JPS6240949B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection system for a large-capacity controlled rectifier in which a plurality of unit control rectifiers are connected in parallel to form a main circuit.

Conventionally, gate shift, bypass pair, gate advance, gate block, etc. are known as protection operations for controlled rectifiers, and protection is performed by combining these and interlocking them.

Here, the gate shift greatly retards the firing angle of the controlled rectifier in the inverse conversion region (firing angle 90°~
180°) and regenerates energy from the DC side to the AC side. Bypass pairing is an operation in which a pair of controlled rectifier elements connected to the same phase on the AC side are energized simultaneously to short-circuit the DC circuit. Gate advance is a protective operation used in a controlled rectifier configured by connecting a plurality of unit control rectifiers in parallel, and is an operation in which the firing angle is advanced to operate in the forward conversion region. That is, the unit control rectifier in which some abnormality has occurred is gate-shifted, bypassed, or gate-blocked, and the firing angle of the remaining healthy control rectifiers is advanced to the forward conversion region, and the unit control rectifiers connected in parallel are This is a protective operation that reduces the current of the unit control rectifier to zero due to the difference in output voltage between the two. Gate blocking is a protective operation by blocking the ignition pulse applied to the control rectifier.

A combination of the protection operations described above is called a protection interlock, and there are protection interlocks such as gate shift to gate block, bypass pair to gate block, gate advance to gate shift, gate block, and instantaneous gate block.

In general, with controlled rectifiers, depending on the type of accident,
Appropriately, the above-mentioned protection interlocks are used, and protection is achieved by finally tripping the AC side switch or disconnector. Figure 1 shows a single line diagram of a controlled rectifier in which four unit controlled rectifiers are connected in parallel to form 24 phases. In Figure 1, 1 is an AC bus bar, 2-
1, 2-2, AC cut-off switches 3-1, 3-2 are rectifier transformers, 4-1 to 4-4 are unit control rectifiers, and 8-1 to 8-4 are unit control rectifiers 4. -1～
A linear reactor suppresses the current flowing between 4 and 4, and 7 is a load. 5 is a DC current detector that detects the current flowing through the load, 5-1 to 5-4 are DC current detectors that detect the current flowing through the unit control rectifiers 4-1 to 4-4, respectively, and 6 is a DC current detector. 6-1 to 6-4 are unit control rectifiers to detect overcurrent of the current flowing to the unit control rectifiers 4-1 to 4-4, respectively. It is an overcurrent relay. Controlled rectifiers generally perform various types of failure detection, but to simplify the explanation, a case of DC overcurrent will be described.

In FIG. 1, when a DC overcurrent or relay 6 is activated due to a load short circuit or an abnormality in the control system, all of the unit control rectifiers 4-1 to 4-4 are caused to perform gate shift and gate block protection interlocking operations.
Immediately reduce the DC current to zero and stop the controlled rectifier. On the other hand, due to an accident within the unit control rectifier 4-1 or a current imbalance between the unit control rectifiers 4-1 to 4-4, the unit control rectifier overcurrent relay 6-
If 1 was activated, an accident occurred. The unit control rectifier 4-1 is a bypass pair gate block,
The well-controlled rectifiers 4-2 to 4-4 perform gate advance, gate shift, and gate block protection interlock. Protection coordination between the DC overcurrent relay 6 and the unit control rectifier overcurrent relays 6-1 to 6-4 is performed by an overcurrent setting level. For example, DC overcurrent relay 6 is 110%, unit control rectifier overcurrent relay 6-
1 to 6-4 are about 140%, and when the DC overcurrent relay 6 is activated, the unit control rectifier overcurrent relay 6-1
~6-4 are set not to operate. However, in consideration of the case where multiple protective relays operate due to some kind of malfunction, protection operations are usually prioritized. Conventionally, the gate block had the highest priority, then the bypass pair, then the gate shift, and the lowest priority was the gate advance. For example, if a gate shift signal and a bypass pair signal are generated simultaneously, the target unit controlled rectifier becomes a bypass pair.

FIG. 2 shows a block diagram of a control circuit for a conventionally used unit control rectifier. In Fig. 2, 9 is an automatic control circuit that controls the current flowing through the load or the voltage applied to the load and outputs an amount equivalent to the required output voltage, and 10 is an automatic control circuit that obtains a signal for gate shift or gate advance in case of an accident. A firing angle determining circuit at the time of an accident outputs an amount corresponding to the firing angle; 11 is a protection interlocking circuit that receives signals from various failure detectors and performs appropriate protection interlocking; 12 is an output signal from the protection interlocking circuit 11; A multiplexer 13 receives the output signal of the multiplexer 12 and selects the firing phase and point. A phase control circuit which determines arc timing and receives a bypass pair signal 51 which is an output signal of the protection interlocking circuit 11 and makes the control rectifier a bypass pair; 14 is a gate shift signal 52 which is an output signal from the protection interlocking circuit 11;
This is an OR element that takes an OR between the gate advance signal 53 and the gate advance signal 53.

The operation of the conventional control circuit will be explained below with reference to FIG.

During normal operation, the output of the automatic control circuit 9 is input to the phase control circuit 13 to determine the ignition timing. If an accident occurs that requires gate shift and gate block protection interlock, the gate shift signal 52 is output from the protection interlock circuit 11, and the firing angle is controlled by the multiplexer 12 from the automatic control circuit 9 at the time of the accident. Arc angle determination circuit 1
The firing angle of the unit control rectifier 4-1 is controlled by the firing angle at the time of the predetermined gate shift. Further, for example, in the case of an accident that should be made into a bypass pair, the bypass pair signal 51 is output to the phase control circuit 13, and the unit control rectifier 4-1 becomes a bypass pair. That is, in conventional control circuits, when a bypass pair signal is generated, the phase control circuit 13 performs bypass pair control while ignoring other controls.

In FIG. 2, the automatic control circuit 9 is common to all control rectifiers. The protection communication circuit 11 performs protection interlock control over the entire control rectifier, but outputs an output signal for each unit control rectifier. Others have individual functions for each unit control rectifier.

By the way, a unit control rectifier 4 as shown in FIG.
When a large inductance load is connected to a multiphase controlled rectifier configured by connecting multiple units of -1 to 4-4 in parallel, the conventional priority order of protection operation as shown in Figure 2 is used. When using such a control circuit, a problem arises in that the entire current is concentrated in a specific unit control rectifier. For example, in FIG. 1, when the DC overcurrent relay 6 operates and the unit control rectifiers 4-1 to 4-4 are being gate-shifted, due to some malfunction, the unit control rectifier overcurrent relay 6-1 of the unit control rectifier 4-1 is activated. When activated, the bypass pair signal 51 is generated only for the control circuit of the unit control rectifier 4-1, and since bypass pair operation has priority, the unit control rectifier 4-1 is bypassed even during gate shift. Become a pair.

FIG. 3 shows a simplified relationship between the DC output voltages in this case. 54 indicates the direction of direct current. Components with the same functions as those in FIG. 1 are indicated by the same symbols. As is clear from this figure, all the load current flows into the unit control rectifier 4-1, and during rated operation, a problem occurs in that four times as much overcurrent flows through the unit control rectifier.

An object of the present invention is to provide a protection method for a controlled rectifier that can eliminate the above-mentioned problems and reliably protect the controlled rectifier even in a multiphase controlled rectifier configured by connecting a plurality of unit controlled rectifiers in parallel. Our goal is to provide the following.

A block diagram of one embodiment of the present invention is shown in FIG. Blocks in the figure having the same functions as those in FIG. 2 are designated by the same reference numerals, and explanations thereof will be omitted. In FIG. 4, 15 is
When the output signal of the OR circuit 14 is "1", the protection interlocking circuit 11 outputs the gate shift signal 52 or
When the gate advance signal 53 is output, the bypass pair signal 51 is an inhibit circuit for inhibiting output to the phase control circuit 13.

The operation of the present invention will be explained below with reference to FIG. The normal operation of the control circuit shown in FIG. 4 has been described above and will not be described in detail. In FIG. 1, if the DC overcurrent detection circuit 6 is activated due to a load short circuit or the like, a gate shift signal is output from the protection interlocking circuit 11 to the control circuits of all unit control rectifiers 4-1 to 4-4. Unit control rectifier 4-1 to 4
-4 is gate shifted. At this time, due to current unbalance or some kind of malfunction, the unit control rectifier overcurrent detector 6-1 of the unit control rectifier 4-1
When the protection interlock circuit 11 operates, the bypass pair signal 51 is sent to the control circuit of the unit control rectifier 4-1. However, in the protection system of the present invention, as shown in FIG. 4, when the gate shift signal is generated, the inhibit circuit 15 prohibits reception of the bypass pair signal 51. Therefore, the gate shift operation of the unit controlled rectifier 4-1 is continued, and the DC current can be safely reduced to zero and the controlled rectifier can be stopped. Also, when the gate advance signal 53 becomes "1", it is exactly the same as when the gate shift signal 52 becomes "1", and the bypass pair signal is locked by the inhibit circuit 15.

As explained above, in the protection method of the controlled rectifier of the present invention, while the unit controlled rectifier is gate shifting or gate advancing, the bypass pair signal to the unit controlled rectifier is not accepted. A particular unit control rectifier becomes a bypass pair, and current does not concentrate on that unit control rectifier. Further, the present invention can be easily implemented by simply adding a few logic gates to a conventional control circuit, and great effects can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a single line diagram of a 24-phase control rectifier constructed by connecting four unit control rectifiers in parallel, Fig. 2 is a block diagram showing an example of a conventional control circuit, and Fig. 3 is a single line diagram of a 24-phase control rectifier constructed by connecting four unit control rectifiers in parallel. FIG. 4, which is a diagram showing the relationship between DC output voltages when only unit control rectifiers form a bypass pair, is a block diagram showing an embodiment of the present invention. 1... AC bus bar, 2-1, 2-2... AC power disconnector, 3-1, 3-2... Rectifier transformer, 4-
1~4-4... Unit control rectifier, 5, 5-1~5
-4...DC current detector, 6...DC overcurrent relay, 6-1 to 6-4...Unit control rectifier overcurrent relay, 7...Load, 8-1 to 8-4...DC reactor, 9... Automatic control circuit, 10... Accident firing angle determining circuit, 11... Protection interlocking circuit, 12...
Multiplexer, 13... Phase control circuit, 14...
...OR circuit, 15...inhibit circuit, 51...
...Bypass pair signal, 52...Gate shift signal, 53...Gate advance signal.

Claims (1)

[Claims] 1. A controlled rectifier configured by connecting a plurality of unit controlled rectifiers in parallel each having an individual protective operation function, which is characterized by locking the bypass pair control circuit when receiving a gate shift or gate advance protection command. Protection method for controlled rectifier.