JPS6326524B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection method when quenching occurs in a superconducting coil equipped with a thyristor converter device as an excitation device.

Superconducting coils have recently been widely put into practical use, but
An example of its application is a superconducting synchronous machine in which the field winding of the synchronous machine is configured in a superconducting state. Compared to general synchronous machines, this type of superconducting synchronous machine has smaller equipment size, lower loss, and is rated for phase-advanced reactive power that can be supplied to the grid.
Full KVA can be obtained (this is not possible with general synchronous machines due to stability restrictions and coil end heating restrictions).
It has the following advantages and has great merits when used in power system generators and phase modifiers.

Since the field winding is in a superconducting state, normally the pure inductance is L, the resistance is practically zero, and the current I _f
When flowing, it stores 1/2Ll ² _f of electromagnetic energy. When a partial breakdown of the superconducting state occurs due to an abnormal phenomenon such as a sudden change in the field magnetic field or an abnormal rise in temperature, that part becomes a resistance r, and due to the flowing current I _f
Generates heat of rI ² _f . This heat generation causes the temperature of the adjacent parts to rise, and the superconducting breakdown area gradually expands. Such superconducting breakdown phenomenon (quenching)
occurs, the electromagnetic energy stored in the field inductance under normal conditions is 1/2Ll ² _f
It is necessary to consume it outside the synchronous machine as soon as possible in order to limit the damage caused by the failure.

A conventionally known method generally involves inserting an external series resistor into the field circuit to measure the external consumption of energy when quenching occurs. If the externally inserted resistance value is increased too much, it is effective for rapid external consumption of field electromagnetic energy, but excessive voltage is generated in the field winding, threatening its insulation. On the other hand, if the external insertion resistance value is too small, the field current decay will be slow and the amount of heat generated inside the synchronous machine will be large, which is not preferable. Phenomena when quenching occurs vary depending on the value of the initial field current and the state of occurrence of partial superconducting breakdown, and it is difficult to select the optimum value of the insertion resistance in the above-mentioned resistor insertion method.

An object of the present invention is to use a superconducting coil equipped with a thyristor converter as an excitation device to regenerate the electromagnetic energy of the coil to the power system as quickly as possible without interfering with the insulation of the coil by the inverter operation of the thyristor converter. An object of the present invention is to provide a protection method that makes it possible to reduce the amount of heat generated by a coil due to quenching.

According to the present invention, the purpose of this is to operate the thyristor converter as an inverter by detecting the occurrence of quenching, and at the same time to cause the quenching to occur from a predetermined maximum value of the DC reverse voltage of the thyristor converter applied to the superconducting coil. This is achieved by limiting the resistance voltage to a value that is reduced by an amount corresponding to the resistance voltage generated by .

Hereinafter, the present invention will be explained in more detail with reference to the drawings.

FIG. 1 shows, in principle, a block diagram of an example in which the present invention is applied to a superconducting synchronous generator. The field winding 2 of the three-phase synchronous generator 1 is a superconducting coil,
A three-phase pure bridge thyristor converter 3 is attached as an excitation device. The field current I _f is constantly supplied from the thyristor converter 3 using the generator output side transformer 4 (combined with a power current transformer 5 as shown if necessary) as a power source. The firing of the individual thyristors in the thyristor conversion device 3 is controlled via the gate angle control section 6 . In normal times, control input to the gate angle control section 6 is provided by an automatic voltage controller (AVR), not shown. The illustrated control input _es led to the gate angle control section 6 is activated by the output signal of the quenching occurrence detection section 7. That is, FIG. 1 is a block diagram of a control system formed by detecting the occurrence of quenching, and in normal times a known automatic voltage control system for a generator is formed.

The control input e _s that acts on the gate angle control unit 6 based on the output signal of the quenching occurrence detection unit 7 is composed of the output signal (voltage command value) of the voltage command calculation unit 8 and the output signal (voltage detection value) of the voltage detection unit 9. This is the voltage control deviation obtained from the comparison result with The voltage command calculation unit 8 receives the output signals of the field voltage detection unit 9 and the field current change rate detection unit 10, and based on this information, calculates the command value of the DC reverse voltage to be generated by the thyristor conversion device 3. calculate.

In order to explain the detection principle of the quenching occurrence detection section 7 and the calculation principle of the voltage command calculation section 8, FIG. Shows the circuit. Here, for the entire field winding (100%), there is a healthy part that maintains a superconducting state by α × 100%, and a faulty part (quenching part) that has transitioned to a normal conducting state exists. (1-
Assume that there is only α)×100%. In this case, let L be the field winding inductance during normal operation with no faulty parts (α=1), and let R be the field winding resistance value when normal conduction occurs throughout the area (α=0).
Then, as shown in the figure, the healthy part can be expressed as an equivalent inductance of αL, while the faulty part can be expressed as an equalized inductance of (1-α)L and (1-α).
α) Equivalent resistance of R. The voltage polarity of each equivalent impedance element in the process of narrowing down the field current I _f is as shown in the diagram, and if the field voltage E _f and the inverter DC reverse voltage E _INV are expressed with the polarities shown, E _f = LdI _f /dt+(1-α)RI _f ...(1) E _INV =-E _f ...(2) The following relation holds true.

As can be seen from equation (1), when α=1, that is, during normal operation, E _f −LdI _f /dt=0, whereas when α≠1, that is, when quenching occurs, E _f −LdI _f /dt=(1−α)RI _f ≠0. The quenching occurrence detection section 7 in _FIG . and information corresponding to the field current change rate dI _f /dt from the field current change rate detection section 11, compare the two, and generate a quenching occurrence detection signal when the balance between the two is lost. Output. Instead of the quenching occurrence detection section 7 that operates on such a detection principle, it is also possible to use one that operates on other known detection principles.

Next, the optimum command value for the inverter DC reverse voltage E _INV to be calculated by the voltage command calculation unit 8 will be explained.

In the equivalent circuit of Fig. 2, if the voltages in the healthy part and the faulty part are E ₁ and E ₂ respectively, then
As a measure of the potential gradient in each winding,
E ₁ /α, E ₂ /(1−α) can be used,
These can be respectively expressed as E ₁ /α=−LdI _f /dt (3) E ₂ /1−α=−LdI _f /dt−RI _f (4). In this case, the values of both equations are positive, and E ₁ /α−E ₂ /1−α=RI _f > 0, so when quenching occurs, the healthy part is stronger than the failed part. The potential gradient inside the winding increases, making it difficult to insulate. The present invention focuses on this and attempts to limit the in-winding potential gradient E ₁ /α of the healthy portion to the maximum value taken into consideration for insulation reasons. In this case, the maximum value is the predetermined maximum allowable field voltage under normal conditions.
It is preferable to select one that corresponds to E _fnax . Here, since the entire field winding is assumed to be 1, it can be treated as the maximum value = E _fnax in the calculation formula. Therefore, since it is sufficient to set the value of equation (3) regarding the potential gradient in the winding in the healthy part as E _fnax , it is understood that -LdI _f /dt=E _fnax (5). From this equation (5) and the above-mentioned equations (1) and (2), E _INV = E _fnax - (1 - α) RI _f ... (6) is obtained. That is, the DC reverse voltage E _INV of the thyristor converter 3 applied to the field winding 2 is reduced from a predetermined maximum value (in particular, the maximum allowable field voltage E _fnax predetermined in a healthy state) by quenching. If we limit it to the value obtained by subtracting only the resistance voltage drop (1-α) RI _f that occurs, then
This makes it possible to rapidly attenuate the field current without threatening the insulation of the superconducting coil. In this case, the above resistance voltage drop is determined by the field voltage E _f and the field current rate of change dI because (1-α) RI _f = E _f - LdI _f /dt holds true from the modification of equation (1). If the actual measured values of _f /dt detected by the detection units 9 and 10 are input to the voltage command calculation unit 8, the calculation unit 8 calculates the resistance voltage drop by taking into account the known coil inductance value L. be able to. Therefore, the calculation command unit 8 can generate the optimal DC voltage command value by similarly subtracting the calculation result from the known E _fnax . The actual value of the DC reverse voltage applied to the field winding is detected by the voltage detection section 9, and the comparison point 1 is detected by the voltage detection section 9.
1, the voltage control deviation is compared with the command value.
e _s is formed. Then, the DC reverse voltage is maintained at the command value by controlling the thyristor conversion device 3 via the gate angle control 6.

FIG. 3 shows an example of operation waveforms from the time point t=0 when quenching occurs. For easy-to-understand illustration, we assume that the proportion α of the healthy part and the proportion (1 - _α ) of the defective part to the whole coil change as shown by the broken line curve. With respect to the attenuation curve, the resistance voltage drop (1-α) RI _f due to the occurrence of quenching and the DC reverse voltage E _INV will change according to the curve as shown in the figure.

As explained above, according to the present invention, the DC reverse voltage applied to the superconducting coil from the thyristor converter, which is shifted to inverter operation upon detection of the occurrence of quenching, is reduced from a predetermined maximum value to the resistance voltage caused by the occurrence of quenching. By limiting the electromagnetic energy of the superconducting coil to a value that reduces the drop equivalent, the electromagnetic energy of the superconducting coil can be rapidly extracted without threatening the insulation of the superconducting coil, making it extremely effective in protecting the superconducting coil when quenching occurs. It is true.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is an equivalent circuit diagram when quenching occurs in a superconducting coil, and FIG. 3 is an explanatory diagram of the operation of the present invention. DESCRIPTION OF SYMBOLS 1... Synchronous generator, 2... Field winding (superconducting coil), 3... Thyristor conversion device, 6... Gate angle control section, 7... Quenching occurrence detection section, 8
...Voltage command calculator, 9...Voltage detection section, 10...
...Current change rate detection section.

Claims (1)

[Claims] 1. In order to protect a superconducting coil equipped with a thyristor conversion device as an excitation device when quenching occurs, the thyristor conversion device is caused to perform an inverter operation upon detection of the occurrence of quenching, and at that time, the superconducting coil is A protection method for a superconducting coil, characterized in that the DC reverse voltage of a thyristor converter applied to the coil is limited to a value that is reduced from a predetermined maximum value by an amount equivalent to the resistance voltage drop caused by the occurrence of quenching. . 2. The superconducting coil protection method according to claim 1, wherein the resistance voltage drop equivalent is calculated from measured values of the voltage and current change rate of the superconducting coil. 3. The superconducting coil protection method according to claim 1 or 2, wherein the maximum value is a maximum allowable voltage value when the superconducting coil is healthy.