JPS6132901B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection device for a forward power converter as an AC-DC converter applied to a DC electric railway power supply system or a DC power transmission system, and more particularly to In the case of a general system in which a transformer is inserted on the AC input side of The purpose is to provide a new protection device that can provide protection.

As is well known, in the power supply system or DC power transmission system of a DC electric railway, a forward power converter is used to convert the AC power input from the commercial frequency power supply bus into DC power. FIG. 1 shows a typical protection method for a system including a power conversion device. In the figure, 1 is a three-phase commercial frequency power supply bus, 2 is an AC breaker, 3 is a current transformer that takes out the phase currents ia, ib, and ic of each phase, and 4 is a forward power supply with thyristors connected in a forward bridge. In the converter, 5 is a DC transformer that takes out the DC current IDC, 6 is the load to which the desired DC power is supplied, and 7 is the one that compares the magnitude of the detected amount taken out from each current transformer 3 and 5. This is a current differential relay that detects internal failures in the forward power converter and provides specified protection. To describe the protection method for the above configuration, the signal related to the phase current extracted from each current transformer 3 and 5 and the signal related to DC current are compared and judged by the current differential relay 7. Forward power conversion device 4
The technical concept of this protection method is to detect the presence or absence of an abnormality in the thyristor element and perform the specified protection. When distinguishing between an accident when the thyristor element loses its blocking ability in the reverse direction and the arm into which the element is inserted short-circuits, an accident occurs when commutation fails.
When commutation fails, the DC current is 1.5 times the steady current value
The judgment is based on the phenomenon that the DC current increases by about twice as much, but when the arm is short-circuited, the DC current becomes almost zero. Therefore, the DC current increases due to an accident caused by a commutation failure in which the DC current increases in this way, and the DC current Accidents caused by arm short circuits, where As a phenomenon, when one phase of the power supply is open due to a failure on the circuit breaker 2 side, both the phase current and the DC current, which are taken out as a judgment element of the current differential relay, are Since there is a period in which there is current and a period in which there is no current, when the signal levels of both currents are compared, they are almost the same level, and an accident at the time of phase loss cannot be detected.

The present invention was invented in view of this point, and in particular, the present invention detects all possible failures even if the conventional current differential protection method is applied,
The present invention is characterized in that it realizes a protection method that can perform predetermined protection, and will be described in detail below based on the specific examples shown in FIGS. 2 and 3.

Figure 2 shows a specific configuration example of the basic protection method of the present invention. In the same figure, the same parts as in Figure 1 are given the same reference numerals, and 8 is one of the objects of protection under this protection law. This transformer is often seen in normal systems, and is used, for example, to step down the input power supply voltage to a predetermined value. However, for example, a Y-△ or △-Y connected transformer is generally used. Now, FIG. 3 shows a specific configuration diagram of the current differential relay 7, which is the main part of the present invention. In the phase current of the phase, idc is the DC current taken out from the secondary side of the DC current transformer 5, and A is a current differential relay that has almost the same function as the conventional differential relay shown in FIG. B is a relay that monitors phase balance, which is the main part of the present invention. Now, the former differential relay A, as shown in the figure, extracts the absolute values |ia|, |ib|, |ic| from the instantaneous values ia, ib, and ic of each phase current and adds these absolute values, respectively. Addition circuit 9 for obtaining instantaneous, instantaneous AC input current Σ|i|, and this circuit 9
The sum of the instantaneous and instantaneous AC input currents Σ|i
| is accumulated over each half-wave period of the input power supply voltage waveform or over one cycle of the input power supply voltage waveform, and the average value of the AC input current is calculated from the accumulated result. Average value calculation circuit 10
and an absolute value circuit 11 that sequentially samples the DC current idc in synchronization with the sampling signal to extract the instantaneous value of the phase current, and extracts the absolute value |idc| from each instantaneous value of the sampled DC current,
Similar to the method described above, the signal output from this absolute value circuit is sequentially accumulated over a period corresponding to each half-wave period of the input power supply voltage waveform, and the average value of the DC current is calculated from the accumulated results. The second average value calculation circuit 12 to calculate the average value Σ of the AC input current
|i| and the average value of DC current kidc are subtracted to obtain Σ|
The first step is to obtain the motion amount i|-kidc and compare this motion amount with the suppression amount representing the dead zone amount Ko.
Similarly, the determination circuit 13 of
kidc and the average value K of AC input current as the suppression amount
Second judgment circuit 1 that compares and judges Σ|i|
4. Note that this second determination circuit 14 is Σ|i|−
kidc, which shows the operating amount and the average value of DC current.
The determination may be made by comparing the amount of suppression. However, the above k and K are each constants, for example, the former constant k
is expressed by the equation k=2α, where α is the current transformation ratio of the current transformer 3. 15 is an AND gate that takes the AND condition of the signals output from the first and second judgment circuits 13 and 14; 16 is a first timer that delays the signal output from the AND gate for a predetermined period; An internal fault in the transformer 8 or an internal fault in the forward power converter 4 is detected using the signal output from this timer. Now, as shown in the figure, relay B that monitors the phase balance outputs signals |ia(t)|, |ib(t)|, |ic( t) | and a signal sampled 60° before these signals | ia (t−
60゜)｜,｜ib(t-60゜)｜,｜ic(t-60
゜）｜Tode｜ia(t)｜−｜ib(t−60゜)｜＋｜ib
(t)｜−｜ic(t−60゜)｜＋｜ic(t)｜−｜ia(t
-60°) | - 60° in the equation is derived on the condition that the six element groups of the forward power converter 4 sequentially commutate every 60°. However, instead of using the instantaneous value of the phase current sampled 60 degrees ago, it is also possible to monitor phase balance by using the instantaneous value of the phase current sampled 120 degrees ago, for example. There is no problem with the various quantities involved. Now, returning to FIG. 3 again, 19 indicates whether the instantaneous value of the AC input current derived from the above formula is accumulated sequentially over a half-wave period of the power supply voltage waveform, or is accumulated in one cycle of the power supply voltage waveform. 20 is a third average value calculation circuit that calculates the average value from the results sequentially accumulated over the crossing, and 20 determines whether there is an accident or not depending on whether the signal output from the third average value calculation circuit 19 is zero or "signal present". A third judgment circuit that performs judgment, 21
In order to obtain the instantaneous value of the phase current, the DC current was sequentially sampled in synchronization with the sampled signal, and the instantaneous values obtained were sequentially accumulated over one cycle of the current and voltage waveforms, and the average value was calculated. A subtraction circuit that subtracts the signal amount Σidc(t) and the signal amount Σ which is the average value of this signal amount one cycle before. 22 is a fourth average value calculation circuit and the signal output from the subtraction circuit 21. 23 is a circuit for determining the presence or absence of an accident based on whether the signal output from the fourth average value calculation circuit 22 is zero or "signal present". 24 is the third
25 is an AND gate that takes the AND condition of the signals output from the and fourth judgment circuits 20 and 23.
This is a second timer that delays the signal output from the AND gate 24 for a predetermined period of time. As described above, the relay B that monitors the phase balance includes the arithmetic circuit 18 - the third and fourth average value calculation circuits 19, 22 - the subtraction circuit 21 - the third and fourth judgment circuits 20, 23 -
Similarly, the current differential relay A is composed of an AND gate 24 - a timer 25, and a current differential relay A is composed of an adder circuit 9 - first and second average value calculation circuits 10, 12 - DC current instantaneous value circuit 11 - first and second Judgment circuits 13, 14-
It is composed of an AND gate 15 and a timer 16, and the output signals P ₁ and P ₂ of both relays A and B are input to an OR gate 17, and the output of an inhibit circuit 28 is inserted into the output side of the OR gate. An internal fault between the transformer and the forward power converter is finally detected using the signal, and an alarm is generated using this detection output to provide a prescribed protection. Note that 26 is a contact a of a malfunction prevention relay (not shown) that prevents relays A and B from malfunctioning due to excitation inrush current flowing through the transformer when the forward power conversion device is started;
7 is a third timer that delays the contact output signal of this relay for a predetermined period of time.

Now, the operation of the present application configured as described above is explained in the fourth section.
This will be explained in detail based on the time charts shown in FIGS. Figure 4 shows the phase currents ia, ib, ic of the input power supply and the primary currents iab, ibc,
ica, secondary currents iAB, iBC, iCA, forward power converter arm currents iAO, iBO, iCO, and direct current idc,
In the mutual relationship of these currents, each phase current ia, ib on the primary side of the transformer,
IC and the secondary side phase currents iA, iB, and iC of the transformer can be considered to be in phase with the current transformation ratio n, and furthermore, the secondary side phase currents iA, iB, and iC of the transformer and the arm current of the forward power converter
iAO, iBO, iCO and DC current idc are iA(=iB=
iC) = iAO (= iBO = iCO) = idc, and the total sum of AC input current Σ|i| is Σ
Since there is a relationship of |i|=|ia|+|ib|+|ic|, therefore, let's pay attention to the time chart during the conduction period of each thyristor of the forward power conversion device in Figure 4. , for example, the conduction width of thyristor TH _A is 120
When the flow width in the first half is 60°, the thyristor
TH _B is conducting, and in the latter half of the current flow width of 60°, thyristor TH _C is conducting, and the thyristor
The flow width of TH _B and TH _C is 1/2 of the flow width of thyristor TH _A. Therefore, when thyristor THA is on and thyristor THB is on, iB=iA, iC=0, so the absolute value at that time is |iA|+|iB|+|iC|=2|iA|, and , when THA is on and thyristor THC is on, iB=0 and iC=iA, so in this case also |iA|+
|iB|+|iC|=2|iA|, and since iA has the relationship iA=iDC as mentioned above, Σ|i′|=2|
iDC｜becomes. Here, the sum of the secondary currents of the transformer Σ|i'| and the sum of the primary currents of the transformer Σ|i| are approximately in phase as described above, and the current value itself is regulated only by the current transformation ratio n. Therefore, if this current transformation ratio n is ignored and the current transformation ratio of the current transformer from which the primary side phase current is taken is α, then the current transformation ratio n is taken out from the secondary side of the current transformer. total transformer primary current Σ |
The relationship between i| and DC current idc is Σ|i|=2αidc
...We can obtain the following relational expression.

Now, to describe the steady state operation based on the relationship between the input and output currents of the transformer and forward power converter, which have the above relationships, the voltage waveform of the AC input current is shown in Figure 4. Assuming that the transition occurs in phase order as shown in Fig. 4B, if each thyristor of the forward power converter is fired in sequence in the pattern shown in Fig. The side output current, that is, the phase current (thyristor current) of the forward power converter, is shown in Figure 4 C, the current flowing through the primary winding of the transformer is shown in Figure 4 D, and the phase current of the AC input current is shown in Figure 4 E. The waveform patterns are as shown in FIG. In such a current mode, the current differential relay A shown in Figure 3
Relay B, which monitors the state of phase balance, first detects the phase currents ia, ib, ic of the AC input power supply and the DC current.
In the case of current differential relay A, each half wave (180°) of the power supply voltage waveform shown in FIG. , or take out the average value of the total sum Σ|i| of the AC input current (shown in FIG. The average value of the DC current idc over a half-wave period or one cycle of the power supply voltage waveform is obtained through 12 paths. Furthermore, for relay B that monitors the state of phase balance, the phase currents ia(t), ib(t), and ic(t) of the AC input currents taken out and the phase currents 60° before the time when these phase currents were taken out are Phase current taken out to
Perform calculations as shown in Figure 4 (t) using ia (t-60), ib (t-60°), and ic (t-60°) to calculate the phase current of the relevant phase and the 60° of the other phase. The difference from the previous phase current (indicating the apparent line current) is taken out, this difference current value is accumulated over a half wave or one cycle of the power supply voltage waveform, and the average value is calculated from the average value calculation circuit 19. Take it out. Similarly, the subtraction circuit 21 and the fourth average value calculation circuit 22 calculate the extracted DC current idc(t) and the DC current idc before this DC current over one cycle.
(t-360°), this operation is performed sequentially over one cycle of the power supply voltage waveform and accumulated, and the average value is taken from the accumulated results. When the average values of the specified currents are calculated using the above method, these average value outputs are inputted to the first to fourth determination circuits 13 to 23 shown in FIG. The determination circuit 13 subtracts the average value Σ|i| of the total sum of AC input currents and the value k|idc|=2α|idc|, which is the average value of DC currents multiplied by 2α, and calculates this subtracted value and suppression. The second determination circuit 14 compares the magnitude relationship with the dead zone value Ko as an amount, and then calculates the calculation result of Σ|i|−k|idc| as the operation amount and the value of kΣ|i| as the suppression amount. The third judgment circuit 20 and the fourth judgment circuit 20
The determination circuit 23 determines whether the signal value output from the average value calculation circuits 19, 22 is "0" or "signal present". As a result of such discrimination, the output of the third average value calculation circuit 19 is zero, as is clear from the current mode shown in FIG. Since the output of the average value calculation circuit 22 is also zero, the AND condition of the AND gate 24 in FIG. 3 is not satisfied, and it is determined that both the transformer to be protected and the forward power conversion device are normal. On the other hand, in the first and second determination circuits 13 and 14 of the current differential relay A, Σ|i| and k
Since |idc|=2α|idc| is the same value, the magnitude relationship between the zero value indicating the current difference and each suppression amount is such that the suppression amount is large and it is determined that both the transformer and the forward power converter are normal. will be done. Note that the operation of the final-stage inhibit circuit 28 shown in FIG. 3 is such that the inrush excitation current of the transformer flows during startup, so
6 is closed and one of the input signals of the inhibit 28 becomes "0". Since the relay contact 26 is in an open state at a fixed time, a signal of "1" is input from the timer 27 to the inhibit 28.

Now, Figure 5 shows the current mode when the thyristor TH _A on the positive side of the forward power converter loses its blocking ability in the reverse _direction and an arm short circuit accident occurs. t ₀ in Figure 5 -
During t ₁ period, the V _A phase of the power supply voltage has the highest potential and the load current changes from thyristor TH _A → TH _B and thyristor
While flowing through the path TH _A → TH _C , the sum of the secondary current of the transformer (shown in Figure 5 C), the DC current shown in Figure 5 D, and the AC input current shown in Figure 5 E The current waveforms of Σ|i| are no different from normal times, and the value obtained by subtracting the signal k|idc| related to DC current from the total sum of AC input currents Σ|i| is as shown in Figure 5. The difference between the current phase current taken out in the same way and the phase current on the other side taken out 60 degrees earlier also has a zero value, as shown in Figure 5.
In this state, thyristor TH _A is connected to thyristor at point _t .
When commutated to TH _B , thyristor TH _A has lost its reverse blocking ability, so the load current flowing through thyristor TH _B (= secondary current of the transformer)
iB would normally flow through the negative side thyristor TH _C , but now flows through the failed thyristor TH _A to the power supply side. Therefore the direct current idc
As shown from t ₁ in Fig. 5D, it gradually decreases and finally reaches zero, making the flow pattern similar to that of a thyristor.
It will maintain a state of approximately zero until it switches to TH _A. On the other hand, since the phase currents iA and iB of the V _A phase and V _B phase increase significantly as shown in Figure 5 C, the total AC input current Σ|i| also increases as shown in Figure 5 E, From these relationships, the total sum of AC input current Σ |
The difference between i| and the signal k|idc| related to the DC current gradually becomes larger than the zero value as shown in FIG. The second judgment circuits 13 and 14 sense and perform a predetermined comparison and judgment, and notify the outside through the AND gate 15 that the forward power conversion device is out of order. On the other hand, in relay B that monitors the state of phase balance, the difference current obtained by subtracting the phase current of the relevant phase and the phase current of the other side taken 60 degrees before this phase current is calculated as shown in Figure 5. Since the value gradually shifts to a value greater than zero, the third determination circuit 20 and fourth determination circuit 23 shown in FIG. 3 sense this change.
The fact that the forward power converter is out of order is notified to the outside through the AND gate 24. Here the third
Current differential relay A and relay B that monitors the state of phase balance shown in the figure both issue a predetermined alarm to the outside in the event of an arm short circuit accident, but which one issues the alarm first depends on the accident. It is determined by the balance between the degree of rise or attenuation of the phase current, the degree of attenuation of the DC current, and the degree of sensing of each relay A, B.

The embodiment shown in FIG. 6 is a case where the thyristor TH _A on the positive side of the forward power converter does not fire at a predetermined firing time because the gate signal is not supplied due to a failure of the gate control unit. For example, from point t ₀ to point _{t 1} in Figure 6 B, the V _A phase of the power supply voltage is at the highest potential, and the thyristor operates during the first half of the 60° period. _TH →
If the load current flows through the path of thyristor TH _B , and the path of thyristor TH _A → thyristor TH _C during the second half of the 60° period, the gate signal of thyristor TH _A is out of phase, so the situation shown in Fig. 6 C and D occurs. As shown, the secondary current of the transformer, that is, the phase currents iA, iB, iC of the forward power converter and the direct current idc are both lost. Therefore, the current differential relay A shown in FIG. 3, which takes in these currents and performs a predetermined operation, and the relay B, which monitors the state of phase balance, are both in the OFF state. In this state, the power supply voltage V _B phase becomes the highest potential during the period from point t ₁ to point t ₂ , and the thyristor TH _B
During the first half of the 60° width period, the thyristor
When the load current starts to flow in the path TH _B → load → thyristor TH _C , the DC current idc and the total sum of AC input current Σ |i | The current value returns to approximately the steady state value (this is when DC bias during the transient period is ignored) and is operated by a signal related to these DC currents idc and the sum of the AC input currents Σ|i| The current differential relay A is in the OFF state as in the normal state.
On the other hand, the arithmetic circuit 18 of relay B, which monitors the state of phase balance, operates at the time when phase currents iB(t), ic(t), and 60 degrees before the time when phase currents are taken out (6th Phase current ic of V _C phase (t-60°), phase current iA of V _A phase (t-60°) during period t ₀ ′ to t ₁ in the figure)
As shown in the period from t ₁ to _{t 2} in FIG. input to circuit 20; Third judgment circuit 2
0 means that the input “signal present” signal immediately ANDs the signal indicating that the forward power converter is malfunctioning.
Output to gate 24. Now, the subtraction circuit 21 of relay B that monitors the state of phase balance is shown in Fig. 6 from _t1 to _t2.
By subtracting the signal related to the DC current idc taken out during the period of the point and the DC current idc one cycle before the extracted DC current signal (indicating the period t ₁ to _{t 2} in Fig. 6), The result of this subtraction is input to the fourth determination circuit 23 through the fourth average value calculation circuit 22. When the fourth determination circuit 23 confirms that the value of idc-id is not zero, it outputs a signal to the AND gate 24 indicating that the forward power conversion device is malfunctioning. Therefore, the AND gate 24 ANDs the signals output from the third and fourth judgment circuits 20 and 23.
When the condition is met, a signal that satisfies this AND condition is used to notify the outside through the path of timer 25 -> OR gate 17 -> inhibit circuit 28 that the forward power conversion device is out of order. In this way, when the gate signal is out of phase, the current differential relay A
Although relay B, which monitors the state of the other phase balance, will surely detect the failure and notify the outside, even if one phase on the secondary side of transformer 8 is open, Since there is a current mode that is exactly the same as in the case of the gate open phase accident described above, it can be detected reliably. Furthermore, in this embodiment, only the cases of internal accidents in the forward power converter, such as arm short-circuit accidents, gate phase failures, and power supply phase failures, have been described, but for example, commutation fails for some reason and overcurrent flows. In this case, if a short circuit occurs in the transformer and a fault current flows, in this application, both the current differential relay A and the relay B that monitors the state of phase balance can reliably handle this kind of large fault current. Needless to say, it is possible to provide a certain amount of protection since ground faults can be detected, and ground faults can also be reliably detected.

As described above, since the present invention organically combines a current differential relay and a relay that monitors the state of phase balance to provide specified protection, it has various effects as shown below. It is.

Not only faults in the forward power converter, but also faults in the transformer installed on the AC input side can be reliably detected, further improving the reliability of the AC-DC conversion system itself.

Accidents such as gate phase failure and power supply phase failure, which were previously considered impossible, can be reliably detected, further improving the fuel sales of the system itself.

Both current differential relays and phase balance monitoring relays can reliably detect most faults, so even if one relay fails, the other relay can provide backup protection, improving reliability. .

Although both analog and digital relays can be implemented, digital relays have the advantage of being able to detect a wide variety of conceivable accidents with high precision.

[Brief explanation of the drawing]

Fig. 1 is a specific example showing a conventional protection method that does not protect a transformer, Fig. 2 is a specific example showing the basic configuration of the protection method according to the present invention, and Fig. 3 is an implementation according to the present invention. A concrete block configuration diagram showing an example, Fig. 4 is a time chart showing the current mode in steady state when this protection method is applied, Figs. FIG. 4 is a time chart showing current mode when the present protection method is applied to time. 1 is a commercial frequency power supply bus, 3 is a current transformer, 4 is a forward power converter, 5 is a DC current transformer, 6 is a load, 7 and A are current differential relays, 8 is a transformer, 9 is an addition circuit, 10, 12, 19, 22 are average value calculation circuits, 13, 14, 20, 23 are judgment circuits, 18
is an arithmetic circuit, 21 is a subtraction circuit, 15 and 24 are
AND gate circuit, 16, 25 and 27 are timers, 17 is an OR gate, 28 is an inhibit circuit, and B is a relay for monitoring phase balance.

Claims (1)

[Claims] 1. In the protection of an AC-DC converter in a system including a transformer and a forward power converter connected to a commercial frequency power supply bus, the absolute value of the phase current flowing into the transformer. and the average value of the absolute values of the DC output instantaneous values of the forward power converter, and subtract the average value of the DC instantaneous values from the average value of the sum total of the phase current absolute values to obtain this subtracted value. a differential relay that compares and determines the subtraction value with a constant serving as a suppression amount, further compares and determines the subtracted value with an average value of the sum of absolute phase current values, and generates an output based on the logical product of each determination result; After sequentially sampling the absolute value of the instantaneous value of each phase current flowing into the transformer, and subtracting the absolute value of the instantaneous value sampled before each other phase from the current sampled value of each phase current, each subtracted value is calculated. The presence or absence of an unbalanced signal related to the phase current is determined by summing up the average value and determining the presence or absence of an unbalanced signal related to the phase current, and accumulating an arbitrary number of instantaneous values obtained by sequentially sampling the DC output current of the forward power converter and sequentially Find the average value, subtract the current average value and the previous average value, find the average value of an arbitrary number of subtracted values to determine the presence or absence of a signal, and compare this signal with the unbalanced signal related to the phase current. 1. A protection device for an AC-DC converter, comprising: a relay for monitoring phase balance that generates an output under a logical product condition.