SU1229888A1 - Device for protection of three-phase electric system against phase loss - Google Patents

Abstract

This invention relates to the protection of ship electrical power systems when powered from shore-based sources of electrical power. The purpose of the invention is to increase the reliability of operation, which is achieved by reducing . I current consumption device. The device contains the first 4, second 5 and third 6 current transformers, connected to them drivers 7, 8 and 9, the outputs of which, respectively, through voltage dividers 12, 13 and 14 and threshold blocks 15, 16 and 17 are connected to execution units 19, 20 and 21. The newly introduced voltage source 10 through threshold block 18 is connected to the specified threshold blocks AND through the element OR 11 to the three specified formers. When one phase breaks, the current sharply decreases to a value corresponding to the feed current through equivalent load 2. Ex and this on the driver of the broken phase, the voltage decreases and the threshold element of this phase changes its position, actuating its executive body. 1 il. sl yu w 00 OS 00

Description

The invention relates to the automation of electric power systems and can be used, in particular, to protect ship electric power systems when powered from a shore source of electric power.

The purpose of the invention is to increase the reliability of operation when the load is reduced or disconnected in the protected phases.

The drawing shows a structural diagram of the device for protection of three-phase electrical systems against phase loss.

The protected electrical system contains a circuit breaker 1, an equivalent load 2 to the point where the protection in question is turned on and an equivalent load 3 after the place of installation of the protection, and the protection device contains the first, second and third current transformers 4-6, the first, second and third drivers 7-9, connected to the specified current transformers, the newly introduced source 10 support mode, the threshold unit 18 does not change its state, since two high voltages from the driver 8 continue to flow to its first input and 9 connected to serviceable phases, and these voltages

5 (each separately) exceed the value of the minimum current sensitivity of protection, determined by the reference voltage of the source 10. Similarly, the device triggers when two

Q other phases separately or any two phases simultaneously.

When reducing the equivalent load 3 to values close to the response thresholds of the protection elements, or when the automatic switch 1 is turned off

15 a decrease in the voltage at the output of all three formers 7–9, which leads to the triggering of the threshold unit 18 and, consequently, to a change in the polarity of the voltage at its output and at the same time at the inputs of the threshold units 15–17, which excludes them

voltage and the element OR 11, the first, a false positive. Moreover, for the second and third voltage dividers 12–14, the first, second, third, and newly introduced fourth threshold blocks 15–18, the executive bodies 19–21 in each phase, respectively.

The device works as follows.

When the phases are in good condition and the circuit breaker 1 is turned on, the secondary windings of current transformers at the inputs of forming elements 7-9 receive alternating voltages whose amplitude is proportional to the current of the equivalent load 3- Forming elements 7-9 include amplitude limiters, rectifiers and filters. As a result, at the output of the forming elements 7-9, there will be a voltage, which is supplied through adjustable voltage dividers 12-14, to the first inputs of the corresponding threshold unit 15, 16 or 17. At the same time, the fourth threshold output voltage is supplied to the second inputs of these blocks. block 18, which in this case is lower than the voltage at their first inputs, and blocks 15-17 are in a position where their outputs will have a high voltage at which the actuators 19-21 do not operate.

At the time of the Break of one of the phases (for example, phase A) to the circuit breaker, there is a sharp decrease in the current in this phase to a value determined by the charging current through the equivalent load 2. At the output of the former 7 connected to the disconnected phase, the voltage drops to residual value determined by the make-up current. Residual voltage less than output voltage

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thirty

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In order to influence the load skew in phases at small values, the threshold of operation of block 18 is chosen somewhat more than the thresholds of operation of blocks 15-17. Thus, the proposed protection device ensures the elimination of false operation of protection when the load is reduced or disconnected in controlled phases.

Claims (1)

Invention Formula A device for protection of a three-phase electrical system against phase loss, containing the first, second and third current transformers a, the primary windings of which are connected respectively to the first, second and third phases of the protected electrical system, and the secondary windings of each trans current transformer through successively connected first, second and the third shaper, the first, second and third voltage dividers and the first, second and third threshold units are connected respectively to the first, second and third executive In order to increase the reliability of operation with a decrease in the load current, an additional fourth threshold unit, a reference voltage source and an OR element, each of whose three inputs are connected to the output of the specified first, second or third driver, are introduced into it, and the output is to the first input of the fourth threshold unit, to the second input of which the output of the reference voltage source is connected, the newly introduced second inputs of setting the specified first, second and third porogochetvertogo threshold unit 18, and the threshold, O blocks are combined with each other and for the 55 block 15 changes state in action the executive body 19. In this VNIIPIZakaz 2233/55 Circulation 612 Subscription Branch PPP "Patent, Uzhgorod, st. Project, 4 k; 1ucheny to the output of the fourth threshold unit. In each case, the threshold unit 18 does not change its state, since at its first input two high voltages continue to come from the formers 8 and 9 connected to the serviceable phases, and these voltages (each separately) exceed the value of the minimum current sensitivity of the protection, determined by the reference voltage of the source 10. Similarly, the device triggers when two other phases separately or any two phases simultaneously. When reducing the equivalent load 3 to values close to the response thresholds of the protection elements, or when the automatic switch 1 is turned off a decrease in the voltage at the output of all three formers 7–9, which leads to the triggering of the threshold unit 18 and, consequently, to a change in the polarity of the voltage at its output and at the same time at the inputs of the threshold units 15–17, which excludes them false alarm. In this case, for the exception triggered. At the same time for exclude In order to influence the load skew in phases at small values, the threshold of operation of block 18 is chosen somewhat more than the thresholds of operation of blocks 15-17. Thus, the proposed protection device ensures the elimination of false operation of protection when the load is reduced or disconnected in controlled phases. Invention Formula A device for protection of a three-phase electrical system against phase loss, containing the first, second and third current transformers a, the primary windings of which are connected respectively to the first, second and third phases of the protected electrical system, and the secondary windings of each trans current transformer through the respective first, second series and the third shaper, the first, second and third voltage dividers and the first, second and third threshold units are connected respectively to the first, second and third executive In order to increase the reliability of operation with a decrease in the load current, an additional fourth threshold unit, a reference voltage source and an OR element, each of whose three inputs are connected to the output of the specified first, second or third driver, are introduced into it, and the output is to the first input of the fourth threshold unit, to the second input of which the output of the reference voltage source is connected, the newly introduced second inputs of setting the specified first, second and third threshold blocks are combined with each other and rootstock blocks are combined with each other and fe; 1yucheny fourth threshold to the output unit.