JPS6036692B2 - Ground fault protection method for DC transmission lines - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ground fault protection system for a DC power transmission line that can reliably protect the DC power transmission line from ground fault accidents.

Conventionally, AC power is converted to DC power by a converter device, which is then transmitted to the destination via a DC transmission line, and then converted to AC power by an inverter device at the receiving end of the transmission line, which is then supplied to the AC system. A DC power transmission system is being implemented.

The problem with such DC power transmission systems is that the phenomena of accidents are very different from those in AC power transmission systems, and therefore require different protection measures than in AC systems.

By the way, as a protection method for the DC transmission line as mentioned above, ``t1'' is a method of detecting the electrical oxidation rate group of the DC transmission line, and detecting and protecting the ground fault from the amount of change.

{2} A method of detecting and protecting voltage drops on DC transmission lines using an undervoltage relay. There is a meaning.

However, due to the method of {1- and ■ above}
However, accidents other than DC transmission line accidents can occur due to voltage changes on DC transmission lines, so in such cases, people may react even though there is no accident on the DC transmission line. In addition, it responds to control transient responses when starting and stopping converter equipment and inverter equipment, making it impossible to determine whether this is a DC transmission line accident (internal accident) or another accident (external accident). be.

Therefore, recently, as a protection method for DC transmission lines,
A change direction comparison method that can determine external accidents;
There are current differential methods, etc.

Of these two methods, the variation direction comparison method is constructed by the logical product of the variation direction comparison device and the DC undervoltage relays installed on the converter side and the inverter side, respectively. Even if the change-in-direction ratio shark relay malfunctions due to an accident, the band condition will not hold;
The operation of converters such as converters and inverters will not be stopped due to malfunction. However, in the current differential system, if there is no equivalent to the DC undervoltage relay mentioned above on either the converter or inverter side, if the current differential relay malfunctions due to an accident in the communication line, etc., there is no locking relay, and the target accident occurs. There was a drawback that the converter would stop operating even if it was not. The present invention has been made in view of the above circumstances, and provides a highly reliable ground fault protection method for DC transmission lines that can eliminate malfunctions and reliably protect DC transmission lines from short-circuit accidents. The purpose is to

First, with reference to the DC transmission system shown in FIG. 1, we will describe the phenomena that occur when a DC transmission line ground fault occurs.

In the figure, IA is a converter device that converts the AC power applied via the AC system 2A, the shatter breaker 3A, and the converter transformer 4A to DC power, and IB is the converter device that converts the DC power converted by the converter device IA to the DC power transmission line. 5, and converts it into AC power.
It is added to the AC system 2B via B. DC reactors 6A and 6B are provided at one output side of the converter device IA and one input side of the inverter device IB, respectively, and connected to the DC power transmission line 5, and a grounding wire 7 is connected between the input and output terminals of the other side. Ren is being attacked. Moreover, 8A and 8B are DC current transformers provided in the DC power transmission line 5 on the converter device IA side and the inverter device side IB, respectively. Here, the converter device IA and inverter device IB are operated by arbitrarily controlling the firing phase of their thyristors, and the DC reactors 6A and 6B smooth the DC side current and suppress the fault current in the event of an accident. The DC current transformers 8A and 8B are for detecting line current. Note that the left side of the figure is a forward conversion station, and the right side is a reverse conversion station.
In such a DC power transmission system, the converter device IA normally controls a preset constant current, and the DC power transmission line 5 performs DC power transmission.

If a voltage fault occurs in the DC transmission line 5 from this state, the current jA increases at the rise determined by the DC reactor 6A at the same time as the ground fault occurs, as shown in Figure 2a, and then the current jA increases by the rise determined by the DC reactor 6A. The constant current is restored to the initial constant current due to the constant current effect. On the other hand, inverter device IB
On the side, as shown in Figure 2b, at the same time as the ground fault occurred,
The current iB decreases with a fall determined by the DC reactor 6B', but in this case, if the fault point resistance is zero, the current iB to the inverter device IB side disappears, and the fault point resistance is large and the fault voltage (inverter device If the daily direction voltage drop of IB is 10 (line voltage drop) or more, the current iB to the inverter device IB recovers to the initial constant current due to the constant current effect of the converter device IA, as shown by the broken line in the figure. Furthermore, in the case of an external fault other than the DC transmission line 5, the electromotive force is lost or decreased in the case of an external fault on the converter device IA side, so currents jA and iB on the converter device IA and inverter device IB sides both increase. do. Therefore, as is clear from such a phenomenon, when a ground fault occurs in the DC transmission line 5, the current iA on the converter device IA side temporarily increases, and the current iB on the inverter device IB side decreases. Therefore, if the converter device IA side and the inverter device IB side detect the DC current flowing to each side and detect the difference current, the DC power transmission line 5
ground faults can be detected.

Hereinafter, with reference to FIG. 3, an embodiment of the DC power transmission line protection system according to the present invention based on the above-mentioned concept will be described.

In FIG. 3, the same parts as in FIG. 1 are denoted by the same reference numerals, and their explanation will be omitted here. That is, in Fig. 3, in addition to Fig. 1, . The above DC current transformers 8A and 8B are installed on the converter device IA side and the inverter device IB side.
Current detection relays 9A and 9B are provided, respectively, which input the secondary current of DC ground fault overcurrent relay with current input 1
2. FIG. 4 shows the configuration of a protection circuit for a DC power transmission line, in which 9A and 12 are the above-mentioned current detection appliances, a DC ground fault overcurrent relay, and 9B is a current detection relay.

13A is a signal transmitting device to which the output of the DC ground fault overcurrent relay 12 on the forward conversion station side is applied; 13B is a signal receiving device provided on the reverse conversion station side; when the DC ground fault overcurrent relay 12 is operated, the signal transmitting device This is for receiving signals transmitted from 13A.

Reference numerals 14A and 14B are signal transmitting/receiving devices which are normally provided at the converting station and inverse converting station, respectively, and mutually transmit the outputs of the current detection relays 9A and 9B, and have a built-in transmitter and receiver.

In addition, 15A and 15B compare the outputs of the current detection relays 9A and 98, respectively, and the outputs transmitted from the converter on the other side through the signal transmitting/receiving devices 14A and 14B, and operate only when there is a difference to output the output signal. It is a current differential relay that sends out . 16A is an AND circuit which inputs the output signals of the DC ground fault overcurrent relay 12 and the current differential relay 15A, respectively, and when the AND condition is satisfied, outputs a signal (converter stop command signal) and outputs the output signal (converter stop command signal) to the converter control device 17A. It is sent via

On the other hand, 16B is an AND circuit which inputs the output signal of the current differential relay 15B and the signal obtained via the signal transmitting/receiving device 13B, and outputs an output signal (converter stop command signal) when the AND condition is satisfied. Converter control device 17B
It is sent via . Next, the operation of the ground fault protection method for a DC power transmission line having such a configuration will be explained.

First, we will discuss the case when the system is healthy.

In this case, a DC current iA on the converter device IA side flowing through the DC power transmission line 5 and a DC current i on the inverter device IB side
The magnitude of B is equal, and the respective currents iA and iB are detected by DC current transformers 8A and 8B. Converter device I
On the A side, the current signal i detected by the DC current transformer 8A
A and signal transmitting/receiving device 14B from the inverter device IB side
and the current signal iB transmitted through 14A are compared by the current differential relay 15A, but since the current iA=jB, the difference current is not detected and the current differential relay 15A
doesn't work. On the other hand, on the inverter device IB side, the current iB detected by the DC current transformer 8B and the current signal iA transmitted from the converter device IA side through the signal transmitting and receiving devices 14A and 14B are compared by the current differential relay 15B. , since the current iB=iA, no differential current is detected and the current differential relay 15B does not operate. Therefore, the AND circuit 16 from the respective current detection relays I5A and 15B
The output is sent to A and 16B as a logic "0" signal. Therefore, the AND condition is not satisfied in both AND circuits 16A and 16B, and the converter control device 17A
No output is sent to and 17B. As a result, the converter device IA and the inverter device IB continue to operate. Next, we will discuss a case where a failure occurs in a communication system such as a signal transmitting/receiving device.

In this case, since the DC power transmission system is normal, currents iA and iB on the converter device IA and inverter device IB sides are equal as described above. Further, since the communication system is abnormal, neither the converter device IA side nor the inverter device IB side can receive a signal from the other side. As a result, the current differential relays 15A and 15B malfunction, and outputs are sent to the AND circuits 16A and 16B as logical values of "1". On the other hand, since no ground fault has occurred in the DC transmission system, the DC ground fault overcurrent relay 12 is inoperable.
Logic value “0” is sent to the AND circuit 16A on the converter device IA side.
The output is sent out as a signal of ``, and the inverter I
Outputs are sent to the B-side AND circuit 16B as a signal with a logic value of "0" via the signal transmitting device 13A and the signal receiving device 13B, respectively. However, which AND circuit 16A
, 16B, the AND condition is not satisfied, so no output is sent out, and the converter device IA and inverter device IB continue to operate as described above. Next, we will discuss the case where a ground fault occurs on a DC power transmission line.

If a ground fault occurs at point F in the DC transmission line 5, the DC current iA flowing through the DC transmission line 5 on the converter device IA side will increase, and the DC current iB on the inverter device IB side will decrease. Therefore, a current difference is generated between both currents iA and iB, and each current differential relay 15A and 15B operates by detecting the difference current, and AND circuits 16A and 1
The output is sent to 6B as a signal with a logic value of "1". On the other hand, since a ground fault has occurred, the DC ground fault overcurrent relay 1
2 operates, AND circuit 16A on the converter device IA side
The output is sent to the inverter IB as a signal with a logic value of "1", and the output is sent as a signal with a logic value of "1" to the asodo circuit 16B on the side of the inverter IB through the same process as described above. As a result, the AND conditions of the AND circuits 16A and 16B are satisfied, and from this, the converter control devices 17A and 1
An output signal (converter operation stop command) is sent through 7B, thereby stopping the operation of the converter device IA and the inverter device IB. In this way, in a DC power transmission system in which a converter device converts alternating current to direct current, the power is transmitted to a destination through a direct current transmission line, and then an inverter device converts the direct current to alternating current.
Current jA flowing to the converter device and inverter device side
and a current differential relay that operates by detecting a differential current of iB,
and the AND condition of both outputs of a DC ground fault overcurrent relay that operates by detecting an overcurrent due to a ground fault in a DC transmission system.
This system detects an internal failure, that is, a ground fault, and protects the DC transmission line. Therefore, even if the current differential relay malfunctions due to a failure in the communication system, it is possible to reliably prevent the operation of the converter, that is, the converter and the inverter device from stopping.

Further, the operation of the converter is stopped only when a ground fault occurs in the DC power transmission line due to the above-mentioned reasons, and the converter can be protected reliably and effectively. In the above embodiment, the A conversion station is described as being on the converter side and the B conversion station as being on the inverter side, but this is not limited to this. Even if the A conversion station is on the inverter side and the B conversion station is on the converter side, the same effect can be obtained. The same effect can be obtained.

As explained above, according to the present invention, the converter device converts the amount of alternating current electricity into the amount of direct current electricity, which is then transmitted as direct current through the direct current transmission line, and at the receiving end, the inverter device converts the amount of direct current electricity into alternating current electricity. In a DC transmission system that converts electricity into electrical quantities, both a current differential relay that detects the difference between the DC currents at both ends of the DC transmission line, and a DC ground fault overcurrent relay that detects an overcurrent in the event of a ground fault. Since a ground fault is determined based on the AND condition of the output, highly reliable DC transmission can respond only to ground faults in DC transmission lines and provide reliable and effective protection. A ground fault protection method for electric wires can be provided.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the general configuration of a DC transmission system, and Figures 2a and b are line current waveforms on the converter and inverter sides when a ground fault occurs in the DC transmission line in Figure 1. FIG. 3 is a diagram showing an embodiment of the ground fault protection system for a DC power transmission line according to the present invention, and FIG. 4 is a diagram showing the configuration of the protection circuit according to the present invention. IA...Converter device, IB...Inverter device, 2A, 2B...AC system, 3A, 3
B...Shin breaker, 4A, 4B...Converter transformer, 5,7...DC transmission line, 6A, 6B...
...DC reactor, 8A, 8B...DC current transformer,
9A, 9B...Current detection relay, 10...
...Grounding current transformer, 12...DC ground fault overcurrent relay, 13A...Signal transmitter, 13B...
...Signal receiving device, 14A, 14B... Signal transmitting and receiving device, 15A, 15B... Current differential relay,
16A, 16B...AND circuit, 17A, 17
B...Converter control device. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. In a DC power transmission system in which a converter device converts an alternating current amount of electricity into a direct current amount of electricity, which is then transmitted as direct current through a DC transmission line, and an inverter device converts the direct current amount of electricity into an alternating current amount of electricity at the receiving end, A current differential relay that detects the DC current at both ends of the DC transmission line, transmits the information to each other, compares it with the DC current at its own end, and operates when there is a difference between the two; A DC ground fault overcurrent relay installed in a grounding circuit that operates when it detects an overcurrent at the time of a ground fault and transmits the output as a signal at its own end and transmits it to the other end, and an output of the current differential relay at its own end. The presence or absence of a ground fault is determined based on the AND condition of the output of the DC ground fault overcurrent relay and the output of the DC ground fault overcurrent relay, and at the other end, the output of the current differential relay and the output information from the DC ground fault overcurrent relay are A ground fault protection method for a DC power line, comprising: a device for protecting the DC power line under an AND condition.