Overload protective arrangement and method for reducing power consumption upon voltage fluctuations

The invention relates to an arrangement for overload protection and a A method for reducing the power consumption at mains voltage fluctuations according to the independent claims.

Compressors for cooling are usually with electric motors driven. When it comes to power voltage drops, can these electric motors overloaded by the stronger current and overheat. This can lead in the extreme case that the Engines to stall. This means overloading of the motor and on the other hand, a load on the supply network. Conversely burden driven by electric motors cooling arrangements the mains very irregular in normal operation because Compressors for cooling usually in a relatively short operated switching cycle, for example, 15 min rest cool and 5 min. In particular, conventional motors, the start-up during the have a high power consumption, have a destabilizing effect on the mains. As a result, there may be network voltage dips come, by which the electric motors charged again will.

The object of the invention to overcome the known problems, especially when driving compressors overload protection to accomplish.

This object is achieved with an arrangement for overload protection an electric motor of a compression unit and a method for the reduction of power consumption for mains voltage fluctuations according to the independent claims.

The arrangement for overload protection of an electric motor of a compression unit with a compressor includes the motor, Compression unit, a mains voltage monitoring unit, means for reducing the load on the motor and a control arrangement. The control arrangement is connected to the mains voltage monitoring unit and with the means for reducing the Load on the engine in such a manner that the engine disconnected from the load and / or the load is reduced once the Netzspannun g a predetermined first threshold value, preferably 80 to 90% of the rated voltage, particularly advantageously 85% of the rated voltage, below.

The load of the engine caused by the compressor work, the pressure difference between inlet and outlet of the compressor generated. To reduce the load on the engine can allow the reduces pressure difference between inlet and outlet of the compressor will. Advantageously, this is done through a by-pass between the inlet and outlet, which opened with at least one valve can be or closed.

Alternatively, the motor may also be via a clutch with the compressor be connected. The load of the compressor can this Clutch adjusted, in particular reduced, and / or all the Motor are separated.

Advantageously, the power voltage monitoring unit includes a Voltage. With this, the mains voltage is continuously monitored. is the response of the voltage advantageous as a maximum of 10 ms.

The control arrangement is preferably operatively connected to a Means for turning off the electric motor. When the undervoltage longer than a predetermined period of time, eg 10 to 60 s continues, the electric motor is switched off. This prevents that the engine is at a long-lasting disruption of consumes network operation power and the power thus continued to weigh. In addition, the motor is thereby protected from overheating.

Particularly preferably, the engine with a device for the reduction the power consumption provided in the startup phase. Advantageous In that regard, the use of thermistors, the serial in the main and in the auxiliary winding of a single-phase electric motor can be switched. In the auxiliary winding a series-connected with the negative temperature coefficient resistor capacitor start advantageously, the capacitance value approximately 3 to 5 times larger than that of the Betriebskondesators. is through the thermistor the initial current limited by the starting capacitor, which capacitive Current peaks reduced in this initial phase. By large capacity of the starting capacitor is a large phase shift the current between the auxiliary winding and the generating main winding, which facilitates the starting of the motor. The NTC thermistor in the main winding reduces the initial current through the main coil, which is also for a reduction in the Current consumption in the start up phase provides. If the nominal speed reached are first the starting capacitor and the upstream to NTC thermistor disconnected from the circuit, only then will the NTC thermistor in the main winding by a switch bridged.

Preferably, the control arrangement is such with the means connected to energize the motor, the motor only is turned on when the mains voltage is above a second predetermined threshold, preferably 90 to 95% of the mains voltage, lies. Otherwise, the switch on the motor is prevented. Thus, the mains voltage is not passed on.

Advantageously, the load is only connected to the motor, when it has reached a certain predetermined speed. This reduces the power consumption in the start-up phase also, with which Fluctuations in the mains voltage can be further reduced. The predetermined Speed ​​is preferably the rated speed of the engine, but it can also below this, eg at 80% of rated speed.

The compressor of the inventive device is preferably installed in an air conditioner or a refrigerator, because the voltage fluctuations produced by cooling systems for whose short cycle are relatively large. In cooling systems is therefore the benefits of the inventive device, particularly big.

The method for reducing the power consumption of an electric motor at a compression unit at mains voltage fluctuations, in particular at a reduction of the mains voltage, umfassent the steps of:<ul><li>Monitoring the mains voltage</li><li>Reduce the load on the engine by the compressor when the Mains voltage drops below a first threshold value, so that the Is about Motor operated at idle.</li></ul>

The reduction of the load on the motor can be realized by reduces the pressure difference between inlet and outlet of the compressor becomes. Particularly advantageously, this pressure difference is reduced to zero, since almost the entire load from the engine then is taken. The reduction should advantageously within a few than 30 ms, particularly advantageously carried out within about 20 ms, thus the reaction time is short enough to a sharp voltage drop discourage and prevent the Engine stops.

The pressure difference can be obtained by the opening and / or closing of one or more valves in a by-pass between the input and Outlet of the compressor can be reduced. It is advantageous, if by opening the by-pass the other way to the compressed medium, for example cooling liquid, are closed. This results in a pressure drop in the cooling system let prevent.

Alternatively, it is also possible that the load via a coupling is uncoupled from the motor. Thus, the load is very fast and taken completely from the engine, it is running in a very short Time idle.

It is also advantageous that the time during which to the engine is idling, is measured, and that after a off predetermined period of time during idling of the engine becomes. This prevents that the motor case of long-lasting Voltage drops the mains voltage still burdened or that it is superheated. Advantage manner is predetermined this Time period in the range of 10 to 60 s.

Particularly preferably, an electric motor is used, while the the start-up phase can be fed with a reduced current can. Thus, the line voltage is less stress when the motor is switched on, than at a conventional Engine would be the case.

One way of an electric motor during the startup phase with to feed a reduced flow, is given if the Turn-a negative temperature coefficient resistor in series with the main winding the motor is switched. This is the initial flow through the main winding reduced. is particularly advantageous also in series with the auxiliary winding to an arrangement of a thermistor connected in series with a starting capacitor. This arrangement should be connected in parallel to the run capacitor, so add up the capacities and thus during power a large phase shift between the Main winding and the auxiliary winding is produced. to capacitive To avoid current peaks, the current to the start-up capacitor limited the time of power by the NTC thermistor and will be increased by the heating of the thermistor. If during the startup of the rotor slip of the motor against is zero, the arrangement is first in series with the auxiliary winding disconnected from the circuit and then the temperature coefficient resistor in series with the Main winding bridged by switches. Thereupon located the engine is in normal operation, the phase difference between the Main and auxiliary winding is only through the operating capacitor produced whose capacitance preferably three to is five times smaller than that of the starting capacitor.

Further, it is advantageous if the electric motor only after reaching a predetermined speed with the load of the compressor is connected. This allows the motor consumes during Tarnishing also less power. The predetermined speed is Preferably, the nominal rotational speed of the engine, but it can also below it.

The first threshold value for the pressure reduction is preferably between 80 and 90% of the rated voltage, more preferably at 85% of the rated voltage. The second threshold for reconstruction the pressure is between 90 and 95% of the rated voltage. In order to is counteracted efficiently overload the electricity network.

The invention is, by way of embodiments and drawings explained in more detail. Show it:<dl tsize="13" compact="compact"><dt>Fig. 1:</dt><dd>schematic representation of the arrangement according to the invention</dd><dt>Fig. 2:</dt><dd>schematic representation of an alternative arrangement,</dd><dt>Fig. 3:</dt><dd>schematic circuit diagram of a preferred electric motor</dd><dt>Figures 4 to 7th:</dt><dd>Diagrams of the power consumption of the electric motor and the pressure difference between inlet and outlet of the compressor,</dd><dt>Fig. 8 and 9:</dt><dd>Diagrams of the course of the average current at a voltage drop and the pressure difference between Inlet and outlet of the compressor</dd></dl>

In the figures, Fig. 1 and Fig. 2, two alternative embodiments, the inventive arrangement shown. Of the Electric motor 1 drives a compressor 2nd A medium, for example a cooling fluid, with a low pressure in the compressor T is compressed to a high pressure H. The mains voltage monitoring unit 3 continuously measures the mains voltage U and passes the information to the control system 4 on. In FIG. 1, the motor is fixed to the compressor inlet E and outlet A of the compressor can be connected to the valves 5, 5 ' be short-circuited via the by-pass. 7 In normal operation of the Compression unit, the valves 5 'are opened and the valve 5 closed. If the mains voltage U first among lowered threshold of 85% of rated voltage, causes the control arrangement 4, the valve 5 is opened and the valves 5 'closed will. The pressure difference between the pressure at the LP Inlet E and the pressure HP at the outlet A is characterized within 20 ms preferably to less than 2 bar, more preferably to less than 1 bar is reduced, the load on the engine 1 takes characterized sharply.

Instead of a by-pass 7 between the inlet E and the outlet A of the compressor 2, the engine 1 as shown in FIG. 2 seen also be connected via a coupling 6 with the compressor the second When the mains voltage U falls below the first threshold value, the clutch 6 dissolved and thus separated the compressor 2 from the engine first

In both cases, the engine 1 is again only with the full Load of the compressor 2 connected when the mains voltage U over the second threshold value of 90 to 95% of the rated voltage increases. If this is not within 10 to 60 s is the case, the motor is 1 is turned off and only switched on again when the mains voltage U exceeds the second threshold value. This prevents on the one hand, that the network is passed on, on the other hand the engine 1 is thus protected against overheating. After turning on the engine 1 only with the load of the compressor 2 connected when a certain speed, preferably at least 80% of the nominal speed has been reached.

The circuit diagram of the preferred electric motor 1 is shown in Fig. 3 shown. The engine 1 comprises a main winding 11 and a Auxiliary winding 12 in series with the primary winding 11 is a negative temperature coefficient resistor 15 switchable. In series with the auxiliary winding 12 is an operating capacitor 13 connected. At the same time, a start capacitor 14 with a second negative temperature coefficient resistor 16 in series in series be connected to the auxiliary winding 12th The switches 17 and 18 are operated by the control assembly 20th

When the motor 1 both NTC thermistor 15 and 16 and the starting capacitor 14 connected in the circuit. Of the NTC thermistor 15 reduces the power consumption of the main winding 11 at the moment of start, the NTC thermistor 16 by those the starting capacitor 14 is characterized in starting capacitor 14 prevents capacitive current peak at start-up. By the two capacitors 13 and 14, the phase shift the currents through the main winding 11 and auxiliary winding 12 large, which favors the motor to start. Once the rotor slip the motor goes to zero, is the control arrangement First the start capacitor 14 via the switch 18 from the made circuit, then the thermistor 15 via the Switch 17 bridges. Then the engine is in normal operation, the phase shift in the auxiliary winding is the operating capacitor 13 generates.

The current curve I at power of a conventional electric motor 1 to a compressor 2 shown in Fig. 4. The Pressure difference between the pressure LP at the inlet E and the pressure HP at the outlet A of the compressor 2 is at the switch Zero. The operating capacity of the engine 1 is 35 microfarads, the initial capacity 88 uF, the supply voltage U is 228 V. The current peak is 86 A. In FIG. 5, the same motor 1 is switched on, but the pressure difference between inlet and outlet E A capacitor 2 is 5.2 bar. is the peak amperage 85 A, the start-up process takes about twice as long. With such an arrangement is the power at each power heavily loaded.

Fig. Figure 6 shows the situation analogous to FIG. 4 with an engine 1 as described in Fig. 3, the line voltage is 229 V U. The peak current is only 28 A. If the Pressure difference between inlet and outlet E A of Kompressords 2 at the beginning of the switch is 3.5 bar, increases the Peak current at 51 A, the duration of the start is approximately doubled. The current waveform I and the course of Pressure LP at the inlet E and HP at the outlet A of the capacitor 2 are shown in Fig. 7.

From these pictures it can be seen that the current peaks can therefore be significantly reduced if the engine 1 is on the one hand is only started when the load on the engine 1 is small, and on the other hand, the voltage supply to the motor 1 according to FIG. is connected. 3

In the figures 8 and 9 are the consequences of a voltage dip shown from 230 V to 160 V. In FIG. 8 is a conventional Device without overload protection visible. The voltage dip the engine 1 falls completely out and runs in the normalization the mains voltage U to not again. The next time Start 5 the engine 1 according to FIG. High starting currents need.

In Fig. 9, the pressure difference between the pressure LP at the inlet E and the pressure HP at the outlet of the compressor 2 A after Voltage drop within 30 ms to about 1/3 of the original Pressure difference is reduced. The engine 1 is characterized by a reduced current I on. If the mains voltage U again the rated voltage is increased, the pressure difference is increased again and the engine 1 is running at the normal power consumption.