JPH10112928A - Grounding detector for system interconnection facility - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely detect the grounding current of the system of a power company and parallel off system interconnection without functioning by mistake and at a low price by breaking a breaker by the materialization of AND condition of the operation signal of a grounding overcurrent relay and the operation signal of a short power relay. SOLUTION: When grounding occurs in the system 2A of a power company, a zerophase current transformer 5 provided on the primary side of a transformer detects a feeble grounding current, and a grounding overcurrent relay 6A outputs an operation signal by the current value. At the same time, also the system 2A of the power company detects the feeble grounding current, and the breaker 2Z on the side of the power company is opened to stop the power supply. A current transformer 9B for a meter provided at a power receiving line 2S and a transformer 8 for a meter detect the short power of the power receiving line 2S, and a short power relay 7 outputs an operation signal by that power value. A breaker 3S for power reception is opened by the materialization of the AND circuit condition of the operation signal of the grounding overcurrent relay 6A and the operation signal of the short power relay 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system interconnection system for supplying power purchased from an electric power company and electric power obtained from a private generator to a plurality of customer loads. The present invention relates to a system-side ground fault detection device.

[0002]

[Prior Art] At the end of 1995, the New Electricity Business Law was enacted,
The grid interconnection guidelines have been revised. As a result, the requirements for installation of the protection device at the time of grid connection are eased, and the number of customers planning to connect the grid by introducing a private generator into the existing power receiving equipment is increasing. In grid connection, the private generator power supply is always operated in parallel with the power company power supply.

[0003] In a system interconnection system in which power purchase from an electric power company and electric power obtained from a private power generator are system-connected to a plurality of consumer loads and are always supplied in parallel, a system in an electric power company system is used. Ground fault protection includes:

[0004] There are two types of protection methods: a protection method for installing a ground fault overvoltage relay and a transformer for a grounding type meter, a protection method for installing a power direction (back electromotive force) relay, and a protection method for installing a ground fault overcurrent relay. In addition,
An example of this type of apparatus is disclosed in JP-A-1-114332.

[0005]

In the above-mentioned prior art, in consideration of a case where a system interconnection facility is newly added to a general substation having no system interconnection facility, a transformer for a grounding type instrument is added. Therefore, the cost of equipment remodeling and the period of system interruption are enormous, and in some cases, additional space cannot be secured.

However, since recent transformers have low loss and small reverse excitation current, existing transformers and relays have insufficient detection sensitivity, and the power direction (back electromotive force) relay may not operate.

However, since the ground fault overcurrent relay needs to operate with a minute ground fault current, it has high sensitivity and may malfunction.

SUMMARY OF THE INVENTION An object of the present invention is to provide a system interconnection system in which power purchased from a power company and electric power obtained from a private generator are always connected in parallel and connected at a low cost without malfunction. It is an object of the present invention to provide a ground fault detecting device of a grid connection facility capable of reliably detecting a ground fault current of a power company grid and disconnecting the grid connection.

[0009]

In order to achieve this object, a ground fault detecting device for a grid interconnection system according to the present invention connects a primary side of a transformer to a power supply side, and connects a primary side of the transformer to a secondary side of the transformer. A grid connection in which the connected receiving wires are connected to a common bus, a breaker is connected to at least one of the primary and secondary sides of the transformer, and a plurality of loads are connected to a private generator on the other side of the common line. In the system equipment, an operation signal of a ground fault overcurrent relay operating based on a current value detected by a zero-phase current transformer of a ground fault current on the primary side of the transformer, and a power detector for detecting power of the secondary distribution line of the transformer. Characterized in that, when an AND condition with an operation signal of an underpowered relay operated according to the power value detected in step (1) is satisfied, the circuit breaker is cut off to disconnect the system interconnection.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a single-line schematic diagram showing an outline of an embodiment of a ground fault detecting device of a grid connection facility according to the present invention. The diagram shows a power purchase from a power company and private power generation for a plurality of consumer loads. This is a power system that constantly supplies power obtained by operating the machine.

A receiving line 2S to which the transformer 1 and the power receiving circuit breaker 3S are connected is connected to a common bus 2B, and a private generator 4 and a plurality of loads 12A to 12F are connected to the other side of the common bus 2B. 3G is a private circuit breaker for turning the private generator 4 on and off. On the primary side of the transformer 1, the power company system 2
A zero-phase current transformer 5 for detecting a small ground fault current of A, and a ground fault overcurrent relay 6A for outputting an operation signal when a current value of the zero-phase current transformer 5 becomes a predetermined value or more are provided. On the secondary side of the transformer 1, an instrument current transformer 9B, an instrument transformer 8 connected to the receiving wire 2S, and an underpower relay 7 for outputting an operation signal when the power of the receiving wire 2S becomes a predetermined value or less. Provided.

Next, the operation of the embodiment of the present invention will be described.

When a ground fault occurs in the power company system 2A, the zero-phase current transformer 5 provided on the primary side of the transformer 1 detects a minute ground fault current, and based on the current value, the ground fault overcurrent relay 6A
Outputs an operation signal. At the same time, the power company system 2A also detects a minute ground-fault current, opens the power company-side circuit breaker 2Z, and stops power supply. The instrument current transformer 9B and the instrument transformer 8 provided on the receiving line 2S detect insufficient power of the receiving line 2S, and the underpower relay 7 outputs an operation signal based on the detected power value. An AND circuit 15 of the operation signal of the ground fault overcurrent relay 6A and the operation signal of the underpowered relay 7 shown in FIG.
When the condition is satisfied, the power receiving circuit breaker 3S is opened. When the power receiving circuit breaker 3S is opened, the indicator light 16 provided on the surface of the switchboard blinks to display a ground fault. In addition, the circuit breaker 3
P may be opened.

[0014]

As described above, according to the ground fault detecting apparatus for grid connection of the present invention, a ground fault accident of the power company grid can be reliably detected at low cost without malfunction. Can be disconnected.

[Brief description of the drawings]

FIG. 1 is a system circuit diagram showing a configuration of a ground fault current detection device according to an embodiment of the present invention.

FIG. 2 is a block diagram of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Transformer, 2B ... Common bus, 3 ... Circuit breaker for power reception, 4 ...
Private generator, 5: Zero-phase current transformer, 6A, 6B: Ground fault overcurrent relay, 7: Underpowered relay, 8: Instrument transformer, 9
... current transformer for instrument, 10 ... power directional relay, 11, 11
A, 11B: overcurrent relay, 12: load.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI // H02J 3/38 H02J 3/38 W (72) Inventor Masayuki Tanibe 1-1-1 Kokubuncho, Hitachi City, Ibaraki Prefecture Inside the Kokubu Plant of Hitachi, Ltd.

Claims (2)

[Claims] 1. A transformer primary side is connected to a power supply side, said transformer secondary side is connected to a common bus, and a circuit breaker is connected to at least one of the primary side and the secondary side of the transformer. In a system interconnection facility in which a plurality of loads are connected to a private generator on the other side of a common line, a ground fault overcurrent relay that operates based on a current value of a ground fault current on the primary side of the transformer detected by a zero-phase current transformer. And the operation signal of the under-power relay operating based on the power value detected by the power detector of the power on the secondary side of the transformer, the circuit breaker is opened and the grid connection is released. A ground fault detection device for grid-connected equipment, which is arranged in a line. 2. The ground fault detecting device according to claim 1, wherein when the circuit breaker is opened, a ground fault is displayed on an indicator light provided on a switchboard.