JPS6152609B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for controlling the input voltage of a DC voltage protection relay of a converter configured by connecting a plurality of Gretzz-connected thyristor converters in series, which is used, for example, in frequency conversion equipment or DC power transmission equipment. It is related to the control method.

FIG. 1 is a diagram illustrating an example of a frequency conversion device to which the present invention is applied, in which thyristor converters 1, 2, 3, and 4 connected with each other are connected to conversion transformers 5, 6, 7, and 8, respectively. The converters 1, 2, 3, and 4 are connected to the AC systems 9, 10 through the converters 1, 2, 3, and 4, and are provided with bypass switches 11, 12, 13, and 14 for bypassing these converters.

15 is a DC reactor for smoothing DC current, 16 is a DC voltage detector, and 17 is a protection device mainly consisting of a protective relay.

In such a converter, for example, when four converters 1, 2, 3, and 4 are in operation,
When turning on the bypass switches 11 and 12 to stop the converters 1 and 2, conversely, the two converters 3 and 4
While operating the bypass switch 1.
There are cases where converters 1 and 2 are operated by cutting off lines 1 and 12.

FIG. 2 is a schematic time chart showing DC voltage values associated with the operating modes of converters 1, 2, 3, and 4. In Fig. 2, at time t ₁ , converters 1 and 2
When the converters start operating, the DC voltage gradually rises and reaches the DC voltage value equivalent to converters 1 and 2 at time t ₂ when converters 1 and 2 complete their operation, and then at time t ₃ the When converters 3 and 4 start operating, the DC voltage rises further and reaches the DC voltage value equivalent to converters 1, 2, 3, and 4 at time t4 when converters 3 and ₄ complete their operation. Conversely, when converters 1 and 2 start to stop at time t ₅ , the DC voltage gradually falls, and at t ₆ when converters 1 and 2 stop, the DC voltage value equivalent to converters 3 and 4 is reached. Then, at t ₇ , converter 3,
4 starts to stop, the DC voltage further falls and becomes zero at time t8 when converters 3 and ₄ stop.

In addition, the rise and fall times of DC voltage are usually several
It is about 100ms.

As is clear from the time chart in Figure 2,
Since the DC voltage value changes depending on the number of converters in operation, if the DC voltage detection value is directly input to the protective relay, the protective relay will malfunction. For example, in the time chart of FIG. 2, when converters 1 and 2 are in operation (interval from t ₂ to t ₃ ),
The input voltage of the overvoltage relay is Vd, and its setting value is
1.2Vd, converters 3 and 4 at time t ₃
As the DC voltage starts to rise, the input voltage of the overvoltage relay also rises, and the DC overvoltage relay operates at time _t0 .

Therefore, it is necessary to convert the input voltage of the protective relay according to the number of operating converters.

FIG. 3 is a time chart showing a conventional method of converting a detected DC voltage value, in which figure a shows the detected DC voltage value, and figure b shows the input voltage value of the protective relay.

In Figure b, the DC voltage detection value is converted to 1/2 at time _t3 and restored to the original value at time _t5 .

For example, as above, if the rated input voltage of a DC overvoltage relay is Vd and its setting value is 1.2Vd, and the rated input voltage of a DC undervoltage relay is Vd and its setting value is 0.8Vd, then the converter is operated.・If the system stops, the DC undervoltage relay will malfunction at _t3 .
Also, it can be seen that the DC overvoltage relay malfunctions at time _t5 .

However, in conventional equipment, the DC voltage detector and the protective relay have a delay time, so the protective relay does not actually malfunction.

However, as systems have become more diverse and complex in recent years, high-speed protection is required and high-speed DC voltage detectors and protective relays have been developed. Shortcomings began to appear.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to eliminate the above-mentioned drawbacks, and to provide an input voltage control method for a DC voltage protection relay that can prevent malfunctions of the protection relay and provide high-speed protection. It's about doing.

FIG. 4 is a circuit diagram showing an embodiment of the present invention.
When the operating signals of converters 1 and 2 and the operating signals of converters 3 and 4 both become "1", the AND circuit 18 becomes "1", the off-delay circuit 19 immediately becomes "1", and the on-delay circuit 20 becomes "1" for a predetermined time. After "1",
Also, when any one of the operating signals of converters 1, 2, 3, and 4 becomes "0", the AND circuit 18
becomes "0", the off-delay circuit 19 becomes "0" after a predetermined time, and the on-delay circuit 20 immediately becomes "0". The signal of the not circuit 21 is an inversion of the output signal of the off-delay circuit 19.
The signal No. 2 is an inversion of the output signal of the on-delay circuit.

The DC voltage detection value Vd is determined by a switch circuit 23 linked to the output signal of the off-delay circuit 19, a gain 1/
DC overvoltage relay 2 via double conversion circuit 24
5, and is also input to the DC overvoltage relay 25 via a switch circuit 26 that is linked to the output signal of the NOT circuit 21.

Furthermore, the DC voltage detection value Vd is input to the DC undervoltage relay 29 via a switch circuit 27 linked to the output signal of the on-delay circuit 20 and a conversion circuit 28 with a gain of 1/2.
The signal is input to the DC undervoltage relay 29 via a switch circuit 30 which is linked to the output signal of 2.

Fig. 5 is a time chart for explaining the operation of the present invention, in which figure a shows the detected DC voltage value, figure b shows the input voltage value of the DC overvoltage relay, and figure c shows the input voltage value of the DC undervoltage relay. .

During the period from t ₃ to t ₆ in FIG. 5, the switch circuit 23 in FIG.
The period from t ₄ to t ₅ in FIG. 5 is the period in which the switch circuit 27 in FIG.
is on and the switch circuit 30 is off. That is, in diagram b, the DC voltage detection value is converted to 1/2 at time _t3 when converters 3 and 4 start operating,
It was returned to its original state at t ₆ when converters 1 and 2 stopped, and figure c shows that converters 3 and 4 have completed their operation.
The DC voltage detection value is converted to 1/2 at time _t4 , and restored to the original value at time t5, when converters 3 and ₄ begin to stop. By controlling the timing of conversion as described above, it is possible to prevent the value of the voltage shown in b in FIG.

Here, for example, as above, set the rated input voltage value of the DC overvoltage relay and DC undervoltage relay to Vd
Even if the DC voltage detector, DC overvoltage relay, and DC undervoltage relay respond instantaneously without delay, the DC overvoltage relay will not malfunction as shown in Figure b, and as shown in Figure C. As such, the DC undervoltage relay will not malfunction between t ₂ and _{t 7} .

It goes without saying that the DC undervoltage relay malfunctions when all converters are stopped or until the rated DC voltage is reached, so its output is locked.

Although the above explanation is for the case where the converters are connected in a two-stage cascade, the same concept can be applied even when a plurality of converters are connected in a cascade.

Further, in the above explanation, the input voltage values of the DC overvoltage relay and the DC undervoltage relay were converted, but it is clear that the same effect can be obtained even if the setting value is converted conversely.

Further, when the conventional method shown in FIG. 3 is adopted, the output signal may be locked during a period in which the DC overvoltage relay and the DC undervoltage relay malfunction.

As described above, the present invention converts the detected DC voltage value, which is the input voltage value of the DC overvoltage relay and the DC undervoltage relay, according to the number of operating converters, and also controls the timing of the conversion. This has the overall effect of preventing malfunctions of DC overvoltage relays and DC undervoltage relays and providing high-speed protection.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conversion device to which the present invention is applied, FIG. 2 is a time chart explaining the operation of FIG. 1, FIG. 3 is a time chart explaining the operation of the conventional method, and FIG. The figure is a circuit diagram showing one embodiment of the present invention, and FIG. 5 is a time chart explaining the operation of the present invention. 1, 2, 3, 4...thyristor converter, 5,
6, 7, 8... Conversion transformer, 9, 10... AC system, 11, 12, 13, 14... Bypass switch, 15... DC reactor, 16... DC voltage detector, 17... Protection device, 18...AND circuit, 19...off delay circuit, 20...on delay circuit, 21, 22...not circuit, 23,2
6, 27, 30... switch circuit, 24, 28...
...conversion circuit with 1/2 gain, 25...DC overvoltage relay, 29...DC undervoltage relay, a, c...
...DC voltage detection value, b...Input voltage value of DC overvoltage relay and DC undervoltage relay, d...Input voltage value of DC overvoltage relay, e...Input voltage value of DC undervoltage relay.

Claims (1)

[Claims] 1. In a converting device in which a plurality of thyristor converters connected in a cascade are connected, the detected DC voltage value is converted according to the number of the plurality of converters in operation, and the voltage value is applied to a DC overvoltage relay, a DC undervoltage When using the input voltage of a protective relay such as a relay, when the converter is additionally operated,
The DC voltage detection value converted by the operation command is used as the input voltage value of the DC overvoltage relay, and the DC voltage detection value converted after a predetermined time from the operation command is used as the input voltage value of the DC undervoltage relay. When stopping some of the converters among the converters, the DC voltage detection value converted by the stop command is used as the input voltage value of the DC undervoltage relay, and the converted DC voltage detection value is set a predetermined time after the stop command. An input voltage control method for a DC voltage protection relay, characterized in that the input voltage value of the DC overvoltage relay is set as the input voltage value of the DC overvoltage relay.