JP3074695B2 - Circulating zero-phase current suppression circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circulating zero-phase current suppression circuit in a bypass circuit of a switch or a circuit breaker having a ground fault trip function.

B. Summary of the Invention The present invention relates to a circulating zero-phase current suppression circuit in a bypass circuit of a switch or a circuit breaker with a ground fault trip function, and a ground fault trip function provided on a service circuit side including an AC three-phase three-wire circuit. When a bypass circuit is formed with a switch or circuit breaker interposed therebetween, a zero-phase suppression impedance component that suppresses a circulating zero-phase current flowing in a circulation circuit formed by the service circuit and the bypass circuit is provided in the bypass circuit. The switch or circuit breaker with the ground fault trip function due to the circulating zero-phase current is not operated unnecessarily.

C. Prior Art For example, when power is supplied to a group of uninterruptible loads in a three-phase three-wire high-voltage distribution line, the power supply side of the high-voltage distribution line may need to be stopped for construction or the like. In such a case, as shown in FIG. 2, for example, an uninterruptible transmission type mobile power supply vehicle 11 (a portion surrounded by a dashed line in FIG. 2) sandwiching a load switch interposed between the high-voltage distribution line and the load. ) Is connected to the high-voltage distribution line 12 in a live state, and a bypass circuit 13 (portion surrounded by a dotted line) is provided. In order to live connect the mobile power supply vehicle 11 to the high voltage distribution line 12, as shown in FIG. 2, the power cable 14 attached to the mobile power supply vehicle 11 is normally connected to the power switch 15 of the high voltage distribution line 12 by the power supply. And the load cable 16 is connected to the load side of the load switch 15 at the live connection parts 17 and 18 in phase. In the figure, 19 is a three-phase AC synchronous generator, 20 is a prime mover, 52C is a bypass circuit breaker, and 52G is a generator circuit breaker. Next, the operation of FIG. 2 will be described. After connecting the power cable 14 and the load cable 16 as shown in FIG.
The bypass circuit breaker 52C of the mobile power supply vehicle 11 is turned on to form the bypass circuit 13. After the bypass circuit 13 is formed, the load switch 15 is opened, and all the uninterruptible load groups are bypassed.
Power will be supplied via 13. By measuring these quantities in the bypass circuit 13, it is also possible to switch to a generator and check whether power transmission is possible. After confirmation,
The three-phase AC synchronous generator 19 is operated, and the generator-side circuit breaker 52G is synchronized with the bypass circuit 13. Then generator 1
After the load is shifted to the ninth side, the bypass circuit breaker 52C is opened. As a result, all the uninterruptible load groups are supplied with power from the generator 19 via the generator-side circuit breaker 52G. As a result, the utility power supply side can perform power outage work, and the uninterruptible load group side is supplied with uninterruptible power by the generator 19. When the power outage on the main power supply is completed, the power on the main power supply is restored. After the power is restored, the bypass circuit breaker 52C is synchronously turned on with respect to the generator 19 during the load operation. After being turned on, the generator load is transferred to the bypass circuit 13, the generator-side circuit breaker 52G is opened, and the operation of the generator 19 is stopped. Next, the load switch 15 is turned on, and after that, the bypass circuit breaker 52C is opened, and then the power cable 14 and the load cable 16 are disconnected from the distribution line 12, thereby completing a series of operations.

D. Problems to be Solved by the Invention In the configuration shown in FIG. 2 described above, the load switch 15 is, for example, a high-pressure air load switch (hereinafter referred to as GR) with an overcurrent lock type ground fault trip as shown in FIG. When the PAS 30 is used, the following problems occur. The PAS30 with GR automatically opened the circuit when a ground fault occurred, and when a ground fault or overcurrent accident occurred simultaneously or when an overcurrent accident occurred, the circuit breaker of the power company distribution substation was activated, and the voltage became zero. The PAS30 with GR automatically opens under the condition
Control box 31 for ground fault relay and overcurrent lock charging control
Is what comes with. In FIG. 3, the ground fault relay in the control box 31 is connected to the ZCT, 32 and 33 are hot-line connectors, 34 and 35 are disconnectors, 36 is an instrument transformer PT, and 37 is an instrument transformer. It is a flower CT.

The bypass circuit 13 configured as shown in FIG.
0 is connected, and when the bypass circuit breaker 52C is turned on,
R-phase current _R = _{R ′} + _{R ″} , S-phase current _S =
_{S ′} + _{S ″} and the T-phase current _T = _{T ′} + _{T ″} are shunted as shown. Here, in the case of the three-phase three-wire system, if a ground fault has not occurred, 1/3 × ( _R + _S + _T ) = 0, that is, the zero-phase current is not included in the power-supply-side and load-side currents. Paying attention to each phase shunt circuit generated by the bypass circuit 13, the hot wire connection part on the distribution line side, the hot wire connectors 32 and 33, the disconnectors 34 and 35 on the bypass circuit 13 side, the circuit breaker 52C, the switch 30 _{R '} and _{R "} , _S' are different due to the difference of each phase and each branch impedance based on the difference of contact resistance and various CT drops, and the difference of each wiring drop and connection condition.
The share ratio between _{S ″} , _{T ′} and _{T ″} is generally different, Circulating zero-phase current will flow. Since this circulating zero-phase current flows through the PAS 30 with GR, the ZCT inside 30 detects this circulating zero-phase current (3 × _{O 2} ), and the grounding relay of the control box 31 operates unnecessarily. There is a risk of tripping. Also, when power is supplied to the load side via the bypass circuit 13 and the PAS 30 with GR is turned on, the ZCT inside 30 detects the circulating zero-phase current and detects the ground fault as described above. If the relay operates unnecessarily, the PAS 30 with GR trips, making it impossible to switch uninterrupted power.

Therefore, conventionally, when forming or disconnecting the bypass circuit 13 across the PAS 30 with the GR as a service circuit, in order to avoid unnecessary operation of the ground fault relay due to the above-mentioned circulating zero-phase current, for example, the bypass with the PA with the GR 30 is bypassed. During the period in which the circuit 13 is simultaneously formed, it is necessary to take measures such as opening the control power supply of the control box 31 to prevent the ground fault relay from operating. However, despite the fact that the mobile power supply vehicle 11 shown in FIG. 2 is a property of the ordinary power company and is a work for repairing the distribution line on the power company side, the PAS 30 with GR is located on the premises of the private customer. It is often provided on the first pillar. In this case GR
Since the attached PAS30 is the property of the consumer (or the range of the contribution), the operation of the ground fault operation lock etc. of the GR-attached PAS30 requires the permission of the private consumer, and it takes time and trouble to communicate and adjust the situation. In such a case, there were inconveniences such as not being able to contact in time.

E. Means for Solving the Problems The present invention relates to a switch or circuit breaker with a ground fault trip provided on the side of an AC three-phase three-wire service circuit (for example, a high-voltage load switch with GR or a ground fault circuit breaker). Connect the bypass circuit of the mobile power supply vehicle with the current transformer for the meter for detecting the quantity of electricity with the
In a configuration in which an electric circuit is switched from the service circuit side to the bypass circuit side or from the bypass circuit side to the service circuit side without interruption, a current transformer for an instrument provided in each phase of the electric circuit on the bypass circuit side In this example, a non-linear resistance element is provided between the secondary side neutral point residual circuit cl and a ground wire is provided between the common side c of the residual circuit and the ground.

F. Action A current transformer for the instrument is provided in each phase of the bypass circuit side electric circuit, and a zero-phase current suppression impedance is formed by connecting a non-linear resistance element to the secondary neutral point residual circuit of the current transformer,
This suppresses the circulating zero-phase current. By this suppression action, at the time of uninterrupted switching from the service circuit side to the bypass circuit side or from the bypass circuit to the service circuit side, unnecessary operation of the switch or circuit breaker with ground fault trip is prevented by the circulating zero-phase current.

G. Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In FIG. 2, the same parts as those in FIGS. 2 and 3 are designated by the same reference numerals.

In FIG. 1, the secondary-side neutral point residual circuit (C−C) of an instrument current transformer 37 provided in each of three phases of the electric circuit of the bypass circuit 13 is provided.
1) The non-linear resistance element 2 is connected. Current transformer for instrument
37 can also be used as a normal measurement circuit, but the measurement circuit is omitted for convenience of explanation. Here, PAS30 with GR (for example, high-voltage load switchgear or earth leakage breaker with GR), bypass circuit breaker 52
C is also closed, that is, bypass circuit breaker with PAS30 with GR interposed
Consider a state in which a closed loop is formed at 52C. In this case, when the service power supply side is a high-voltage distribution system, three-phase three-phase
Because of the wire system, regardless of load side balance or unbalance, each phase current is composed of only positive phase component and reverse phase component unless there is a ground fault in the electric circuit. When the current is divided, a zero-phase current circulating in the closed loop is generated due to the impedance imbalance of each phase and each branch constituting the closed loop as described above. In this case, FIG. 4 shows the relationship between the positive-phase, negative-phase, and zero-phase currents flowing through the primary and secondary phases of the current transformer 37 for the instrument shown in FIG. FIG. 4 shows the current transformer 37
In order to describe the effect of the non-linear resistance element 2 connected to the secondary-side neutral point residual circuit, a switch 2 for explanation is added in parallel with the non-linear resistance element 2. Current transformer for convenience of explanation
The current transformer ratio of 37 is assumed to be 1: 1. Now, in FIG. 4, when the switch 3 is closed, that is, when the secondary side of the normal current transformer is connected, the currents in the positive phase of each phase are _{R1 '} , _S1' , _{T1 '} ,
_{R2 '} , _S2' , _{T2 '
If O ′} , the sum of the three-phase currents of the positive phase component and the negative phase component becomes zero, so the neutral point residual circuit (C
-1), which is irrelevant to the opening and closing of the switch 3.
On the other hand, the zero-phase component flows through the neutral point residual circuit as 3 × _{O ′ when the} switch 3 is closed, but when the switch 3 is opened, the circulating zero-phase current component is greatly limited by the non-linear resistance element 2 and almost limited. It will be negligible.

In order to explain the effect of this nonlinear resistance element 2,
5 (a) and 5 (b) show equivalent circuits focusing only on the zero-phase components in the closed loop. FIG. 5A shows the case where the switch 3 is closed, and FIG. 5B shows the case where the switch 3 is open. 5 (a) and 5 (b), _O is a zero-phase electromotive force generated in a closed loop, and
_Assuming that _a , _b , and _c are the closed-loop phase impedances ignoring the influence of the current transformer 37, the equivalent zero-phase impedance is _O = 1/3 x ( _a + _b + _c ).

In FIG. 5 (a), the secondary side of the current transformer for the instrument is short-circuited even with respect to the zero-phase current. Does not contribute as equivalent zero-sequence impedance in the closed loop A zero-phase current flows. In FIG. 5 (b), since the non-linear resistance element 2 is inserted into the neutral point residual circuit of the current transformer for instrument 37, the zero-phase current on the secondary side of the current transformer is _{O ″.}
( _{O ″} ≪O _′ ), which is almost negligible, but the positive-phase component and the negative-phase component can flow irrespective of the neutral point residual circuit. And this acts as an equivalent zero-sequence impedance, not as positive and negative-sequence impedances (however,
When the load imposed by the instrument connected to the secondary side of the current transformer is ignored). Therefore, in the case of FIG. 5 (b), since the equivalent zero-phase impedance in the closed loop is larger than _O , the zero-phase current _O on the primary side of the current transformer is much larger than _{O ′ in} FIG. 5 (a). Decrease. ｛In the case of Fig. 5 (b), the current transformer ratio is 1:
Even if the primary and secondary zero-phase currents of the current transformer are _{O Ｏ
O "} . Most of the primary zero-sequence current _O is the excitation input corresponding to the neutral point residual voltage (voltage between C and I) on the secondary side of the current transformer. Since the linear resistance element is used, _{O "} is very small, so that the primary current for canceling the AT due to the CT secondary current is usually almost negligible. In contrast to the circulating zero-phase circuit of FIG. Since the current transformer circuit has a large effect as an equivalent zero-sequence impedance, the effect of suppressing the circulating zero-sequence current is remarkable. On the other hand, in FIG. 1, a countermeasure will be described below on the assumption that the entire one-phase circuit of the three-phase circuit is bypassed due to some abnormality such as poor connection. As an example of this case, FIG. 6 shows a case in which an R-only bypass circuit is formed. Since this case current _R flows in only the primary side R-phase CT, commercial power side to the primary side of the CT connected non-linear resistance element 2 on the secondary side R
This means that the phase current _R is flowing. Therefore, if the non-linear resistance element 2 is not connected, it means that the primary current has flowed in the so-called CT secondary side open, and there is a possibility that abnormalities such as CT secondary side insulation breakdown may occur due to the CT secondary open abnormal voltage. In this case as well, if the non-linear resistance element 2 is connected to the neutral point residual circuit of the CT 37, the above-mentioned abnormal CT secondary abnormal voltage can be limited to be lower than the CT secondary breakdown voltage. Also, as shown in FIG. 6, when measuring instruments 4 such as ammeters are provided in each branch of the CT secondary side in the CT secondary circuit, the CT secondary abnormal voltage is applied to these measuring instruments between the ground. By providing the grounding line 5 at the point C of the neutral point residual circuit so that the CT37 is not performed, the CT 37 can also be used for a measurement circuit.

When the CT37 is also used for the measurement circuit, when the current is measured in each phase on the CT secondary side while the circulating circuit is formed, the actual primary current differs from the zero-phase component (the current ratio is
(Assuming 1: 1), but the circulating zero-phase current is usually negligibly small compared to the main circuit current, and the purpose of this measurement circuit is to measure each phase current on the bypass side during the formation of the circulation circuit Rather, the main purpose is to measure each phase current during single power transmission from the bypass side to the uninterruptible load group, so there is no problem in normal use.

This invention is applicable not only to PAS with GR, but also to all other switches with ground fault trip, bypass circuit with circuit breaker,
The present invention is applicable not only to a circulating zero-phase current suppression circuit in a circuit circuit, but also to a circuit voltage other than a high voltage, and is applicable regardless of the circuit voltage.

H. Effects of the Invention As described above, according to the present invention, when a bypass circuit is formed across a load switch with a ground fault trip, or from the bypass circuit to the load switch with a ground fault trip without interruption. When switching circuits, unnecessary operation of the load switch with a ground fault trip due to the circulating zero-phase current can be suppressed. Further, since the present invention can suppress as described above, an operation such as control power lock of the load switch with a ground fault trip is not required.

Further, there is an advantage that it is not necessary to check in advance whether a load switch that needs to constitute a bypass circuit has a ground fault trip or a load switch without a ground fault trip mechanism when constructing a high-voltage distribution line.

Furthermore, in the present invention, the zero-sequence impedance can be easily determined according to the value of the circulating zero-sequence current. In ZCT, the primary side is a through conductor, so the zero-phase impedance has to increase the cross-sectional area of the iron core. This makes the ZCT a very large special product. In contrast, in the present invention using 3CT, the impedance is (CT primary winding number) ² × (Cross-sectional area of iron core)
Because it is proportional to, the number of turns on the primary side of the CT and the iron core can be freely determined. In addition, the number of primary windings is 3 even with a general-purpose CT.
Since there are ~ 5 volumes, the required zero-phase impedance can be obtained with a general-purpose CT. In ZCT, the number of primary windings is 1, so
Core cross-sectional area is 3 ^{2-5 2} times the generic CT, that is, require special ZCT must be more than 10 times. Therefore,
The present invention can be used not only as a bypass circuit for a load switch with a ground fault trip according to the present invention, but also as a countermeasure against zero-phase circulating current in a parallel two-circuit distribution line.

Further, in the case where a linear impedance such as a resistor is used in place of the non-linear resistance element 2 in the neutral point residual circuit of the CT 37 in the circuit of the present invention, for example, even when only one line of the bypass circuit constitutes the bypass circuit, an abnormality occurs. Since it is necessary to determine the impedance so that the CT secondary voltage does not become an abnormal voltage, the normal target circulating zero-phase current also flows more easily than when a non-linear resistance element is used. The circulating zero-sequence impedance becomes smaller. Further, according to the present invention, since the non-linear resistance element is connected to the secondary neutral point residual circuit of the current transformer for the instrument and the ground wire is provided, the abnormal voltage is not applied to the instrument. Can be protected.

In addition, because of the circuit configuration, the current transformer can also be used for the measurement circuit, so that, for example, ZCT and other main circuit devices do not need to be specially prepared.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a conventional example, FIG. 3 is a circuit diagram illustrating a problem to be solved by the invention, and FIG. 5 (a) and 5 (b) are equivalent circuit diagrams focusing only on the zero-phase component in a closed loop for explaining the current-limiting effect due to the zero-phase suppression impedance, FIG. 6 is a circuit diagram showing another embodiment of the present invention. 2 ... Non-linear resistance element, 4 ... Measuring instruments, 5 ... Ground line, 11 ... Uninterruptible power transmission type high-voltage mobile power supply vehicle, 13 ... Bypass circuit, 30 ... PAS with GR, 31 ... Control Box, 37 ... Instrument current transformer.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02J 9/00-11/00 H02J 3/00-5/00

Claims (1)

(57) [Claims] 1. A method for detecting a quantity of electricity across a switch or circuit breaker with a ground fault trip (for example, a high-voltage load switch with GR or earth leakage breaker) provided on the side of an AC three-phase three-wire service circuit. In a configuration in which a bypass circuit of a mobile power supply vehicle having a current transformer for an instrument is connected and an electric circuit is switched from the service circuit side to the bypass circuit side or from the bypass circuit side to the service circuit side without interruption, A non-linear resistance element is provided between the neutral point residual circuit c-1 of the secondary side of the current transformer for the instrument provided in each phase of the electric circuit on the bypass circuit side, and the common side c of this residual circuit is connected to the ground. A circulating zero-phase current suppression circuit, wherein a ground wire is provided between the circuits.