What is the inverter?
Inverters should not be confused with other softstart devices, which have similar appearances but different operating concepts, characteristics and performances.
The softstart is an electronic starter that allows the motor to be started and stopped gradually by acting on the voltage and current parameters, but once starting is complete, it powers the motor at a fixed frequency of 50 Hz, or even bypassed.
The inverter, on the other hand, manages the variation in motor speed by varying the power supply frequency. The ability to vary the frequency is not only limited to the start and stop phases but also throughout the entire running time of the motor. They are specifically designed for the electronic control and management of pumping systems with the aim of guaranteeing low operating costs, constant pressure and silent operation. The achievement of these objectives is made possible by the reduction of the inrush currents in the starting phase, by the lower absorption of the electric pumps when running and by the gradual switching off of the motors whose rotation is modulated according to the quantity of liquid withdrawn from the system. This eliminates the waste of energy typical of pumping units operated by pressure switches or other electronic equipment.
The smoothness with which the pumps start and stop also contributes to the substantial reduction of water hammer to the benefit of the comfort and longevity of the system. The inverters can manage surface pumps, submersible pumps, heating and refrigeration pumps regardless of their flow rate and operating pressure; in addition to the electrical connection they only require a sensor that reads the system's water pressure. They can be installed either on board the motor, replacing the cover used to close the terminal block, or on the wall and are presented in horizontal or vertical versions; they easily replace the electric pumps' magnetothermic protection panels, protecting them from failures caused by overvoltages, anomalous current absorption, dry running or closed delivery.
They stand out for their reliability and ease of installation because they are self-installing devices that automatically detect the pump curve and all the parameters necessary for calibration, reading the electrical quantities of the motor from the power cable alone and then, based on these and the data received from the pressure sensor, vary frequency and voltage automatically proceeding with the regulation of the delivery pressure. Both the maximum working pressure of the pump and the minimum stop flow for closed delivery and dry running are self-adjusted with excellent precision.
The 3 main reasons to choose to use an inverter
Inverter technology has been revolutionizing the world of hydraulics for some years now. However, many wonder if it is just a marketing gimmick.
Below we see three reasons why it can be very useful.
CONSTANT PRESSURE
The inverter can vary the voltage and frequency of the alternating current output, thus allowing the engine speed to be modulated according to the water demand and therefore always guaranteeing a constant pressure regime in the system. So stop sudden changes when opening the taps, or annoying lack of pressure when you need enough water. Once you have chosen the desired pressure, the inverter will give you constant pressure, always.
ENERGY SAVING
If the engine revolutions are modulated based on the actual request, the inverter will make the system operate not always at its maximum potential but always on the basis of the requested load. This guarantees not only energy savings but also durability, resulting in less wear of the system. Some models combine all these functions with the comfort of greater silence and an important parameter such as soft start, to guarantee adequate starting when the system is started.
TOTAL PROTECTION
Linked to inverter technology is the possibility of better and more precisely controlling any changes in operating regimes. Added to this is a series of additional protections such as dry running control of the pump, overpressure protection, supercharging, anti-blocking function and restart control.
When is the inverter used in pumping systems?
The applications of the inverter in pumping systems become even more varied when the operating logic is understood. For example, in addition to allowing me to keep the pressure constant, an inverter can allow me to keep the flow rate or water level constant.
It is good to clearly define what you want to achieve as the inverter is often used improperly (only to achieve gradual starts and stops) or incorrectly, rendering its use and investment made in vain. It does not make much sense to use the inverter to obtain flow or pressure adjustments on more than 2 units operating in parallel, as the adjustment could be subject to oscillations, furthermore the use of 3 or 4 machines in parallel, operating at fixed speed , already allow a good fractionation of the total pumping capacity. In wastewater pumping, inverter management, as an alternative to the on-off system, can be used to reduce energy losses; this in cases where the hydraulic system has high pressure losses due to friction, compared to the geodetic difference in height (pumping under pressure on long pipelines)
Use of the inverter to maintain constant pressure
Our pumping system takes water from a storage tank and pumps into a distribution network. The aim is to maintain a certain pressure in the network, although the flow rates requested by users vary considerably from moment to moment.
Solution:
By adopting an inverter and managing pumping with the "constant pressure" logic, we can solve the problem. By detecting the pressure on the manifold, with a pressure sensor it will be possible to regulate the speed of the pumps and consequently the pressure in such a way that a set-point set by the operator is maintained. In these cases, an absolute constant pressure is not required, but rather operation within a certain range.
Example of constant pressure pumping:
Working logic. The operator defines a pressure set-point. The system is activated upon operator consent, speed regulation is carried out according to a PID algorithm which depends on the deviation of the measured pressure compared to the set set-point. If the pressure increases, the pump will be operated at a slower speed, if the pressure drops, the pump will increase in speed. By doing so, you will obtain an almost constant pressure in the network, and in any case within the set tolerance bands.
Required equipment: 1 analog pressure sensor. 1 pump inverter.
Use of the inverter to keep the level constant
We have a sewer well or a wastewater storage tank. The inflows of liquids vary considerably from moment to moment, therefore we find large variations between the maximum and minimum inlet flow rates. The pump is stressed by numerous starts and stops.
Solution:
By adopting an inverter and managing pumping with the "constant level" logic, we can solve the problem. By measuring the level in the tank with an analogue meter it will be possible to adjust the speed of the pump and consequently the flow rate in such a way that the level remains constant, i.e. as much water enters the tank, so much is pumped away from the system.
Example of constant level pumping:
Working logic. The operator defines a level set-point such as to obtain the maximum blanketing capacity of the well; the system is activated when the enabling threshold is reached, speed regulation is carried out according to a PID algorithm which depends on the deviation of the level in the tank compared to the set set-point. If the level rises, the pump will be operated at a higher speed, if the level drops, the pump will slow down. By doing so, the number of pump start and stop sequences will be limited to the maximum.
Required equipment: 1 analog level sensor. 2 digital level switches. 1 pump inverter. 1 management controller.
Use of the inverter to maintain constant flow
We are carrying out an initial pumping of a purifier. our aim is to feed the treatment line with a constant flow in order to obtain maximum efficiency from the system.
Solution:
By adopting an inverter and managing pumping with the "constant flow" logic, we can solve the problem. By measuring the flow rate on the manifold, with a flow meter it will be possible to adjust the speed of the pump and consequently the flow rate in such a way that a set-point set by the operator is maintained. It is obvious that this system requires a buffer tank to compensate for peak and low flow moments.
Example of constant flow pumping:
Working logic. The operator defines a flow set-point. The system is activated when the enabling threshold is reached, speed regulation is carried out according to a PID algorithm which depends on the deviation of the measured flow rate compared to the set set-point. If the flow rate increases, the pump will be operated at a slower speed, if the flow rate decreases, the pump will increase in speed. By doing so you will obtain a pumped flow with an almost constant flow rate. It is important to have adequate lung volume.
Required equipment: 1 analog level sensor. 1 flow meter. 2 digital level switches. 1 pump inverter. 1 management controller.
