JP2014011810A - Control device and variable speed generator motor starting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a variable speed generator motor, whose variable speed operation range is limited in an adjustable speed pumped storage power generation system, to be started without incurring an increase in equipment size or cost when the generator motor is started by a secondary exciting device.SOLUTION: According to an embodiment, a control device 4 is applied to an adjustable speed pumped storage power generation system, in which a variable speed generator motor 2 is connected to a utility grid via an on-load tap changer equipped transformer 9, and the variable speed generator motor 2 is started from a stopped state by supplying drive power from a secondary exciting device 3 to the secondary winding of the variable speed generator motor 2. The control device 4 exerts control in such a way that when the revolution speed of the variable speed generator motor 2 has exceeded a prescribed revolution speed while the variable speed generator motor 2 has its primary side voltage lowered by altering the winding ratio of the on-load tap changer equipped transformer 9 by changing the taps, speeding-up by drive power from the secondary exciting device 3 is completed and the variable speed generator motor 2 is thereby paralleled-in with the utility grid.

Description

  Embodiments described herein relate generally to a control device and a variable speed generator motor starting method for controlling the start of a variable speed generator motor in a variable speed pumped storage power generation system or the like.

  As a starter for a generator motor of a large-capacity pumped storage power plant, in general, a stationary starter using a frequency converter made of a semiconductor element is used to accelerate from a stopped state to a rated rotational speed, and the system voltage and generator motor terminal After synchronizing the voltage, a system is adopted in which the system is inserted by a parallel circuit breaker and pump operation is started. As such a stationary starter, a thyristor starter is known. This type of starting device has a large output of about 20 MW, and its cost and reduction in installation space are required.

  On the other hand, against the background of global warming countermeasures in recent years, there are an increasing number of cases where double-feed AC generators (hereinafter referred to as “variable speed generator motors”) are applied to variable speed pumped storage power plants. When a large-capacity variable speed generator motor is applied to a variable speed pumped storage power plant, a frequency converter (hereinafter referred to as “secondary excitation device”) having an output exceeding 20 MW may be used for the excitation device. Depending on the variable speed pumped storage power plant, this “secondary excitation device” can be used as a starter without the need to install the thyristor starter separately to generate variable frequency drive power from the secondary winding of the variable speed generator motor. A method of injecting into the electric motor and accelerating from the stop state to the vicinity of the synchronous speed (hereinafter referred to as “self-starting method (secondary side)”) is adopted.

“Current Status and Design / Maintenance Standards for Power Electronics Equipment for Power Systems”, Electric Cooperative Research, 2001, Vol. 57, No. 2, pp. 38-40 "Verification test using variable speed pumped storage power generation system 4,000kW model", Toshiba Review, 1988, Vol. 43, No. 12, Section 4.1, right column on page 3. “Okinawa Yanbaru Seawater Pumped Storage Power Plant Operation Starts”, Toshiba Review, 1999, Vol. 54, No. 12, Section 3.2, page 55, right column

  In the “self-starting method (secondary side)”, the target speed for synchronously entering the system is set to be equal to or higher than the lowest speed in the so-called variable speed operation range.

  However, in recent years, variable speed pumped storage power plants have a variable range of selected variable speeds that have been reduced from about ± 5 to 7% to about ± 4% with the increase in capacity of the high head. For this reason, the output frequency range and output voltage range required for the frequency converter used as the excitation device are also reduced in proportion to the variable speed operation range. Even if a secondary excitation device is connected to the motor and used as a starting device to supply driving power, the output voltage is low, so that it is impossible to increase the speed to the lower limit speed of the variable speed operation range.

  To deal with such problems, in addition to (1) a method of separately installing a thyristor starting device (thyristor starting method) as described at the beginning, (2) a large-current branch circuit bus, a disconnector, etc. are provided. Method of switching main circuit and injecting necessary driving power from primary winding side of generator motor (self-starting method (primary side)), (3) Step-up transformer used only at start-up, branch circuit bus, disconnector, etc. Is applied to the secondary winding side, boosts the secondary voltage at startup, and injects the necessary drive power from the secondary winding side (self-starting method (with secondary step-up transformer)) In any of these cases, large equipment / equipment will be installed separately, which will increase equipment costs, complicate the layout design of the power plant, increase the size of the building, and increase civil engineering costs. become.

  The problem to be solved by the invention is to start up a variable speed generator motor whose variable speed operation range is limited in a variable speed pumped storage power generation system with a secondary excitation device without causing an increase in the size of the device or an increase in cost. It is an object of the present invention to provide a control device and a variable speed generator motor starting method capable of starting the variable speed generator motor.

  In the control device of the embodiment, a variable speed generator motor is connected to a power system via a transformer with a load tap changer, and a driving power is supplied from a secondary excitation device to a secondary winding of the variable speed generator motor. Thus, the present invention is applied to a variable speed pumped storage power generation system that starts the variable speed generator motor from a stopped state. In this control device, the rotational speed of the variable speed generator-motor is reduced in a state where the winding ratio of the transformer with a load tap changer is changed by tap switching to lower the primary voltage of the variable-speed generator motor. And a means for controlling the variable speed generator motor so that the variable speed generator motor is juxtaposed with the electric power system by completing the speed increase by the driving power from the secondary excitation device when a predetermined rotational speed is exceeded.

The block diagram which shows an example of the basic composition of the variable speed pumped storage power generation system which concerns on embodiment. An explanatory view showing a variable speed operation range. The figure which shows the example of 1 structure of the secondary excitation apparatus control function which a control apparatus has. The flowchart which shows an example of the operation | movement by a control apparatus.

  Hereinafter, embodiments will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a basic configuration of a variable speed pumped storage power generation system according to an embodiment.

  The variable-speed pumped-storage power generation system includes, as main elements, a pump-turbine 1, a variable-speed generator-motor 2 (hereinafter sometimes abbreviated as “generator-motor 2”) realized by a double-feed AC machine, and this variable-speed power generation. The secondary excitation device 3 connected to the secondary winding of the electric motor 2 to apply a variable frequency alternating current, the control of the alternating voltage, current, frequency and phase output from the secondary excitation device 3, and the switching equipment 5 and 6 Control device 4 that performs open / close control, drive control of a water surface depressing device (not shown), parallel-connection circuit breaker 5 connected to the stator side of variable speed generator motor 2, variable speed generator motor 2 Disconnecting switch 6 for short-circuiting the stator winding ends of the coil, an excitation transformer 7 as a power transformer for the secondary excitation device 3, and a secondary excitation device connected to the excitation transformer 7 3 is the excitation circuit breaker 8 and the primary winding is connected to the power system side (high voltage side). In addition, the main transformer 9 with a load tap changer (hereinafter, may be abbreviated as “main transformer 9”) whose secondary winding is connected to the variable speed generator motor 2 side (low voltage side), the system voltage Instrument transformer 10 for measurement, instrument transformer 11 for measurement of terminal voltage of variable speed generator motor 2, rotation speed or rotation speed of rotor of variable speed generator motor 2 (hereinafter referred to as “speed”) A phase detector 13 for detecting the phase of the rotor of the variable speed generator motor 2 and the like.

  The main transformer 9 is one of the main transformers in the present system, and here, a general “transformer with load tap changer” is applied. A transformer with a tap changer at the time of loading is not subject to a power outage in a loaded state, but by changing the number of turns on the high voltage side by switching the tap, the transformer turns ratio (also called “turn ratio”) It is a transformer that can change the voltage on the low voltage side arbitrarily. The main transformer 9 can be manually operated, but may be configured so that the control device 4 can be operated.

  Further, the control device 4 has a function of performing control for starting the variable speed generator-motor 2 from a stopped state by supplying drive power from the secondary excitation device 3 to the secondary winding of the variable-speed generator motor 2. .

  Particularly in the present embodiment, the control device 4 rotates the variable speed generator-motor 2 in a state in which the primary voltage of the variable-speed generator-motor 2 is lowered by changing the turns ratio of the main transformer 9 by tap switching. When the speed exceeds a predetermined rotational speed, the variable speed generator motor 2 has a function of controlling the variable speed generator motor 2 to enter in parallel with the power system by completing the speed increase by the driving power from the secondary excitation device 3. For example, before the variable speed generator motor 2 is started, control is performed so that the winding ratio of the main transformer 9 is increased, and control is performed so that the winding ratio of the main transformer 9 is decreased after parallel insertion with the power system. To do.

  Further, the control device 4 completes the speed increase and enters the system in parallel, and the speed is lower than the lower limit speed of the general variable speed operation range before the tap change and the variable speed generator-motor 2 is not used. One of the secondary voltage and the secondary current in the load operation state is set to a speed equal to or higher than the maximum output voltage or the maximum output current of the secondary excitation device 3.

  The reason for adopting such control will be described below in comparison with the prior art.

  Generally, in a variable speed pumped storage power generation system, as shown in FIG. 2, it is required from the range of the maximum head (head) Hpmax and the minimum head (head) Hpmin of the plant, the pump operation characteristics of the pump turbine, and the turbine operation characteristics. Range of maximum input (output) Pmax, minimum input (output), and the rotational speed range determined to be within the maximum output voltage and maximum output current value as the continuous rating of the frequency converter (for example, N = N0 The variable speed operation range R is determined within the upper and lower limit speed range of ± 5%). Therefore, stable continuous operation (steady operation) can be performed in all regions within this range.

  However, as described above, the variable speed operation range, which was conventionally about ± 5 to 7% of the rated rotational speed, is about ± 4% in the recent variable speed pumping system using a high-speed large-capacity pump turbine. On the other hand, the repulsive torque of the rotating body increases due to the higher speed of the pump turbine, so in the above-mentioned conventional technique, the speed at which the system can be entered at a speed exceeding the lower limit speed of the variable speed operation range. Until now, it has become impossible to accelerate and accelerate a variable speed generator motor that is an induction motor using a secondary excitation device.

  Therefore, it is verified with reference to the formula whether or not system parallel insertion at a speed lower than the lower limit speed of the general variable speed operation range is possible.

  The relationship between the high-voltage side voltage (system-side voltage) and the low-voltage side voltage (generator motor primary voltage) of the main transformer 9 is expressed using mathematical formulas as follows.

V ₀ / V ₁ = α (1)
V ₂ = V ₁ × s (2)
Where V ₀ : Main transformer high voltage (system voltage)
V ₁ : Main transformer low voltage (generator motor primary voltage)
α: Main transformer winding ratio V ₂ : Output voltage of secondary excitation device (secondary voltage of generator motor)
s: Slip As can be seen from the above relational expression, “the output voltage of the secondary excitation device (the generator secondary voltage) V ₂ ” is “the main transformer low voltage side voltage (the generator motor primary voltage) V ₁ ” × “the slip. from equal to s', under the condition of the same secondary voltage V _2, by lowering the primary voltage V _1, it is possible to increase the slip s. Therefore, by switching the tap position of the main transformer 9, changing the main transformer turns ratio, decrease the primary voltage V ₁ of the variable speed generator-motor 2, increasing the ratio of the rated primary voltage of the same secondary voltage V _2.

Thereby, system variable insertion of the variable speed generator-motor 2 can be performed by supplying the secondary voltage V ₂ corresponding to a slip frequency larger than that during the rated voltage operation of the variable-speed generator motor 2. That is, in the state where the slip frequency exceeds the maximum slip frequency in the variable speed operation range before tap switching, the speed increase by the drive power from the secondary excitation device 3 is completed and the variable speed generator motor 2 is inserted into the power system. be able to. Accordingly, the variable speed generator-motor 2 can be connected to the system at a speed lower than the lower limit speed of the variable speed operation range at the rated primary voltage (normal time) (speed at the time of large slip). Become.

  For example, when the variable speed operation range is ± 5%, if the transformation ratio of the main transformer 9 is changed from, for example, 275 / 16.5 kV to 275 / 16.0 [kV] by tap switching of the main transformer 9. From the above relational expression (2), the value of the slip s can be increased as follows.

V ₂ = 16.5 [kV] × 5 [%] = 16.0 [kV] × s
s = 5.16 [%]
That is, the lower limit of the variable speed operation range of the variable speed generator-motor 2 can be expanded from 5 [%] to 5.16 [%] by tap switching of the main transformer 9. Moreover, if the voltage adjustment range of tap switching of the main transformer 9 is made larger, a greater effect of reducing the entry speed can be expected.

  FIG. 3 shows a configuration example of the secondary excitation device control function of the control device 4.

  The secondary excitation device control function of the control device 4 includes a self-starting control unit 21, a secondary excitation control unit 22, a comparison unit 23, and switches SW1 and SW2.

  The switches SW1 and SW2 are in a closed state and an open state, respectively, when the signal from the comparison unit 23 is OFF, and output from the self-start control unit 21 of the self-start control unit 21 and the secondary excitation control unit 22. Is supplied to the secondary excitation device 3. On the other hand, when the signal from the comparison unit 23 is turned on, the switches SW1 and SW2 are switched to an open state and a closed state, respectively, and the secondary excitation control unit 22 of the self-starting control unit 21 and the secondary excitation control unit 22 is switched. Is supplied to the secondary excitation device 3.

  The self-start control unit 21 executes a control mode (hereinafter referred to as “self-start control mode”) for starting the variable speed generator-motor 2 (and the pump turbine 1) using the secondary excitation device 3 as a start device. This is a function, and the control signal is sent to the secondary excitation device 3 when the switch SW1 is in the closed state. This control signal gradually increases the output frequency of the secondary excitation device (frequency converter) 3 from 0 Hz to the vicinity of the system frequency.

  The secondary excitation control unit 22 is a control mode (hereinafter referred to as “secondary excitation control mode”) for controlling the variable speed operation of the variable speed generator motor 2 when the variable speed generator motor 2 is installed in the system and after the parallel installation through the secondary excitation device 3. The control signal is sent to the secondary excitation device 3 when the switch SW2 is in a closed state.

  In the control device 4, a predetermined mode switching speed set value Nc is held in a storage unit or the like. Note that this set value may be configured to be taken in from the outside of the control device 4. The mode switching speed set value Nc defines what value the rotor speed N of the variable speed generator motor 2 is to be switched from the self-starting control mode to the secondary excitation control mode. That is, the speed of the rotor of the variable speed generator-motor 2 is determined when the speed increase by the drive power from the secondary excitation device 3 is completed and the variable-speed generator motor 2 is put in the system.

  The comparison unit 23 compares the speed N detected by the speed detector 12 with the mode switching speed set value Nc, and sets the output signal to an off state while the speed N does not reach the mode switching speed set value Nc. Yes. In the meantime, the switch SW1 is closed and the switch SW2 is open, and a control signal from the self-start control unit 21 is sent to the secondary excitation device 3, and the self-start control mode is executed. On the other hand, when the speed N reaches the mode switching speed setting value Nc (when the speed N becomes equal to or higher than the mode switching speed setting value Nc), the comparison unit 23 turns on the output signal. As a result, the switch SW1 is opened and the switch SW2 is closed, the control signal from the secondary excitation control unit 22 is sent to the secondary excitation device 3, and the secondary excitation control mode is executed.

  In particular, the mode switching speed set value Nc is lower than the lower limit speed of the variable speed operation range before tap switching as described above, and the secondary voltage and secondary current in the no-load operation state of the variable speed generator motor 2 are set. Is set to be equal to or higher than a speed equal to the maximum output voltage or the maximum output current of the secondary excitation device 3.

  Next, an example of the operation by the control device 4 will be described with reference to FIG.

  When the variable speed generator motor 2 (and the pump turbine 1) is stopped, the tap is switched so that the winding ratio of the main transformer 9 is increased under the control of the control device 4 or manually. Then, the primary side voltage of the variable speed generator motor 2 is lowered (step S1).

  The control device 4 starts starting the variable speed generator-motor 2 (and the pump turbine 1) according to the starting operation (step S2). In this starting, the control device 4 opens the parallel circuit breaker 5 and closes the starting circuit breaker 6, thereby making the variable speed generator-motor 2 an induction motor and executing a self-starting control mode. The secondary excitation device 3 is operated as a drive device that outputs variable frequency and variable voltage, and the AC output is changed from approximately 0 Hz to near the system frequency, thereby accelerating / accelerating the variable speed generator motor 2 (step S3). .

  The control device 4 compares the speed N of the variable speed generator motor 2 with the mode switching speed set value Nc (step S4), and when the speed N reaches the mode switching speed set value Nc (when N ≧ Nc is established), The control mode is switched from the self-starting control mode to the secondary excitation control mode (step S5). That is, the control device 4 opens the starting disconnector 6 in a state where the speed N of the variable speed generator motor 2 is lower than the lower limit speed of the variable speed operation range before tap switching, and then measures with the instrument transformer 11. The AC output voltage, current, frequency and phase of the secondary exciter 3 are controlled so that the terminal voltage of the variable speed generator motor 2 to be synchronized with the power system voltage measured by the instrument transformer 10 is confirmed after the synchronization is confirmed. The parallel circuit breaker 5 is closed and the system is inserted (step S6).

  After the grid connection, the control device 4 accelerates the variable speed generator motor 2 with the drive power from the secondary excitation device 3 and the power system to increase the speed to the variable speed operation range, and performs pumping operation using the pump turbine 1. Start (step S7).

  Finally, under the control of the control device 4 or manually, the tap is switched so that the turns ratio of the main transformer 9 is reduced, and the primary voltage of the variable speed generator-motor 2 is increased (step S8). ). That is, the winding ratio of the main transformer 9 is returned to the original state before the starting operation.

  In addition, you may make it implement the said embodiment suitably deform | transforming in the range which does not deviate from the summary. For example, in FIGS. 3 and 4 of the above embodiment, the rotational speed of the variable speed generator-motor 2 is focused, and this rotational speed exceeds a predetermined rotational speed that is lower than the lower limit speed of the variable speed operating range before tap switching. In this example, the case where the variable speed generator motor 2 is controlled so as to be installed in parallel with the power system by completing the speed increase by the driving power from the secondary excitation device 3 is limited to such control. There is no need.

  Instead of focusing on the rotational speed of the variable speed generator-motor 2, for example, focusing on the output frequency in the “self-starting control mode” of the secondary excitation device (frequency converter) 3, the output frequency of the secondary excitation device 3 When the rotational speed exceeds a predetermined rotational speed lower than the output frequency corresponding to the lower limit speed of the variable speed operation range before tap switching (the output frequency that achieves the lower limit speed of the variable speed operation range), the secondary excitation device 3 It may be realized that the variable speed generator motor 2 is controlled so as to be parallel to the power system by completing the speed increase by the driving power.

  In this case, more specifically, the output frequency in the “self-starting control mode” of the secondary excitation device 3 is lower than the output frequency corresponding to the lower limit speed of the variable speed operation range before the tap switching, and the variable speed. Either the secondary voltage or the secondary current in the no-load operation state of the generator motor 2 is set to be equal to or higher than the output frequency corresponding to the speed at which the maximum output voltage or the maximum output current of the secondary excitation device 3 is equal.

  Further, in place of the mode switching speed setting value Nc described above, a mode switching output that determines what value the output frequency of the secondary excitation device 3 is to switch from the self-starting control mode to the secondary excitation control mode. A frequency setting value may be adopted. This mode switching output frequency setting value is lower than the output frequency corresponding to the lower limit speed of the variable speed operation range before tap switching, and the secondary voltage and secondary current in the no-load operation state of the variable speed generator motor 2 are set. Either one is set to be equal to or higher than the output frequency corresponding to the speed equal to the maximum output voltage or the maximum output current of the secondary excitation device 3. Then, the output frequency of the secondary excitation device 3 is compared with the mode switching output frequency set value, and when the output frequency of the secondary excitation device 3 reaches the mode switching output frequency setting value (the output frequency of the secondary excitation device 3 is When the mode switching output frequency setting value is exceeded, the control mode may be switched from the self-starting control mode to the secondary excitation control mode.

  3 and 4 of the above embodiment, the case where the control mode is switched based on the speed of the variable speed generator motor 2 has been described. Instead, the secondary excitation device 3 for the variable speed generator motor 2 is described. The control mode may be switched based on the slip frequency.

  In this case, the control device 4 completes the speed increase by the driving power from the secondary excitation device 3 in a state where the slip frequency exceeds the maximum slip frequency of the variable speed operation range before the tap change, and the variable speed generator motor 2 It has a function of controlling to be juxtaposed with the power system. More specifically, the slip frequency when completing the speed increase and entering the system is higher than the maximum slip frequency in the variable speed operation range before tap switching, and in the no-load operation state of the variable speed generator motor 2. Any one of the secondary voltage and the secondary current is set to be equal to or lower than the slip frequency equal to the maximum output voltage or the maximum output current of the secondary excitation device 3.

  According to the above embodiment, in the “self-starting method (secondary side)”, it is possible to enter the system at a speed lower than the lower limit speed of the variable speed operation range at the normal time of the variable pumping system. There is no need for a stationary starter or a starting transformer, which makes it possible to reduce enormous equipment costs and a large installation space. In particular, when applied to underground power plants in recent years, the effect of reducing civil engineering excavation costs is enormous. In addition, there is little processing of the remaining soil on the ground, and the contribution to the global environment is great. Furthermore, since the system can be entered at a lower rotational speed, the starting time can be shortened.

  As described above in detail, according to the embodiment, when starting a variable speed generator motor whose variable speed operation range is limited in the variable speed pumped storage power generation system by the secondary excitation device, the size of the equipment is increased and the cost is increased. The variable speed generator motor can be started without inviting.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Pump turbine, 2 ... Variable speed generator motor, 3 ... Secondary excitation device, 4 ... Control device, 5 ... Parallel circuit breaker, 6 ... Start disconnector, 7 ... Excitation transformer, 8 ... Excitation break 9: Main transformer with load tap changer 9, 10 ... Instrument transformer, 11 ... Instrument transformer, 12 ... Speed detector, 13 ... Phase detector.

Claims (5)

A variable speed generator-motor is connected to the power system via a transformer with a load tap changer, and the drive power is supplied from a secondary excitation device to the secondary winding of the variable-speed generator motor, thereby the variable-speed generator-motor A control device applied to a variable speed pumped storage power generation system that starts the engine from a stopped state,
In a state where the winding ratio of the transformer with a load tap changer is changed by tap change and the primary voltage of the variable speed generator motor is lowered, the rotation speed of the variable speed generator motor becomes a predetermined rotation speed. A control device comprising means for controlling the variable speed generator motor so that the speed increase by the drive power from the secondary excitation device is completed and the variable speed generator motor is juxtaposed with the power system when the power exceeds the upper limit.   The speed at which the acceleration is completed is lower than the lower limit speed of the variable speed operation range before the tap switching, and the secondary voltage and secondary current in the no-load operation state of the variable speed generator motor are 2. The control device according to claim 1, wherein one of the speeds is equal to or higher than a speed equal to a maximum output voltage or a maximum output current of the secondary excitation device.   The winding ratio of the transformer with a load tap changer is controlled before starting the variable speed generator motor, and the winding ratio of the transformer with a tap changer on load is adjusted after parallel insertion with a power system. The control device according to claim 1, wherein the control device is controlled so as to be small.   A variable speed pumped storage power generation system comprising the control device according to any one of claims 1 to 3. In a variable speed pumped storage power generation system in which a variable speed generator motor is connected to a power system via a transformer with a load tap changer, driving power is supplied from a secondary excitation device to the secondary winding of the variable speed generator motor. A variable speed generator motor starting method for starting the variable speed generator motor from a stopped state by:
In a state where the winding ratio of the transformer with a load tap changer is changed by tap switching by the control device and the primary voltage of the variable speed generator motor is lowered, the rotation speed of the variable speed generator motor is set to a predetermined value. The variable speed generator-motor is controlled so that the variable speed generator-motor is juxtaposed with the electric power system by completing the speed-up by the driving power from the secondary excitation device when the rotation speed exceeds How to start.

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