RU1820438C - Device for protection of motor from phase break in three-phase power line - Google Patents

Abstract

Usage: to build protection of the motor against phase failure of the network. SUMMARY OF THE INVENTION: the device comprises current transformers 2.3 in two phases, two rectangular pulse generators 4.5, the outputs of which are connected via coincidence element 5 to series-connected integrator 7, threshold element 8 and output organ 9. When phase B breaks, currents in phases A and C are equal in magnitude and opposite in direction. The signals at the output of the drivers 4 and 5 are also out of phase, and therefore the signal at the output of the matching circuit 6 has only a negative sign. The voltage at the integrator 7 reaches the trigger level of the threshold element 8, and the device trips. 2 ill. S

Description

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The invention relates to the electric power industry and is intended to realize the relay protection of electric motors against phase failure.

The purpose of the invention is to expand the scope and increase the reliability of the device.

A diagram of the proposed device is shown in figure 1.

The device for protecting the electric motor 1 contains current transformers in two phases 2, 3, rectangular pulse shapers 4, 5, the outputs of which are connected via a matching circuit 6 to a series-connected integrator 7, a threshold element 8 and an output organ 9.

In FIG. 2 shows current and voltage curves to illustrate the operation of the device in the following modes: a) in normal mode; b) in case of phase failure without a current transformer; c) in case of phase failure with a current transformer.

The threshold element 8 is configured so that it is triggered at angles between the input signals of the matching circuit less than 60 e. hail.

Consider the operation of the device.

In normal mode, the currents of phases A and C-Ol, ic) are shifted by 120 degrees. The corresponding rectangular pulses at the output of the shapers 4 and 5 are shifted by the same angle. In this case, the duration of the positive signals at the output of the matching circuit 6 is 60 electric degrees, and negative - 120. The signal at the output of the integrator 7 during the time of the coincidence of negative the signals do not reach the trigger voltage of threshold organ 8 (Ucps), and the device does not trip.

When the phase breaks, the currents in phases A and C are equal in magnitude and opposite in direction. The signals at the output of the drivers 4 and 5 are also in antiphase and, therefore, the signal at the output

match pattern 6 has only a negative sign. The voltage at the integrator 7 reaches the trigger level of the threshold element 8 and the device trips. YctpoftcTso works similarly with

phase failure with current transformer. The only difference is that there is no signal at the corresponding input of the matching circuit.

Claims (1)

The claims A device for protecting electric motors from phase failure of a three-phase network, containing a current transformer of one of the phases, an integrator connected through a threshold element to the actuator, and the current transformer is additionally introduced to expand the scope of application and increase the reliability of the device the second phase, rectangular pulse shapers, a matching element, and the inputs of the matching element are connected via rectangular pulse shapers with the secondary windings of the transformer s current, and the output of the element coincides Denis is connected to the input of the integrator. Lam LA t-c / and. , Ј and, aj ± c Uj UB t t 51