SU955329A1 - Device for indicating transformer saturation mode - Google Patents

Description

one

The invention relates to electrical engineering, in particular, to a section of relay protection devices, with the help of which it is possible to detect the saturation regime of a power supply circuit, a transformer, and to block the protection of a transformer in case of inrush current.

A device connected to the secondary circuits of current transformers connected to the output windings of a power transformer (autotransformer) is known, and contains functional and logic elements for measuring and comparing with the specified value of the dead time in the derivative of the differential current. The mode of saturation of the transformer is fixed if the value of the dead time is greater than the received threshold value 1.

A disadvantage of the known device is that when the current transformer magnetic circuits saturate in short-circuit modes in power transformers, current-free current transformers appear blank current pauses that exceed the threshold, and the device erroneously fixes the transformer saturation mode. Another disadvantage is the limited speed of detection of the saturation mode of the transformer, since it is necessary to measure the duration of the dead time not less than the industrial frequency period.

Closest to the proposed device is a device that contains current transformers in a grounded neutral Q transformer, current transformers connected to the phase terminals of low voltage transformer windings, the secondary windings of these current transformers form a zero-sequence current filter, differential current element, threshold elements, logical the BAN element, the time element and the reacting organ.

The transformer saturation mode is detected in this device by comparing the currents in the transformer neutral and at the output of the zero sequence current filter with the corresponding threshold values, and the saturation mode is fixed if one of its currents exceeds the corresponding threshold value 2. The disadvantage of this the device is the possibility of excessive operation in single-phase and two-phase short circuits to earth in the protected transformer, at which it is possibly saturated The current transformer magnetic circuits, while the current at the input of one threshold element may be less than the operation current, and at the input of the other, more current of operation, as a result of which the device erroneously detects the transformer saturation mode. The purpose of the invention is to increase the selectivity and reliability of the device for detecting the transformer saturation mode. The goal is achieved by the fact that the device for detecting the pastern mode of the transformer, containing a current transformer installed in the grounded neutral of the transformer, current transformers mounted on the transformer windings, connected to a star, current transformers mounted on the phase windings of the transformer, are connected to a triangle, and their secondary windings form a zero-sequence current filter, a differential current organ, two threshold organs, the first element BAN, The time delay block and the reacting body were additionally introduced into the differentiating unit, the second element is BANCH, and the threshold organs are made with a time delay for the signal to disappear, the secondary windings of the current transformers forming the zero sequence current filter and the current transformer installed in the clamped neutral of the transformer connected to the inputs of a differential current organ, the output of which, through a differentiating unit connected in series, is the first threshold organ and the first element BAN connected to the reacting authority, and the secondary windings of current transformers installed at the terminals of the transformer windings connected in a star are connected to the second threshold organ, the output of which is connected through the second BANGE element connected in series and the time delay block is connected to the requesting input of the first BANNER element, and the output of the first the threshold authority is also connected to the requesting input of the second element BAN. FIG. i is a diagram of the device in FIG. 2 - potential diagrams of device operation during saturation of a transformer and inrush of magnetizing current (a), short circuit in a transformer (b), short circuit in a transformer and saturation of current transformers of low voltage terminals (c). A device for detecting the transformer saturation mode contains a transformer 1, current transformers 2, 3 and 4, a differential current organ 5, a differentiating unit 6, threshold organs 7 and 8, having a delay time for signal loss, BAN elements 9 and 10, a block 11 exposure time and the reacting body 12. Differential current body 5 and the differentiating unit 6 can be implemented using a transreactor having two primary windings connected to current transformers in neutral 4 and to the output of the filter 3 currents of zero sequence and the secondary winding connected to the input of the threshold organ 7. Moreover, the primary windings of the transreactor are connected to the secondary circuits of current transformers so that the emf in the secondary winding corresponds to the difference of currents in the primary windings. The primary windings of the transreactor must be branched to equalize the unbalance of the currents related to the windings of a transformer with different nominal voltages. Threshold bodies 7 and 8, with a time delay for signal loss, logical elements BANKS 9 and 10, time block 11 and reacting body 12 can be implemented using standard semiconductor functional and logical elements. Shown in FIG. 2 designations show: current of current transformers installed at the terminals of transformer windings connected in a star, 1f-current of current transformer installed in transformer neutral, i - current at the output of current transformers installed at delta connected windings of the transformer, Us-Ut2 - the voltage at the output of the corresponding unit 1f. and Ucp.- current and operation voltage of blocks 8 and 7. The device operates as follows. In the mode of single-phase inrush of magnetization current and transformer saturation through one of the transformer windings connected to the STAR and the transformer neutral current flows, and in the windings connected in a triangle it is equal to zero (Fig. 2a). A signal is generated at the outputs of blocks 5 and 6, causing the threshold organ 7 to operate. The current in the phase of one of the current transformer windings connected to a star triggers the threshold organ 8 in the event that the current iq exceeds the amplitude of the load current from which the current is offset Itp trigger. threshold organ 8. Tripping voltage Ucp. threshold authority 7 is selected according to the condition of detuning from the voltage unbalance of the signal at the output of differentiating unit 6, resulting from inaccurate alignment of currents of the current transformer installed in the neutral ifj, and current transformers installed at the terminals of the transformer windings connected in delta JK. Since the derivative of current 1c rises faster than current 1f, the signal at the output of threshold organ 7 appears earlier than the signal at the output of threshold element 8. If the amplitude of the inrush of the magnetizing current does not exceed the response current 1cr, there is no signal at the output of threshold element 8 . From the output of the threshold organ 7, the signal enters the input of the first element BANCH 10 and the control input of the second element BAN 9. Since the signal from the output of threshold element 8 enters the input of the BAN 9 element after the signal appears at its control input or does not enter at all the signal at the output of the element of the Prohibition 9 is absent. The signal at the output of time block 11, which provides a delay for the occurrence of a signal at its output after the occurrence of a signal at the input, as well as a delay for the signal at the output, is also absent. Consequently, after the triggering of the threshold organ 7, the reacting organ 12 is triggered.

When two-phase inrush current magnetization device operates similarly, because the current io in the windings, connected in delta, is absent, and the currents i and 1f are different from zero. With three-phase inrush current, all currents are io, IN and non-zero. The difference between the currents i and io, given in one voltage level, is also different from zero and almost equal to the value of current io, since the periodic component of the current is close to zero. The device in this mode works similarly to the modes of single-phase and two-phase inrush of magnetizing current.

With short circuits in the transformer on the ground, not accompanied by the saturation of the magnetic cores of current transformers (Fig. 26), the values of currents 1 and f reduced to one step of the voltage are equal and only the unbalance signal can appear at the input of threshold organ 7 due to voltage regulation transformer under load or inaccurate alignment of the currents io and IN at the input of the differential current organ and, and from the unbalance signal is provided a detuning by the voltage of operation Ucp. The signal at the input of the first element of the Ban 10 is absent and the reaction body 12 does not work.

When current transformers are saturated, for example, the zero-sequence currents included in the filter circuit 3, a significant unbalance signal appears at the output of the differential current body 5 and differentiating unit 6. However, the current transformers are saturated and an unbalance signal occurs after the process starts, therefore, the signal at the control input of the element BANCH 9 occurs after some time, after the appearance of the signal at its main input connected to the output n stratum element 8. The output member 9 Vits inverted pulse signal, the duration of which is determined by time of an ideal current transformer. The time delay t for the occurrence of a signal at the output of the time block 11 after its occurrence at the input is chosen to be less than the possible minimum pulse durations at the output of the BAN 9 element, therefore at the output of the time block 11 in the considered mode a signal occurs until the signal appears at the output of the threshold organ 7. The signal from the output of the time block 11 is fed to the control input of the BAN 10 element and blocks the passage of the signal from the output of the threshold organ 7

through the element BANKS 10. The time block has a time delay for the disappearance of the signal at its output, which is determined by the possible time for the existence of a short circuit mode, followed by the saturation of the current transformer magnetic circuit. Therefore, blocking the signal from the output of the threshold organ 7 is reliably ensured during the entire time that the unbalance signal exists. The time delay for the occurrence of a signal at the output of the time block 11 can be adjusted in the range of 1-5 ms, within which the possible minimum saturation time of the current transformer headset saturation lies. The proposed device allows to increase the selectivity and reliability of detecting the saturation mode of the transformer and inrush current of magnetization in order to prevent the intrinsic operation of the relay protection of the transformers and to reduce the underutilized electricity of consumers.

By increasing the detection speed of the transformer saturation mode, it is possible to increase the speed of relay protection of transformers during internal short circuits, thereby reducing the cost of repairing them, and it is also possible to increase the transmission capacity of the power lines adjacent to these transformers.

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Claims (1)

Invention Formula  A device for detecting the transformer saturation mode, containing a current transformer installed in a grounded neutral of a transformer, current transformers installed at the terminals of transformer windings connected in a star, current transformers installed at the phase terminals of a transformer windings connected in delta, and their secondary windings form zero sequence current filter, differential current organ, two threshold organs, first BAN element, time delay block and reactive op An, characterized in that, in order to increase selectivity and reliability, a differentiating unit is additionally introduced in it, the second element is banned, and the threshold organs are made with a time delay for signal loss, with the secondary windings of current transformers forming the zero-sequence current filter and current transformer installed in the grounded neutral of the transformer are connected to the inputs of a differential current element, the output of which is connected in series through a differential the unit, the first threshold unit and the first element BANGE is connected to the reacting body, and the secondary windings of current transformers installed on the terminals of the transformer windings connected in a star are connected to the second threshold body, the output of which is connected in series through the second BANE element and the time delay unit to - prohibiting the entrance of the first element BAN, and the output of the first threshold organ is also connected by prohibiting the entrance of the second element BAN. Sources of information taken into account in the examination 1. USSR author's certificate No. 266909, cl. H 02 H 7/04, 1969. 2 USSR Author's Certificate No. 477948, cl. H 02 H 7/04, 1972.