Recommendations for the selection of frequency converters for water supply and heating pumps. Why do you need a frequency converter for a pump? How a frequency converter works for a pump motor

This article will show you how to organize automatic water supply using a frequency converter. Let's consider the choice of a converter, the compilation of an automation system, additional opportunities for monitoring, control and protection induction motor pump.

To achieve efficient water supply and at the same time ensure maximum protection of the pump motor is possible only with the use of specialized converter technology, made on the basis of an autonomous voltage inverter. This solution allows you to organize the automation of uninterrupted water supply used both for your own needs and for industrial needs.

Regardless of the purpose for which the pump is used (borehole, pumping, self-priming, etc.), almost all the motors used in them can be divided into two types - single-phase and three-phase asynchronous motors. It is depending on the drive motor used in the pump that the required converter is selected.

What is a converter

This is an electrical unit that converts the electrical power of the network in accordance with the incoming task and outputs an adjustable voltage to the motor in the range from 0 to 220 V or from 0 to 380 V with a frequency of 0 to 120 or more Hz. Inside the converter is:

An uncontrolled or semi-controlled Larionov bridge, which provides rectification of the mains voltage, built on a semiconductor base of diodes or thyristors.
Capacitor link, smoothing the resulting voltage.
Key for resetting the voltage recovered during braking.
Autonomous voltage inverter based on IGBT switches, providing an alternating voltage of a given value and frequency.
Microprocessor control system responsible for all operations in the converter and motor protection.

Typical structure of a three-phase frequency converter based on an autonomous voltage inverter

Transmitter Selection Criteria

The first thing to consider is the suitability of the converter for the type of power supply (220 V or 380 V). The second is the correspondence of the power of the motor power converter, while it is desirable to have a small margin in terms of rated power for the purchased converter (on average by 20-50%), which will ensure operation if the system needs to be turned on and off frequently, as well as in various emergency situations.

For ease of commissioning, the converter must have a control screen. Most modern converters already have built-in discrete and analog signal processing units in their basic configuration, which in the future will allow building a low-level automation system on its basis, if they are not available, you need to order them.

One of options design of terminals used to connect discrete and analog signals to the converter

The main thing that the pump should provide is to maintain a given pressure value in the system with a constantly changing flow rate of the supplied water. At the same time, a slight decrease in the speed of rotation of the pumping part of the pump, performed by the converter, since the pump operates with a "fan" type of load, leads to a more significant decrease in the required torque electromagnetic moment and, as a result, to a decrease in energy costs.

Additional equipment for organizing automatic water supply

Analog pressure sensor.
System start/stop buttons.
Water temperature sensor (for deep pumps).
Input high-speed fuses.
output contactor.
Input and output choke (may not be installed at low powers).

Buttons "Start" and "Stop" are connected to the discrete inputs of the converter and acquire the necessary properties in the process of adjustment. The analog pressure sensor is connected to the corresponding analog input on the converter panel and is parameterized to set the speed of the pump motor.

How automation works

After pressing the "Start" button, the converter automatically turns on the output contactor and, in accordance with the readings of the pressure sensor, starts the pump motor. After that, it smoothly brings its speed to the required one to maintain the set pressure.

If the converter detects an emergency situation or when the Stop button is pressed, the converter reduces the motor speed to a minimum with the intensity required depending on the situation and turns off the contactor.

A water temperature sensor for borehole pumps is needed to indirectly control the temperature of the pump, since the use of a converter reduces the amount of water flow and, as a result, worsens cooling. This control can be neglected if the water temperature is guaranteed not to rise above 15-16 degrees Celsius.

If the motor has a built-in temperature sensor, it should be connected to the corresponding input on the converter, this guarantees 100% protection of the motor from overheating during operation.

What you need to know when assembling the circuit and setting up the converter

It is necessary to carefully read the instructions for the pump and converter. When setting up the system, it will be necessary to record in the converter information on the rated speed of the motor, its power, rated current, voltage and frequency of the supply network, the optimal acceleration and deceleration time, the permissible overload of the motor at start-up and during operation.

You will need to define the functions of the analog and digital inputs and output to control the contactor. After that, select the control law, in this system - U / F or vector control. After that, you will need to turn on automatic paramitrization, during which the converter itself will determine the resistance of the motor windings, calculate all the parameters necessary to create its mathematical model.

All the necessary settings in modern digital converters can be made using the control panel with a liquid crystal display. A number of transducer models are supplied with special software, having installed it on a personal computer, it is possible to contact the control system via USB or COM port.

Converter control panel

It is important to correctly connect all components of the automation system and the engine. Most converters have a built-in 24V power supply that can be used for circuiting and indication of system operation using digital outputs and LED lights.

Advantages of using the converter-pump motor system

When properly configured, the transducer monitors the pressure in the water supply system and protects it from exceeding the set pressure.

The converter itself turns on the pump motor and rotates it at the speed at which, in accordance with the water consumption, the required pressure is maintained, usually this speed is lower than the nominal one, due to which energy savings are achieved. The motor is accelerated within the time specified during commissioning (according to the so-called ramp), this option allows not only to reduce the starting current in the system and, as a result, motor overload, but also to minimize the load on the mechanical part, which prolongs the life of the pump and reduces overrun electricity.

Only with the help of a converter can pumps with a three-phase asynchronous motor be efficiently used when powered by a 220 V household power supply.

The protections built into the converter constantly monitor the current consumed by the motor, its rotation speed, temperature, which allows you to protect against short circuits, power phase failure, mechanical jamming, overload and overheating.

Pumps used in systems autonomous water supply and heating, are productive, but at the same time quite costly equipment in terms of operation due to the high level of energy consumption. You can reduce costs and significantly extend the life of the pump by equipping it with a frequency converter, which we will discuss in this article.

You will find out why you need and what functions a frequency converter performs. The principle of operation of such devices, their varieties, technical characteristics will be considered, and recommendations will be given on the choice of transducers for downhole and circulation pumps.

1 Why do you need a frequency converter?

Almost all modern pumps, implemented in the budget and middle price categories, are designed according to the principle of throttling. The electric motor of such units always operates at maximum power, and the change in the flow rate / pressure of the fluid supply is carried out by adjusting the shut-off valves, which changes the cross section of the through hole.

This principle of operation has a number of significant drawbacks, it provokes the appearance of water hammer, since immediately after turning on the pump begins to pump water through the pipes at maximum power. Another problem is the high energy consumption and rapid wear of the system components - both the pump and the shut-off valves with the pipeline. Yes, and there can be no talk of fine-tuning such a water supply system at home from a well.

The above disadvantages are unusual for pumps equipped with a frequency converter. This element allows you to effectively control the pressure created in the water supply or heating pipeline by changing the amount of electricity supplied to the motor.

As you can see in the diagram, pumping equipment is always calculated according to the power limit parameter, however, in maximum load mode, the pump operates only during periods of peak water consumption, which is extremely rare. In all other cases, the increased power of the equipment is unnecessary. The frequency converter, as statistics show, allows you to save up to 30-40% of electricity during the operation of circulation and borehole pumps.

1.1 Device and operation algorithm

A frequency converter for water supply pumps is an electrical device that converts the direct voltage of the mains into an alternating voltage according to a predetermined amplitude and frequency. Almost all modern converters are made according to the double current change scheme. This design consists of 3 main parts:

uncontrolled rectifier;
pulse inverter;
control system.

The key design element is a pulse inverter, which in turn consists of 5-8 transistor keys. A corresponding element of the stator winding of the electric motor is connected to each of the keys. Foreign converters use IGBT class transistors, while Russian converters use their domestic counterparts.

The control system is represented by a microprocessor, which simultaneously performs the functions of protection (turns off the pump in case of strong current fluctuations in the mains) and control. In borehole water pumps, the control element of the converter is connected to a pressure switch, which allows the pumping station to operate in a fully automatic mode.

The operation algorithm of the frequency converter is quite simple. When the pressure switch determines that the pressure level in the hydraulic tank has fallen below the permissible minimum, a signal is transmitted to the converter and it starts the pump electric motor. The engine accelerates smoothly, which reduces the hydraulic loads affecting the system. Modern converters allow the user to independently set the acceleration time of the electric motor within 5-30 seconds.

During the run-up process, the signal transmitter continuously reports the pressure level in the pipeline to the transmitter. After it reaches the required value, the control unit stops acceleration and maintains the set engine speed. If the water point connected to the pumping station begins to consume more water, the converter will increase the supply pressure by increasing the pump capacity, and vice versa.

1.2 Operation of the pump in tandem with a frequency converter (video)

If the pump you are using does not have a built-in frequency converter, then you can purchase and install such a power controller yourself. As a rule, pump manufacturers in technical passport indicate which particular converter is suitable for this equipment model.

Power - the voltage converter is always selected based on the power of the electric drive to which it is connected.
Input voltage - indicates the current strength at which the converter remains operational. Here it is necessary to choose with an eye to the fluctuations that may be in your power supply (low voltage leads to the device stopping, with increased voltage it can simply fail). Also consider the type of pump motor - three, two or single phase.
Adjustment frequency range - for borehole pumps, the optimal range will be 200-600 Hz (depending on the initial power of the pump), for circulation pumps 200-350 Hz.
The number of strokes and control outputs - the more of them, the more commands and, as a result, the operating modes of the converter, you can configure. Automation allows you to set the speed at start-up, several modes of maximum speed, acceleration rates, etc.
Control method - for a borehole pumping station, it will be most convenient to use remote control, which can be located inside the house, while a converter with a remote control is perfect for circulation pumps.

If you have filtered out all the devices on the market and are faced with the fact that there is simply no equipment suitable for the characteristics, it is necessary to narrow the selection criteria to a key factor - the current consumed by the motor, according to which rated power converter.

Also, when choosing a frequency control unit, especially from domestic or Chinese manufacturers, consider the warranty period. By its duration, one can indirectly judge the reliability of the technique.

A few words about manufacturers. The leading company in this area is Grundfoss (Denmark), which supplies the market with over 15 different models of converters. So, for pumps with three-phase electric motor the Micro Drive FC101 model is suitable, for single-phase (operating from a standard 220V mains) - FC51.

More affordable in terms of price is equipment from Rockwell Automation (Germany). The company offers a line of PowerFlex 4 and 40 converters for low-power circulation pumps and a PowerFlex 400 series for borehole pumping stations (3 pumps connected in parallel can work from one converter at once.

Keep in mind that the price of a good converter can sometimes reach the cost of a pump, so the connection and configuration of such a device should be carried out exclusively by specialists.

Automation of the operation of pumping equipment can be considered the most important aspect in the field of technical development of water supply and sanitation systems. This is important not only for stations that provide water to settlements.

A smart pump for a well will also make the operation of an autonomous water supply system comfortable. To do this, it is very important to correctly calculate the borehole pump, and, accordingly, to select a frequency converter for it.

The video in this article will help you do it yourself.

Advantages of automatic water supply

In order to achieve the most gentle operation of the equipment, everything is automated at pumping stations - from starting and stopping the units, and ending with the control of water flow. Devices that help to exercise total control over the system transmit signals to the scoreboard in the control room.

Approximately the same, only on a smaller scale, occurs in the case of home pump automation. Let's look at the advantages that automation gives to the system.

So:

The most important thing is that the smooth start and stop of the pump motor reduces the likelihood of water hammer to zero, and the careful operation mode helps to extend the life of any equipment. This reduces the costs associated with the operation of the water intake.
First of all, it is the consumption of electricity. Its price is steadily growing, and everyone feels it: both individuals and enterprises. Frequency regulation of the operation of pump motors makes it possible to reduce the volume of storage tanks, and even completely abandon them.

In such cases, they use a device called: "inverter control unit for a borehole pump" - it is what you see in the photo above. The inverter combines various combinations control devices, which the pump itself is not equipped with, and, among other things, has a built-in frequency converter.

Functionality and selection of the frequency converter

It is clear that the maximum water consumption occurs only at certain moments, and most of the time the pump power is excessive. The frequency converter allows you to configure the system so that during the "rush hour" the pump gives out full power, and the rest of the time reduced speed.

From the number of rotations in a certain period of time of the pump wheel, the pressure developed by it depends, and, accordingly, the performance. The essence of using a frequency converter is to make the motor shaft rotate at a given pace. At the same time, the frequency alternating current received from the mains, changes its value.
Modern converters have the widest range, and are able to convert voltage both above and below the characteristics of the mains supply. The circuit of this device is divided into two parts: a power one, consisting of a group of transistors or thyristors, and a control one, which, in fact, is an electronic key.
The control part consists of digital microprocessors, and performs all control and protective functions. Since the structure of the power section has characteristic differences, frequency converters are divided into two groups. One of them includes devices with an intermediate DC link.

The second group does not have this link, and is called "frequency converters with direct connection". Devices without an intermediate link have a higher efficiency, and are able to "curb" the most powerful high-voltage motor. Despite the fact that the price of this option is higher, the system in which it is implemented is much more economical in terms of costs.
What is the cost savings? The fact is that such converters have a small frequency range, and it cannot be equal to or exceed the characteristics of the supply network. The standard frequency of the current in the network is 50 Hz, and the device converts it to 30 Hz and below, down to zero. Consequently, the consumption of electricity is reduced - here's the savings for you!

Such a limited range does not allow the use of converters of this type in industrial scale. But for household pumps this is just what you need.

Selection of a pump for a well

First of all, it must be borne in mind that the power characteristics of the pump must exceed the calculated consumption. That is, there should always be a reserve of power.

The calculation is based on the following data:

depth and
Casing pipe diameter
, and if it is simpler - the distance from the water mirror in the well to the surface of the earth with the pump running
Total daily water consumption for a family, keeping animals and watering (calculated based on existing standards)
Well distance from home
Height of water supply (taking into account the number of storeys of the building)
Pressure pipe diameter

The pump head for a well, from which water will be supplied directly to the house, is the sum of the length of vertical and horizontal distances, multiplied by the resistance of the pipeline - this coefficient is a constant value, and is equal to 1.15.

If there is a storage tank in the water supply system, then the pressure of the hydraulic tank is also added to the sum of the distances. Pressure is expressed in atmospheres, and each atmosphere is equal to 10 vertical meters.
Consider how the calculation will look like specific example. Let's say you have a well with a dynamic level of 35 m. It is located 20 m from two-story house 7 m high. At the same time, a hydraulic accumulator with a capacity of 60 liters and a pressure of 3 atm is installed in the house.

The calculation of the pressure will look like this: H \u003d (35 + 20 + 7 + (3 * 10)) * 1.15 \u003d 105 meters.

If we take into account a small margin, then you can buy a pump with a pressure characteristic of 110-115m. As you can see, this calculation is not particularly difficult. Now let's talk about the criteria for selecting a frequency converter, abbreviated PE.

Transducer selection

Concerning specifications PE, then they must be related to the type and power of the electric motor to which it will be connected. Further, it is necessary to take into account the required control range, as well as the level of tuning accuracy and maintaining the torque on the motor shaft.

The design features of the inverter, that is, its dimensions, configuration, built-in or remote control, also matter. The vast majority of installed asynchronous motors. To them, the frequency converter is selected according to power, and it is better if this characteristic of the converter is an order of magnitude higher than that of the pump.

There are converters with vector control that allow you to maintain the rotation speed under variable loads, as well as work without reducing the speed in the zero range. Such converters most accurately control the torque and shaft speed. This is especially important when there are two pumps in the network.
In general, frequency converters have their own classification. Like any other electrical equipment, they can be single-phase and three-phase. The version of the inverters can be household, for a 220V network. There are also industrial converters with power up to 500V, and high-voltage converters up to 6000V.
The degree of IP protection is also different. By type of control, PE are divided into vector and scalar. All leading manufacturers of pumping equipment offer consumers inverter units. Typically, manufacturers link converter models to specific pump modifications and give recommendations for their use.

The buyer does not even need to think much about the choice: the sales consultant will show you the converter model suitable for this pump and explain to you what the features of its use are.

The frequency converter for the pump (inverter) performs frequency regulation of pumps, stabilizes, automates and regulates their operation. They provide the ability to change the voltage frequency to increase the efficiency and economy of pumping equipment for water supply systems, as well as increase its wear resistance.

It has been established that an electric water pump with a frequency converter can save up to 50% of electricity, and its operation is much more convenient to control.

1 What are frequency converters?

Often, manufacturers of water pumps, even at the stage of assembling their designs, include frequency converters in them. For example, as in Grundfos pumps, which are in high demand. In more expensive models microprocessors are used as converters, however, not all electric water pump equipment provides for frequency converters and their separate purchase and installation may be required.

Thus, you can choose both a pump with a frequency converter already included in the system with all options, or purchase them separately with the ability to connect additional features depending on changing needs.

Inverters for pumps are a combination of an asynchronous motor with a phase rotor, which operates in the generator-converter mode. It is controlled by a microprocessor equipped with great functionality, and the chastotnik itself, despite the rather complex structure, has a simple interface, thanks to which it can be easily controlled by a regular user.

The frequency controller for the water pump is installed on the electric motor, at the location of the standard terminal box or on the wall, in a special cabinet. The inverters themselves differ in power and weight and are characterized by the presence reliable protection from overload.

1.1 Why use chastotniki?

It protects the motor from current overloads and voltage surges.
It eliminates the occurrence of destructive water hammers, smoothing out the starting torques of the engines.
It protects the pump from idling.
It increases the efficiency of the pump by 30-50%, and also reduces the number of breakdowns.

All frequency converters are equipped with a special pressure sensor that automatically turns the pump on or off, while monitoring that the user-set pressure in the system remains unchanged.

This makes it possible to pump freely, regardless of its temperature, and even pump aggressive liquids.

1.2 Complete sets of frequency converters

There are many types of pumps on the market with frequency regulation for any choice with different functionality. Among the pumps with a frequency converter, there are equipment equipped immediately with everything necessary to ensure the safe and economical operation of your pump, as well as those that need additional equipment.

In the first case, you will get a more expensive, versatile and robust design, and in the second - the frequency converter itself will be inexpensive, for which each option purchased will cost a little more, and its connection and configuration will have to be done by hand.

2 How to choose a converter?

What you should pay attention to when selecting frequency converters for your pump:

Equipment power - this determines the speed of the pump, controlled by the converter.
Input voltage range - the voltage level in the network at which the frequency converter retains its functionality. In this case, it is worth calculating what voltage can occur in the network. This indicator will allow the converter to "survive" the voltage fluctuations in the network, fully maintaining its performance.
Frequency Range - Make sure the equipment you select is producing the exact frequency that the pump mechanism and motor can support.
Number of control inputs - to enter various commands that may be required when controlling the pump (start, reverse, stop, emergency stop and etc.). The inputs are set by the user. If you are trying to build a complex system, in which case the more inputs the better, a frequency converter with a small number of inputs is suitable for everyday use.
Number of output signals - will be required for analog control of the converter.
Control method - how the converter is controlled online (through control inputs from a stand-alone or local console, from a PC or controller, switchable or combined control).

Given the characteristics presented, you will be able to choose the equipment that is right for your pump and for your needs.

2.1 SIRIO ENTRY 230 frequency converter for pumps (video)

3 What is needed for a quality installation of the converter?

Chastotniki are installed in a special pump control cabinet (shun) with a frequency converter or in any other place where the basic requirements for their normal functioning are met.

To be produced correct installation frequency converter, it is necessary to take into account the following nuances:

Good ventilation must be ensured at the location of the chastotnik.
Temperature environment should not be below 10˚C and above 45˚C.
The relative humidity must be less than 90%, and the installed equipment must not be exposed to water.
There must be no flammable and flammable materials and liquids in the immediate vicinity of the frequency converter.
The device must not be exposed to direct sunlight.
Do not allow oil, dust or steel chips to be present nearby.
It must be placed in a place with completely absent vibrations.
Installation must be carried out on a stable surface without slopes.
Do not install the equipment in an area of electromagnetic interference.

Also note that the higher the inverter is installed above sea level, the higher its power rating will be.

Using the recommendations presented, you can choose a frequency converter for pumps that is perfect for organizing the operation of your water pumping equipment. Various Models are perfect both for downhole equipment and for fountain and other compressors that are used in residential and private homes.

Most common industrial models of frequency converters can be used to control pumps, but for this they need to be programmed in a special way.

Frequency converters for pumps are adapted devices and show the best results when working with pumping equipment. Frequency converters for pumps are more economical and functional in their field.

Models of devices and analogues

The table below shows short review several pump-optimized models. Detailed information on models can be obtained on the card of the corresponding frequency converter.

Model	Power range	entrance	Exit	Protection level	Medium temperature	Notes, Features
PD20	0.75…18.5 kW	3F 380V	Output frequency 0…50/60 Hz	IP65	-10…+40°С	Fully featured, high protection drives, motor-mountable, dedicated for multi-pump applications
	0.37…2.2 kW	1F 220V	Output frequency 0…50/60 Hz	IP65	-10…+40°С	Fully featured, high protection inverters, can be mounted on the motor, specialized for single small pumps
	15…315 kW	3F 380V	Output frequency 0…400 Hz	IP20	-10…+40°С	Scalar control, multi-functional outputs and inputs, full range of pump functions
	0.75…400 kW	3F 230V 3F 460V	PID	IP20	-10…+50°С	Specialized Models
	0.75…220 kW	3F 230V 3F 460V	PID	IP20	-10…+40°С	Special models available
	0.4…4 kW	1F 220V 3F 380V	Output frequency 0…600 Hz	IP20	-10…+50°С	For pumps and fans

Applications for frequency converters for pumps

Pump inverters are optimized for the following applications:

Ventilation and air conditioning systems (compressors, etc.)
Housing and communal services, water supply and sanitation, heating systems (hot / cold water pumps, boiler room equipment, sewerage)
Energy (equipment of thermal power plants, thermal power plants, boiler units)
Technological lines in the processing industry (sand, slurry pumps)
Other pumping units (pumping stations for water supply networks or power distribution points)
Submersible, borehole pumps

Despite the above applications, such devices are also suitable for general industrial applications.

Purpose of frequency converters for pumps

Optimized control in pumping systems to maintain certain parameters at a given level (pressure, temperature, level, flow, water consumption)
Group control of pumps
Saving water and electricity at enterprises, saving resources at pumping stations
Protecting pipelines from water hammer, increasing the service life of fittings
Full protection of electric motors in pumping installations
Automation of pumping stations

Advantages

Frequency converters for pumps have the following advantages:

They usually have more high level protection
Thanks to their specialization, they implement the most effective control in pumping systems.
In most cases, they are multifunctional devices that can fully automate the pumping station.

Flaws

The disadvantages of devices are influenced by the principles of regulation used in them. Depending on whether it is a scalar or a vector converter, certain disadvantages are inherent in it. (links to pages)

The principle of operation of frequency converters for pumps

The frequency converter for pumps converts the input power voltage into the output voltage that is optimal for the selected operating mode of the pump. In this case, a control loop is formed in the system with feedback on the selected parameter (for example, on the water pressure in the water supply system). The pressure sensor transmits information to the electronic unit of the inverter, and the converter, in turn, changes the output (frequency, voltage) in one direction or another to maintain a constant water pressure in the pipeline.

Examples are shown in the figures:

Pump station for two pumps
(automatic maintenance of pressure, start-up of an additional pump from the network)