The use of frequency drive in compressor equipment

The article is devoted to the frequency drive of electric motors of compressors and the criteria for their selection.

In many compressors, the power of the electric motors is selected taking into account the maximum performance of the equipment, although the time corresponding to the operation of the equipment at maximum performance is usually 15-20% of the total operating time. Therefore, motors operating at a constant speed consume significantly (up to 60%) more electricity than is required to operate the equipment in an optimal operating mode, taking into account the performance.

Now one of the most promising ways to optimize the operation of the equipment is to switch to frequency control of the rotation speed of drive electric motors... Performance frequency control devices for electric motors (hereinafter abbreviated FC — frequency drive) allows you to realize the following advantages:

• smooth (controlled) start and stop of the engine, providing a sparing mode of operation of both the equipment itself and the switching elements of the power circuit, which helps to increase their service life several times and reduce operating costs for repairs;

• operational control of the operation of the equipment (compressors) in continuous operation depending on their load, maintaining the required output pressure. In this case, the maximum effect of energy saving is achieved (reduction of electricity consumption by 40-50%). This effect is achieved due to the sharp dependence of the consumed electrical energy on the performance value of the equipment. For example, when the compressor capacity is halved, the electrical energy consumption of the electric motor is reduced eight times.

Until recently, the main obstacles preventing the widespread adoption of frequency drives (FC) were the relatively high cost of the frequency converter and the lack of representatives of manufacturers who provide technical support for the implementation of the frequency converter, warranty and post-warranty service. Currently, a network of specialized development companies has been formed in the CIS countries, which are engaged in both the sale and technical support of products of almost all leading manufacturers of frequency inverters.

As for the cost of inverters, the established practice of implementing equipment shows that the most acceptable payback period for the purchase of inverters should not exceed two years, which should be taken into account when deciding on the economic feasibility of introducing inverters.

The main technical characteristics of inverters from different manufacturers are quite similar in terms of the construction principles of the power section of the converters and the element base. The main differences between the equipment offered by foreign companies are related to the user interface used, programming procedures and a set of implemented management and control functions. Due to these characteristics, the price range of inverters with the same power has a fairly wide distribution, which requires a clear knowledge of the characteristics of the inverter application in order to exclude equipment that is redundant in functionality (and price), as for example from Mitsubishi Electric.

In order to ensure an optimal choice of equipment, it is necessary to first inspect the object of implementation of the frequency drive, since the most important condition for achieving maximum efficiency of the implementation of the frequency drive is the correct (optimal) setting of the frequency drive, taking into account the following characteristics:

• the nature of the load on the drive motor, the method of cooling, cooling and lubrication of the compressor;

• frequency drive programming features, including the ability to identify motor parameters (power consumption, rpm, etc.);

• performing internal diagnostics of the health of the main frequency drive units;

• adequate response to short-term power outages;

• tracking the modes of stopping the mechanism in case of malfunctions;

• implementing the ability to monitor and switch external switching devices.

According to the results of the analysis of technical and price indicators, currently the most acceptable products are the products of Danfoss and Schneider Electric, which also have a developed network of technical support for the products sold.