GB2095059A - Distance relay - Google Patents

Abstract

In a distance relay of the kind where defects are detected at 1A, 1B, 1C and, in response, signals VF, ZR IF and VH are produced at 7 from line voltages and currents VA, VB, VC, IA, IB, IC and in turn operating vector EOP and reference vector EPOL are derived to produce at 6 a protection signal 6a, it is arranged that a phase shifter (8) connected to the input of a phase discrimination circuit (16) shifts the phase of VH by the same predetermined amount for all kinds of the defects, on any line. <IMAGE>

Description

SPECIFICATION Distance relay The present invention relates to a distance relay for protecting power systems.

The distance relay has its operation characteristics determined depending upon a distance between a point where it is installed and a point where defect has developed. The operation timing varies depending upon the distance. Therefore, the distance relay is equipped with an ohmmeter for measuring the distance up to the defective point and with a timing element.

With the conventional distance relays of this type, it was necessary to control a phase shifter by control means so that the phase could be shifted by 600 or 900 depending upon the kind of defect such as ground of a wire of phase A or short-circuiting of three phases. Therefore, the construction was complicated, reliability was small, and the manufacturing cost was expensive.

For instance, Fig. 1 shows a conventional distance relay, in which detecting parts 1 A, 1 B and 1 C are installed for each of the phases A, B and C of the transmission lines (not shown), and work to detect any defect if it develops. A switching part 2 introduces signals 1 Aa, 1 Ba, 1 Ca produced by the detecting parts 1 A, 1 B, 1 C, currents IA, IB, IC of each of the phases A, B, C of the transmission lines, and voltages; VA' VB' BC' and performs a predetermined operation to produce signals VF' VH and ZRIF (where ZR denotes an impedance of the transmission lines). A subtraction circuit 3 is connected to the output ends of the switching part 2, and performs the subtraction between the signals VF and ZRIF that are sent from the switching part 2.A phase shifter 4, on the other hand, is connected to the remaining output terminal of the switching part 2, and shifts the phase of the signal VH produced by the switching part 2 responsive to a control signal 5a fed from a control circuit 5 that will be described later. Relying upon signals 1 Aa, 1 Ba, 1 Ca produced by the detecting parts 1 A, 1 B, 1 C, the control circuit 5 produces a control signal 5a to control the phase shifter 4. A phase discrimination circuit 6 is connected to the output terminals of the subtraction circuit 3 and the phase shifter 4, and produces an output signal 6a relying upon an output signal Eop from the subtraction circuit 3 and an output signal EPOL from the phase shifter 4.

Operation of the above conventional relay will be described below conceretely. Let it now be assumed that a wire of the phase A is grounded. The detecting part 1A detects the defect and produces an output signal 1 Aa which will be sent to the switching part 2. The switching part 2 then learns the kind of defect, and produces signals VF and ZRIF for operation vectors and a signal VH for reference vector, depending upon the kind of defect. Table 1 illustrates the conditions depending upon the kinds of defects. The subtraction circuit 3 fir.ds a difference between the output signals VF and ZRIF sent from the switching part 2, and produces the signal Eop which serves as an operation vector.On the other hand, the phase shifter 4 advances the phase of the signal VH for reference vector produced by the switching part 2 by 600 or 900 responsive to the output signal 5a from the control circuit 5, as will be mentioned later, and produces a signal EPOL which serves as the reference vector. The signals Eop and EPOL are also shown in Table 1.

TABLE 1

Output of Switching Part Kind of Defect VF ZR'F VH EOP EPOL Ground of phase A VA ZR'A VCB VA-ZR'A VCB /90 Ground of phase B VB ZR'B VAC VB-ZR'B VAC /90 Ground of phase C VC ZR'C VBA VC-ZR'C VBA /90 Short-circuit or ground of phases A-B VAB ZR'AB VCA VAB-ZR'AB VCA /60 Short-circuit or ground of phases B-C VBC ZR'BC VAB VBC-ZR'BC VAB /60 Short-circuit or ground of phases C-A VCA ZR'CA VBC VCA-ZR'CA VBC /60 Short-circuit or ground of three phases VCA ZR'CA VBC VCA-ZR'CA VBC /60@ When a phase difference between the signals Eop and EPOL is smaller than +900, the phase discrimination circuit 6 regards it as the internal defect and produces a signal 6a which breaks a circuit breaker that is not shown to protect the power system from the defect.

Operation of the coventional distance relay wil be described below with reference to vector diagrams and characteristics diagrams of Figs. 2 to 5 in case phase A of the transmission lines is grounded and in case three phases are short-circuited.

(a) When the phase A is grounded, from Table 1, E,, = VA - ZRIA EPOL = Vo A300 whence the relation holds true as shown in a vector diagram of Fig. 2, Here, the signal EPOL assumes a phase opposite to the vector VA which forms the signal E0p. Consequently, the internal defect when the phase A is grounded resides in a range described by a circle with the vector ZRIA as a diameter, as shown in the characteristics diagram of Fig. 3.

(b) When the three phases are short-circuited, from Table 1, E0p = VCA ZRICA EPoL=VBc Ao0 whence the relation holds as shown in a vector diagram of Fig. 4. Even in this case, the signal E POL which serves as the reference vector assumes the phase opposite to the vector VCA. Hence, the internal defect exists in a range described by a circle with the vector ZRICA as a diameter, as shown in the characteristics diagram of Fig. 5.

What is common when the phase A is grounded and when the three phases are short-circuited is that the signal EPoL which serves as the reference vector assumes the phase opposite to that of the signals VA, V CA for operation vectors. In order to obtain such a reference vector, therefore, the vector VCB was so far advanced by 900 in case the phase A was grounded, and the vector VBC was advanced by 600 in case the three phases were short-circuited.

In the conventional distance relays as mentioned above, the phase shifter had to be controlled so that the phase was shifted by 600 or 900 depending upon the kind of defect. Therefore, the construction was complex, the reliability was small, and the manufacturing cost was high.

The object of the present invention is to provide a very simply constructed and highly reliable distance relay, in which the phase of the phase shifter which obtains reference vector from the signals (for obtaining reference vector) is shifted by a predetermined amount for all kinds of defects.

According to an embodiment of the present invention, therefore, there is obtained a distance relay comprising: a) detecting means provided for each of the phases of the transmission lines to detect defects for each of the phases of the transmission lines; b) switching means which receives vector signals of currents and voltages detected from each of the phases of the transmission lines, which discriminates the kind of defects based upon the output signals produced by said detecting means, and which produces voltage and current signals for operation vectors and a signal for reference vector depending upon the kind of defect; c) a subtraction circuit which finds a difference between the voltage signal and the current signal for operation vectors;; d) a phase shifter which introduces said signal for reference vector, which prepares reference vector from said signal for reference vector for all of the defects in the transmission lines, and which shifts the phase of the output signals all by a predetermined amount; and e) a phase discrimination circuit which so discriminates that the defect has developed within a loop of transmission lines when the phase difference between the output signal of the subtraction circuit and the output signal of the phase shifter is smaller than a predetermined value, and which produces an output signal to protect the transmission lines.

Fig. 1 is a block diagram of a conventional distance relay; Fig. 2 is a vector diagram of a distance relay of Fig. 1; Fig. 3 is a diagram illustrating characteristics of the distance relay of Fig. 1; Fig. 4 is a vector diagram of the distance relay of Figs. 1 and 6; Fig. 5 is a diagram illustrating characteristics of the distance relay of Figs. 1 and 6; Fig. 6 is a block diagram of a distance relay according to an embodiment of the present invention; Fig. 7 is a circuit diagram illustrating a concrete setup of the switching part 7 in the distance relay of Fig. 6; Fig. 8 is a circuit diagram illustrating a concrete setup of the subtraction circuit 3 in the distance relay of Fig. 6; Fig. 9 is a circuit diagram illustrating a concrete setup of the phase shifter 4 in the distance relay of Fig. 6;; Fig. 10 is a circuit diagram illustrating a concrete setup of the phase discrimination circuit 6 of Fig.

6; Figs. 11 and 12 are diagrams illustrating waveforms at each of the portions of Fig. 10; and Fig. 13 is a vector diagram of the distance relay of Fig. 6.

Figs. 6 to 13 illustrate an embodiment of the present invention. In Fig. 6, the switching part 7 receives the same inputs IAT IB, IC, VA, VB and Vc as those of Fig. 1. Concrete setup of the switching part 7 is shown in Fig. 7, in which logic signals lAa, IBa and ICa from the detecting parts IAF 1B and IC are sent to the inverters G1, G2, and G3, and are inverted. The inverted signals and the logic signals are sent to AND gates G1 1 to G17. Outputs of the AND gates G1 1 to G17 are sent to OR gates G101 to G104, G107,G115 to G1 17, and G120 to G121. These inverters, AND gates and OR gates may be constituted by discrete transistors, or by the logic gates of the integrated circuits.Coils RY1 to RY2 1 of a switching relay are connected to the output terminals of the OR gates; the coil is excited when a logic signal "1" is received as an input, whereby a corresponding contact point is closed.

Upon receipt of voltages VA, VB and Vc of each of the phases of the transmission lines, transformers TEA, TEB and TEC produce voltage outputs proportional to the inputs. Further, upon receipt of currents IAT I B and IC of each of the phases of the transmission lines, the gap transformers TXA, TXB and TXC produce voltage outputs ZRIA, ZRIB and ZRIC (ZR denotes an impedance of the transmission lines) which are proportional to the inputs.

In the following description, the logic signals are denoted by digital notation having a value "1" or a value "0".

When the phase A is grounded, for instance, 1 Aa = "1", and 1 Ba = 1 Ca = "0". In this case, outputs of the inverters G1, G2 and G3 are "0", "1 " and "1", respectively. Therefore, output of the AND gate G 11 is "1", and outputs of AND gates G 12 to G 17 are "0". Accordingly, switching relays RY1, RY7, RY8, RY14, RY17 and RY21 are excited, but other switching relays are not excited.

Consequently, outputs ZRl F' V F from the switching part 7 to the subtraction circuit 3, and outputs ZRIF' VF and VH from the switching part 7 to the phase shifter 8, are given as, ZRIF = ZRIA VF=VA VH = VC The above results are in agreement with the output of the switching part 7 corresponding to the ground of phase A of Table 2. Output voltage of an operation amplifier Al 5 gradually rises starting from the lower limit thereof, and the detector detects the moment at which the potential of the negative terminal of the operation amplifier Al 6 is inverted from the positive polarity to the negative polarity.

Here, the anode potential of a diode ZD20 is 1/4VCC. Further, since R28 = R29, the detection level is given by +1/4Vcc which is produced by the operation amplifier Al 5. Once the detection is made, the output voltage of the operation amplifier Al 6 assumes the low level. Under this detection condition, the diode Dl 3 is served with a voltage in the forward direction, and is rendered conductive.

Outputs ZRIF, VF, VH ofthe circuit of Fig. 7 corresponding to defects of other types, are also in agreement with the outputs of the switching part 7 of Table 2.

Fig. 8 is a concrete circuit diagram of the subtraction circuit 3 of Fig. 6, which is based upon a differential amplifier consisting of an operation amplifier Al, and resistance elements RV, RI, R1 and R2.

Namely, this circuit introduces voltage signals VF and ZR1F, and produces an output VFZRlF.

Fig. 9 is a concrete circuit diagram of the phase shifter 8 of Fig. 6, which consists of an operation amplifier A2, resistors R, R3, R4 and a capacitor C.

The circuit of Fig. 9 is a filter circuit. If the resitance R3 is selected to be equal to R4, the transfer function T is given by, s - #a 1 T= (#a= ) s + #a RC Further, the angle 0 of phase shift (phase difference of the output V0 relative to the input VH) is given by, 0 = 180 - 2 tan-1 (wCR) where C : capacity of the capacitor C, R : resistance of the resistance element R, # : angular frequency.

For instance, w = 2# x 50(Hz) = 1 007r for the power system of 50 Hz. in this case, the combination of C and R is so selected that 0 will be 600.

Fig. 10 illustrates a concrete setup of the phase discrimination circuit of Fig. 6, Fig. 11 illustrates waveforms at each of the portions when the non-detection condition is changed into the detection condition, and Fig. 12 illustrates waveforms when the detection condition is changed into the nondetection condition. The phase discrimination circuit 6 of Fig. 10 is made up of operation amplifiers Al 1 to Al 6, resistance elements R1 1 to R32, capacitor C11, diodes Dl 1 to D13, and constant-voltage diodes ZD 11 to ZD2 1. The phase discrimination circuit 6 is driven on power-supply voltages +Vcc and Vcc. Usually, +Vcc will have a voltage of about + 12 volts.

Further, the circuit elements will have the following values: R15=R16=R20=R21 =R22=r(kQ) R17=r (k#) R23 = 4r (k#) R28 = R29 R31 =R32 The following values will also be selected as Zener voltages of VZD of the constant-voltage diodes: VZD11 = VZD12 = V2D13 = VZD14 # VCC VZD15 # VCC VZD16 = VZD17 # VCC VZD18 = VZD19 # VCC VZD20 # 1/4VCC VZD = 21Vc0 Operation of the circuit of Fig. 10 will be described below by employing the above values.

The phase discrimination circuit 6 of Fig. 10 receives, as a-c input signals, the output Eop of the subtraction circuit 3 of Fig. 6 and the output EPOL of the phase shifter 8, and produces an output of the low level when the absolute value of phase difference between Eop and EPOL is smaller than 900, and produces an output of the high level when the absolute value is greater than 900. Here, the high level stands for nearly the power-supply voltage Vcc and the low level stands for nearly the power-supply voltage Vcc.

For instance, if the circuit is adapted to a distance relay for the power transmission system having a frequency of 50 Hz, the outputs Eop and EPOL serve as a-c signals each having a frequency of 50 Hz.

These signals Eop and EPOL are transmitted to the operation amplifiers Al 1,A12 via resistance elements R1 1, R1 3, and are converted into rectangular waves. The outputs of the operation amplifiers Al 1,A12 have an amplitude -Vcc being determined by the constant-voltage diodes ZD1 1, ZDl 2, ZDl 3 and ZD14.

Further, the output of the operation amplifier A14 assumes the value-VCC when output signals of the operation amplifiers Al 1, Al 2 have the same polarity, and assumes the value +VCC when the output signals have opposite polarities relative to each other. The operation amplifier Al 5 is an integrator, and the upper limit and lower limit of its output is limited to ++Vcc and z1Vcc by the diodes ZDl 8 and ZDl 9. The output of the operation amplifier Al 5 increases when the output of the operation amplifier A14 is-VCC and decreases when the output of the operation amplifier A14 S'++Vcc.

When the phase difference between the a-c signals Eop and EPOL is 900, the rising width and breaking width in the output of the operation amplifier Al 5 come into agreement; i.e., operation limit is reached. When the phase difference between the signals Eop and EPOL is smaller than 900, on the other hand, the rising width in the output of the operation amplifier Al 5 becomes greater than the breaking width, and the output increases as a whole. Consequently, if the output of the operation amplifier Al 5 exceeds the detection level of a detector by the operation amplifier Al 6, the output of the operation amplifier Al 6 assumes the low level.That is, the detector by the operation amplifier Al 6 develops difference between the detection level and the reset level, and presents so-called hysteresis characteristics.

Under the non-detection condition, the operation amplifier Al 6 produces output of the high level.

Under this condition, however, the diode Dl 3 is served with a voltage in the reverse direction, and remains non-conductive. Therefore, anode of the constant-voltage diode AC21 assumes zero volt and positive terminal of the operation amplifier Al 6 also assumes zero volt. Accordingly, anode of the constant-voltage diode ZD2 1 assumes VCC. Here, since R3 1 = R32, positive terminal of the operation amplifier Al 6 assumes -1/4VCC. The output voltage of the operation amplifier Al 5 then gradually decreases from the upper limit, and the detector resets at a moment when the potential of the negative terminal of the operation amplifier Al 6 is inverted from 41Vcc into the negative potential. In other words, the output potential -1/4VCC of the operation amplifier Al 5 is a reset level. The detector by the operation amplifier Al 6 has hysteresis characteristics, such that the logic output can be produced continuously.

With the thus constructed distance relay of the present invention, the switching part 7 (Fig. 6) is capable of discriminating the kind of defects shown in Table 2, unlike the switching part 2 of Fig. 1, and produces voltage signal VF for operation vector, current signal Zip for operation vector, and signal VH for reference vector, that are corresponded to the kind of defect.The phase shifter 8 receives the output signal VH from the switching part 7, and produces a signal EPOL of which the phase is advanced by 600. TABLE 2

Output of Switching Part 7 Kind of Defect VF ZR'F VH EOP EPOL Ground of phase A VA ZR'A VC VA-ZR'A VC /60 Ground of phase B VB ZR'B VA VB-ZR'B VA /60 Ground of phase C VC ZR'C VB VC-ZR'C VB /60 Short-circuit or ground of phases A-B VAB ZR'AB VCA VAB-ZR'AB VCA /60 Short-circuit or ground of phases B-C VBC ZR'BC VAB VBC-ZR'BC VAB /60 Short-circuit or ground of phases C-A VCA ZR'CA VBC VCA-ZR'CA VBC /60 Short-circuit or ground of three phases VCA ZR'CA VBC VCA-ZR'CA VBC /60 Operation will be explained below with reference to Table 2.

i) When the phase A is grounded, from Table 2, E0p= VA - ZRIA EpoL=VC /600 Fig. 13 is a vector diagram of these outputs. In this case, the signal EFoL which serves as reference vector has a phase opposite to the voltage signal VA for operation vector. Like that of the conventional device, therefore, the range of internal defect is described by a circle with the vector ZRIA as a diameter as shown in Fig. 3.

ii) When the three phases are short-circuited, from Table 2, EOP = VCA ZRICA EPOL=VBC /600 In this case, the relation of vectors is as shown in Fig. 4. As mentioned above, therefore, the vector of signal EPOL has a phase opposite to the vector VCA. Consequently, the range of internal defect is described by a circle with the vector ZPICA as a diameter as shown in Fig. 5.

The signals VF, ZRIP produced by the switching part 7 are fed to the subtraction circuit 3.

Subtraction is effected between these two signals, and the subtraction circuit 3 produces the signal E0p.

Further, the phase shifter 8 shifts the phase of the signal VH by 600, to produce the signal EPOL.

When the phase difference between the signals EPO and EpoL is smaller than, for example, +900, the phase discrimination circuit 6 discriminates it as an internal defect, and produces a signal 6a. The signal 6a breaks a circuit breaker which is not diagrammed to protect the system.

According to the present invention as mentioned above, the angle for shifting the phase by the phase shifter can be fixed to a predetermined value to obtain reference vector. Therefore, the distance relay of the present invention features very simpie construction, cheap manufacturing cost, and increased reliability.

Claims (5)

1. A distance relay comprising: a) detecting means provided for each of the phases of the transmission lines to detect defects for each of the phases of the transmission lines; b) switching means which receives vector signals of currents and voltages detected from each of the phases of the transmission lines, which discriminates the kind of defects based upon the output signals produced by said detecting means, and which produces voltage and current signals for operation vectors and a signal for reference vector depending upon the kind of defects; c) a subtraction circuit which finds a difference between voltage signal and the current signal for operation vectors;; d) a phase shifter which introduces said signal for reference vector, which prepares reference vector from said signal for reference vector for all of the defects in the transmission lines, and which shifts the phase of the output signals all by a predetermined amount; and e) a phase discrimination circuit which so discriminates that the defect has developed within a loop of transmission lines when the phase difference between the output signal of the subtraction circuit and the output signal of the phase shifter is smaller than a predetermined value, and which produces an output signal to protect the transmission lines.

2. A distance relay according to claim 1 , wherein the angle for shifting the phase is set to be constant by selecting a time constant of a time-constant circuit which constitutes the phase shifter.

3. A distance relay according to claim 2, wherein said time-constant circuit consists of a capacitor and a resistor element.

4. A distance relay according to claim 1, wherein an operation amplifier which constitutes the output stage of said phase discrimination circuit has hysteresis characteristics.

5. A distance relay substantially as described herein with reference to or as illustrated in Figs. 6 to 1 3 of the accompanying drawings.