JPH0343693Y2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to a low-loss operation control device for a cooler of a power transformer.

[Prior art and its problems]

In power transformers, in order to reduce power costs, there is a need to reduce losses such as transformer body losses such as no-load loss and load loss, and power consumption of cooler motors, that is, auxiliary equipment loss. In order to quantitatively evaluate the power loss reduction effect, we introduced the concept of annual expenses, and calculated KW from the depreciation of power generation and substation equipment, interest paid, and other annual expenses per 1KW.
A method is known in which the loss value is expressed as an assessed value consisting of the sum of the KWh value and the KWh value determined from the fuel cost per 1 KWh. Therefore, if you are planning to make additional investments to reduce losses, consider how much the annual reduced loss evaluation value obtained by reducing losses will exceed the annual expenses of the additional investments. According to
Since it is possible to decide whether or not to make additional investments, the low-loss operation control system for coolers can be used to control coolers in groups or in numbers so that the sum of the total loss of the transformer and the assessed value of auxiliary equipment loss is minimized. What has been done is known.

FIG. 4 is a schematic configuration diagram showing an example of a conventional device. In the figure, an oil-immersed transformer 1 is equipped with a load current detector 3 such as a current transformer that detects the load current, and a temperature detector 4 that equivalently detects the winding temperature, and the outputs of both detectors. The signal is A/D converter 5A,
5B, etc., to a loss calculation circuit 6 having a no-load loss setting device 6A, and the total loss of the transformer 1, which is the sum of the temperature-corrected load loss and no-load loss, is determined. 7 is an auxiliary equipment loss signal generation unit of the cooler corresponding to the output total loss signal of the loss calculation circuit 6, and in the evaluation circuit 8, the total loss signal and a plurality of auxiliary equipment loss (range value) signals are each converted into an evaluation value. The sum of the two is determined, and the cooler operating condition signal that minimizes the sum of the two is output. This signal is input to the cooler number setting circuit 9, and the switching control circuit 10 operates based on the on/off control signal of the setting circuit 9, thereby controlling the circulation pump 2A connected to the transformer 1 by the circulation passage 2C, Cooling fans 2B A necessary unit or a necessary number of cooling fans 2B are driven out of the cooler (auxiliary equipment) 2 consisting of a plurality of units.

FIG. 5 is a characteristic diagram of auxiliary equipment loss versus load factor in the prior art described above, and curve 101 shows the load factor of multiple unit coolers divided into two groups (the rated load of transformer 1 is 100%). Curve 102 shows the characteristics when the circulation pump 2A and cooling fan 2B are controlled in two stages according to the change in the cooling fan 2B, and the characteristic when the circulation pump 2A and the cooling fan 2B are controlled in multiple stages according to the change in the load factor. It can be seen that the more detailed the control is, the more the loss of auxiliary equipment can be reduced. However, cooler units are generally connected to different positions of the transformer 1 via individual circulation piping 2C, and by controlling on/off multiple units, the insulating medium inside the transformer can be It is said that this often increases the non-uniformity of the flow velocity, and the windings in areas where the flow velocity is low are insufficiently cooled, inhibiting the effect of reducing resistance loss (load loss), which increases in proportion to the winding temperature. There's a problem. Also, while the cooling performance of the cooler increases in proportion to the first power of the rotation speed of pumps, etc., the loss of auxiliary equipment increases by approximately 3 times the rotation speed.
Therefore, depending on the method of controlling the cooler on and off, there is a drawback that the effect of reducing auxiliary equipment loss, which is inversely proportional to the cube of the rotation speed, cannot be utilized at all.

[Purpose of invention]

This idea was created in view of the above-mentioned situation.
It is an object of the present invention to provide a control device for a transformer cooler that can finely measure the auxiliary equipment loss of the cooler based on the evaluation value of the total loss of the transformer and the auxiliary equipment loss, and therefore has a large loss reduction effect. shall be.

[Key points of the idea]

The present invention is characterized by the fact that the annual evaluation value per 1KW of uncontrolled auxiliary equipment loss is higher than the annual evaluation value per 1KW of total loss of a power transformer, and that the auxiliary equipment loss is higher than the annual evaluation value per 1KW of total loss of a power transformer. ), and by converting the total loss of the transformer and the loss of auxiliary equipment of the cooler necessary to cool it into an appraised value, we evaluated both. An evaluation circuit that calculates the operating frequency of the cooler electric motor that minimizes the sum of the values, a control circuit that receives the output signal of this evaluation circuit and outputs a voltage/frequency control signal, and a control circuit that receives the output signal of this control circuit and calculates the operation frequency of the cooler electric motor. Variable voltage variable frequency inverter (hereinafter referred to as VVVF) that controls variable speed
The above-mentioned object can be achieved by arranging an inverter (referred to as an inverter).

[Example of idea]

The present invention will be explained below based on one embodiment.

FIG. 1 is a schematic diagram showing an embodiment of the present invention. In the figure, output detection signals from a detector 3 such as a current transformer that detects the load current of an oil-immersed transformer 1 and a temperature detector 4 such as a resistance thermometer that equivalently detects the winding temperature are transmitted to a converter 5. is input to a loss calculation circuit 6 having a no-load loss setting device 6A, and the total loss of the transformer 1 is determined. This apparatus is similar to the conventional apparatus already explained with reference to FIG. 4 in that it includes an accessory loss signal generating section 7 that outputs an accessory loss (or rotational speed) signal having a predetermined width of 2. In this embodiment, the output total loss signal of the loss calculation circuit 6 and the plurality of output auxiliary equipment loss signals within a predetermined width of the auxiliary equipment loss signal generator 7 are input to the evaluation circuit 18, and are inputted to the evaluation circuit 18 based on predetermined calculation conditions. At the same time, the auxiliary equipment loss evaluation amount that minimizes the sum of the total loss evaluation amount and the auxiliary equipment loss evaluation amount is calculated, and the auxiliary equipment 2 corresponding to this auxiliary equipment loss evaluation amount is calculated.
A control circuit 1 that outputs an operating frequency (or rotational speed) signal, receives the output frequency (or rotational speed) signal of the evaluation circuit 18, and outputs a variable speed control signal for the auxiliary equipment 2 consisting of the circulation pump 2A and the cooling fan 2B.
9 and the output current of the VVVF inverter 20 controlled by the output control signal of the control circuit 19, the plurality of circulation pumps 2A and cooling fan 2B of the cooler (auxiliary equipment) 2 are controlled at variable speed.

In general, variable speed control of the auxiliary machine 2 consisting of an induction motor can be performed by changing the operating frequency F and voltage V of the auxiliary machine, and by changing the frequency F of the output current of the VVVF inverter 20, the auxiliary machine It is configured to reduce auxiliary equipment loss by controlling the rotation speed and by controlling the ratio of frequency F and voltage V (referred to as V/F ratio) to be constant.

In the device configured as described above, the auxiliary machine 2
When the operating frequency of the auxiliary equipment is gradually lowered from the rated frequency, the rotational speed of the auxiliary equipment decreases in approximately direct proportion to the decrease in frequency, and at the same time, the auxiliary equipment loss decreases in approximately inverse proportion to the cube of the rotational speed. In addition, when the rotational speed of the auxiliary equipment decreases, the flow rate of the cooling medium in the transformer 1 decreases, and the cooling performance decreases, causing the winding temperature to rise, and as the winding resistance increases, the winding resistance loss (copper losses) will increase somewhat. If the winding temperature rise is kept within the transformer's allowable temperature rise range, the increase in resistance loss is only a few percent of the total loss, but when compared with auxiliary equipment loss, it is a value that is competitive with each other. Therefore, by utilizing the inversely proportional relationship between changes in accessory loss and resistance loss, it is possible to find the operating frequency of the accessory where the sum of the total loss and the accessory loss is minimized. By the way, if the evaluation values of resistance loss and auxiliary equipment loss are equal, sufficient economic effects can be obtained by performing variable speed control of auxiliary equipment under conditions that minimize loss, but if auxiliary equipment is not controlled In this state, the estimated value of auxiliary loss is at least several times higher than the evaluated value of transformer load loss, so the operating frequency of the auxiliary equipment that minimizes the sum of both evaluated values is the operating frequency that minimizes loss. does not match,
Higher economic effects can be obtained by variable speed control of the auxiliary equipment at the operating frequency that minimizes the assessed value. In the device shown in FIG.
8 calculates the auxiliary equipment loss evaluation amount corresponding to the operating frequency condition of the auxiliary equipment within a predetermined range and the total loss evaluation amount that takes into account the change in resistance loss, and the sum of the two is minimized. By being configured to determine the operating frequency of the auxiliary equipment, it is possible to perform variable speed control of the auxiliary equipment that is most economically advantageous.

FIG. 2 is an example of the auxiliary equipment loss versus load factor characteristic diagram in the above-mentioned embodiment, and the characteristic curves 101 and 102 in the conventional device already explained with reference to FIG.
This is shown in comparison with In the figure, the curve 103 obtained in the example is the multi-step control curve 102.
The auxiliary equipment loss is further reduced compared to the previous model, and exhibits a characteristic that is approximately proportional to the third power of the load factor.

FIG. 3 is a diagram showing the saving loss of auxiliary equipment loss versus load factor characteristic diagram in the above-mentioned embodiment, and shows the difference between the two-stage control curve 101 and the multi-stage control curve 102 (curve 102A) in FIG. 103 (curve 103A).
At an average load factor of 40 to 60% of the transformer, by using the variable speed control method of the example (curve 103A), it is possible to reduce the auxiliary equipment loss by about 10KW compared to the two-stage control method, and the annual It is possible to save 1 million to 1.5 million yen in terms of loss reduction evaluation value.

[Effect of idea]

As mentioned above, the present invention converts the total loss signal obtained based on the detection signal of the detector and the corresponding multiple auxiliary equipment loss signals into an evaluation value, and then performs compensation such that the sum of both evaluation values is the minimum. The auxiliary equipment was configured to be controlled at variable speed by the output current of the VVVF inverter, which was controlled by the machine's operating frequency signal. As a result, compared to conventional devices that control auxiliary equipment in stages, the control system for transformer coolers can control the operation of auxiliary equipment in a more detailed manner, resulting in a large loss evaluation value and a large economic effect. can be provided.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram showing an embodiment of the present invention, Fig. 2 is an auxiliary equipment loss vs. load factor characteristic diagram in the embodiment,
FIG. 3 is a characteristic diagram of reduction loss of auxiliary equipment loss versus load factor in the embodiment, FIG. 4 is a schematic configuration diagram of a conventional device, and FIG. 5 is a characteristic diagram of auxiliary loss versus load factor in the conventional device. 1...Oil-immersed transformer (main body), 2...Auxiliary equipment (cooler), 2A...Circulation pump, 2B...Cooling fan,
2C circulation path, 3...Load current detector, 4...Temperature detector, 6...Loss calculation circuit, 6A...No-load loss setting device, 7...Auxiliary equipment loss signal generator, 8, 18...
...Evaluation circuit, 9...Cooler number setting circuit, 10...
Switching control circuit, 19... Control circuit, 20... Variable voltage variable frequency inverter (VVVF inverter).

Claims (1)

[Scope of utility model registration request] Based on the detector that equivalently detects the temperature of the transformer winding, load current, etc., and the output signal of this detector, determine the total loss of the transformer and the auxiliary equipment loss range value of the cooler corresponding to the total loss. An evaluation circuit that converts each of the total loss and auxiliary equipment loss range value into an evaluation value and calculates the operating frequency of the auxiliary equipment that minimizes the sum of both evaluation values, and the evaluation circuit that is equipped with a loss calculation means. A transformer cooling system characterized by comprising a control circuit that receives an output signal and outputs a voltage/frequency control signal, and a variable voltage variable frequency inverter that receives an output signal of this control circuit and controls an auxiliary machine at variable speed. device control device.