DE824369C - Backup circuit for three-phase asynchronous motors - Google Patents

Description

Support circuit for three-phase asynchronous motors From the norm, the exciter Coupling directly with your generator is a thing of the past in recent times. Of the This is compulsory when the main wave in Unterwasserkraft @ verken is too long. Difficulties in the coupling are encountered when on both sides of the generator Power or work machines are on the fly, z. 13. turbine runners, hydraulic coupling, lungs and the like. To unfavorable dimensions of the exciter leads when placed on the main shaft its large diameter, especially at Kaplan turbines. l) ic often low speed of the generators forces them to be uneconomical rumble models of exciters, while high-speed exciters do too in operational terms with their smaller time constants for voltage regulation are cheaper. Difficulties in the construction of the directly coupled or The built-up exciter also prepares the deflection and play of the main shaft. Furthermore, by installing the exciter machine separately, the overall height of vertical machine sets significantly decrease. The drive motor of the exciter is then due to the power plant's own three-phase current supply.

Requirement for the installation of a separate excitation converter is its operational reliability, especially in the event of network disruptions. With this one If the voltage drop occurs, the exciter converter must not go out of operation.

For this purpose, the drive motor of the exciter is supported carried out by means of a transformer, the flowing in the primary winding Generator overcurrent in the secondary winding an additional voltage for generated the drive motor. Such a transformer is in acquisition and Original delivery very unfavorable and has a large demand for raw materials.

According to the invention, an asynchronous motor is used as the drive motor of the exciter used in star-delta connection. In normal operation, the motor is connected in star. When the voltage drops, it is switched to triangle, which reduces its torque-related load capacity rises three times. With an overload capacity of the motor of, for example i, 8 (breakdown torque to nominal torque), the motor can therefore reduce voltage drops by up to 5o% endure well. On the other hand, increasing the overload capacity alone would be of little advantage bring. According to the invention, the gain lies in switching to triangle.

Experience has shown that the residual voltage in power plants is around 50% in the event of short circuits in the high-voltage network. The proposed star-delta changeover thus ensures the excitation in normal operation. With heavy machine short circuits In any case, the excitation no longer plays a role, since then the maintenance of synchronizing forces become useless.

You can switch to delta and switch back to star in a simple way automatically by means of voltage relays with or without time delay take place.

A brief electrical overload that occurs during the switchover does not damage the motor, it can also be protected against prolonged overloading will.

If you put z. B. again based on an overload capacity of 1.8, so decreases the breakdown torque at 740/0 of the nominal voltage down to the nominal torque. With the one necessary here Switching to delta, the motor would receive a voltage that is 30% too high. Man can therefore also initially upstream ohmic and / or inductive resistance, the prevents this excess voltage on the motor. The breakdown torque of the motor has been reached then again at about 56% the value of the nominal torque. Here you can see the series resistors bridge, whereby any overstressing of the motor can be avoided.

The new circuit can be further developed in that when the voltage rises again, the motor automatically resumes with or without a time delay is switched back to star. A further improvement can be achieved by that to avoid overloads the duration of the delta connection by purely temporal or also through current and / or voltage-dependent delayed, automatic switching back is limited to star or, if necessary, by switching off. Furthermore, it can be special be advantageous to implement the circuit according to the invention in such a way that those lying in the motor circuit, which produce the star position in normal operation Switching devices are latched switches which, in the event of a fault, create a delta connection switchgear manufacturing, on the other hand, contactors that come from an independent power source be fed.

The procedure described here can also be used in other cases if motorized drives are still in operation even with a strong voltage drop should be kept.

Claims (7)

PATENT CLAIMS: i. Back-up circuit in the event of a voltage drop for three-phase asynchronous motors, in particular of exciter converters, characterized in that the motor in the normal Star-connected operation and delta operation when the voltage drops is switched. 2. Support circuit according to claim i, characterized in that when switching to triangle, first ohmic and / or inductive resistances upstream. 3. Support circuit according to claim i and 2, characterized in that that the series resistors are short-circuited if the voltage drops further. Support circuit according to claim i and / or the following, characterized in that the switchover of the motor automatically depending on the decrease in voltage with or without a time delay is initiated. 5. Support circuit according to claim i and / or the following, characterized characterized in that when the voltage rises again, the motor automatically restarts is switched back to star with or without a time delay. 6. Support circuit according to claim i and / or the following, characterized in that to avoid of overloads, the duration of the delta connection due to purely temporal or current- and / or voltage-dependent delayed automatic switch back to star or is limited by switching off if necessary. 7. Support circuit according to claim i to 6, characterized in that those lying in the motor circuit, the star connection Switchgear producing switching devices in normal operation are latched switches that in the event of a fault The switching devices producing the delta connection, on the other hand, come from an independent power source fed contactors.