JP2006262556A - Power system stabilizer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power system stabilizer that prevents misoperations of ground fault protection relays. <P>SOLUTION: There is arranged in the power system stabilizer a Y-connected SVR 11 (step-type voltage regulator), that performs voltage adjustment in a high-voltage distribution line (6 kV, for example) that is large in ground capacitance and long in route length. All of taps of windings of three phases (A phase, B phase and C phase) are switched in the Y-connected SVR 11. In other words, voltage adjustment is performed, by boosting or stepping down all the voltages of the three phases. In this case, the neutral point of a voltage vector is not moved. According to this, residual voltage, generated at the high-voltage distribution line at the voltage adjustment, is suppressed as compared with those of a prior art that have used a V-connected SVR, and accordingly, misoperations of the ground fault protection relay are prevented. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a power system stabilizing device, and more particularly, to a power system stabilizing device that performs voltage adjustment and ground fault protection of a high-voltage distribution line.

  FIG. 6 is a diagram illustrating a configuration of a main part of a conventional power system stabilizing device. Referring to FIG. 6, the power system stabilizing device includes an SVR (step type automatic voltage regulator) 31, a residual voltage detector 222, a ground fault protection relay 23, and a cutoff unit 24.

  The SVR 31 is provided in a high-voltage distribution line with a large voltage drop, and adjusts the distribution line voltage by automatically switching the tap of the internal transformer. Usually, a V-connection SVR is used for a high-voltage distribution line (for example, 6 KV) system. In the V-connection SVR, the winding taps of two phases (for example, A phase, C phase) of three phases (A phase, B phase, C phase) are switched. As a result, the two-phase phase voltage is boosted or lowered to perform voltage adjustment.

  The residual voltage detector 22 receives a three-phase (A phase, B phase, C phase) voltage from the high-voltage distribution line and detects a residual voltage (zero phase voltage). This residual voltage occurs when a ground fault occurs in which a current flows between the high-voltage distribution line and the ground due to insulation deterioration or insulation failure. The ground fault protection relay 23 outputs a control signal for controlling the operation of the interruption unit 24 based on the detected level of the residual voltage. The interruption unit 24 includes a plurality of circuit breakers CB corresponding to the distribution lines of each phase, and interrupts the distribution line system in response to a control signal from the ground fault protection relay 23. This prevents the expansion of the power outage range and public disasters when a ground fault occurs.

  FIG. 7 is a diagram showing voltage vectors of each phase of the SVR 31 of the V connection shown in FIG. FIG. 7 shows vector trajectories when the phase voltages Ea and Ec of the A phase and the C phase are boosted. Here, when the phase voltages Ea, Eb, and Ec before boosting are three-phase balanced, the voltage vector Eo ↑ (where arrow ↑ indicates a vector) at the neutral point before boosting is expressed by the following formula (1 ).

Eo ↑ = (Ea ↑ + Eb ↑ + Ec ↑) / 3 = 0 ↑ (1)
Further, assuming that the transformation ratio of SVR 31 is n, the voltage vectors of phase voltages Eaa, Ebb, Ecc after boosting are respectively expressed by the following formulas (2) to (4).

Eaa ↑ = Ea ↑ + n (Ea ↑ −Eb ↑) (2)
Ebb ↑ = Eb ↑ (3)
Ecc ↑ = Eb ↑ + n (Ec ↑ −Eb ↑) (4)
Therefore, the voltage vector Eoo ↑ at the neutral point after boosting is expressed by the following formula (5).

Eoo ↑ = (Eaa ↑ + Ebb ↑ + Ecc ↑) / 3
= {(0 ↑) + n (Ea ↑ + Ec ↑ -2Eb ↑)} / 3
= {(0 ↑) + n (0 ↑ -3Eb ↑)} / 3
= -NEb ↑ (5)
From this, it can be seen that the neutral point after boosting is shifted in the negative direction of the B-phase voltage vector Eb ↑. As described above, in the V-connection SVR, the neutral point moves during voltage adjustment by tap switching, and the three-phase voltage becomes unbalanced, so that a residual voltage is generated.

  Therefore, when the SVR 31 of V connection is provided in the high-voltage distribution line, there is a problem that the ground fault protection relay 23 malfunctions due to the influence of the residual voltage generated when adjusting the voltage by the SVR 31. If the interruption | blocking part 24 performs interruption | blocking operation | movement by malfunctioning the ground fault protection relay 23, it will cause a power failure unnecessarily.

  The greater the number of SVRs 31 installed in the distribution line, the higher the residual voltage generated during voltage adjustment, and thus the greater the risk that the ground fault protection relay 23 will malfunction. In addition, a distribution line having a long cable length (distribution line with many underground lines) has a large capacitance to ground, and the larger the ground capacitance, the higher the residual voltage generated during voltage adjustment by the SVR 31.

  Here, when the ground capacitance on the power source side of the SVR 31 is C1 and the ground capacitance on the load side is C2, the residual voltage V generated by the SVR 31 is simply expressed by the following formula (6).

V = (nEb × C2) / (C1 + C2) (6)
Therefore, it can be seen that the generated residual voltage V increases as the load side ground capacitance C2 increases.

  On the other hand, the ground fault protection relay 23 operates when the residual voltage is equal to or higher than the set value. However, in the distribution line having a large ground capacitance, the set value is set to a small value because the residual voltage generated at the time of the ground fault is low. The That is, there is a high possibility that the ground fault protection relay 23 malfunctions in response to the residual voltage generated during voltage adjustment by SVR. Therefore, there is a high possibility that the ground fault protection relay 23 malfunctions in a distribution line having a large number of installed SVRs 31 and a large ground capacitance.

Patent Document 1 below discloses a distribution line ground fault current amplifying device that can prevent a ground fault protection relay from malfunctioning due to a residual current generated when a distribution line is loop-connected.
JP 2003-134659 A

  As described above, in the distribution line in which the V-connection SVR 31 is installed, when the ground capacitance is large, the ground fault protection relay 23 malfunctions due to the influence of the residual voltage appearing on the distribution line during voltage adjustment by the SVR 31. The possibility was high.

  Therefore, a main object of the present invention is to provide a power system stabilizing device that prevents malfunction of a ground fault protection relay.

  A power system stabilization device according to the present invention is a power system stabilization device that performs voltage adjustment and ground fault protection for a long high voltage distribution line having a large ground capacitance, and is provided at a predetermined position of the high voltage distribution line. An automatic voltage regulator that adjusts the voltage of the high-voltage distribution line, a switch that is inserted in the high-voltage distribution line and protects the power system from a ground fault, and a high-voltage distribution line. And a ground fault protection control means for detecting a generated residual voltage and controlling the switch to be cut off in response to detection of a predetermined level of the residual voltage.

  The power system stabilizing device according to the present invention includes a Y-connected three-phase transformer provided at a predetermined position of the high-voltage distribution line, an automatic voltage regulator for adjusting the voltage of the high-voltage distribution line, and a high-voltage distribution line. A switch that protects the power system from a ground fault and a ground fault that detects residual voltage generated in the high-voltage distribution line and shuts off the switch when a predetermined level of residual voltage is detected. Protection control means. Therefore, no residual voltage is generated in the high-voltage distribution line during voltage adjustment by the automatic voltage regulator. For this reason, it is prevented that a ground fault protection control means malfunctions.

  FIG. 1 is a block diagram showing a part of an interconnection system of a small hydroelectric power plant according to an embodiment of the present invention. In FIG. 1, the power plant 1 includes a generator (G) 21 having a power supply capacity of 2900 kW, a residual voltage detector 22, a ground fault protection relay 23, and a cutoff unit 24. The power plant 2 includes a generator 25 having a power capacity of 7400 kW, a residual voltage detector 26, a ground fault protection relay 27, and a cutoff unit 28. The substation 3 is connected to the power plant 2 and other distribution line systems, and performs adjustment of the connected distribution line voltage, system switching, power flow control, accident handling, and the like.

  The power plants 1 and 2 are connected by a high-voltage distribution line (for example, 6 kV) having a long length (for example, 25 km). The high-voltage distribution line includes a long underground line (for example, 13 km). The high-voltage distribution line between the power plants 1 and 2 is provided with a plurality of (for example, six) Y-connected SVRs 11 for voltage adjustment. The SVR 11 is attached in the middle of a high-voltage distribution line having a large voltage drop, and adjusts the distribution line voltage by automatically switching the taps of the internal transformer.

  The residual voltage detector 22 detects the residual voltage from the high voltage distribution line of the power plant 1. The ground fault protection relay 23 outputs a control signal for controlling the operation of the interruption unit 24 based on the detected level of the residual voltage. The interruption | blocking part 24 interrupts | blocks a distribution line system in response to the control signal from the ground fault protection relay 23. FIG. The residual voltage detector 26 detects a residual voltage from the high voltage distribution line of the power plant 2. The ground fault protection relay 27 outputs a control signal for controlling the operation of the blocking unit 28 based on the detected level of the residual voltage. In response to the control signal from the ground fault protection relay 27, the interrupting unit 28 interrupts the distribution line system. This prevents the expansion of the power outage range and public disasters when a ground fault occurs.

  If the V-connection SVR 31 shown in FIG. 6 is provided in the high-voltage distribution line between the power plants 1 and 2 instead of the Y-connection SVR 11, a residual voltage is generated during voltage adjustment by tap switching. Since the number of SVRs installed on the high-voltage distribution line is as large as six, the residual voltage generated during voltage adjustment is high. In addition, this high-voltage distribution line has a long span and a long underground line, so that the ground capacitance is large. For this reason, the residual voltage generated at the time of voltage adjustment by the SVR 31 becomes very high. Furthermore, since the ground capacitance is large, the settling value of the ground fault protection relay is set to a small value. Therefore, when the conventional V-connection SVR 31 is provided on the high-voltage distribution line, the ground fault protection relays 23 and 27 are likely to malfunction.

  FIG. 2 is a diagram illustrating a calculation result of a residual voltage generated in the vicinity of the power plant 1 when a conventional V-connection SVR 31 is provided in the distribution line. Referring to FIG. 2, this data shows the result of prediction of residual voltage using EMTP (Electro Magnetic Transients Program) assuming various load forms and generator output power level patterns.

  A region inside the triangle surrounded by a dotted line is a region where the ground fault protection relay 23 does not malfunction. A region outside the triangle surrounded by a dotted line is an A-phase operation region where the ground fault protection relay 23 malfunctions according to a residual voltage generated in the A-phase voltage vector direction, and a residual voltage generated in the B-phase voltage vector direction. Accordingly, the ground fault protection relay 23 malfunctions, and the B phase operation area malfunctions in response to the residual voltage generated in the direction of the C phase voltage vector. In this case, it is predicted that a maximum residual voltage of about 3.7 V is generated in the A-phase operation region (the portion surrounded by a round line), so that the ground fault protection relay 23 provided near the power plant 1 malfunctions. There is a fear. The reason why a large amount of residual voltage is generated in the A-phase operation region is considered to be that a residual voltage is generated in the A-phase operation region by the SVR 31 closest to the power plant 1.

  FIG. 3 is a diagram showing a calculation result of a residual voltage generated in the vicinity of the power plant 2 when a conventional V-connection SVR 31 is provided on the distribution line. Referring to FIG. 3, this data shows the result of prediction of residual voltage using EMTP in the same manner as in FIG. 2, assuming various load forms and generator output power level patterns. In this case, it is predicted that a maximum residual voltage of about 2.7 V is generated in both the B-phase operation region and the C-phase operation region (the portion surrounded by a round line). There is a possibility that the ground fault protection relay 27 may malfunction. The reason why a large amount of residual voltage is generated in both the B-phase operation region and the C-phase operation region is that the SVR 31 closest to the power plant 3 generates a residual voltage in the B-phase operation region and is the second closest to the power plant 3. This is probably because a residual voltage is generated in the C-phase operation region by SVR31. In addition, referring to FIGS. 2 and 3, the generated residual voltage is different because the ground capacitance on the power source side and the ground capacitance on the load side are different between power plant 1 and power plant 2. Conceivable.

  Therefore, in this embodiment, instead of the conventional V-connection SVR 31, the Y-connection SVR 11 is used. In other words, six Y-connected SVRs 11 are installed on the high-voltage distribution line between the power plants 1 and 2 shown in FIG.

  FIG. 4 is a diagram showing a configuration of a main part of the power system stabilizing device according to one embodiment of the present invention, and is compared with FIG. Referring to the power system stabilizing device of FIG. 4, the difference from the power system stabilizing device of FIG. 6 is that the V-connection SVR 31 is replaced with the Y-connection SVR 11. In the Y-connection SVR 11, all the taps of the windings of the three phases (A phase, B phase, C phase) are switched. As a result, all three-phase voltages are boosted or stepped down, and voltage adjustment is performed.

  FIG. 5 is a diagram showing voltage vectors of the respective phases of the SVR 11 of the Y connection shown in FIG. FIG. 5 shows vector trajectories when the phase voltages Ea, Eb, and Ec of the A phase, B phase, and C phase are boosted. In this case, the neutral point of the voltage vector does not move before and after boosting. Thus, since the neutral point does not move, no residual voltage is generated in the high-voltage distribution line.

  As described above, in this embodiment, a Y-connected SVR is used in a high-voltage distribution line with a large number of SVRs installed and a large ground capacitance. For this reason, no residual voltage is generated in the high-voltage distribution line at the time of voltage adjustment by SVR. Therefore, it is possible to prevent the ground fault protection relay from malfunctioning.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a block diagram which shows a part of interconnection system of the small hydropower station by one Embodiment of this invention. It is a figure which shows the calculation result of the residual voltage which generate | occur | produces near the power station 1, when providing SVR of the conventional V connection in a distribution line. It is a figure which shows the calculation result of the residual voltage which generate | occur | produces near the power station 2, when SVR of the conventional V connection is provided in the distribution line. It is a figure which shows the structure of the principal part of the electric power grid stabilization apparatus by one Embodiment of this invention. FIG. 5 is a diagram illustrating a voltage vector of each phase of SVR of Y connection shown in FIG. 4. It is a figure which shows the structure of the principal part of the conventional electric power system stabilization apparatus. It is a figure which shows the voltage vector of each phase of SVR of the V connection shown in FIG.

Explanation of symbols

  1, 2 power plant, 3 substation, 11, 31 SVR, 21, 25 generator, 22, 26 residual voltage detector, 23, 27 ground fault protection relay, 24, 28 breaker.

Claims (1)

A power system stabilizing device that performs voltage regulation and ground fault protection for a long high voltage distribution line with a large capacitance to ground,
An automatic voltage regulator that includes a Y-connected three-phase transformer provided at a predetermined position of the high-voltage distribution line, and performs voltage adjustment of the high-voltage distribution line;
A switch inserted in the high-voltage distribution line to protect the power system from a ground fault, and a residual voltage generated in the high-voltage distribution line is detected, and a predetermined level of residual voltage is detected. An electric power system stabilization device comprising a ground fault protection control means for controlling the cutoff of the switch.

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