JPS5992778A - Ground protecting circuit for inverter - Google Patents

Abstract

PURPOSE:To effectively detect the ground-fault trouble by providing current cut-off means at an AC power distribution system side and an inverter side by the branch point of a load and the inverter, and providing a switch between the inverter side of the current cut-off means and a ground. CONSTITUTION:An inverter 14 is operated in cooperation with an AC power distributing system 11 at the system normal time. A leakage breaker 12a is tripped to the ground-fault trouble such as an electric shock, leakage or the like in a demander to cut off the supply of the accidental current. An inverter 14 detects the malfunctions of the voltage and frequency from a PT16 for detecting the system voltage at the power interruption time of the system 11 to operate an AC switch 13 so as to open the contact 13a to disconnect to the system 11. Simultaneously, a contact 13b is closed to ground one of the AC terminals of the inverter 14. When the ground-fault trouble occurs in the AC charger such as a load 15, a leakage breaker 12b is tripped, thereby cutting off the supply of the accidental current.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ground protection circuit for an inverter that connects an AC power distribution system and an AC output terminal, and performs both interconnected operation and independent operation with the system.

For example, as shown in FIG. 1, an inverter 3a and a load 4a are connected to a pole transformer 1 (only the secondary side is shown) via an AC switch 2a, and an inverter 3b is connected to a pole transformer 1 (only the secondary side is shown) via an AC switch 2b.
and load 4b are connected, and these inverters 3a, 3b
is connected to a power generating device such as a solar battery (not shown), and when the AC system is healthy, it operates in connection with the grid and sends power to the grid, or in somewhat special cases, it takes power from the grid and supplies it to the DC side of the inverter. On the other hand, when there is a power outage in the grid, the inverter disconnects the connection between the output end and the grid, operates independently from the grid, and supplies power to the load independently. Conceivable.

The inverter used in such a system is required to be protected from ground faults such as electrical leakage in the load in either of the two operating modes described above.

Incidentally, such an inverter for a power generation system is currently in the research and development stage, and there is no established grounding protection technology yet.

-Instead of a power generation system, an inverter is used as a constant voltage and constant frequency power supply, and normally the impark is operated in forward conversion mode and the storage battery is floatingly charged, and in the event of a power outage, it is disconnected from the grid and reverse conversion operation is performed to supply power to the load. There are systems, but
Even with this system, there is no established grounding protection technology.

As mentioned above, the object of the present invention is to provide an inverter ground protection circuit that can reliably detect a ground fault in a load regardless of the operating mode of the inverter, which operates in two modes: grid, interconnected operation, and independent operation. Our goal is to provide the following.

According to the present invention, in an inverter that performs interconnected operation with an AC distribution system or disconnects from the grid to supply power to a load, the branch point between the load and the inverter is located between the AC distribution system side and the inverter side. and a switch that further grounds a line on the inverter side of the current interrupting means on the inverter side and interrupts the ground wiring during interconnection operation with the inverter system. This is achieved by providing

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
.

Figure 2 is a circuit diagram showing an embodiment of the method of the present invention.
is an AC distribution system, and 14 is this AC distribution system 11 and load 1.
The inverter 14 has its DC input side connected to a power generating device such as a solar cell, and when the system is normal, it performs interconnected operation with the AC distribution system 11 and supplies power to the load 15. It is something to do.

AC power distribution system 1 at the branch point between load 15 and inverter 14
An earth leakage breaker (ELB) 12a using a differential CT is provided on the AC power distribution system 11 side as a first current interrupting means that operates based on differential current detection. A switch contact 13a that is activated and disconnects the inverter 14 from the grid 11, and an FT for detecting grid voltage.
(Transformer) 16 is provided.

There is still an earth leakage breaker (ELB) 12b that uses a differential CT as a second current interrupting means that operates by detecting a differential current from the branch point between the load 15 and the inverter 14 to the inverter 14 side.
Furthermore, a line on the inverter 14 side is grounded, and a switch contact 13b is provided in the middle of the wiring to this ground, which serves to cut off the connection of the inverter 14 with the system 11 during operation.

As for the contacts 13a and 13b, it is advantageous to use interlocking mechanical contacts such as a contactor as shown in the figure as the contacts of the AC switch 13 in terms of strength against leakage current and fault current when the circuit is opened. Being and 13a
Other devices may be used as long as the condition that 13'b and 13'b can operate simultaneously is satisfied.

In addition, a combination of an earth leakage protection relay and a circuit breaker may be used instead of the earth leakage breakers 12a and 12b. In that case, if both conductors are inserted into the through hole as the primary conductor, the protective relay can be saved. Additionally, due to the nature of the accident, it is desirable to use multiple types of circuit breakers for both circuit breakers and to shut them off all at once.

Next, to explain the operation, when the system is normal, the inverter 14 performs interconnected operation with the AC power distribution system 11.
At this time, an earth leakage breaker 12a is installed at the receiving end of the consumer, so in the event of a ground fault such as an electric shock or leakage within the consumer, the earth leakage breaker 12a trips and cuts off the supply of fault current. do.

In addition, in the event of a power outage in the system i1, the inverter 14 detects abnormalities in voltage, frequency, etc. from the PT 16 for detecting system voltage, operates the AC switch 13, opens the contact 13a, disconnects the connection from the system 11, and At the same time, contact 13b is closed to ground one of the AC terminals of inverter 14. In this way, when a ground fault occurs in an AC charging part (non-grounded side) such as the load 15, the earth leakage breaker 12b trips and the supply of the fault current is cut off.

Note that if the inverter 14 is connected to the grid 11 while the ground circuit remains connected, for example, even if there is an electric shock accident in the load 15, the fault current will in the worst case be detected by the earth leakage circuit breakers 12a and 12b. The sum of the currents will increase compared to the case without grounding. Therefore, it is dangerous especially when there is no earth leakage breaker izb.

The above embodiment shows an example using a single-phase inverter, but 3
Similarly, in phase inverters, ground faults in load equipment can be detected by switching the ground circuit. In this case, the grounding of the 3-phase 200cm distribution line may be 1-phase grounding, neutral point grounding, or 2-phase center point grounding, and the voltage applied to the faulty part in the event of a ground fault is somewhat different for each. Although it is different, the ability to detect ground faults and the need to switch the ground circuit remain the same.

As described above, the inverter grounding protection circuit of the present invention is applicable to power generation systems using solar cells, fuel cells, etc. and so-called uninterruptible power supplies that charge storage batteries by forward conversion operation of the inverter when the system is normal. When the AC output terminal is connected to the AC distribution system and the inverter is operated in connection with the grid, or when the inverter is disconnected from the grid and supplies power to the load, there is always an unbalanced current between the load and the power supply source. If a ground fault occurs in the load or in the wiring that supplies power to the load because the intermediate potential of one line or phase of the power supply source is grounded, this must be used. It can be detected and blocked.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing an example of a solar power generation system, Figure 2 is a circuit diagram showing an example of a solar power generation system.
The figure is a circuit diagram showing an embodiment of the ground protection circuit of the present invention. 1... Pole transformer 2al 2b... AC switches 3a, 3b... Inverter 4a+4b... Load 11... AC power distribution system 12
a, 12b...Earth leakage breaker 13...AC switch 13a, 131)...Switch contact 14...Inverter 15...Load 16...PT for detecting system voltage Applicant: Fuji Electric Manufacturing Co., Ltd.

Claims (1)

[Claims] When operating in connection with the AC distribution system or disconnecting from the grid to supply power to the load, it operates by detecting the difference in current between the AC distribution system side and the inverter side from the branch point between the load and the inverter. Further, a switch is provided to ground a line on the in-park side of the current interrupting means on the inlet/output side, and to cut off the ground wiring when the inverter is connected to the inverter system. An inverter ground protection circuit characterized by: