JPS6238931B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an arm short circuit detection device for a controlled rectifier.

One of the failure modes of controlled rectifiers is what is commonly referred to as arm short circuit. An arm short circuit is a state in which at least one of the arms constituting the controlled rectifier is short-circuited.

FIG. 1 shows a main circuit connection diagram of a three-phase bridge control rectifier, and FIG. 2 shows a phase voltage waveform when the arm of the U phase in FIG. 1 is short-circuited. In Fig. 1, 1 is an AC bus, 2 is a rectifier transformer, 3 is an AC current detector that detects AC current on the secondary side of the rectifier transformer, 4 is a controlled rectifier, and 8 ₁ to _{8 6} are controlled rectifiers. Element 5 is a DC current detector that detects the current on the load side, 6 is the load, and 7 is a component that detects an arm short circuit of the control rectifier 4 based on the difference between the output from the AC current detector and the output from the DC current detector. It is a differential protection relay.

FIG. 2 shows a phase voltage waveform when an arm short circuit occurs in the U phase of the controlled rectifier 4 in FIG. 1.
In FIG. 2, even if an arm short circuit occurs in the U phase at time t, normal operation occurs while the U phase is energized. When an ignition pulse enters the V phase, the U phase control rectifier 8 ₁ turns off in normal operation, but if an arm short circuit occurs, the U phase control rectifier 8 ₁ does not turn off, so the 2
This results in a phase short circuit (in the case of the figure, an R-S phase short circuit). Therefore, an overcurrent begins to flow on the alternating current side. If some kind of protective operation is not performed in this state, the Z phase will then be commutated to the X phase, and the U phase and the X phase will form a bypass pair, but since the V phase is also energized, the two-phase short circuit will still continue. Next, when the ignition pulse enters the W phase, the R-
After a three-phase short circuit occurs in the ST phase, the V-phase control rectifier ₈₂ is turned off, and a two-phase short circuit occurs in the RT phase. Next, when an ignition pulse is applied to the Y phase, commutation occurs from the X phase to the Y phase, and the bypass pair is released. When the U-phase voltage becomes higher than the W-phase voltage again, the W-phase control rectifying element ₈₃ is turned off, and the U-phase and Y-phase are energized.

When an arm short circuit occurs, the above operation is repeated, but the AC current at the time of a two-phase short circuit is only suppressed by the % impedance of the rectifier transformer, and when the controlled rectifier is operated in the forward conversion region. is a very large value, and in a normal system, an AC overcurrent several times the rated value flows. For this reason, conventionally, arm short circuits have been detected promptly and known protection interlocks such as instantaneous gate blocking and shunt tripping have been performed. FIG. 1 shows a conventional arm short circuit detection device. There are other causes of AC overcurrent, such as a short circuit on the load side, so conventionally, the output of the AC current detector 3 and the output of the DC current detector 5 on the load side are compared, and the difference is greater than or equal to the set value. The arm short-circuit was detected by the differential relay 7, which was activated.

By the way, as is clear from Fig. 1, in the conventional method, it is necessary to detect the DC current on the load side and the AC current of the controlled rectifier. constitutes,
In controlled rectifiers that also require large currents, the busbar on the secondary side of the rectifier transformer becomes very thick, making it impossible to detect alternating current with a normal bushing current transformer, and requiring a large number of alternating current detectors. Because of this, the alternating current is detected on the primary side of the rectifier transformer. Figure 3 shows a main circuit configuration diagram when two unit control rectifiers are connected in parallel. Components in the figure that have the same functions as those in FIG. 1 are designated by the same reference numerals. 9 is an AC overcurrent detector that detects overcurrent on the AC side. In FIG. 3, when attempting to detect an arm short circuit using the conventional arm short circuit detection method and using a differential protection relay that operates based on the difference between the output of the AC current detector 3 and the DC current detector, the unit control rectifier 4 A problem occurs in that it is not possible to determine which arm is short-circuited between -1 and 4-2.

When multiple unit control rectifiers are connected in parallel, only the unit control rectifier in which an arm short circuit has occurred is instantaneously gate-blocked, and the other control rectifiers are once operated in the forward conversion region, and the unit control rectifier in which an arm short circuit has occurred is gate-blocked. Since it is necessary to reduce the current of the control rectifier to zero and then perform protective interlocking such as gate shift → gate block → circuit breaker trip, it is not possible to determine which unit control rectifier has an arm short circuit in order to protect the control rectifier. Very important.

The object of the present invention is to solve the above-mentioned problems, and to provide a polyphase controlled rectifier in which a plurality of unit controlled rectifiers are connected in parallel. An object of the present invention is to provide an arm short-circuit detection device for quickly determining which unit control rectifier has an arm short-circuit even in a power supply system in which alternating currents of control rectifiers are detected all at once.

FIG. 4 shows a block diagram of an embodiment of the present invention. For simplicity, FIG. 4 shows an example of the case where the present invention is implemented in a controlled rectifier device in which two unit controlled rectifiers are connected in parallel, as explained in FIG. 3. Fourth
In the figure, 9 is an overcurrent detector having the same function as the overcurrent detector explained in FIG.
When the primary current of the rectifier transformer becomes an overcurrent, a logic signal "1" is generated. 10-1, 10-2
11-1 and 11-2 are the outputs of the bypass pair detectors 10-1 and 10-2, respectively, which detect that the unit control rectifiers 4-1 and 4-2 have become a bypass pair. and an AND circuit that takes the AND condition of the output of the overcurrent detector 9,
12-1 is a block for detecting an arm short circuit of the unit control rectifier 4-1, and 12-2 is a block for detecting an arm short circuit of the unit control rectifier 4-2.

The operation of the present invention will be described below with reference to the phase voltage waveform when an arm short circuit occurs in Fig. 2, the main circuit configuration diagram of a control rectifier in which two unit control rectifiers are connected in parallel in Fig.
DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention shown in FIG.

In FIG. 3, if an arm short circuit occurs in the U phase of the unit control rectifier 4-1, the R-S
There is a short circuit between the two phases, resulting in an overcurrent on the AC side, and the fourth
The output of AC overcurrent detector 9 in the figure is logic “1”
becomes. X after 60° after the ignition pulse is generated in the V phase
When an ignition pulse is generated in the phase, as shown in Fig. 2, the U phase and the Logic "1" is obtained at the output of 11-1, and unit control rectifier 4
-1 can detect that an arm short circuit has occurred.
The bypass pair detector in Figure 4 10-1 and 10-2 detects the arm current and detects that the two arms connected to the same AC phase have become a bypass pair when current flows at the same time. A bypass pair detector is equipped with a barotropic and reverse pressure detector on each arm of the three-phase bridge, and when the barostatic pressure and reverse pressure of two arms connected to the same AC phase disappear at the same time, the bypass pair is detected. There are bypass pair detectors that detect is common.

As explained above, the arm short circuit detector of the present invention utilizes the fact that when an arm short circuit occurs, the unit control rectifier in which the arm short circuit occurred always becomes a bypass pair, and uses the output of the AC overcurrent detector and the bypass pair detection It is detected that the outputs of the devices become logic "1" at the same time, and it is detected that an arm short circuit has occurred.

FIG. 5 shows a modification of the present invention. In FIG. 5, parts having the same functions as those in FIG. 4 are denoted by the same reference numerals. In Fig. 5, 13-1, 13-2 are bypass pair closing commands to unit control rectifiers 4-1, 4-2, respectively, and 14-1, 14-2 are bypass pair closing commands 13-1, 13-2, respectively. 2 constitutes an inhibit circuit that cuts off the outputs of the AND elements 11-1 and 11-2.

In a controlled rectifier, a unit controlled rectifier may be intentionally inserted into a bypass pair for control protection. Therefore, in FIG. 5, when the bypass pair input commands 13-1, 13-2 are generated, the inhibit circuits 14-1, 14-2 cut the outputs of the AND elements 11-1, 11-2, and short-circuit the arms. It is distinguished from a bypass pair.

The present invention has been described above with respect to a controlled rectifier in which two unit controlled rectifiers are connected in parallel as shown in FIG. 3, but the same applies to the case of one unit controlled rectifier or the case of three or more unit controlled rectifiers.

As is clear from the above explanation, the arm short circuit detection device of the present invention is a controlled rectifier in which a plurality of unit control rectifiers are connected in parallel. Even in a power supply system in which alternating currents of rectifiers are detected all at once, it is possible to easily identify a unit control rectifier with an arm short circuit, and to provide appropriate protection. Also unit control rectifier 1
Even in the case of a stand, there is no need for a DC current detector or differential protection relay.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional arm short circuit detection device.
Figure 2 is a phase voltage waveform diagram when the U phase arm is short-circuited in a three-phase bridge rectifier, Figure 3 is a configuration diagram of a controlled rectifier in which two unit control rectifiers are connected in parallel, and Figure 4 is the arm of the present invention. FIG. 5 is a block diagram of one embodiment of the short circuit detection device. FIG. 5 is a block diagram of a modified example of the present invention. 1... AC bus, 2... Rectifier transformer, 3... AC current detector, 4... Unit control rectifier, 5... DC current detector, 6... Load, 7... Differential protection relay, 8 ₁ ~
8 ₆ ...Control rectifier, 9...AC overcurrent detector, 1
0-1, 10-2...Bypass pair detector, 11-
1, 11-2...AND circuit, 12-1, 12-2
...Arm short circuit detection circuit, 13-1, 13-2...Bypass pair command, 14-1, 14-2...Inhibit circuit.

Claims (1)

[Claims] 1. In a controlled rectifier consisting of a plurality of unit controlled rectifiers connected in parallel with each other, an AC overcurrent detector detects AC overcurrent, and an AC overcurrent detector detects the forward voltage of the upper and lower arms to indicate that the controlled rectifier is in a bypass pair state. , a bypass pair detector that detects the absence of reverse voltage in both cases, and an AND circuit that takes an AND condition between the AC overcurrent signal from the AC overcurrent detector and the bypass pair signal from the bypass pair detector. An arm short-circuit detection device for a controlled rectifier, which determines an arm short-circuit when the AND condition is satisfied.