JP2011155783A - Ac/dc converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an AC/DC converter which can identify a ground fault spot without using a zero-phase current transformer and a direction ground fault relay. <P>SOLUTION: The AC/DC converter includes a breaker 2 with one end connected to a power system, a breaker 101 with one end connected to the other end of the breaker 2, an interconnecting transformer 102 with the primary side connected to the other end of the breaker 101, a converter 103 with the AC side connected to the secondary side of the interconnecting transformer 102 to convert AC power into DC power, an NAS battery 150 connected to the DC side of the converter 103, an auxiliary transformer 105 with the primary side connected to a common connection point between the breaker 2 and the breaker 101 and the secondary side connected to a heater of the NAS battery 150, and a ground fault protection relay 108 connected to a common connection point between the other end of the beaker 2 and one end of the breaker 101. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a ground fault protection system for an AC / DC converter for a power storage NAS battery.

  A NAS (sodium / sulfur) battery is used for day and night load leveling. In order to operate, this NAS battery needs to be heated to about 300 ° C. using a heater and heat generated during discharge.

  When the NAS battery is connected to an AC system, an AC / DC converter is required to convert it into DC power. The AC / DC converter converts the power of the AC system into direct current so as to charge the NAS battery, and converts the direct current power of the NAS battery into AC and supplies it to the AC system.

  Here, the apparatus structure regarding a NAS battery and an AC / DC converter is demonstrated. First, the on-site equipment connected to the AC / DC converter will be described.

  FIG. 3 is a configuration diagram of the premises equipment connected to the AC / DC converter. One end of a circuit breaker 201 is connected to the system. Circuit breakers 202a to 202n are connected between the other end of the circuit breaker 201 and each of the local loads 205a to 205n. Zero-phase current transformers 203a to 203n are inserted in the respective electric paths connecting the circuit breakers 202a to 202n and the premises loads 205a to 205n.

  In addition, directional ground fault relays (DGR) 204a (not shown) to 204n are connected to the zero-phase current transformers 203a to 203n, respectively. “N” in these codes represents each number.

  In addition, a zero-phase voltage detector including two capacitors connected in series between the other end of the circuit breaker 201 and the ground and a transformer connected in parallel to the ground-side capacitor of the two capacitors ( ZPC) 206 is connected. The output of the zero-phase voltage detector 206 is input to the directional ground fault relays 204a to 204n and the ground fault protection relay (OVGR) 208. The ground fault protection relay 208 operates in both ground faults inside and outside the AC / DC converter 100.

  A circuit breaker 209 is connected between the other end of the circuit breaker 201 and the AC / DC converter 100, and a NAS battery 150 is connected to the AC / DC converter 100.

  Here, the local bus, the internal load feeder and the AC / DC converter feeder described in FIG. 3 are defined.

  The local bus is an electric circuit to which the other end of the circuit breaker 201, the circuit breakers 202a to 202n, the circuit breaker 209, and one end of the zero-phase voltage detector 206 are connected.

  The feeders for on-premises loads are respective electric paths from the on-site bus to the on-site loads 205a to 205n.

  The feeder for the AC / DC converter is an electric circuit from the local bus to the AC / DC converter 100.

  In addition, operation | movement of the circuit breaker 201, the circuit breakers 202a-202n, and the circuit breaker 209 is as follows.

  The circuit breaker 201 is opened when a short circuit or ground fault occurs on the campus bus.

  The circuit breakers 202a to 202n are opened when a short circuit or ground fault occurs in the campus loads 205a to 205n.

  The circuit breaker 209 is opened when a short circuit accident occurs in the feeder line from the circuit breaker 209 to the AC / DC converter 100. The circuit breaker 209 is also opened when a short circuit accident occurs at a site (short circuit of the lead-in conductor) that cannot be removed by the circuit breaker inside the AC / DC converter 100.

  Next, the AC / DC converter 100 and the NAS battery 150 will be described.

  FIG. 4 is an internal configuration diagram of the AC / DC converter 100 and the NAS battery 150. Further, the AC / DC converter 100 and the NAS battery 150 in FIG. 4 are the AC / DC converter 100 and the NAS battery 150 in FIG. 3.

  In the AC / DC converter 100 of FIG. 4, it is assumed that the possibility of a ground fault in the AC / DC converter is low for the following reason.

  That is: 1. The inside of the device is connected by a conductor bus and is sufficiently separated from the ground. This is because the interconnection transformer 102 and the auxiliary transformer 105 in the apparatus employ a molded transformer, so that the probability of occurrence of dielectric breakdown is low.

  For these reasons, the AC / DC converter 100 of FIG. 4 has the following configuration.

  The circuit breaker (52PR) 101 has one end connected to the system and the other end connected to the primary side of the interconnection transformer 102. The secondary side of the interconnection transformer 102 is connected to the AC side of the converter 103, and the DC side of the converter 103 is connected to the battery of the battery unit 151 of the NAS battery 150.

  The converter 103 performs power conversion using a semiconductor switching element such as an IGBT.

  The load switch (89H) 104 has one end connected to a common connection point between the system side and the circuit breaker 101, and the other end connected to the primary side of the auxiliary transformer 105. The secondary side of the auxiliary transformer 105 is connected to the heater of the battery unit 151 of the NAS battery 150. Also, two capacitors connected in series between the common connection point of one end of the circuit breaker 101 and one end of the load switch 104 and the ground, and a transformer connected in parallel to the ground-side capacitor of the two capacitors. Are connected to a zero-phase voltage detector 106. A ground fault protection relay 108 is connected to the zero phase voltage detector 106.

  As described above, the AC / DC converter shown in FIG. 4 is not provided with a protective device for preventing an internal ground fault because the possibility of a ground fault inside the AC / DC converter described above is low. Note that the ground fault protection relay 108 in FIG. 4 is intended for a ground fault on the system side higher than the power receiving section.

  However, the possibility of a ground fault inside the AC / DC converter is not zero. If a ground fault occurs in the auxiliary transformer 105, the AC / DC converter 100 cannot remove the ground fault.

  In this case, as shown in FIG. 3, since the circuit breaker 201 is interrupted by the ground fault protection relay 208 connected to the zero-phase voltage detector 206, the on-site loads 205a to 205n are all cut off. Depending on sex, it may not be allowed.

  In order to prevent this, the circuit breaker 209 may be interrupted by the ground fault protection relay 108 connected to the zero phase voltage detector 106. However, the zero phase voltage detector 106 can be used in the event of a ground fault outside the AC / DC converter. Since it operates, the possibility of unnecessary operation is high.

  Auxiliary transformer 105 supplies heater power to NAS battery 150, but NAS battery 150 may be broken unless it is constantly maintained at 300 ° C. by the heater. is there. Therefore, opening operation of the circuit breaker 209 is not preferable. For this reason, since it is necessary to distinguish whether a ground fault has occurred either inside or outside the AC / DC converter 100, it is necessary to deal with an internal ground fault.

  FIG. 5 shows an apparatus configuration for dealing with the internal ground fault. The same components as those in FIG. 4 are denoted by the same reference numerals, and description thereof is omitted. 4 differs from FIG. 4 in that the load switch 104 is a circuit breaker (52H) 109 that can be opened in sequence. In addition, a zero-phase current transformer 110b is provided on the electric circuit connecting the circuit breaker 101 and the interconnection transformer 102 and connected to the direction ground fault relay 111b, and the circuit breaker 109 and the auxiliary transformer FIG. 5 is also different from FIG. 4 in that a zero-phase current transformer 110a is provided on the electrical path connecting to 105 and connected to the directional ground fault relay 111a.

  The AC / DC converter 120 of FIG. 5 is disposed at the location of the AC / DC converter 100 of FIG.

  In this way, there are those that specify the ground fault location using the direction ground fault relay, but instead of using the direction ground fault relay, a plurality of circuit breakers are provided between the system and the load, and each circuit breaker is provided. Patent Document 1 discloses that a ground fault location can be specified by switching between ON and OFF.

JP 2004-180468 A.

  In order to cope with the ground fault accident inside the AC / DC converter with the device configuration as shown in FIG. 5, the following measures are required and the cost increases.

  In other words, in order to prevent unnecessary disconnection of the auxiliary transformer 105, a ground fault in the AC / DC converter occurred on the interconnecting transformer 102 side or occurred on the auxiliary transformer 105 side. The addition of the zero-phase current transformers 110a and 110b and the directional ground fault relays 111a and 111b to determine whether two circuits (interconnection transformer side + auxiliary transformer side) are required. The other is that the load switch 104 needs to be electrically operated or changed from the load switch 104 to the circuit breaker 109 in order to make the switch that can be tripped and opened in the event of a ground fault.

  However, if the ground fault location can be specified by switching the circuit breaker as in Patent Document 1, it is considered that the facility can be simplified and the cost can be reduced.

  This invention is made | formed based on the said subject, and is providing the AC / DC converter which can pinpoint a ground fault location, without using a zero phase current transformer and a direction ground fault relay.

  In order to solve the above problems, the present invention provides a first circuit breaker having one end connected to the power system, a second circuit breaker having one end connected to the other end of the first circuit breaker, A first transformer whose primary side is connected to the other end of the second circuit breaker, and an AC / DC that has an AC side connected to the secondary side of the first transformer and converts AC power into DC power A primary side is connected to a common connection point of the conversion means, the NAS battery connected to the DC side of the AC / DC conversion means, and the first circuit breaker and the second circuit breaker, and the heater of the NAS battery A second transformer connected to the secondary side, a ground fault protection relay connected to a common connection point between the other end of the first circuit breaker and one end of the second circuit breaker, and the ground fault Control means for controlling the first circuit breaker and the second circuit breaker based on a signal from a protective relay. The features.

  According to the above configuration, by arranging the first circuit breaker, the second circuit breaker, and the ground fault protection relay as described above, the AC / DC conversion can be performed without using the zero-phase current transformer and the directional ground fault relay. It is possible to respond to a ground fault occurring inside the device.

  In addition, when the ground fault protection relay operates, the control means opens the first circuit breaker and the second circuit breaker, and then reopens the first circuit breaker, and the ground fault It is characterized in that it is determined whether or not the protective relay has been reactivated.

  According to the above configuration, a ground fault accident occurs, the ground fault protection relay operates, the first circuit breaker and the second circuit breaker are opened, the ground fault protection relay returns, and only the first circuit breaker When the ground fault protection relay is restarted after the power is turned on again, it is determined that a ground fault has occurred in the second transformer. On the other hand, when the ground fault protection relay is restarted after the first circuit breaker is turned on again and the second circuit breaker is turned on again, it is determined that a ground fault has occurred in the first transformer. If the determination is made in this way, it is not necessary to consider the direction of the ground fault, so that the location of the ground fault can be specified without using the zero-phase current transformer and the direction ground fault relay, and the cost can be reduced.

  In addition, when a ground fault occurs in the first transformer, the first circuit breaker is turned on again, so that power is continuously supplied to the heater of the NAS battery.

  According to the invention of claim 1, by using the first circuit breaker, the second circuit breaker, and the ground fault protection relay as described above, the zero phase current transformer and the direction ground fault relay are used. Therefore, it is possible to cope with a ground fault occurring inside the AC / DC converter.

  According to the invention of claim 2, the ground fault accident occurs, the ground fault protection relay operates, the first circuit breaker and the second circuit breaker are opened, the ground fault protection relay returns, If the ground fault protection relay is restarted after reconnecting only the circuit breaker, it is determined that a ground fault has occurred in the second transformer. On the other hand, when the ground fault protection relay is restarted after the first circuit breaker is turned on again and the second circuit breaker is turned on again, it is determined that a ground fault has occurred in the first transformer. If the determination is made in this way, it is not necessary to consider the direction of the ground fault, so that the location of the ground fault can be specified without using the zero-phase current transformer and the direction ground fault relay, and the cost can be reduced.

  In addition, when a ground fault occurs in the first transformer, the first circuit breaker is turned on again, so that power is continuously supplied to the heater of the NAS battery.

The block diagram of the AC / DC converter in this invention. The flowchart which shows control of the AC / DC converter at the time of the ground fault in this invention. The block diagram of the premises equipment of an AC / DC converter. The block diagram of the conventional AC / DC converter. The block diagram of the conventional AC / DC converter.

  Hereinafter, an AC / DC converter according to an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is an apparatus configuration diagram of this embodiment. The difference from FIG. 5 is that the circuit breaker (52PP) 2 is provided at a common connection point between the system and the circuit breaker 101 instead of the circuit breaker 109, and the zero-phase current transformer 110a, 110b and the directional ground fault relays 111a and 111b are removed. The other components that are the same as those in FIG.

  The AC / DC converter 1 of FIG. 1 is disposed at the location of the AC / DC converter 100 of FIG.

  The circuit breaker 2 corresponds to the first circuit breaker, the circuit breaker 101 corresponds to the second circuit breaker, the interconnection transformer 102 corresponds to the first transformer, and the auxiliary transformer 105 is the first circuit breaker. The converter 103 corresponds to AC / DC converting means.

The operation will be described with reference to the flowchart of FIG. It is assumed that the flowchart is executed by a control unit (not shown).
Process 1
A ground fault occurs, the ground fault protection relay 108 operates (STEP 1), and the control unit opens the circuit breakers 2 and 101 (STEP 2).
Process 2
When the circuit breaker 2 is opened and the AC / DC converter 1 is disconnected from the system, the ground fault protection relay 108 is restored (STEP 3).
Process 3
The control unit re-inserts only the circuit breaker 2 (STEP 4).
Process 4
The control unit determines again whether or not the ground fault protection relay 108 has been operated (STEP 5). When the ground fault protection relay 108 is operated, the control unit determines that a ground fault has occurred on the auxiliary transformer 105 side (STEP 6), and releases the circuit breaker 2 (STEP 7). The AC / DC converter 1 stops operation because the heater power cannot be supplied (STEP 8).
Process 5
When the ground fault protection relay 108 does not operate in STEP 5, the control unit turns on the circuit breaker 101 again (STEP 9).
Process 6
The control unit determines again whether or not the ground fault protection relay 108 has been operated (STEP 10). When the ground fault protection relay 108 is operated, the control unit determines that a ground fault has occurred on the interconnection transformer 102 side (STEP 11), and opens the circuit breaker 101 (STEP 12). The AC / DC converter 1 stops its operation, but since the circuit breaker 2 is turned on again, power supply to the heater is continued (STEP 13).
Process 7
When the ground fault protection relay 108 does not operate in STEP 10, the control unit determines that the system side ground fault (success in removing ground fault in the AC / DC converter 1) (STEP 14) and resumes the operation of the AC / DC converter 1. (STEP 15).

In the above processing 1 to 7, when a ground fault is detected by the ground fault protection relay 108 inside the AC / DC converter 1, the following occurs.
(1) When a ground fault occurs on the side of the interconnection transformer 102 The ground fault protection relay 108 does not restart in the process 4, but restarts in the process 6, and thus the process up to the process 6 is executed. In this state, the circuit breaker 2 is “ON” and the circuit breaker 101 is “OFF”. That is, since the circuit breaker 101 is “OFF”, the faulty point of the interconnection transformer 102 is removed. In addition, the circuit breaker 2 is turned on again in the process 3, so that power supply to the heater of the battery unit 151 of the NAS battery 150 is continued through the auxiliary transformer 105.
(2) When a ground fault occurs on the auxiliary transformer 105 side Since the ground fault protection relay 108 is reactivated in the process 4, the process 5 and subsequent steps are not executed. In this state, both circuit breakers 2 and 101 are “OFF”. That is, since the auxiliary transformer 105 has failed, power supply to the heater of the NAS battery 150 is stopped. Further, since the AC / DC converter 1 cannot be operated when the auxiliary transformer 105 is stopped, it is inevitable that the circuit breaker 2 is “off” even if the interconnection transformer 102 side is healthy.
(3) When a ground fault occurs outside the AC / DC converter 1 (premises equipment) The ground faults outside the AC / DC converter 1 are the directional ground fault relays 204a to 204n and the ground fault protective relay described in FIG. The accident is eliminated by 208 etc. That is, following the detection of the ground fault protection relay 108 in the process 1 on the AC / DC converter 1 side (time coordination is attempted so that it is slightly delayed from the detection time limit by the ground fault protection relay 108 on the AC / DC converter 1 side). The fault protection relay 208 and the like operate to eliminate the ground fault.

  In this case, since the AC / DC converter 1 has completed the accident removal at the premises equipment when the process 3 is executed, the ground fault is detected again inside the AC / DC converter 1 even if the circuit breakers 2 and 101 are turned on again. It will not be done. Therefore, the process up to process 7 is executed, and the AC / DC converter 1 can resume operation.

  Here, a case where a ground fault occurs outside the AC / DC converter 1 will be described.

  When a ground fault occurs at the on-site loads 205a to 205n described in FIG. 3, the circuit breaker provided for the corresponding on-site load is opened, and the ground fault is eliminated.

  In this case, the ground fault protection relay 108 of the AC / DC converter 1 also operates, but the above-described process of FIG. 2 is performed up to the process 7 and the operation of the AC / DC converter 1 is resumed.

  When a ground fault occurs on the local bus, the ground fault protection relay 208 operates and the ground fault protection relay 108 also operates. However, since neither the AC / DC converter 1 nor the on-site loads 205a to 205n removes the ground fault, the circuit breaker 201 is opened, and the on-premises bus fails. In this case, the power return operation of the AC / DC converter 1 is performed after removing the ground fault of the local bus.

  When a ground fault occurs on the system side, even if the circuit breaker 201 is opened, the ground fault has continued on the substation side, so the sending circuit breaker (not shown) is opened on the substation side. The power restoration operation of the AC / DC converter 1 is performed after removing the ground fault on the system side.

  The present invention provides the AC / DC converter 1 without using the zero-phase current transformer and the directional ground fault relay by arranging the circuit breakers 2 and 101 and the ground fault protection relay 108 as described above as shown in FIG. It is possible to respond to a ground fault accident that occurred inside.

  In addition, in this configuration, a ground fault occurs, the ground fault protection relay 108 operates, the circuit breakers 2 and 101 are opened, the ground fault protection relay 108 returns, and only the circuit breaker 2 is turned on again. When the fault protection relay 108 is activated again, it is determined that a ground fault has occurred in the auxiliary transformer 105. On the other hand, when the circuit breaker 2 is turned on again and the ground fault protection relay 108 is restarted after the circuit breaker 101 is also turned on again, it is determined that a ground fault has occurred in the interconnection transformer 102. If it determines in this way, since it is not necessary to consider a ground fault direction, a ground fault location can be specified without using a zero phase current transformer and a direction ground fault relay, and cost reduction is achieved.

  When a ground fault occurs in the interconnection transformer 102, the circuit breaker 2 is turned on again, so that power is continuously supplied to the heater of the battery unit 151 of the NAS battery 150.

Although the present invention has been described in detail only for the specific examples described above, it is obvious to those skilled in the art that various changes and modifications are possible within the scope of the technical idea of the present invention. Such variations and modifications are naturally within the scope of the claims.

DESCRIPTION OF SYMBOLS 1,100,120 ... AC / DC converter 2,101,109,201,202a-202n, 209 ... breaker 102 ... interconnection transformer 103 ... converter 104 ... load switch 105 ... auxiliary transformer 106,206 ... zero Phase voltage detector (ZPC)
108, 208 ... Ground fault protection relays 110a, 110b, 203a to 203n ... Zero phase current transformers 111a, 111b, 204a to 204n ... Directional ground fault relay 150 ... NAS battery 151 ... Battery unit 205a-205n ... On-site load

Claims (2)

A first circuit breaker having one end connected to the power system;
A second circuit breaker having one end connected to the other end of the first circuit breaker;
A first transformer having a primary side connected to the other end of the second circuit breaker;
AC / DC conversion means for connecting the AC side to the secondary side of the first transformer and converting AC power to DC power;
A NAS battery connected to the DC side of the AC / DC converting means;
A second transformer having a primary side connected to a common connection point of the first circuit breaker and the second circuit breaker, and a secondary side connected to a heater of the NAS battery;
A ground fault protection relay connected to a common connection point between the other end of the first circuit breaker and one end of the second circuit breaker;
An AC / DC converter comprising: control means for controlling the first circuit breaker and the second circuit breaker based on a signal from the ground fault protection relay.   When the ground fault protection relay is operated, the control means opens the first circuit breaker and the second circuit breaker, and then reopens the first circuit breaker, and the ground fault protection relay 2. The AC / DC converter according to claim 1, wherein it is determined whether or not the operation has been restarted.

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