OPERATING MODES OF VENTILATION AND AIR CONDITIONING SYSTEMS ACCORDING TO ENERGY EFFICIENCY CRITERIA - Scientific conference
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Рік заснування видання - 2011

OPERATING MODES OF VENTILATION AND AIR CONDITIONING SYSTEMS ACCORDING TO ENERGY EFFICIENCY CRITERIA

31.05.2022 23:08

[3. Technical sciences]

Author: Gorodetskyi Viktor, associate professor, PhD, National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”; Dubovyk Volodymyr, senior lecturer, National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”; Listovshchyk Leonid, associate professor, PhD, National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”; Livishchenko Dmytro, student, National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”, Kyiv, Ukraine


It is known that the mechanical and dynamic characteristics, energy performance of an induction motor (AD) in a frequency-controlled electric drive are determined by the used law of frequency control, frequency control method, algorithmic and hardware implementation of automatic control system (ACS).

Frequency control of induction motors most often uses the laws of maintaining the constancy of stator flux (Y1 = const), maintaining the constancy of the main flow of the machine (Y0 = const), maintaining the constancy of rotor flux (Y2 = const) and adjusting the amount of flux depending on the load value ((Y1, Y0, Y2) = f (M)).

The first law (Y1 = const) is realized by maintaining a constant ratio of the electromotive force (EMF) of the stator to the angular frequency ω of the field. The main disadvantage of this law is the reduced overload capacity of the motor when operating at high frequencies, due to increased inductive resistance of the stator and, consequently, reduced flux coupling in the air gap between the stator and rotor with increasing load.

Maintaining the stability of the main flow increases the overload capacity of the engine, but complicates the hardware implementation of the control system and requires some changes in the design of the machine, or the presence of special sensors.

When maintaining a constant flux coupling (Y2 = const), the motor torque does not have a maximum, but with increasing load increases the main magnetic flux, which leads to saturation of magnetic circuits and, consequently, to the inability to maintain constant flux coupling.

A common disadvantage of the laws of maintaining the constancy of the flow coupling is the low reliability due to the presence of sensors built into the engine and the loss of steel during operation of the engine with a load torque less than the nominal. These losses are caused by the need to maintain a constant nominal flux coupling in different modes of operation.

You can significantly increase the efficiency of the motor by adjusting the magnetic flux of the stator (rotor) depending on the magnitude of the load torque when changing the slip. The disadvantages of this control are the low dynamic characteristics of the drive due to the large value of the rotor time constant, due to which the magnetic flux of the machine is restored with some delay and there is some complexity of the technical implementation of the control system.

To implement the control of the electric drive, the system must provide:

• start and stop the engine;

• change of engine shaft speed;

• registration and visualization of the main parameters of the engine (information should be displayed on the screen for the operator in a user-friendly form using tables and graphs);

• emergency stop of the engine in case of receipt of an alarm signal from sensors at deviation of values of operating modes from admissible technological limits;

• redundancy of measuring channels.

The introduced new energy-saving technology in the operation of high-power turbines allows them to be regulated also in the hours of maximum load and thus reduce energy costs at a two-rate tariff.

Thus, the use of adjustable electric drive turbomechanisms allows to create a new energy saving technology, which saves not only electricity but also thermal energy and reduces air consumption due to its leakage when exceeding the pressure in the highway at low cost.

The conducted researches on application of the regulated electric drive of turbomechanisms allow to formulate the basic conclusions and recommendations.  The most rational way to regulate short-circuited induction motors is the frequency method, which is able to carry out the most cost-effective modes of operation in the entire range of regulation of the performance of turbomechanisms.

Modernization of existing unregulated electric drives in order to save energy allows to obtain the maximum possible economic effect at the expense of capital minimum costs.

Frequency control at maximum torque is the main way to achieve maximum performance of asynchronous electric drive in static modes. At a frequency below 40 ... 50 Hz it is most rational to use control on a minimum of stator current with restriction Idop = 1 (in relative units) at higher frequencies of control on a minimum of losses with restriction Rdop / Rnom = 1.

Technological features of electric drives of turbomechanisms allow to consider them as object-oriented, working mainly in static modes. The greatest manifestation of the dynamics of the drive occurs when starting turbomechanisms with large inertial mass. The thermal state of an induction motor should be characterized by a constant magnetic flux, when the speed of the motor is equal to or less than the nominal value.

Conclusions. With frequency control while maintaining the constancy of the flux coupling, the efficiency of the motor is increased by regulating the magnetic flux of the stator. 

References

1. Otterpol G., Hübner R. Technical and economic aspects of the use of energy-saving electric drives in pump and fan mechanisms (from the experience of "Elpro AG", Germany) - Scientific and technical seminar "Energy-saving electric drive of pumps and fans in industry and utilities", Abstracts, M., 1995, pp.12-16 (In Russian).

2. Bergner MS, Galtsev Yu. K., Golygin AF, Davidenko PV, Danilkin NI Pump and fan economy in the structures of modern production. Scientific and technical seminar "Energy-saving electric drive of pumps and fans in industry and utilities". Abstracts of reports. - M., 1995, p.23-25 (In Russian).



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