SU46995A1 - Device for differential protection of a dual busbar system against earth faults - Google Patents

Description

As the experience of exploitation shows, the greatest number of accidents on tires of 110 kilovolt substations is associated with earth faults. This circumstance testifies to the need to protect tires, first of all, from sinking to the ground.

Therefore, at one of the substations, Mosenergo has already implemented tire protection based on the differential principle and is designed to quickly deflect tires in the event of a ground fault. A description of this protection is given in Article x Ing. V.S. Kash Taleva (“Electric stations No. 8, 1934) and Ing. V. G. Ekle (“Mosenergo Bulletin No. 2, 1934).

Due to the differential principle of protection, a damaged tire system is quickly and reliably disconnected under a wide variety of operating modes, such as when the headphone is turned on or off, powered by one or both of the tire systems, etc. duty personnel of various switching current protection circuits depending on changes in the switching circuit.

(338)

The Teploelektroproekt developed a differential tire protection circuit against earth faults, which automates the switching processes of current circuits (see, for example, the article by engineer A. B. Chernin in the journal. Electric stations No. 7 for 1934). Automation is achieved in this case using signal disconnectors, through which the neutral wires of current transformers are passed.

However, as is usually the case in practice, all the protection schemes, which represent well-known advantages, are at the same time not devoid of certain disadvantages.

According to the author's instructions, it is sufficient in the above scheme to have an accidental break of the neutral wire circuit at one of the signal contacts so that a non-selective disconnection of substation buses occurs during an external short circuit.

This concern is all the more significant because under normal operating conditions the current in the neutral conductor is absent and, therefore, the state of the neutral conductor circuit is not monitored. Meanwhile the flow

through the signal contacts of high current disconnectors with severe short circuits in the system associated with damage to the ground, may pose a certain threat to the safety of the signal contacts themselves, which are not designed for the circulation of secondary short circuits.

Furthermore, the correct protection action is not ensured if one of the lines is driven through disconnectors simultaneously to both bus systems.

Finally, the question is somewhat complicated in the case of an inter-drip oil cooler and related operations.

In its second variant of differential protection of tires against grounding, the Thermoelectroproject avoids switching the neutral wires of current transformers, and the selection of a damaged bus system is made by volt-meter relays powered by zero-sequence voltages of one and the other bus systems. However, in practice there are cases when such a scheme is not very convenient. Apart from the inter-drip oil pan, it should be borne in mind that the correct operation of the circuit is possible only in the case when the values of the zero-sequence voltages of both bus systems differ markedly from each other. Meanwhile, the practice of exploiting complex networks shows that this condition is not always fulfilled.

In the presence of electrical communication between bus systems (through the line and buses of the nearest substation or station), the zero sequence voltage of both bus systems may differ from each other with known catches, which, if this circuit were used, would turn off the entire substation.

Taking into account the above, the author proposes a differential tire ground fault protection circuit, adapted to work in complex network conditions with two tire systems and an inter-ear valve, but without alternating current circuits.

The proposed device is based on the following principle: if short

The closure on one of the bus systems in an open inter-drip oil cell is a difference between the zero voltages of both bus systems due to the electrical connection through the adjacent substation is relatively small, in any case the absolute value of the difference of these voltages is different from zero and sufficient to actuate a sensitive directional switch. At the same time, depending on which of the bus systems the accident occurred, the difference in the zero sequence voltage will be represented in E.IDS vector, directed either in one or in the diametrically opposite direction. While the voltage difference vector is changing its direction, the total zero-sequence current of all 110 kilovolt feeders (linear and transformer) when any bus system is shorted to ground keeps the same direction. This circumstance allows the selection of a damaged bus system by means of a directional relay (one two-contact or two one-contact relays). In this case, the voltage difference can be easily obtained using a special intermediate low-power transformer.

In FIG. 1 shows the electric circuit of the device proposed and FIG. A 2-mentioned intermediate transformer for obtaining the voltage difference of the zero-phase phase of the monitored bus systems.

In the drawing / and // designate two bus systems, LS - inter-oil oil switch (oil), L, - coarse current relay, A - sensitive current relay, R / U -directed relays, YAR-intermediate relays, PB - relay time, B-blenders, C - signal.

The Dz of directional relays, namely PHI, are powered by the same feeder current transformers as the AI relay.

and Af, l is also the difference Ug-6 of zero sequence voltage in the controlled two bus systems, as shown in the drawing.

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The DF of other directional relays I / i - 2 is powered by a zero-sequence current, flowing through an interlock oil MB, and a zero-sequence voltage fo (any bus system).

For operational reasons, it is important to supply the voltage Ur via the contacts of the intermediate relay operating from the differential relay (not shown in the drawing).

If there is an electrical connection between the buses through the inter-drip oil and when the bi-bus systems are powered, the i6op of the damaged system is produced by a directional relay connected to the neutral conductor of the transducer current transformers and powered by a zero sequence voltage, for example, from the transformer of FIG. 2

At the same time, it is desirable that for the time of flow of the zero-sequence current through the inter-shaft oil, a continuous relay, regulating the difference in the zero-sequence voltages, is blocked. Such a blocking can be easily achieved using a current relay (not shown in the drawing) included in the neutral conductor of the inter- drip valve current transformers.

It should be noted here that the moment

A / o (Uo-Ua) obtained by subtracting voltages by means of an intermediate transformer can, if desired, be achieved in another way, such as the moment difference / g / o G7 „- / o /„ G „. To do this, it is necessary to have a nprpmsnnoy rple with two independent 1G n, nitsygichnymi kttuschklmi voltage ,nvsphennymi on a common axis (node relay / h 11 -5).

In the latter case, the directional relay of the inter-drip oil should be powered by the zero-sequence voltage of one of the bus systems (i.e. f / cl or i).

It must be borne in mind that the latter method can be applied only under the condition of complete identity of both coils of the directional relay operating at the moment difference, in mind

which preference should be given to the first method.

In case of short circuits on the tires with the interstate oil cooler turned on and the power supply from the undamaged tires off, it is planned to turn off the interstate oil after approximately 0.3 seconds. after the action of the differential relay A (the time delay is necessary to ensure the action of the directional relay of the oil drip in the previous case).

Further, in case of an electrical connection between the buses through the disconnectors of one of the feeders, a simple DC block is provided through the signal contacts of the disconnectors, giving instantaneous disconnection of all feeders during a short circuit to one of the bus systems using the two-contact intermediate relay PR.

Finally, as a safety net in case of failure of the main protection, it is necessary to install a time relay with a delay of about 1.5 seconds, which acts to turn off all lubricants from the differential relay A.

For the purpose of rapidly detecting the interruption of any current transformer circuit, a differential relay A is provided, which has a more sensitive adjustment than A and acts on the signal.

It should be borne in mind that in the case of filling and disconnection of one of the masliks with the transfer of the protection of this feeder to the mezzanine area, the current transformers of the intermedia oil jet are connected according to the Holmgreenp scheme. must be connected to a common zero current transformer circuit.

As in all other schemes of differential protection of tires, with different transformation ratios of current transformers, it is necessary to introduce intermediate current transformers to compensate for the difference in the transformation ratio.

In summary, we can draw the following conclusion: the differential tire protection scheme applied by Mosenergo, as well as the proposed new differential tire protection scheme, has certain advantages and disadvantages.

The advantages of the first scheme include the purely differential principle of protection operation, the drawback of the scheme is the need to produce manual switching of current circuits for all changes in the switching circuit,

The advantages of the proposed tire protection scheme include the absence of switching devices, the disadvantages of non-compliance with the purely differential principle due to the introduction of the directional element.

The subject matter of the invention.

Device for differential protection of double busbar system against locking qDnrl

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ground, characterized in that to control the circuit off the applied relay relays PH 1, powered by a difference voltage of zero sequence in a controlled two bus systems, and directed relays PH 2, powered by zero-sequence current flowing through the inter-oil oil switch MB, and the zero-sequence voltage of any bus system, so that the PH 1 relay selectively turns off the damaged bus when the MB switch is open, and the PH 2 relay turns off the same when AC closed circuit breaker

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