JPH0451961B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cooling system for a forced cooling type transformer such as an oil feed air-cooled type, and particularly relates to a cooling system for a forced cooling type transformer such as an oil feed air-cooled type, and particularly relates to a cooling device for a forced cooling type transformer such as an oil feed air-cooled type, and in particular to a cooling device for a forced cooling type transformer such as an oil feed pump and fan operation (hereinafter referred to as auxiliary loss). related to improvements aimed at reducing

FIG. 1 is a block diagram mainly showing a cooling device for a conventional oil-feeding, air-cooled transformer. 1 is the transformer body, which contains oil as a cooling medium. 2 is a cooler; 3 is an oil pump and motor (hereinafter referred to as oil pump motor) that circulates oil, which is a cooling medium, between the transformer body 1 and the cooler 2; and 4 is sent to the cooler 2. A fan and a motor for blowing air to cool the oil (hereinafter referred to as fan motor); 5 a detection unit that detects the load current or oil temperature of the transformer; 6 a detection unit that detects the load state of the transformer detected by the detection unit 5; A control unit that opens and closes the power supply circuit of the oil pump motor 3 and fan motor 4 using an electromagnetic contactor 7, 8 a no-use circuit breaker that opens and closes the power supply for the entire cooling system, and 9 a control unit 6, an electromagnetic contactor 7, and a no-use circuit breaker. 10 is a commercial power supply. Note that the oil feed pump motor 3 and the fan motor 4 are induction motors.

FIG. 2 is a block diagram showing the main parts of the cooling device shown in FIG. 1, and shows a case where four coolers or four groups of coolers are connected. In Figures 1 and 2, among the connection lines between each device and device, solid lines indicate power lines, broken lines indicate signal lines, and dash-dotted lines indicate control lines to electromagnetic contactors. The same applies to the following figures. shall be.

A conventional oil-feeding, air-cooled transformer is constructed as described above, and the cooling device is selected so that the temperature of the transformer is below a specified temperature rise limit under rated load conditions. Therefore, under light load conditions where the load on the transformer is lower than the rated load, the loss generated by the transformer will be lower than under the rated load condition, and even if some coolers are stopped, the temperature of the transformer will remain below the specified temperature rise limit. It is possible to drive. For this reason, the number of operating coolers 2 is controlled by opening and closing the electromagnetic contactor 7 according to the load state of the transformer, such as the transformer load current and transformer temperature detected by the detection unit 5. In this case, the auxiliary equipment loss of the entire cooling system is proportional to the number of operating coolers, and the auxiliary equipment loss can be reduced compared to the case of rated operation.

However, in recent years, from the perspective of energy saving,
Transformers are also required to further reduce auxiliary loss.

As a method for further reducing auxiliary losses as a transformer cooling device compared to conventional devices, the oil feed pump motor 3 and fan motor 4 of the cooler 2 are replaced with a variable voltage variable frequency inverter (hereinafter referred to as a variable frequency inverter). ) to control the rotational speed of the oil pump and fan.

FIG. 3 is a block diagram showing the main parts of the improved cooling device, and shows a case in which four (or four groups) of coolers are connected. In Figure 3,
2-5, 7g, 10 are the same as in Figure 2, 12
is a variable frequency inverter that converts the electric power from the commercial power supply 10 into electric power with a frequency determined by the output signal of the control unit 13 and supplies it to the oil pump 3 and the fan motor 4; This is a control unit that determines the drive frequencies of the oil feed pump motor 3 and fan motor 4 and outputs the signals to the variable frequency inverter 12.

In the cooling system configured as described above, if the output frequency of the variable frequency inverter 12 is changed, the rotation speeds of the oil pump motor 3 and the fan motor 4 are changed, and the amount of oil and air blown changes. The cooling capacity of the cooler 2 and the auxiliary equipment loss change.

Figures 4 and 5 show an example of the characteristics of the rotational speed N of the oil pump motor 3 and fan motor 4, the cooling capacity C of the cooler, and the auxiliary equipment loss W. While power changes approximately in proportion to the cube of the rotational speed, changes in cooling capacity due to changes in the rotational speed of oil pumps and fans are generally more gradual than changes in auxiliary equipment loss. Changes in the overall cooling capacity of the oil pump motor 3
If this is done by changing the rotational speed of the fan motor 4, the auxiliary equipment loss will be lower even with the same cooling capacity, compared to the case where it is done by changing the number of operating coolers as in the conventional device.

Therefore, based on the signal detected by the detection unit 5, the control unit 13 determines the required cooling capacity according to the load condition of the transformer, and obtains the corresponding rotational speed of the oil pump motor 3 and fan motor 4. If the output frequency of the variable frequency inverter 12 is controlled so as to reduce the auxiliary equipment loss compared to conventional cooling devices. In this case, the lower the rotational speed of the oil pump motor and fan motor, the lower the auxiliary equipment loss will be, but the cooling capacity of the cooler will also decrease, so the limit due to the temperature rise of the transformer and the increase in winding temperature will decrease. There is a limit due to the accompanying increase in loss in the transformer body, and the required rotation speed is determined in accordance with the transformer load current as shown in FIG. 6a.

However, the load current of a transformer is usually not constant, but is generally a variable load that changes over time as shown in FIG. 6b. If the rotation speeds of the oil feed pump motor and fan motor are controlled according to FIG. 6a while the transformer is being operated with a variable load as shown in FIG. 6b, the rotation speeds of the oil feed pump motor and fan motor will be as follows. , constantly changes as shown in FIG. 6c in response to changes in the load of the transformer. As a result, the oil pump and fan motor are accelerated or decelerated even in response to slight load fluctuations, and there is a risk that efficiency may deteriorate due to transient currents, temperature rises, and damage may occur due to mechanical fluctuation stress.

This invention was made in order to eliminate the above-mentioned drawbacks, and by driving the oil pump motor and fan motor with a variable frequency inverter, it aims to reduce auxiliary equipment loss, and also reduces the loss of auxiliary equipment due to frequent changes in transformer load. The purpose is to prevent acceleration and deceleration.

FIG. 7 shows an embodiment of the present invention, and in FIG. 7, 2 to 5 and 7, 8, 10,
Reference numeral 12 is the same as that shown in FIG. 3, 14 is a level determination unit that determines which of the preset current classifications the transformer load current detected by the detection unit 5 corresponds to, and 15 corresponds to the current classification. This is a control unit that controls the output frequency of the variable frequency inverter 12 so that a preset rotation speed is obtained.

Figure 8a shows an example of setting the rotation speed corresponding to the current classification. When the load current I is less than _{I 1} , N ₁
The case where the setting is N ₂ when I ₂ or less, and _No when I ₂ or more is shown.

The effects of this invention will be explained with reference to FIGS. 8b and 8c.

With the above configuration, even when the transformer is operated with a variable load as shown in Figure 8b, the rotational speed of the oil pump motor and fan motor changes as shown in Figure 8c. device load current is threshold
It is limited to when I ₁ or I ₂ is raised or lowered, and is kept constant for load fluctuations that do not raise or lower the threshold, so frequent acceleration and deceleration accompanying load fluctuations of the transformer can be prevented.

Note that the dashed line in FIG. 8a indicates the rotation speed given in FIG. 6a, and if the rotation speed corresponding to each current division is set higher than that in FIG. 6a as shown in FIG. The operating temperature of the transformer can be maintained lower than in the case of FIG. 6a.

FIG. 9a shows another embodiment of the present invention, in which the threshold of the transformer load current for a decrease in rotational speed is set lower than the threshold for an increase in rotational speed, and a hysteresis characteristic is added. It shows.

The effects of this invention will be explained with reference to FIGS. 9b and 9c. When the load on the transformer fluctuates around the threshold value _I2 , in the case of Figure 8a, the rotation speed changes every time it exceeds the threshold value _I2 , but if hysteresis is added as in Figure 9a, After the load current exceeds I ₂ and the rotation speed is set to N _o , even if the load current slightly decreases below I ₂ , the rotation speed will be maintained at N _o until it falls below I ₂ ′, so the threshold value Frequent acceleration and deceleration due to load fluctuations in the vicinity can be prevented.

In addition, in the above explanation, the case where the variable frequency inverter is controlled by detecting the transformer load current with the detection unit 5 was explained, but the detection unit 5 detects the transformer operating state such as the transformer oil temperature or the winding temperature. Similar effects can be expected when applied to detect other corresponding signals.

In addition, although the above embodiment describes an oil feed air-cooled transformer, it is also possible to use a cooling system that has only either an oil feed pump motor or a fan motor, such as an oil feed self-cooling type or an oil-immersed air-cooled type, or other cooling methods. Similar effects can be expected even when the present invention is applied to a cooling system using a cooling medium, for example, an oil-fed water-cooled transformer.

As explained above, this invention reduces auxiliary machine losses and at the same time transforms the Frequent acceleration/deceleration due to fluctuations in equipment load can be prevented.

[Brief explanation of the drawing]

Fig. 1 is a block diagram mainly showing the cooling system of a conventional oil-feeding air-cooled transformer, Fig. 2 is a block diagram of the cooling system shown in Fig. 1, and Fig. 3 is a block diagram of an improved cooling system. Figure 4 shows the driving frequency (rotation speed) of the cooler.
Figure 5 is a diagram showing an example of the characteristics of cooling capacity and cooling capacity, Figure 5 is a diagram showing an example of the characteristics of cooler drive frequency (rotation speed) and auxiliary equipment loss, Figure 6 is a diagram explaining the operating state of the cooler, and Figure 7 is this diagram. A block diagram showing an embodiment of the invention, FIG. 8 is an explanatory diagram of the operating state of a cooler according to an embodiment of the invention,
FIG. 9 is an explanatory diagram of the operating state of a cooler according to another embodiment of the present invention. In the figure, 1 is the transformer body, 2 is the cooler, and 3
is an oil pump motor, 4 is a fan motor, 5 is a detection unit, 10 is a power supply, 12 is a variable frequency inverter,
14 is a level discrimination section, and 15 is a control section. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. A cooling mechanism in which a cooling medium in a transformer is cooled by a fan or a pump driven by an induction motor, a detection unit that detects the operating state of the transformer, and a signal level from the detection unit that is set to a plurality of levels. a level determining unit that determines which of the classifications it belongs to; a control unit that determines an output frequency to be supplied to the induction motor according to the classification determined by the level determining unit and generates a frequency designation signal; and a control unit that generates a frequency designation signal. A variable voltage variable frequency inverter converts power into power of a predetermined frequency based on a command from the detection section, and drives the induction motor at variable speeds, and the signal level detected by the detection section and the variable voltage variable frequency inversion A transformer cooling device characterized in that the correspondence with the output frequency of the converter is set in a stepped manner. 2. The transformer cooling device according to claim 1, wherein the detection section is constituted by a current detector that detects the load current of the transformer. 3. The transformer cooling device as set forth in claim 1, wherein the detection section includes a temperature detector that detects the oil temperature or winding temperature of the transformer. 4. A cooling mechanism in which the cooling medium in the transformer is cooled by a fan or pump driven by an induction motor, a detection unit that detects the operating state of the transformer, and a signal level from the detection unit that determines which of the plurality of categories the level of the signal from the detection unit falls into. a level discriminating unit that determines whether the signal belongs to the above-mentioned one and changes the range of the classification depending on when the signal level rises or falls, and supplies the signal to the induction motor according to the classification determined by this level discriminating unit. a control unit that determines an output frequency and generates a frequency command signal; and a variable voltage variable frequency inverter that converts power to power of a predetermined frequency based on commands from the control unit and drives the induction motor at variable speeds. A transformer cooling device, characterized in that the correspondence between the signal level detected by the detection section and the output frequency of the variable voltage variable frequency inverter is set in a stepwise manner with hysteresis.