Control system for a pump

Abstract

The present invention relates to pumps comprising variable frequency drive means and methods for operating such pumps. The inventive method for operating a pump (1) comprises the steps of obtaining values of operating parameters of the pump (1) indicating pump conditions, communicating said values of operating parameters from variable frequency drive means (2) to a control device (11), determining if a predetermined condition is fulfilled, communicating instructions from the control device (11) to the variable frequency drive means (2), based on the fulfillment of said predetermined condition. Furthermore, a computer program product loadable into a memory of a digital computer device, including software code portions for performing the inventive method, a pump (1), a pump system and a control device (11) for a pump are described.

Description

TECHNICAL FIELD OF THE INVENTION[0001]The present invention relates generally to the field of pumps, and more specifically the present invention relates to pumps comprising variable frequency drive means. Furthermore, the present invention also relates to a method for operating such pumps.BACKGROUND OF THE INVENTION AND PRIOR ART[0002]Pumps comprising variable frequency drive means, such as sewage pumps, drainage pumps and de-watering pumps as well as submersible pumps, for example, are commonly used for pumping fluids in mining applications such as in mining shafts, wells, at construction sites, or at other applications. Normally, submersible pumps are submersed, wholly or partly, during long periods of time both when they are in operation and when in an off-state.[0003]A problem often encountered with pumps in general and with submersible pumps in particular, is so called snoring operation, which means that the pumps sucks partly liquid and partly air. This is due to the fact that...

AI Technical Summary

Benefits of technology

[0013]It is a further object of the present invention to provide an improved pump, pump system including such a pump, a computer program, a control device for such a pump and a method for controlling such a pump and pump systems in a manner that reduces the wear of the pump and extends the pump life.

[0027]Thus, the present invention is based on the idea of obtaining values of operating parameters of the pump substantially continuously from the variable frequency drive means, which operating parameters indicate pump conditions and which are measured in an easy and inexpensive way and at the same time with high accuracy; and controlling the variable frequency drive means based on the obtained values of operating parameters, wherein the operation of the motor is adjusted in accordance with said pump conditions. Thereby, the pump is operated in an efficient way with respect to output capacity at varying flows, energy consumption and durability of the pump. Moreover, since the wear of the pump parts such as the impeller and the seals is reduced, the pump life can be extended. Due to the fact that all information required for the control of the pump and pump motor and variable frequency drive means is obtained from the variable frequency means, no external sensors are required.

[0029]In a preferred embodiment of the present invention, the event of dry running of the pump is determined based of the obtained values of operating parameters, e.g. the power of the motor at different motor speeds are compared with a predetermined reference value. If it is determined that the power of the motor is lower than the predetermined reference level, the operation of the pump motor is stopped during a period of time having a predetermined length. Moreover, the motor is restarted when the predetermined period of time has expired and the same check is performed once again until the predetermined condition is fulfilled. Thus, the snoring operation problem, which, as discussed above, causes extra wear of the pump, and in particular of the impeller, may cause the pump motor to overheat and also leads to unnecessary energy consumption, is dealt with and an efficient way of operating a pump comprising variable frequency drive means in respect of energy consumption and durability can thereby be obtained. Furthermore, the pump life can be extended owing to the fact that the wear of pump parts such as the impeller, seals and suction cover is significantly reduced.

[0031]According to an another embodiment of the present invention, a detection whether the pump is clogged is performed; and if it is detected that the pump is clogged, the pump is ran reversely at a predetermined speed during a period of time having a predetermined length. Thereafter the pump is stopped and started in the normal direction. Moreover, the step of running the pump impeller reversely, stopping it and change the operating direction is repeated until it is detected that the clogging condition has ceased. Thus, the problem of clogging or jam of the intake and / or pumping house, which may be caused by particles in the fluid that sediment at the intake and at the impeller and build silt having a relatively thick or solid consistency, is dealt with. Owing to the fact that pump runs backwards and forward again in a repeated manner, the clogging can be removed in an efficient way. Thereby the starting reliability can be increased. In addition, this embodiment provides for an efficient way of operating a pump comprising variable frequency drive means in respect of energy consumption and durability since the wear of, especially, the pump impeller is reduced. Moreover, since the clogging condition can be removed in an efficient way the energy consumption of the pump can also be reduced.

Problems solved by technology

A problem often encountered with pumps in general and with submersible pumps in particular, is so called snoring operation, which means that the pumps sucks partly liquid and partly air.

This is due to the fact that the liquid level has fallen below the required level of the pump causing the pump to start sucking partly air.

From this moment the pump is no longer productive and uses energy unnecessarily.

As long as the pump is in this snoring state, those particles remain at the hydraulics and cause extra wear on the impeller, the suction cover, the seals, etc.

This ineffective pumping contributes in a significant way to the increase of the overall operating costs of the pump.

In addition, this snoring operation may damage the pump motor due to overheating.

However, these level sensors may, for example, be blocked or be subjected to a level shift due to a collision with subjects in the fluid such as a tree branch, and will thus in such a case deliver an erroneous signal.

However, this pump system embraces great disadvantages.

In another case, the pump system is not able to detect if the water level is high enough for pump operation upon start of the pump, since in this state there cannot be a sudden increase of the speed of the motor or a sudden drop of the motor torque.

Thereby, the pump will run for a considerable time until it is switched off due to overheating, and the pump runs the risk of getting seriously damaged.

Another problem of frequent occurrence, especially when the pump has been in an off-state for quite a long period of time, is clogging of the intake and / or the impeller, which is caused mainly by particles in the fluid that sediment at the intake and in the impeller and build silt having a relatively thick or solid consistency.

This consumes large amounts of energy and also wears the pump impeller and the motor.

When the pump has been in an off-state for a long period even a maximum starting torque may not be enough and in such cases the pump has to be manually cleaned.

In addition, a pump may also be clogged during running, for example, by particles sucked into the impeller.

Thus, the reliability of pumps operated in such environments is low.

However, this method is erroneously directed to keep the motor running even if it is determined that the pump is clogged.

The aim is to get a stronger pump which is able to overcome the strength of the solid matter, but a stronger motor combined with a hard pollutant may lead to damages of the impeller, the impeller seat, the pump housing, etc.

Another known problem with pumps comprising conventional variable frequency drive means, is that the latter is usually mounted distant from the pump at a dry location above ground.

More precisely, this necessitates a long power cable leading from the variable frequency drive means to the motor of the pump, which for conventional variable frequency drive means can result in severe problems with electromagnetic interference.

However, the operation of the variable frequency drive means in this case is adversely affected by the heat emitted from the motor, which may lead to erroneous operation of the variable frequency drive means.

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