JPH0160925B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method of operating a forced cooling transformer cooler.

[Technical background of the invention and its problems]

In recent years, for the purpose of energy saving, etc., the speed of the transformer cooling device is controlled depending on the load or temperature of the transformer, and when the load on the transformer is light, the rotation speed of the cooler motor is reduced. Methods have been implemented to reduce the power consumption of devices. As a device for this speed control,
Inverters are commonly used to change the power frequency and/or voltage of the cooler motor. The capacity of this inverter needs to be large enough to correspond to the capacity of the cooler motor that is operated when the transformer is at 100% load factor.
Transformers with large cooler capacities, such as large-capacity transformers, have the drawbacks of increased inverter capacity, increased dimensions, and increased cost. This will be explained with reference to FIG.

FIG. 1 shows an example of a conventional variable speed operating device for a transformer cooler, where 1 is a power source, 2 is a variable speed control power source device consisting of a variable frequency inverter or a variable voltage device, 3 is an oil-immersed transformer, and 4 is a cooler for the transformer 3, and a fan 5, a motor 5a for the fan, a radiator 6, a motor 7a for the pump 7, etc. are attached to the cooler 4. 8 is a transformer 3 such as an oil temperature detector or winding temperature relay.
This is a temperature sensing device. Alternatively, a load factor detection device such as a bushing current transformer may be provided instead. 9 is a speed command device.

The temperature or load factor of the transformer 3 detected by the detection device 8 is input to the speed command device 9,
Based on this, a command is issued to achieve the required speed. According to the command from the speed command device 9, the inverter 3
converts the voltage and frequency from the power source 1 into voltage and frequency according to the temperature or load factor and supplies power. Thereby, the fan motor 5a and the pump motor 7a attached to the cooler 4 are operated at variable speeds, and the amount of heat radiated from the radiator 6 is controlled. The output from the inverter 3 is maximum when the load factor is 100%, which determines the rated capacity of the inverter. For this reason, the capacity of the inverter is large for a large-capacity transformer that has a large number of cooler groups.

On the other hand, as an example of the annual load factor of a transformer, the second
It will look like the figure. In this figure, the horizontal axis is the load factor of the transformer, and the vertical axis is the annual operating time at each load factor and its ratio. According to this, the load factor exceeds 60% in 5 out of 1 years.
% of the time. Also, it rarely exceeds 65%. By the way, the power required for the cooler depends on the amount of heat generated by the transformer to be cooled, that is, the generated loss, so here we calculate the generated loss W inside the transformer when the load factor is 65%, and calculate the amount at 100% load. Let's compare it with that of .

W=W _L +W _N =p ²・W _LO +W _N ...(1) Where, W: Transformer generated loss at load factor p W _L : Load loss at load factor p W _LO : Rated load (load factor 100% ) Load loss W _N : No-load loss p : Load factor Generally, the ratio of W _LO to W _N is about 5:1 to 10:1 in large capacity transformers, so if it is set to 5:1, W _LO =5W _N ...(2) Substituting equation (2) into equation (1), W=p ²・10W _N +W _N = (10p ² +1) W _N ...(3) Assuming the load factor is 65%, Since p=0.65, this
Substituting into equation (3), W=3.1W _N ...(4) Also, if the load factor is 100%, p=1.0, so,
Substituting this into equation (3), W = 6.0W _N ... (5) From equations (4) and (5), the transformer when the load factor is 65% and when the load factor is 100%. Comparing the generated losses, the transformer generated loss when the load factor is 65%/the transformer generated loss when the load factor is 100% = 3.1/6.0≒0.52...(6) The temperature rise due to the generated loss in the transformer is caused by the cooler. need to be cooled by That is, at this time, the relationship between the required cooling capacity C of the cooler and the loss W generated by the transformer is as follows: C=k・W (7) where k: margin coefficient. Must be 1.0 or higher.

By the way, the load torque T of the fan and pump that constitute the cooler has a square torque characteristic that changes in proportion to the square of the rotation speed N, and the shaft power L of the motor is proportional to the rotation speed N and the torque. It is proportional to T. In other words, as shown in the formula below, the shaft power L is the rotation speed N
It is proportional to the third power of

T∝N ² L∝N・T∝N ³ ...(8) Moreover, the required electric power P of the motor is proportional to the shaft power L and inversely proportional to the efficiency η. Efficiency varies depending on the rotation speed and is not constant. Therefore, the relationship between the rotational speed and the required power of the cooler motor is complicated.

On the other hand, the cooling capacity C of the cooler is approximately proportional to the rotation speed N.

C∝N ...(9) Therefore, from equations (9), (8) and (7), the required power P
becomes P∝C ³ /η∝W ³ /η ...(10).

Considering the above points, it is expected that the required power P of the cooler changes significantly more than proportionally to the loss W generated in the transformer. An example of actual measurement of the relationship between the load factor of the transformer and the required power of the cooler is shown in Fig. 3. From Figure 3, when the load factor is 100% and when the load factor is 65%, the power required for the cooler is approximately
It will be 30%. That is, if the load factor becomes smaller, the required power of the cooler becomes significantly smaller.

As mentioned above, with the current method of operating the cooler,
The capacity of the inverter is determined by the power required for the cooler at 100% load, making it extremely uneconomical when the load factor of the transformer is low.

[Purpose of the invention]

The present invention has been made in view of the above points, and an object of the present invention is to provide an economical method of operating a transformer cooler by reducing excessive auxiliary input to the cooler and reducing the capacity of the speed control inverter. With the goal.

[Summary of the invention]

In order to achieve the above objects, the present invention provides a method for operating a transformer cooler that detects the load factor of the transformer and controls the operation of the motor of the transformer cooler. an inverter for speed control that is connected to the secondary side of the power transformer and adjusts at least one of voltage or frequency; and a cooler motor connected to the output side of the inverter or the primary side of the power transformer. When the load factor of the transformer is below a certain set value, the motor is operated by the speed control inverter, and when the set value is exceeded, the motor is operated by the speed control inverter. The feature is that the motor is operated by the side power source.

[Embodiments of the invention]

Hereinafter, one embodiment of the method of operating a transformer cooler of the present invention will be described with reference to FIG.

10 is a power transformer that reduces the voltage of power supply 1;
1 is a power supply device for variable speed control, for example, a power switching device capable of connecting and switching the motors 5a, 7a of the cooler 4 to either the output side of the inverter 2 or the primary side of the power transformer 10; 12 is an operation control device The operation control device 12 includes a load factor determination unit 1 of the transformer 3.
3. A load factor setting section 14, a speed command section 15, and a power supply switching command section 16 are built-in. 8 is a load factor detection device. This load factor detection device can also detect the oil temperature or winding temperature, or by detecting an electrical quantity such as the actual load current.

Next, the operation of the present invention will be explained. The load factor of the transformer 3 detected by the load factor detection device 8 is input to the operation control device 12 . Then, the determining unit 13 determines whether the load factor exceeds the set value of the load factor from the setting unit 14. If the set value is not exceeded, the speed command unit 15 gives a speed command according to the load factor to the inverter 2, and the motor 5 of the cooler 4
a and the motor 7a. In addition, if the load factor exceeds the set value, the power supply switching command unit 16
gives a command to the power switching device 11 to switch the motors 5a and 7 of the cooler 4 to the primary side of the power transformer 10.
Connect a. That is, when the load factor exceeds the set value, the speed control by the inverter 2 is not performed. This operating situation will be explained with reference to FIG. Fifth
The horizontal axis of the figure is the load factor of the transformer 3, and the left vertical axis is the ratio of operating time corresponding to the load factor, that is, curve A.
The vertical axis on the right side shows the required power for the cooler corresponding to the load factor, that is, the values for curves B and C. For example, the load factor setting value is set to 65%, which is considered to be rarely operated based on curve A. The required power for the cooler is approximately 30% of the rated power based on curve B and the value on the vertical axis on the right side.
Since it is sufficient to set the inverter capacity P ₂ to correspond to this, it is possible to significantly reduce the capacity compared to the case where the inverter capacity P ₁ corresponds to 100% load. can. Also, if the load factor exceeds the set value, the cooler will operate at 100%, but as seen from curve A, the operating time is predicted to be zero or a very short time, so the power required for the cooler during that time will be reduced. The excess amount can be considered negligible. That is, the cooler is operated as shown by curve C. Regarding the load factor setting value, since the load situation is considered to be different depending on the electric power station, the optimum value should be selected.

As mentioned above, when the load factor exceeds 65%, the motors 5a and 7a of the fan 5 and pump 7 are connected to the primary side of the power transformer 10 by the power switching device 11. At this time, the transformation ratio of the power transformer 10 is 2:
Set it to 1. For example, if the voltage of power supply 1 is 400V
If so, it would be economical to use a 200V inverter if the rated input voltage of the inverter is 200V. The cooler motors 5 and 7 must be able to be used at the voltage of the power supply 1, so in this case they are rated at 400V. By doing this, the inverter 2 has half the voltage of the power supply 1, and the capacity of the transformer 3 is as described above.
It can be reduced to about 30% at 100% load.

Note that by forming the power transformer 10 as an autotransformer, the equivalent capacity can be made small.

By the way, in the above example, the power supply 1 is 400V,
If the primary rated input voltage of inverter 2 is 200V, the output of inverter 2 will generally range from 0V to 200V.
Therefore, if the set load factor is exceeded, the voltage will change from 200V to the primary side of the power transformer 10.
It will be switched to 400V. At this time,
Since the characteristics of the cooler are not necessarily proportional to the voltage, 400V was applied to the cooler that can provide the necessary cooling performance when the output of inverter 2 is 200V, that is, the cooling performance corresponding to the set load factor. In this case, the required cooling performance may not always be achieved when the load factor of the transformer 3 is 100%, and there is a possibility that a large difference in cooling performance may occur. A method for preventing the occurrence of excess and deficiency will be explained with reference to FIG. Components that are the same as those in FIG. 4 are designated by the same reference numerals. In FIG. 6, the power transformer 17 is provided with taps 17a and 17b, and the tap voltage is set to a voltage that can provide the required cooling performance of the cooler at a load factor of 100%. When the set load factor is exceeded, by connecting the motor power source of the cooler from the output side of the inverter 2 to this tap 17a of the power transformer 17, the necessary cooling capacity can be produced without excess or deficiency. Although the above embodiment describes a comparison between a detected value and a set value as a load factor, the comparison of the temperature of a transformer or the amount of electricity is also included in the scope of comparison of load factors.

〔Effect of the invention〕

As explained above, according to the present invention, in a region lower than the set load factor where there is a high possibility that the transformer will be operated, the speed is controlled by the inverter according to changes in the load factor, and the speed is controlled by the inverter in accordance with changes in the load factor. In such cases, the motor is operated by the power transformer, which enables energy-saving operation of the cooler.
Moreover, it is possible to obtain a method of operating a closed transformer cooler in which the capacity of the inverter for variable speed operation is reduced.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing an example of a conventional variable speed operation device for a transformer cooler, Fig. 2 is a curve diagram showing an example of the annual load factor of a transformer, and Fig. 3 is a diagram showing the transformer load factor and the cooler. A characteristic diagram showing an actual measurement example of the required power, FIG. 4 is an explanatory diagram showing an example of the operating method of the transformer cooler of the present invention, and FIG. A curve diagram showing a comparison of the required inverter capacity, and FIG. 6 is an explanatory diagram showing another embodiment of the present invention. 1...Power source, 2...Inverter, 3...Oil-immersed transformer, 4...Cooler, 5...Fan, 5a...Motor, 6...Radiator, 7...Pump, 7a...Motor, 8...Detection device, 9...Speed command device, 1
0...Power transformer, 11...Power switching device, 12
... Operation control device, 13 ... Judgment section, 14 ... Setting section, 15 ... Speed command section, 16 ... Power switching command section, 17 ... Power transformer with tap, 17a, 1
7b...Tap.

Claims (1)

[Claims] 1. A method for operating a transformer cooler that detects the load factor of the transformer and controls the operation of a motor of the transformer cooler, which comprises: a power transformer that transforms a power supply voltage; a speed control inverter connected to the secondary side of the power transformer to adjust at least one of voltage or frequency; and a cooler motor connected to either the output side of the inverter or the primary side of the power transformer. When the load factor of the transformer is below a certain set value, the motor is operated by the speed control inverter, and when the set value is exceeded, the motor is operated by the primary power source of the power transformer. A method of operating a transformer cooler characterized by operating a transformer cooler. 2. The method of operating a transformer cooler according to claim 1, characterized in that the ratio of the primary voltage to the secondary voltage of the power transformer is 2:1. 3. The method of operating a transformer cooler as set forth in claim 1, wherein the power transformer is an autotransformer. 4. If the power supply transformer is a tap transformer, the tap voltage value shall be at least a value that can provide the required power for the cooler at a load factor of 100%, and when the load factor of the transformer is below a certain set value, the speed control inverter will 2. The method of operating a transformer cooler according to claim 1, wherein the motor is operated and if the set value is exceeded, the motor is connected to the corresponding tap of the power transformer. 5. A method of operating a cooler for a transformer according to claims 1 to 4, characterized in that the load factor is detected by detecting at least one of the temperature of the transformer or the amount of electricity. .