Organization of automatic water supply using a frequency converter

Recommendation points

• What is the converter
• Converter selection criteria
• Additional equipment for organizing automatic water supply
• How automation works
• What you need to know when assembling a circuit and setting up a converter
• Pros of using the system converter – pump motor

In the article we will talk about how to organize an automatic water supply using a frequency converter. Consider the choice of the converter, the composition of the automation system, additional possibilities for monitoring, controlling and protecting the asynchronous pump motor.

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

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

What is the converter

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

1. Uncontrolled or semi-controlled Larionov bridge, which provides rectification of the mains voltage, built on a semiconductor base of diodes or thyristors.
2. Capacitor link, smoothing the received voltage.
3. Key to reset the regenerative voltage during braking.
4. Autonomous voltage inverter based on IGBT switches, providing alternating voltage of a given value and frequency.
5. Microprocessor control system responsible for all operations in the inverter and motor protection.

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

Converter selection criteria

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

For ease of commissioning, the converter must have a control screen. Most modern converters already in the basic configuration have built-in blocks for processing discrete and analog signals, which in the future will make it possible to build a small automation system on its basis, if they are not there, you need to order them.

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

The main thing that the pump must provide is to maintain the set pressure in the system at a constantly changing flow rate of the supplied water. At the same time, a slight decrease in the rotation speed 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 reduction in the required electromagnetic torque and, as a consequence, to a decrease in energy costs.

Additional equipment for organizing automatic water supply

1. Analog pressure sensor.
2. System start-stop buttons.
3. Water temperature sensor (for submersible pumps).
4. Input fast-acting fuses.
5. Output contactor.
6. Input and output choke (at low power it is possible not to install).

The buttons “Start” and “Stop” are connected to the discrete inputs of the converter and in the process of setting up they acquire the necessary properties in software. The analog pressure sensor is connected to the corresponding analog input on the converter panel and is parameterized to set the pump motor speed.

How automation works

After pressing the “Start” button, the converter automatically turns on the output contactor and, according to the pressure sensor readings, starts the pump motor. Then it smoothly brings its speed to the required one to maintain the given pressure.

In the event that the converter detects an emergency or when the “Stop” button is pressed, the converter with the required intensity depending on the situation reduces the motor rotation speed to a minimum and switches off the contactor.

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

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

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

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

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

All necessary settings in modern digital converters can be made using a control panel with a liquid crystal display. A number of models of converters are supplied with special software, which can be installed on a personal computer to communicate with 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 schematics and system operation indication using digital outputs and LED lamps.

Pros of using the system converter – pump motor

With the correct setting of the converter, it 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 a speed at which, in accordance with the water consumption, the required pressure is maintained, usually this speed is lower than the nominal, thereby saving energy. Motor acceleration takes place in the time specified during commissioning (along 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, thereby extending the pump’s service life and reducing overspending electricity.

Only with the help of the converter can you effectively use pumps with a three-phase asynchronous motor when powered from a 220 V household power supply.

The protection built into the converter constantly monitors the current consumed by the motor, its rotation speed, and temperature, which makes it possible to protect against short circuit, supply phase loss, jamming of the mechanical part, overload and overheating.