SU1309149A1 - Device for current protection of three-phase electrical installation against short-circuit - Google Patents

Abstract

The invention relates to power engineering, in particular to relay protection, and can be applied to protect three-phase electric motors and transformers that supply a motor load. The purpose of the invention is to increase sensitivity and speed. The goal is achieved by introducing into the device a switching combined organ 3 of voltage and two elements 11 to 12 of the return delay. This allows the protection to operate with a short time in case of damage in the protected electrical installation. The protection is also reliably rebuilt from any starting and self-starting mode of the specified electrical installation. 1 il. (O (L with about with 4 :; WITH

Description

The invention relates to power engineering, namely, relay protection, and can be used to protect three-phase electric motors and transformers that supply a motor load, in addition, a false operation of the protection against self-starting currents during external short circuits is possible.

The purpose of the invention is to increase the sensitivity and speed of protection.

The drawing shows a block diagram of the proposed device.

Device for protection against phase to phase. contains the first 1 and second 2 current starting bodies, the starting combined body 3 voltage, elements 4 and 5, the first 6 and second 7 elements And, the first 8, second 9 and third 10 elements of the delay on operation, the first 11 and second 12 elements return delays, element OR 13, protection executive body 14, electrical installation switch 15. The inputs of the current starting organs 1 and 2 are connected to the current transformers of the respective phases of the protected electrical installation, and the input of the starting combined voltage regulator 3 is connected to the voltage transformer of the section to which the protected electrical installation is connected. Starting body 1 is connected to the executive body 14 of the protection through the element OR 13, and the starting body 2 is connected to the other two inputs of the element OR 13 through the delayed delay element 8, as well as through the delayed delay element 9 and the element 6.

The series-connected elements 7, 10 and 11 are a blocking element, and the output of the starting body 2 is connected to the second input of the element 7 7 through the element 4.

The device works as follows.

The setpoint of the first current start-up organ 1 is adjusted in magnitude from the start-up currents (self-starting) of the protected electrical installation. Therefore, in the event of a tripping, the start-up body 1 without shutter speed through the element OR 13 and the executive body 14 acts to turn off the switch 15 of the protected electrical installation. However, with a standard sensitivity factor, only the cables with which the electrical installation is connected to the switch are protected. The setpoint of the second current start-up organ 2 is adjusted only from the rated current of the protected electrical installation. In this case, the detuning from the start mode (self-starting) of the protected electrical installation is carried out using the first element 8 of the operation delay, on which the delay time exceeding the max.

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The maximum possible start-up time (self-starting) of an electrical installation (on the order of 20-40 s). In the event of damage outside the zone of the current starting device 1, disabling this damage with such a time delay leads to the destruction of the protected electrical installation. Therefore, in order to realize a high sensitivity of the current starting organ 2, an additional disconnection clamp from this organ is made through the second element 9 on the response delay, on which the time delay is set for about 0.5 s and the first element 6.

If the protected electrical installation is damaged in normal mode and the current triggering device 2 is triggered, the signal from the output of the second element 9 will go through the element 6 through 0.5 seconds and will switch off the protected electric installation, since in this mode there is no signal at the output of the starting combined organ 3 voltage and, therefore, there is a signal at the output of the second element HE 5, as well as during the time determined by the first element 11 back to return (it is selected about 0.75 s), the signal is present and the output of the body 14 of protection.

Failure of the high-speed sensitive protection in the start-up and self-start mode of the protected electrical installation is provided as follows.

Before starting, switch 15 was turned off and there was no signal at its control output. At the same time, respectively, there was no signal at the output of the second element And 7, the third element 10 of the response delay, the first element 11 of the return delay and, therefore, there was no signal at the output of the protection body 14. After switching on the switch 15, a signal appears at its control output, however, due to the fact that starting current begins to flow through the protected installation, the second current starting element 2 is triggered, and thereby removes the signal from the output of the first element HE 4 and the second element I 7 The signal at the output of the second element And 7 immediately after switching on the switch 15 will be present only during the response time of the current trigger 2, however, this time is less than the delay time of the third delay element 10 triggered. e (selected order of 0.25) and therefore for the entire start time za- n | ischaemoy electrical current until the starting body 2 is in the energized state, the output signal of the protection body 14 is absent. Consequently, the signal from the output of the second element 9 of the delay on operation during the entire start-up time will not be able to pass through the first element 6 and falsely disconnect the protected electrical installation. The signal at the output of the protection body 14, which introduces the sensitive protection into operation, is only achieved within 0.25 s after the end of the start-up and the return of the starting body 2 regardless of the start time. This reduces the withdrawal time of sensitive protection during start-up to the minimum required. If the triggering organ 2 operates in the event of damage in the protected installation, when the installation was turned on and the load current did not exceed the nominal, then despite the disappearance of the signal from the output of the protection organ 14, it will disappear only after the return time of the element 11 expires. time is chosen equal to 0.75 s, then sensitive protection with a time of 0.5 s, set on element 9, has time to act on the disconnection of the protected electrical installation.

When self-starting during external short-circuit. or external voltage leads; false protection operation is prevented by the operation of the starting combined voltage body 3, which contains the filter of the reverse sequence voltage relay and the relay, which reacts to a decrease in phase-to-phase voltage. The input of the starting organ 3 voltage is connected to the voltage transformer of the section from which the protected electrical installation is powered, therefore for any damage the organ 3 measures the voltage drop as a direct sequence at the three-phase short circuit and the reverse sequence at two phase to . з. on the resistance of the corresponding sequence of the supply system. Since these resistances are in order of magnitude smaller than the corresponding starting resistance of the protected electrical installation, when the closures are at the end of the zone protected by the current starting organ 1, the starting body 3 voltage measures small values of the reverse sequence voltage (up to 10 V secondary) asymmetrical short-circuits and small decreases in inter-phase voltage (to 0.8 UH) with three-phase short-circuit voltage. If the triggering body 3 is rebuilt from these values, then o will not operate in the zone of action of the sensitive current triggering body 2, the output of the second element 5 will not have a signal, allowing the sensitive current body 2 through the second delay element 9 and the first element 6 to work on shutdown of the protected electrical installation in case of its damage. In case of an external short circuit, when the protected electrical installation self-starts and the sensitive current is triggered

Body 2, the starting body 3, the voltage measures large negative-sequence voltage values (more than 40 V secondary) and a decrease in the phase-to-voltage voltage below 0.2 UH with asymmetric and three-phase short-circuit voltage. accordingly and reliably works. In this case, the signal from the output of the second element NOT 5 disappears, and the signal from the output of the second element 9 of the response delay cannot pass through the first element Ib and falsely disconnect the protected electrical installation. With deep, even short-term voltage drops, a long-term self-start of the protected electrical installation is possible, but a false disconnection will not occur, since after the voltage is restored, the signal at the output of the second element HE 5 is only visible after a time determined by the time of the second element 12 for a return delay (1 s ), and after 0.75 s after the operation of the current starting organ 2, the signal from the output of the protection organ 14 will already be removed. Consequently, for any duration of self-start of the protected electrical installation, the signal from the output of the second element 9 of the response delay cannot pass through the first element 6 and cause a false shutdown.

Thus, the inclusion of the starting combined voltage device and delay elements for returning and triggering as part of the blocking body allows to perform highly sensitive protection, triggered with a short time in the event of damage in the protected electrical installation, and reliably rebuilt from any starting and self-starting modes of this installation.

Claims (1)

Invention Formula A device for overcurrent protection of a short-circuit three-phase electrical installation containing the first and second starting current organs, the inputs of which are connected to the secondary windings of current transformers of the respective phases of the protected electrical installation, the first actuation delay element whose input is connected to the output of the second starting current organ, the second and third elements of the delay on operation, the first logical element And the first logical element is NOT, the output of which is connected to the first input of the second the logical element AND, the output of which is connected to the first input of the first logical element OR, the second logical element is NOT, the executive body, the output of which is connected to the control input of the switch of the protected electrical installation, characterized in that will feel : 1 of speed and speed, a starting combined voltage device is additionally introduced in it, the input of which is connected to the voltage transformer of the section to which the protected electrical installation is connected, the output of the said body is connected to the input of the first logical element HE, through the newly introduced first delay element the second element of the return delay, the output of which is connected to the second input of the second logic element I, while the inputs of the second logic element are connected to the output of the second starting element of the NOT and the second element of the response delay, the output of the first element beyond the triggering and output of the first starting current organ are connected respectively to the second and third inputs of the first OR element, the output of which is connected to the actuator input, the output of the second logical element NOT and the control output of the switch of the protected electrical installation are connected respectively to the first and second inputs of the first logical element And, the output of which is connected through the third element of the delay on operation with the input of the second element of the delay to return, and the output of the second element on delay is connected to the third input of the second logic element I.