily have to decrease to 30 Hz. It can be gradually decreased every 5 Hz, as long as the frequency reached by the decrease can start the system.
The lower limit of the base frequency should not be lower than 30 Hz. From the perspective of torque, the lower the lower limit, the greater the torque. However, it should also be considered that the IGBT may be damaged when the voltage rises too quickly and the dynamic du/dt is too large. The actual use result is that this torque boosting measure can be safely and confidently used when the frequency drops from 50 Hz to 30 Hz.
Some people are concerned that, for example, when the base frequency is lowered to 30 Hz, the voltage has already reached 380 V. Therefore, when normal operation may require reaching 50 Hz, should the output voltage jump to 380 V so that the motor cannot withstand it? The answer is that such a phenomenon will not occur.
Some people are concerned that if the voltage reaches 380 V when the base frequency drops to 30 Hz, normal operation may require an output frequency of 50 Hz to reach the rated frequency of 50 Hz. The answer is that the output frequency can certainly reach 50 Hz.
The relationship between dynamic pressure, static pressure, and total pressure is as follows:
Static pressure is the pressure (head) required at the outlet of a water pump until the highest point, typically 1 kg of water pressure per 10 meters of water column.
Dynamic pressure is the pressure drop caused by the flow velocity difference between the liquid and the pipe wall, valves (regulating valves, return valves, pressure reducing valves, etc.), and different layers of the same section during the process of water flow. This part is difficult to calculate, and based on actual experience, dynamic pressure is assumed to be 20% (maximum) static pressure value.
Total pressure=(static pressure+dynamic pressure)=1.2 static pressure.
The lower limit frequency of the water pump must be set at about 30 Hz, otherwise it is easy to evacuate the water in the closed pipe. Due to the large amount of air dissolved into the water, when the water pump is started, it is easy to generate an air chamber, which poses a high pressure hazard.
The introduction of 12 experience points and economic values is as follows:
The application of frequency converters is feasible for various devices to achieve power saving, which has been confirmed by many successful practical cases.
Experience value is relatively conservative and has a high level of wealth, not the most economical, and has potential to be tapped. When using experience values, they should be arranged according to the actual site conditions, and there should be certain changes in the operating parameters, with the lower limit condition being that it does not affect normal use. This is a prerequisite for achieving energy conservation.
Economic value is based on the principle of meeting the lower limit conditions of the system, moderately reducing the empirical value, and exploring potential to achieve energy-saving effects. If the operating parameters remain unchanged, how can energy conservation be achieved? Moreover, the frequency converter itself is not an energy generating device (generator, battery, solar energy), and its own efficiency is very high, ranging from 97% to 98%, but there is still a loss of 2% to 3%.