DE1047931B - Method and device for monitoring three-phase motors, in particular for switching them off during single-phase operation - Google Patents

Description

GERMAN

As a rule, it is necessary that three-phase consumers, especially three-phase motors, if they fail immediately disconnected from the grid in one phase. It is well known that z. B. the single-phase running of motors as a result of the increase in slip, a considerable reduction in speed and torque with a simultaneous strong increase in the currents. This will make the proper Work process at machining and processing machines significantly disrupted. But above all, they lead here occurring overcurrents to overheating of the motors and thereby to damage or to Burning of the motor windings.

With the thermal overcurrent relays of normal design, e.g. B. using the bimetal principle, one can largely counteract this damage. However, with these relays the tripping time is different from the Dependent on the size of the overcurrent. As a result, the overcurrent required to trip is at partial load possibly reached too late or not at all. Furthermore, these relays have the disadvantage that they each time the starting current is switched on, thermal are charged and therefore with frequently switched engines such. B. crane and elevator motors, too cause shutdowns frequently and under certain circumstances at an inopportune time.

Another known protective measure to prevent single-phase operation consists in installing a voltage monitor that respond to the voltage drops that occur during single-phase operation. Now the response voltage of this voltage monitor is z. B. at about 85% of normal stress, d. H. in the range of operational mains voltage fluctuations. As a result, the Monitoring using voltage monitors is unsatisfactory.

The invention aims at a new method for monitoring three-phase motors for single-phase operation which is simple and cheap and completely avoids the disadvantages outlined above. The inventive The method is based on the use of a previously unknown measured variable for this purpose Triggering, namely that it occurs in the three phases of the consumer supply line Waves on an arrangement that adds the frequencies of the three phases that are offset in time are brought to action, which in a preferably caused by the failure of a phase Change of the frequency sum a display element and / or a switch off the monitored consumer Switching element controls.

With suitable interconnection within the meaning of the invention, the time-shifted frequencies occur of the three-phase adding device in the method and device

for monitoring three-phase motors, in particular for switching them off

with single-phase operation

Applicant:

Schiele Industriewerke KG,
Hornberg Black Forest Railway

Horst Hinrichs, Hornberg Black Forest Railway,
has been named as the inventor

a network frequency of 50 Hertz to the sum of 150 Hertz. The interruption of a phase line has the consequence that the sum frequency is only 100 Hertz. This change in the sum frequency is so powerful that it can easily trigger signals or switches can be made usable.

A very simple and reliable device for carrying out the method according to the invention consists in that the secondary windings of three current transformers assigned to the three motor phases on the one hand connected by a half-wave rectifier in star and on the other hand by a common one Derivation are directly connected to each other and that the star point and the common The derivation is connected to a frequency-sensitive device that adds the supplied frequencies, a signal when the normal sum frequency changes, for example from 150 hertz to 100 hertz and / or triggers the shutdown of the monitored motor.

The triggering effecting frequency-sensitive device can be one or more electrical or contain mechanical oscillation elements, their pulse sum, if necessary after corresponding Amplification, can be made usable for actuating signaling or switching devices.

An exemplary embodiment of the invention is explained below with reference to the drawing:

The phase lines R, S, T of the three-phase consumer (not shown) are equipped with current transformers 1, 2, 3. The secondary windings of these current transformers are on the one hand connected in star via lines 4, 5, 6 and rectifiers 7, 8, 9 at point 10, while on the other hand they are connected to a common conductor

809 727/23 *

Claims (5)

device 11 are connected. The discharge line 11 and a line 12 connected to the star point 10 lead to a frequency-sensitive device 13, which is only indicated schematically. H. a wavy direct current occurs within the device 13, which can be imagined to be composed of a direct current and a superimposed alternating voltage. The frequency of this superimposed alternating current is 150 Hertz at a mains frequency of 50 Hertz. If a phase fails, the frequency of the superimposed alternating voltage drops to 100 Hertz, provided that the alternating currents flow in opposite directions (the motor's star point is not earthed). At the same time, the amplitude of the superimposed alternating voltage also changes. With an appropriate design of the control elements of the frequency-dependent device, sufficiently strong tripping currents for generating signals or for actuating high-speed switches can be achieved without difficulty. The device according to the invention can be matched to a certain nominal current range within which the operating current of the power consumer, in particular the three-phase motor, may move by appropriate dimensioning of the elements of the frequency-dependent devices and by appropriate dimensioning of the current converters and rectifiers. Patent claim: 1. Method for monitoring three-phase consumers, in particular three-phase motors, preferably for their shutdown in single-phase operation, characterized in that the in occurring in the three phases of the consumer supply line Waves on one, adding up the temporally offset frequencies of the three phases Arrangement are brought into effect, which is preferably due to the failure of a Phase-related change in the frequency sum on a display and / or on the monitored consumer switching off switching element controls. 2. Apparatus for performing the method according to claim 1, characterized in that the secondary winding of three current transformers (1, 2, 3) assigned to the three motor phases is connected on the one hand via a half-wave rectifier (7, 8, 9) in star (10) and on the other hand are directly connected to one another by a common derivation (11), and that the star point (10) and the common derivation (11) are connected to a frequency-sensitive device (13) which adds the supplied frequencies and which, for example, when the normal sum frequency changes from 150 Hertz to 100 Hertz triggers a signal and / or the shutdown of the monitored consumer. 3. Apparatus according to claim 2, characterized in that the frequency-sensitive device one or more electrical oscillating members matched to the frequencies occurring, e.g. B. Resonance circles. 4. Apparatus according to claim 2, characterized in that the frequency-sensitive device one or more mechanical oscillation elements matched to the frequencies occurring, z. B. in the manner of the tongues of frequency meters. 5. Device according to claims 2 to 4, characterized in that it contains one or more contains electrical or mechanical oscillation elements, their pulse sum, if necessary after corresponding amplification, for actuating optical and / or acoustic signaling devices and / or electrical switches located in the circuit of the monitored consumer are used. Considered publications:
German patents No. 806 151, 808 857,
230,714 598,939 462; German utility model No. 1 691 162. 1 sheet of drawings © 809 727/23 * 12.58