DE1241526B - Current transformer circuit for selective protection - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

HOIh

H02h

German class: 21 c - 68/50

Number:
File number:
Registration date:
Display day:

S92565VIIIb / 21c
August 11, 1964
June 1, 1967

With the increase in performance in the high-voltage networks and with the resulting The demands on the selective protection devices are increasing the transmission voltages and to the current transformers for mapping the currents flowing in the lines for the selective protection devices, getting bigger. In networks with high voltages that are designed for the transmission of large powers, - based on the rated current - both very high and low Rige short-circuit currents occur, all of which are mapped with sufficient accuracy by current transformers must, if a correct measurement of the fault location is to be guaranteed:

Current transformer circuit for selective protection

Applicant:

Siemens Aktiengesellschaft, Berlin and Munich,

Erlangen, Werner-von-Siemens-Str. 50

Named as inventor:

Dipl.-Ing. Friedrich Geise f, Erlangen

or amplifier circuits

use

In addition, at maximum voltages the relationship is to be seen,
nis between the inductive and the ohmic In addition, with a time delay in-resistance of the lines and the transformer direction for electrical protective relays, a current in relation to the values in the medium-voltage converter circuit is known, in which two current networks are very large. In the event of a short circuit occurring in the unfavorable eye-walker core with different saturation perspectives, 20 stops are provided, the primary windings of which are in series with one another due to the high inductive resistance. With this current transformer, the ohmic component - the direct current element in the circuit, the secondary windings with respect to the short-circuit current decay very slowly, so that it is switched on to the other, so that with a small primary current with normally constructed current transformers the output value zero is particularly available on the secondary side, with high short-circuit currents it saturates very quickly. 25 while with a larger primary current the saturation phenomena occur, which the measured values of one transformer core reduce the secondary voltage.

falsify and cause the selective protection device to respond incorrectly. The secondary stream of a saturated current transformer

tion of the other increases more so that now one of. Sets zero different output variable. This known circuit is not used for

then the primary current neither in the size nor in the mapping of an alternating current and is therefore as the phase position, d. That is, not even the times of the zero current transformer circuit for selective protection Primary and secondary currents no longer match. _ As a result,

also in differential protection devices where

suitable.

The new current transformer circuit for mapping an alternating current for selective protection (di-

from the position of the zero crossings to the direction 35 punch protection, differential protection) is especially for of the current is closed, faulty switching on high-voltage systems, in which there is a twitch can. see the smallest and the largest possible-

The fault current that occurs with high currents is a considerable problem to eliminate, one has already made a difference, using several Converters built in a special design, which iron 40 converter cores connected in series on the primary side cores with large air gaps or pure air with different saturation behavior, depending on the contain cores and a relatively large amount of copper. carry at least one secondary winding. The new This current converter circuit, generally referred to as a “linear coupler”, exists according to the invention Converters are designed in such a way that they also work in that for each alternating current to be mapped 45 two converter cores are provided, of which guess, but the power that can be drawn is only saturated at high currents, and that is over the normal converters very small. Because of that see the secondary windings and the trip circuit extremely low performance of the above-described downstream selective protection device Linear coupler is therefore forced to ge measuring units for the current-dependent switching switching device the downstream selective protection 50 is switched, which activates the trip circuit in the case of small fault devices, z. B. distance protection relay or differential currents with the secondary winding on the saturation relay, expensive special designs for a bare core and for large fault currents with the

709 588/264

3 4

Secondary winding on the non-saturable core converter 11 is now connected to the primary current, to take portional stream, the z. B. over the

With the new solution, the resistor 14 'and the Zener diodes 15 come to one another Reversal of linear couplers without special design.

tion for the measuring units of the protective devices from 5 can be converted. In which the zener diodes

and generally no additional transformer 16 connected downstream is required either

borrowed effort for the current converter circuit, since square wave voltage differentiates, so that in the

as the second converter core, one of the zero crossings of the current / 3 that is always present in the winding 13

normal current transformer cores can also result in pulses. In Fig. 2 b are among each other

can. These advantages can be seen through the new io sinusoidal current / 3 in the winding 13 and the

Achieve arrangement because the power of all current at the transformer 16 to be drawn pulses

converter shown as the square of the primary current increases, for example to the other end

or falls. As a result, line 1 can also be transmitted at corresponding and in

high primary current the performance of a linear coupling - their phase position is similar at the other end of the line -

lers are sufficient to compare normal protective devices to 15 borrowed pulses. For

actuate. this comparison can then be a phase comparison

In FIG. 1, the equalizing devices to be used for a current transformer are plotted, because of the power N which are required, as a function of the flowing corresponding Lei primary current Ip to be taken from the current transformer. The curve represents stung, can be set up simply.
Nl the course of the removable power from 20 Another application and Schaltungsmögeinem normal transformer core and the curve Nl friendliness is shown in FIG. 3. The same parts are herein with a linear coupler the power to be removed by the same reference numerals as in F i g. 2 is provided. Parallel to the abscissa, a is denoted by Na . Here the current transformer circuit is plotted for a nete dashed line, which uses distance protection as an example. The intermediate converter 11 is omitted for the response of a protective device. For this purpose, two measuring units 17 and 18 are intended to represent the power required for processing. As present from the distance protection. The input terminals Fig. 1 can be seen, in this case with a for the current in the measuring unit 17 are above the Wick primary current, which is greater than 3In, the power to be taken from the line 9 of the switching device to the secondary close coupler is sufficient, winding 4 connected. The input terminals for a reliable response of the downstream 30 the current in the measuring unit 18 are to be guaranteed directly to the protective device. It is therefore sufficient to switch the secondary winding 5. In addition, in this example, if the core of the normal is a voltage transformer 19, whose secondary current transformer is not yet saturated with the current value 3In through the series resistors 20 or 21 to the. The switching device is set in the input terminals of the measuring units 17 and 18 for this case so that the Se- 35 voltages are connected to the current 3In. The depending on the secondary winding on the normal core and current in the winding 9 (current relay) switching that on the non-saturable core (linear switch 12 is in a trip coil 22 coupler) is switched on. of a circuit breaker containing tripping current

A circuit example is shown in FIG. circle and is in the rest position via the output line 1 leads the alternating circuit to be mapped 40 of the measuring mechanism 17 and in the working current. It is led through an iron core 2 and a development via the output circuit of the measuring mechanism air-gap core 3, so that it represents the primary winding with the positive pole "+" of a DC voltage for both cores. Each core contains a connected voltage source whose negative pole "-" is also connected to a secondary winding 4 or 5, the end not connected to the changeover switch 12.
4 shows the current transformer circuit for the voltages are connected to the secondary windings with differential protection of a busbar system with levels 6 and 7 respectively. The secondary branches 23, 24 and 25. Each of the abutments 4 of the iron core 2 is routed via an ammeter 8, branch lines 23 to 25 through an iron core 2, the winding 9, a current relay 50 and an air gap core 3. The cores carry the switching device, the primary winding 10 each - as in Fi g. 2 and 3 - the secondary winding of an intermediate transformer 11 and the boy 4 or 5 in the resting position. The switching contact 12 of the winding 4, which is closed in series with each secondary winding position, is connected to the winding 26 of a current switching device. In. same way is relay. Each of these current relays contains a secondary winding 5 of the air gap core 3 via 55 working contacts 27, all of which are connected on the one hand to the positive contacts connected to the 12 pole "+" of a DC voltage source in the working position of the changeover contact and via the primary winding and on the other hand via a delay time 12 α of the intermediate converter 11 connected. The stage 28 and via the winding 9 of a switching number of turns of the primary windings 12 and 12a device to the negative pole "-" the equivalent of the intermediate converter 11 are selected so that a voltage source is routed to 60. The secondary winding 13 of the intermediate converter 11 gene 4 are all connected in parallel and connected to a differential relay 29 proportional to the primary current in the conductor 1. Current flows in the same way, irrespective of whether the switching contact switches the secondary windings 5 to one another in parallel, 12 assumes its rest or working position and is connected to a differential relay 30. Via the intermediate transformer U and also via the 65 As in FIG. 3 are the output circuits of the Dif resistors 6 and 7, an adaptation of the differential relays 29 and 30 is possible via the different transmission ratios of the two associated changeover contacts 12 with a trip core to the winding 9. The secondary winding 13 of the intermediate circuit is connected, which in turn is controlled by the tripping

Claims (6)

coil 22 is indicated for one or more circuit breakers. Due to the delay time stage 28, the changeover switch 12 is actuated with a delay when the fault current increases. As a result, the higher performance of the normal converter core is used longer. Since the iron cores 2 are not yet saturated in the first half-waves after a short circuit - due to the direct current element - the current is still correctly mapped during the delay time. The delay time of the delay time stage 28 therefore depends on the level of a direct current element to be expected and on the decay time constant of the same. With this arrangement, too, it is ensured that in each case that differential relay is used for the measurement which delivers a result that is not falsified by saturation phenomena and which delivers sufficient power for triggering. In addition to the customary converters with iron ao or air gap cores and secondary windings applied to them, those with Hall generators or magnetic field-dependent resistors are also known which are located in the air gaps of the cores. The new current converter circuit can also be implemented with converters constructed in this way. In this case, the connections of the Hall generators or the magnetic field-dependent resistors take the place of the secondary windings 4 and 5, respectively. 1.Current transformer circuit for mapping an alternating current for selective protection (distance protection, Differential protection), especially for high voltage systems where between there is a considerable difference between the smallest and the largest possible fault current consists, using several converter cores connected in series on the primary side with different saturation behavior, each with at least one secondary winding, characterized in that two converter cores for each alternating current to be mapped (2, 3) are provided, of which only one (2) saturates at high currents, and that between the secondary windings (4, 5) and the trip circuit (13 to 16) of the downstream Selective protection device a current-dependent switching switching device (9, 12) switched is that the trip circuit with small fault currents with the secondary winding (4) on the saturable Core and in the case of large fault currents with the secondary winding (5) on the non-saturable Core connects. 2. Current converter circuit according to claim 1, characterized in that the switching device between the secondary windings and a secondary side to the selective protection device connected intermediate transformer with two primary windings, so that each one Primary winding of the intermediate transformer to its associated secondary winding on one of the two Converter cores is connected. 3. Current converter circuit according to claim 1, characterized in that each secondary winding A separate selective protection device (distance protection relay, Differential protection relay) is connected downstream, whose output circuits are dependent on a current switching switching device are connected to a trip circuit. 4. Current converter circuit according to claim 1 to 3 for differential protection, characterized in that that the switching device is dependent on the current in the branch line that carries the greatest current. 5. Current converter circuit according to claim 1 to 4, characterized in that the switching device contains a time delay element. 6. Current converter circuit according to claim 1 to 5, characterized in that in place of the ■ Secondary windings on the converter cores Hall generators or magnetic field-dependent Resistors are arranged in air gaps of these cores. Considered publications:
German publication No. 1124 587. 1 sheet of drawings 709 588/264 5.67 © Bundesdruckerei Berlin