RU2162269C2 - Backup protective device for line with transformers on taps - Google Patents

Abstract

FIELD: protective gear. SUBSTANCE: device provides for monitoring moduli of backward-, forward-, and zero-sequence phase currents, phase relations of forward- and backward-sequence currents, forward- sequence voltages and currents including backward-sequence current and preceding forward-sequence load current. Device operating currents and voltages are set depending on preceding abnormal operation of circuit under protection. EFFECT: improved sensitivity and selectivity of device. 1 dwg

Description

 The inventive device relates to electrical engineering and can be used for relay protection of radial overhead lines and cable lines having branches with transformer substations.

 Known technical solutions for the backup protection of overhead lines with transformers on the branches described in [1, 2, 3].

 So, for example, in [1] a technical solution is proposed, the principle of which is based on the targeted introduction of distortions of the current shape during short circuit (short circuit) behind the branch transformer. To do this, a reactor is installed at the branch substation, which is saturated during short circuit, which causes the balanced relay to operate at the supply end of the overhead line (OHL). This implementation of protection requires the installation of additional equipment at the branch substation, which complicates the protection scheme and reduces its reliability.

 In [2], the construction of protection was proposed on the basis of a reverse sequence current relay, a power direction relay and a direct sequence current relay, an increment relay, and a direct sequence current decay relay. The protection is started from the reverse sequence current relay, and the "pick-up" of protection during the transition to a symmetrical short-circuit is performed through the current relay chains and the direct sequence power direction relay. The disadvantage of this device is the failure of protection during the short-term existence of interphase faults and the insufficient speed of the reverse sequence current relay. The increment (decay) of the currents of the direct sequence also occurs when the motors start up (self-start) and when the line is turned on in the automatic reclosure cycle, which must be taken into account when choosing the settings and this limits its sensitivity.

 In [3], the implementation of backup protection with switching settings based on measuring and starting current relays and delay elements was considered. To increase the sensitivity, it is necessary to increase the number of protection levels, which leads to more complicated protection. In addition, a detuning from the inclusion mode of the loaded line is necessary. It is also necessary to roughen the protection in the presence of a motor load. The protection is made in a two-phase design, which limits its sensitivity in case of a two-phase short circuit on the low voltage side of the transformer, the windings of which are connected in a triangle.

 In [4], a device was proposed for back-up current protection of a dead-end line with branches from a phase-to-phase short-circuit, which consists of a linear current-to-voltage converter, a multi-bit ADC, a subtractor, a shift register, a comparison unit, a set point, the first, second logical elements, OR NOT, first - fourth time elements, first - third logical elements AND, memory element, clock generator, actuator, line circuit breaker, voltage to voltage converter, limiter amplifier, fil A low-frequency converter of the reactive current component.

 The advantage of this protection device is its increased sensitivity compared to overcurrent protection reacting to full currents. Such a construction allows to reduce the tripping current to the level of a lower load current of the maximum power transformer. However, the disadvantage of the described technical solution is the need for detuning from switching on the line in time, reducing sensitivity in the presence of a powerful motor load on the branches of the line.

The closest technical solution (prototype) is a long-range backup device of the type UDR AH 94.2 [5], consisting of measuring current and power directions, a time delay organ, an output organ, an indication relay, a control organ, and an external alarm system included in currents and phase voltages. The principle of operation of this protection device is based on monitoring the current and phase angle between current and voltage. The power direction body has an angular characteristic of less than 180 ^o , which makes it possible to distinguish the short circuit mode from the load mode. The current element and the power directions of each phase are combined by the AND gate, and the AND elements are connected to the inputs of the OR gate, the output of which is connected to the input of the time delay organ.

 The disadvantage of the described technical solution is the need for detuning from the inclusion of the line in time, a decrease in sensitivity in the presence of a powerful motor load on the branches of the line. The application of this technical solution is also limited by radial lines and only in some cases can it be used on transit light-loaded lines, because with significant reactive components of the overflow power, detuning is complicated and, as a result, the protection sensitivity during short-circuit behind low-power transformers is insufficient.

 The purpose of the invention is to increase sensitivity and selectivity.

 This is achieved by the fact that the backup line protection device with transformers on the branches, containing current sensors of all three phases of the line, the outputs of which are connected to the inputs of reverse, direct and zero sequence current filters, voltage sensors connected to interphase voltages, the outputs of which are connected to the filter inputs direct sequence voltage, and its output is connected to the second input of the first phase comparison circuit, the output of which is connected to the seventh input of the logic unit, the sixth input of which is connected to the output of the the first module comparison circuit, the input of which is connected to the output of the zero sequence current filter, the outputs of the first current sensor and the negative sequence filter are connected to the inputs of the second and fourth current module comparison circuits, and their outputs are connected to the second and fourth inputs of the logic unit, the output of which is connected to the input of the output organ, additionally introduced the first and third circuits for comparing the modules, the inputs of which are connected to the output of the first current sensor and current filter of the negative sequence, and their outputs to the first and t to the network inputs of the logic block, the second phase comparison circuit, the inputs of which are connected to the outputs of the current and reverse sequence current filters, and its first output is connected to the fifth input of the logic block, the set-up unit, the inputs of which are connected to the outputs of the reverse, direct sequence current filters and the second the output of the second phase comparison circuit, and its output is connected to an additional third input of the first phase comparison circuit.

In FIG. 1 shows a structural diagram of the proposed device. The device contains current sensors (DT) 1 - 3 phases A, B, C and voltage sensors (DN) 4, 5, connected to line voltages, for example to voltage U _AB and U _BC, respectively, reverse sequence current filters (FTOP) 6, direct (FTPP) 7 and zero sequence (FTNP) 8, direct sequence voltage filter (FNPP) 9, the first, second, third, fourth module comparison circuits (CCM) 10-14, the first and second phase comparison circuits (SSF) 15, 16, the setpoint formation circuit (SFU) 17, the logic and time delay unit (BLVV) 18, the output organ (VO) 19.

 Current sensors (DT) 1 - 3 perform the conversion of current to voltage, voltage sensors (DN) 4, 5 provide the conversion of voltage to voltage. Filters of symmetric component current (FTOP, FTTPP, FTNP) 6 - 8 provide the selection of signals proportional to the currents of the reverse, direct and zero sequence, respectively, and the voltage filter of the forward sequence (FNPP) 9 emits a signal proportional to the voltage of the direct sequence at the output.

где I_КЗmin - ток короткого замыкания (КЗ) за трансформатором наименьшей мощности в минимальном режиме; k_ч - коэффициент чувствительности.The module comparison circuits (CCM1 - CCM4) 10-14 provide a comparison of one value (voltage proportional to current) with a given value. The module comparison circuits (SSF1, SSF2) 10, 11 are connected to the outputs of the current sensors of the DT of one of the phases, for example, phase A (as shown in the structural diagram). The operating current of the CCM 10 is selected from the condition:

where I _KZmin - short circuit current (KZ) behind the transformer of least power in minimum mode; k _h - sensitivity coefficient.

The operating current of the CCM 11 is selected from the condition:
I _SSM11 ≥ k _n · I _KZmax ,
where I _KZmax is the short-circuit current behind the transformer of the highest power in maximum mode; k _n - reliability coefficient.

 Comparison schemes of modules 12, 13 are connected to the output of the reverse sequence current filter. The conditions for selecting the parameters of the SSM 12, 13 are the same as those given above for the SSM 10, 11.

 The comparison circuit of the modules 14 provides control of the zero sequence current and its operation current is selected from the condition of the detuning from the unbalance current due to an external three-phase short circuit.

 The phase comparison circuit 15 provides control of the phase relationships between the currents of the forward and reverse sequence.

Phase comparison circuit 16 provides phase angle control between voltage and direct sequence current. In contrast to SSF 15, the response parameters of SSF 16 depend on the type of fault (two-phase or three-phase fault), as well as the previous load mode. The width of the angular characteristic of the SSF 16 is determined by the expression:
Δφ _SSF16 = Δφ _max -Δφ ₂ (I _2, I ₁ ) -Δφ ₁ (I _1ng ), (3)
where Δφ _max is the maximum width of the angular characteristic of the SSF 16; Δφ ₂ (I ₂ , I ₁ ) is the correction component of the angular characteristic of the SSF, depending on the magnitude of the current of the negative sequence and current of the direct sequence (emergency component), as well as on the output signal of the SSF 15; Δφ ₁ (I _1ng ) is a component of the correction of the angular characteristic, which depends on the current of the direct sequence in the previous mode.

The formation of the components Δφ ₁ and Δφ ₂ is performed by the setpoint generation circuit 17.

 Block logic and time delay 18 provides the formation of the output effects of the protection device, which are amplified and converted by the output organ 19.

The algorithm for generating output actions can be described, for example, by the expression:
F ₁₈ = F ₁₆ · [(F ₁₁ + F ₁₃ ) · D ^t1 + F ₁₅ · F ₁₃ · D ^t2 ] · (F ₁₀ + F ₁₂ + F ₁₄ )], (4)
where F ₁₀ - F ₁₆ - output signals CCM 10 - 14 and SSF 15, 16; D ^t1 and D ^t2 - response delay operators (time delay body).

 In normal network operation mode, the described device is in the following state. The output signals of current sensors 1 to 3 are determined by the value of the load currents of the line, the output voltages of voltage sensors 4 and 5 are close to the nominal values and, accordingly, close to the nominal value of the voltage at the output of the direct sequence voltage filter 9. The output signal of the FTP 7 is also determined by the value of the load currents. The output signals of FTOP 6 and FTNP 8 are close to zero and are determined only by unbalance currents.

The comparison circuit of module 11 may be in the operating state if I _CCM11 <I _ng , where I _ng is the load current. The rest of the SMS (10, 12, 13, 14) are in an idle state and a logic signal 0 is present at their outputs.

 At the output of the SSF 15, 16, signal 0 is present. In the first case, this is due to the absence of a negative sequence current, and in the second, to the absence of conditions for operation due to the direct sequence current vector being in the zone of load conditions.

 At the output of the BLVV 18 and VO 19 there are logical signals 0.

и обратной последовательности

обусловленного группой соединения обмоток трансформатора "звезда - треугольник", появляется дополнительный фазовый сдвиг между токами

что фиксируется схемой сравнения фаз ССФ 15. При этом также срабатывает схема сравнения модулей (ССМ 4) 13.In the case of a two-phase short circuit behind one of the transformers on the side connected in a triangle connected to the OHL branch, the device operates as follows. Due to the different shift of the components of the direct currents

and reverse sequence

due to the star-delta transformer windings connection group, an additional phase shift between currents appears

which is fixed by the phase comparison circuit of the SSF 15. This also triggers the module comparison circuit (CCM 4) 13.

 The width of the angular characteristic of the SSF 16 in this case is maximum, which leads to its reliable operation and the formation of a trip signal according to algorithm (4).

 With a two-phase short circuit on the side of the transformer on the branch with the windings connected to the star, the formation of the shutdown signal is ensured by the operation of the SSM 13 and SSF 16. The width of the angular characteristic of the SSF 16 is determined taking into account the previous mode and the presence of the reverse sequence current and the output signal of the SSF 15, which is not triggered in this case. In this case, it is also possible to operate the CCM 11, which is an additional channel for generating the output signal of the BLVV unit 18, according to (4).

 When three-phase fault behind transformers on branches at any group of transformer connections, the SSM 11 and SSF 16 are triggered. The SFU 17 circuit provides the formation of the width of the angular characteristic taking into account only the previous mode.

 In case of two-phase or three-phase short-circuit on the line, when the short-circuit current exceeds the maximum possible value of the short-circuit currents behind the maximum power transformer, the CCM 10 (for three-phase short-circuit) or CCM 12 (for two-phase short-circuit) is triggered, which ensures protection blocking according to (4).

 With a single-phase short circuit, which is possible only on overhead lines, the SSM 14 is activated, connected to the zero-sequence current filter FTNP 8, which also leads to blocking of protection according to (4).

 When the line is turned on in the reclosure cycle and there is a motor load at the transformer substations, it is possible to operate the SSM 11, however, in this case the SSF 16 does not operate, because the width of its angular characteristic is set taking into account the previous load mode, which provides reliable detuning from this mode.

 Thus, the use of the proposed device allows to increase the sensitivity to interphase short-circuit behind transformers with a star-delta connection group, as well as to increase the detuning from load conditions and, as a result, to increase the sensitivity to three-phase short-circuit behind transformers due to the adaptive formation of the width of the angular characteristic of the phase comparison circuit currents and voltages of direct sequence.

Literature
1. Device for backup protection of the soldering transformer. A.S. USSR 1319144, MKI H 02 H 7/04. Kuznik Yu.S. Publ. 06/23/87, Bull. N 23.

 2. Device for backup line protection with soldering transformers. A.S. USSR 1737611, MKI H 02 H 7/28. Kuznik Yu.S. Publ. 10/17/89, Bull, N 20.

 3. Device for current protection against interphase short circuit of a three-phase electrical installation. A. s. USSR 1116488, MKI H 02 H 3/08, H 02 H 7/00. Bogdan A.V., Kletsel M.Ya., Nikitin K.I. - Publ. 09/30/84, Bull. N 36.

 4. A device for backup current protection of a dead end line with branches from an interphase short circuit. A.S. USSR 1361668, MKI H 02 H 3/08. Kletsel M. Ya., Kopbaev M.A., Nikitin K.A., Polyakov V.E. - Publ. 11.23.87, Bull. N 47.

 5. Long-range backup device UDR AH - 94.2 / Tez. doc. scientific and technical conference "Relay protection and automation of power systems - 96" - Moscow, 1996

Claims (1)

A backup line protection device with transformers on the branches, containing current sensors of all three phases of the line, the outputs of which are connected to the inputs of reverse, direct and zero sequence current filters, voltage sensors connected to interphase voltages, the outputs of which are connected to the inputs of the direct sequence voltage filter, output which is connected to the second input of the first phase comparison circuit, the output of which is connected to the seventh input of the logic unit, the sixth input of which is connected to the output of the fifth mode comparison circuit lei, the output of which is connected to the output of the zero-sequence current filter, the outputs of the first current sensor and the reverse-current filter are connected to the inputs of the second and fourth module comparison circuits, and their outputs are connected to the second and fourth inputs of the logic unit, the output of which is connected to the input of the output organ characterized in that the first and third circuits for comparing modules are additionally introduced, the inputs of which are connected to the outputs of the first current sensor and to the output of the negative sequence current filter, the outputs of which are integrated with the first and third inputs of the logic block, the second phase comparison circuit, the inputs of which are connected to the outputs of the current and reverse sequence current filters, and its first output is connected to the fifth input of the logic block, the setpoint formation circuit whose inputs are connected to the outputs of the reverse current filters, direct sequence and second
the output of the second phase comparison circuit, and its output is connected to an additional third input of the first phase comparison circuit, which provides control of the phase angle between the voltage and current of the direct sequence.