JPH0139302B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AC/DC cross contact detection relay applied to an AC/DC parallel system.

Conventionally, in AC/DC parallel systems in which AC and DC transmission lines run in parallel, a circuit system such as the one shown in Figure 1 has been frequently used as a means of detecting short circuits between the two transmission lines, that is, AC/DC cross contact. ing. In this Figure 1, 1 and 2 are AC busbars, 3, 4,
5 and 6 are disconnectors connected to each power transmission system, 7
and 8 are transformers for forward conversion and inverse conversion, which apply AC secondary voltage to AC/DC converters 9 and 10, respectively.
Further, 11 and 12 are DC reactors inserted into the DC transmission line, 13 is a first DC current transformer represented by, for example, a Kramer type that is an application of a saturation type DC transformer, and 14 is a DC reactor that passes only commercial frequencies. The first filter 15 is a first level detector that detects the output signal of the filter 14.

Next, when an AC/DC cross-contact accident occurs, such as a short circuit between the AC line of the AC/DC parallel system and the DC transmission line, an AC component current also flows in the DC transmission line. Therefore, the short circuit current flowing through the DC transmission line is detected by the DC current transformer 13 and inputted to the level detector 15 via the filter 14 to detect the occurrence of an accident and execute necessary protective actions. I'm doing it like that.

However, with conventional AC/DC cross contact detection relays, it is well known that AC current flows through the DC line even when two-phase commutation of the inverter fails. There were drawbacks such as the unclear judgment as to whether both the AC and DC transmission systems should be stopped in the event of an accident or only the DC transmission system in the case of a two-phase commutation failure.

The present invention was made in order to eliminate the above-mentioned drawbacks of the conventional system.
It is an object of the present invention to provide an AC/DC cross contact detection relay that can reliably determine whether it is an AC/DC cross contact accident or a two-phase commutation failure accident by using a set of commercial frequency intrusion relays, and can promptly take system protection measures.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. In FIG. 2, the same parts as in FIG. 1 are designated by the same reference numerals. In FIG. The second one, which only passes the frequency
18 is a second level detector; 19 and 20 are inverter circuits; 21, 22, and 23 are AND circuits that constitute a logic circuit together with the respective inverter circuits; 24 is a two-phase commutation failure detection output;
5 is a short circuit detection output between the neutral line and the AC line, and 26 is an AC/DC cross contact detection output.

Next, the operation of the present invention will be explained using FIG.
First, when a two-phase commutation failure occurs in DC power transmission, alternating current flows only in the DC system, as shown in FIG. 3a. In addition, when a short circuit occurs between the AC line and the neutral line or the return line, AC current will be commutated to the neutral line and ground line as shown in Figure 3b, but in the case of a DC transmission line. No alternating current flows to the positive or negative electrode. Furthermore, when an AC line and a DC transmission line come into contact, alternating current is commutated to both the neutral wire, the grounding wire, and the DC transmission line, as shown in FIG. 3c. Therefore, in order to identify each of these accidents without fail, as shown in Figure 2, DC current transformers 13 and 16 are installed to detect alternating current on the positive terminal side of the DC transmission line and the ground wire of the neutral line, respectively.
When detecting alternating current, the fault current is determined by level detectors 15 and 18 through filters 14 and 17 that allow only commercial frequencies to pass through, and when it is determined that alternating current is present, the output is set to logic "1". ”, and the inverter circuits 19, 20 and the AND circuits 21, 22, 23 identify the accident. The output 24 of the AND circuit 21 becomes logic "1" when the two-phase transition fails, and the output 24 of the AND circuit 22 becomes logic "1".
5 becomes "1" when there is a ground fault to the neutral line, and the output 26 of the AND circuit 23 becomes "1" when AC/DC cross contact occurs.The conditions for the logical operation are shown in FIG. 3(d).

As described above, according to the present invention, two sets of a DC current transformer for AC detection, a filter that passes only AC components, and a level detector for the output signal of the filter are provided at predetermined locations on a DC transmission line, and each The output signals of the level detectors are led to a logic circuit and combined so that they are automatically determined, and the results can be used to identify AC/DC cross contact accidents, ground faults between the neutral line and AC line, and two-phase commutation failures. The accident situation of the parallel system can be quickly clarified, and the effect of taking accurate protective measures is extremely large.

[Brief explanation of drawings]

Fig. 1 is a circuit configuration diagram showing a conventional contact detection relay system, Fig. 2 is a circuit configuration diagram showing an embodiment of the present invention, and Fig. 3 a, b, and c are AC/DC cross contact or two-way contact detection relays.
An explanatory diagram showing the flow of alternating current at the time of a phase commutation failure accident, and d of the same figure is a diagram of logical operating conditions. 1, 2... AC bus, 3, 4, 5, 6... Line breaker, 7, 8... Conversion transformer, 9, 10... AC/DC converter, 11, 12... DC reactor, 13
...First DC current transformer, 14...First filter, 15...First level detector, 16...Second
DC current transformer, 17... second filter, 18...
...Second level detector, 19, 20...Inverter circuit, 21, 22, 23...AND circuit, 24
... Output of two-phase commutation failure, 25 ... Output of neutral line ground fault, 26 ... Output of AC/DC cross contact. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1. A first DC current transformer provided on the grounding wire side of a DC transmission neutral line in an AC/DC parallel overhead transmission system, and a second DC current transformer provided on the positive transmission line side of the DC transmission line,
first and second filters that are connected to the first and second DC transformers and pass only commercial frequency components; and a second filter that binarizes the output signals of the first and second filters and determines the level. 1. A second level detector, first and second inverter circuits that invert the polarity of the first and second level detector output signals, respectively, and the first and second level detector output signals. an AC/DC logic determination circuit that logically determines the output signals of the first and second inverter circuits to automatically determine AC/DC cross contact accidents, ground faults between the neutral wire and the AC circuit, and two-phase commutation failures; Contact detection relay.