DD285004A5 - CIRCUIT ARRANGEMENT FOR THE PROTECTION OF AC ELECTRIC MOTORS AND DOWNSTREAM MECHANICAL SYSTEMS - Google Patents

Abstract

The invention relates to a circuit arrangement for the protection of AC motors and downstream mechanical systems, which are endangered by overcurrent from spontaneous mechanical overload or erroneous change in the load. For this purpose, the load current is evaluated on the type of change. The alternating voltage obtained in a converter (E) and corresponding to the motor current is rectified twice and amplified. Two comparators (C, D) realize via a memory element (G) and a switching amplifier (H) the actuation of the emergency stop, in the event of a fault failure occurring rapid power changes. The display module (J) signals the instantaneous current consumption of the motor and at the same time assumes a shutdown of the electromechanical system when the maximum motor current is reached. A switch-on system (I) makes it possible to start up the system, thus rendering the high starting current of the motor, which would inevitably lead to premature switch-off of the system, ineffective for the time of switch-on. {Active rectifier; comparator; converter; integrator; Storage; Schaltverstaerker; Timer; Voltage divider; Indicator Unit}

Description

For this 3 pages drawings

Field of application of the invention

The invention relates to a circuit arrangement for the protection of alternating current motors and downstream mechanical systems, which are endangered by overcurrent from spontaneous mechanical overload or erroneous change in load.

This Scheitungsanordnung justifies its use in propulsion technology on conveyor systems, machine tools, compressor systems and continue for DC-powered consumers, which receive their operating power from an AC network.

Characteristic of the known state of the art

Electric drive systems are provided with previously known protective devices such as thermal motor protection switches, electronic overcurrent switches, mechanical couplings odjr monitoring systems with sensor technology

 A generic similar method electronic overcurrent switch is described in patent DE 3215181 (HO2H 3/13). This circuit can only register a phase failure of a three-phase system. The switch-off pulse during phase failure is obtained via the different charging times of two capacitors in connection with a sensing device. Conditions of this circuit is that the phase failure must last a certain minimum time

 The disadvantage of this solution is that only three-phase systems can be evaluated.

Another method for detecting a phase loss in a three-phase system is described in patent DE 3214367 C2 (HO2H 3/13). This method is based on the formation of the difference between the maximum and minimum harmonic value of a phase when subsequently compared with a fixed reference voltage. The three Phasön are evaluated successively in time multiplex operation.

Significant differences of the solution to both patents are that only one phase of an input or

 Polyphase system is evaluated and that the reference voltage adapts to the input signal.

Object of the invention

The object of the invention is to provide a universally applicable circuit breaker that operates maintenance-free and protects electromechanical systems with motor hubs in the entirety of their assemblies from destruction within unwanted operating conditions.

With such a protection circuit systems are to be equipped, which by unforeseen shocks or

 Burdens are endangered.

Explanation of the essence of the invention

It was the object of finding a solution to shut down systems in case of overloads, before destruction of Masch'ineneinrichtungen can occur.

According to the invention the object is achieved in that the circuit arrangement for protecting electromechanical systems with electromotive drives an ELECTRONIC PROTECTION SWITCH provides, which allows to detect electrical or mechanical errors and makes the shutdown when an undesirable operating condition occurs. The electronic protection circuit consists of a current / voltage converter, two active rectifiers, two comparators, an integrator, a display with limit switching off, a memory, a Einschaltsystem and a switching amplifier. An AC voltage corresponding to the motor current, which is produced via the current / voltage converter, is rectified, amplified and integrated before it forms the reference voltage for 2 comparators. At the same time, a non-integrated voltage corresponding to the motor current is supplied to the same comparators via a second active rectifier, so that comparisons between these two variables can take place. A comparator switches when falling below and the other comparator when the reference value is exceeded. These switching signals, together with the Maximalstromabschaltsignal act on the reset input of the memory and thus disable the system in case of failure, d. H. any disturbance in the system that is reflected in the change in motor current, e.g. For example, if the current goes unscheduled to zero at phase loss; the motor current exceeds its maximum value, with permanent mechanical overload or the current increase or decrease speed exceeds a certain value, d. H. in the case of a spontaneous load change (accident) of the downstream mechanical system, the system is switched off before the maximum value has been reached. The switch-on system deactivates the protection circuit for an adjustable time (1 ... 120s), as high starting currents can cause the system to switch off in the starting area of the motor.

exemplary

The invention will be explained in more detail below using an exemplary embodiment.

The present in a boiler house deashing belt with a length of fifty meters to be protected by the circuit arrangement for the protection of AC motors and downstream mechanical systems from destruction by tarnishing, jumping, tearing, jamming. Conventional protection devices, such as thermal switches, interlocking, friction clutches or contact chain monitoring could not prevent the destruction of the transport chain or elements of the inclusion of ash band, according to experience. By a circuit arrangement of the invention, protection against destruction is given. Show it

FIG. 1: Block diagram

Figure 2: Circuit diagram (without display module)

Figure 3: Display module

The principle of the motor protection circuit is that an AC voltage corresponding to the motor current at two comparators (C, D) is checked for changes. For recovering this AC voltage, a current / voltage converter (E) is used. In the input part of the protection circuit, two operational amplifiers (A, B) function as active rectifiers. Both independently provide the rectified, boosted voltage for the comparators (C, D). One of the output voltages of the OVs is the reference for the opposing comparators (C, D) and is delayed in time by an integrator (F) for voltage changes. By using the voltage divider K is the. Setting of the sub-value switching point realized.

Due to the non-fixed reference value, the magnitude of the instantaneous current consumption of the motor has no effect on the sensitivity of the protection circuit. That is, normal load changes of the engine within the operating conditions cause no shutdown of the system.

Be! short current rise or fall times, e.g. B. tearing a motor-driven chain or jamming of gears, the reference voltage at one of the comparators (C, D) is exceeded or exceeded, so that it comes to the switching operation. This switching pulse resets the D flip-flop (G) and the emergency stop contact of the system is actuated via the switching amplifier (H) or the relay stage.

In order to ensure the self-preservation of the protective circuit in the starting region of the motor, in which fast current changes due to start-up currents prevail, the starting pulse has been extended over time. This is realized in the embodiment by a monoflop circuit with a timer (I). After the start pulse by the switch, the timer output assumes Η level and thus acts directly on the switching amplifier (H) for the set delay time. During this active time of the timer (I), the memory (G) has no influence on the switching amplifier (H) or on the relay stage; It is ensured that the rated motor current can engage, without causing premature shutdown of the system by starting currents of the motor. When the timer (I) has elapsed, the output of this stage switches to the L level, and at the memory (G) the negation of the timer signal causes an L / H jump at the clock input and the Η information applied to the D input arrives the memory output. Thus, the switching state of the output stage (H) is maintained because the base current for the switching amplifier transistor is now supplied from the memory (G).

Now the protection circuit is activated and an incoming switching pulse of the comparators (C, D) leads to the triggering of Nutauskontaktes or to stop the system. A non-starting of the motor accordingly causes an immediate actuation of the Notauskontaktes after the switch-on has expired. Exceeding the motor maximum current is prevented by the Grenzwortabschaltung in the display module (J) by the non-integrated output voltage of the active rectifier A is indicated by an integrated circuit J on an LED line and thus represents the instantaneous power consumption of the engine. When adjusting the system, set the display (J) so that the last LED of the line corresponds to the motor maximum current value. A TTL level adjustment of the last LED of the line ensures a shutdown when the limit value is reached. Dabji acts on this shutdown signal as well as the comparator outputs on the reset input of the memory (G).

Claims (4)

1. Circuit arrangement for the protection of AC motors and downstream
mechanical systems, characterized in that via the transducer (E) an evaluation
the motor current of a single or multi-phase system is made for the presence of the current or its change and its maximum value. 2. A circuit arrangement according to claim 1, characterized in that the circuit arrangement of the active rectifiers (Ä, B), the integrator (F), the comparators (C, D), the
Voltage divider (K), the timer (I), the memory (G), the display module (J) and the
Switching amplifier (H) exists. 3. Circuit arrangement according to claim 1,2, characterized in that a
AC signal via two analog active rectifiers (A, B) on the
Comparators (C, D) acts while one of the DC voltages integrated as a reference voltage and the second is assigned according to the other inputs of the oppositely acting comparators and this second DC voltage at the same time the control signal for the
Display module is. 4. Circuit arrangement according to claim 1,2,3, characterized in that a timer (I) during the startup time of the motor acts directly on the switching amplifier (H) and after this time a memory (G) is activated, thereby changing a shutdown pulse due of currents in the
Consumer system, coming from the comparators (C, D) and / or from the display module,
which represents the instantaneous current consumption and changes the memory contents so that the
Emergency stop will eventually be activated.