JPH0119559Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to an AC/DC cross contact detection relay in an AC/DC parallel system.

Conventionally, there has been a device of this type as shown in FIG. In this Figure 1, 1 and 2 are AC busbars,
3, 4, 5, 6 are wire breakers, 7, 8 are conversion transformers, 9, 10 are AC/DC converters, 11, 12 are DC reactors, 13 is a DC transformer, 14 passes only commercial frequencies 15 is a level detector.

Next, the operation will be explained. During normal operation of DC power transmission, a DC current flows through the primary side of the DC current transformer 13, so the secondary side of the DC current transformer 13 also contains only a DC component and does not include a commercial frequency component. Therefore, since the output of the filter 14, which passes only the commercial frequency component, is zero, the level detector 15 does not operate.

Next, when an AC line and a DC transmission line in an AC/DC parallel system are short-circuited and an AC/DC cross contact accident occurs, an AC component current also flows in the DC transmission line. This alternating current component current is detected by a direct current transformer 13 and inputted to a level detector 15 via a filter 14 to detect an accident and perform necessary protective operations.

However, it is well known that AC current flows through the DC line even when a two-phase commutation failure occurs in an inverter, and conventional detection circuits can prevent AC/DC cross-contamination accidents that stop both the AC and DC systems. However, it had the disadvantage that it was difficult to distinguish between two-phase commutation failure, which stopped only the DC system.

This invention was made to eliminate the drawbacks of the conventional ones as described above, and uses DC current transformers installed on both sides of the grounding point on the neutral wire to extract the commercial frequency components and compare their phases. The purpose of the present invention is to provide an AC/DC cross contact detection relay that can detect only AC/DC cross contact accidents.

An embodiment of the present invention will be described below with reference to the drawings.
In FIG. 2, the same parts as in FIG. This is the second filter. 20 is a detector that detects that the output waveforms of the first filter 18 and the second filter 19 are in opposite phase;
FIG. 3 shows a block diagram of the detector. In this FIG. 3, 21 is the output signal of the first filter 18 in FIG. 2, 22 is the output signal of the second filter 19, 2
3 and 24 are a first waveform shaping circuit that outputs a pulse during a period when the input waveform is positive; a second waveform shaping circuit;
5 is an inverter, 26 is an AND element, 27 is a timer, and 28 is an output.

Next, the operation of the present invention will be explained below with reference to the circuit diagram of FIG.

Normally, in a DC system, the neutral wire or return wire is grounded, and in an AC system, the neutral point of the transformer is grounded, so if an AC/DC cross-contact accident occurs where the AC circuit and DC transmission line are short-circuited, The virtual AC power supply indicated by the dotted line is inserted. In this case, Z is the impedance determined by the transmission line impedance and the neutral point resistance. As a result, there is a direct current in the DC system.
Id, the alternating currents Ia ₁ and Ia ₂ flow in the direction of the arrows, and as can be understood from FIG. 4, the alternating currents Ia ₁ and Ia ₂ have opposite phases.

When two-phase commutation fails, no current flows in the grounded circuit, and alternating current flows in the same circuit as the direct current Id.

Therefore, the first and second DC transformers 1 in FIG.
If it is determined that the AC components in the output signals 6 and 17 have opposite phases, an AC/DC cross contact accident can be detected. In this case, to detect that the signals are in opposite phases, it is sufficient to invert one of the signals, take an AND condition for the two signals after waveform shaping, and determine that the signals are in opposite phases if they continue for a certain period of time.

Note that in the above embodiment, the determination of the opposite phase was made based on the overlap of pulses after waveform shaping, but the invention is not limited to this, and the determination of the opposite phase may be performed by other means.

As described above, according to the present invention, only AC/DC cross-contamination accidents can be accurately identified because the AC components in the output of the first and second DC current transformers installed on both sides of the grounding point are in opposite phases. , a highly accurate AC/DC cross contact detection relay that can reliably perform protection operations for AC and DC systems can be obtained.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a conventional AC/DC cross contact detection relay system, Fig. 2 is a block diagram showing an embodiment of the present invention, and Fig. 3 is a configuration diagram showing an embodiment of the present invention for detecting anti-phase determination. 4 are circuit diagrams illustrating the current system at the time of an accident. 1, 2... AC bus bar, 3, 4, 5, 6... Line breaker, 7, 8... Conversion transformer, 9, 10... AC/DC converter, 11, 12... DC reactor, 1
3...DC current transformer, 14...Filter, 15...
Level detector, 16...first DC current transformer, 17
...Second DC current transformer, 18...First filter, 19...Second filter, 20...Detector,
23...First waveform shaping circuit, 24...Second waveform shaping circuit, 25...Inverter, 26...AND element, 27...Timer. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Scope of utility model registration request] A first DC transformer and a second DC transformer provided on both sides of a ground point on the neutral wire of a DC transmission system in an AC/DC parallel power transmission system, and connected to the output side of the first DC transformer. a first filter connected to the output side of the second DC current transformer and passing only the commercial frequency; An AC/DC cross contact detection relay comprising a phase determiner to which the output of a filter is supplied and detects whether the output is in opposite phase.