JPH0312443B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cooler operation device for a forced cooling type transformer, such as an oil feed air-cooled type, and particularly relates to a cooler operation device for a forced cooling type transformer such as an oil feed air-cooled type, and particularly relates to a cooler operating device for a forced cooling type transformer such as an oil feed air-cooled type, and in particular, the power required for operating a cooler oil feed pump and a cooling fan (hereinafter referred to as supplementary power). The present invention relates to a cooler operation device for reducing machine loss (referred to as machine loss).

Figure 1 is a configuration diagram centered on the cooling system of a conventional oil-feeding air-cooled transformer, where 1 is the transformer body, 2 is the cooler, and 3 is the oil pump and electric motor (hereinafter referred to as the electric oil pump). ), 4 is a cooling fan and electric motor for air blowing (hereinafter referred to as electric cooling fan), 5 is a detection unit that detects the load current or temperature of the transformer, 6 is an electromagnetic contactor, and 7 is the detection unit 5. A control unit that opens and closes the power supply circuit of the electric oil pump 3 and the electric cooling fan 4 using an electromagnetic contactor 6 according to the detected load condition of the transformer; 8 is a no-use circuit breaker that opens and closes the power supply for the entire cooling device; 9 is a no-use circuit breaker; A commercial frequency power supply 10 is a cooler control panel that houses a control unit 7, an electromagnetic contactor 6, a no-use circuit breaker 8, and the like.

FIG. 2 is a block diagram showing the main parts of the cooling system shown in FIG. 1, and shows a case in which two groups of four coolers are connected. FIG. 3 is a wiring diagram showing an example of the main circuit configuration per cooler. In the figure, 11 is a no-use circuit breaker, and 12 is a thermal overcurrent relay for overload protection of the electric oil pump 3. ,1
3 is an overcurrent protection device for overload protection of the electric cooling fan.

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 in the rated state is below a specified temperature rise limit. 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 the rated condition, and even if some coolers are stopped, the transformer will continue to operate below the specified temperature rise limit. can do.
For this reason, the number of operating coolers 2 is controlled by opening and closing the electromagnetic contactors 6 according to the state of the transformer, such as the load current or 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 conservation,
Electrical equipment is also required to further reduce loss.

As a method for further reducing auxiliary losses as a transformer cooling device compared to conventional devices, the number of rotations of the electric oil pump 3 and the electric cooling fan 4 (hereinafter both referred to as the cooler electric motor) of the cooler 2 is improved. It is possible to control the

FIG. 4 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 4, 2
5, 8, and 9 are the same as those in FIG. 2, and 14 is a variable frequency power supply that converts the power from the commercial frequency power source 9 into power at a frequency determined by the output signal of the control unit 15 and supplies it to the cooler motor. A power supply device, 15 is a control unit that determines the drive frequency of the cooler motor based on the signal from the detection unit 5 and outputs the signal to the variable frequency power supply device 14, and 16 is an electromagnetic contact that opens and closes the variable frequency power supply device 14. It is a vessel.

In the cooling device configured as described above, if the output frequency of the variable frequency power supply device 14 is changed,
The rotational speed of the cooler electric motor changes, and the amount of oil and air blown changes, so the cooling capacity and auxiliary equipment loss of the cooler 2 change, but the change in cooling capacity due to the rotational speed change is generally due to the auxiliary equipment loss. Since the change is gradual compared to the change, the auxiliary equipment loss per cooling capacity decreases with the rotation speed, as shown in FIG. However, in Figure 5, Nn is the rated rotational speed of the cooler motor, Cn and
Wn represents the cooling capacity of the cooler and auxiliary equipment loss at the rated rotation speed, respectively.

On the other hand, in conventional equipment, the cooling capacity of the entire cooling system and auxiliary equipment loss are proportional to the number of operating coolers, so the ratio of auxiliary equipment loss to cooling capacity remains constant and does not change depending on the number of operating coolers. be. Therefore, if the cooling capacity of the cooling device is controlled by changing the rotational speed of the cooler electric motor, the auxiliary machine loss will be lower even with the same cooling capacity, compared to the case where it is controlled by changing the number of operating units.

Therefore, based on the signal detected by the detection unit 5, the control unit 15 determines the required cooling capacity according to the load condition of the transformer, and the variable frequency power supply device is configured to obtain the rotation speed of the cooler motor corresponding to the required cooling capacity. By controlling the output frequency of 1, it is possible to reduce auxiliary loss compared to conventional cooling devices.

However, the thermal overcurrent relay 12 and overcurrent protection device 13 (hereinafter both referred to as overload protection devices) used for overload protection of the cooler motor
If is selected so that it will operate properly when the cooler electric motor is operated at the rated frequency, there is a risk that the overload protection device will not operate properly when the cooler electric motor drive frequency is lower than the rated frequency. This problem will be explained with reference to FIG. In the figure, f _N represents the rated frequency, Ia represents the load current of the cooler motor, and I _S represents the restraint current. An overload protection device is activated by an overcurrent caused by motor restriction or other abnormality, and is used to cut off the power supply circuit of the motor and prevent the motor from overheating and burning out. Therefore, the sixth
As shown in the figure, if the load current of the motor at the rated frequency f _N is Ia _N and the restraint current is I _SN , overload,
The protection device does not operate at the load current Ia _N during normal operation of the cooler motor, but must operate at the restraint current I _SN . That is, the operating current I _R of the overload protection device is selected to be greater than Ia _N and smaller than I _SN .
However, when the cooler motor is driven at variable speeds by a variable frequency power supply, the applied voltage is also changed approximately in proportion to the frequency, so the load current Ia and restraint current I _S of the cooler motor generally vary with the frequency as shown in Figure 6. decreases with In this case, the rated frequency f _N
At lower frequencies, the locking current I _S may be less than the operating current I _R of the overload protection device. Figure 6 shows the case where the locking current is below I _R at frequency f _R or below, and when driving at frequency below f _R , even if an abnormality such as motor lock occurs, overload will occur. The protective device will not operate and the power will not be cut off. In a locked state, the cooling capacity of the motor is reduced, so if the locked state continues, there is a risk of damage due to overheating. Therefore, if we take as an example the case where the output frequency of the variable frequency power supply device is controlled as shown in FIG. 7 in response to the load of the transformer, from time t ₁ to t ₂
Since the frequency exceeds f _R in the section, the overload protection device will be activated if the cooler motor is restricted for some reason. However, in other sections, the driving frequency of the cooler motor is lower than f _R , so the restraining current is smaller than the operating current I _R of the overload protection device, and the overload protection device does not operate.

This invention was made to eliminate the above-mentioned drawbacks, and it is possible to detect a restriction abnormality of the cooler motor in a cooler operating device that uses a variable frequency power supply to drive the cooler motor at variable speeds. The purpose is to

FIG. 8 shows an embodiment of the present invention, in which numerals 2 to 5, 8, 9, and 14 to 16 are the same as in FIG. 4. Reference numeral 17 denotes a current detecting device for the cooler motor, which is composed of, for example, a current transformer. 18 is an electromagnetic contactor that opens and closes the power supply circuit of the cooler electric motor; 19 is an electric current of the cooler electric motor detected by the detection device 17;
This is a comparison/judgment device that opens the electromagnetic contactor 18 when a predetermined threshold value as a function of the power supply frequency is exceeded. FIG. 9 shows an example of a threshold value used in the comparative judgment device 19 to compare and judge the current flowing through the cooler motor. In the figure, Ip is the threshold value, Ia is the load current of the cooler motor, and I _S is the restraining current. The threshold value Ip is the load current of the cooler motor
It is set to be larger than Ia and smaller than the restraint current I _S , but since Ia and I _S decrease with frequency, the threshold
Ip is not a constant value, but takes different values depending on the drive frequency of the cooler motor, as shown in FIG.

In the cooler operating device configured as described above, the current flowing through the cooler motor is detected by the detection device 17, the level and frequency of the detected current are discriminated by the comparison/judgment device 19, and the current flowing through the cooler motor is determined in advance as a function of the frequency. If the electromagnetic contactor 18 is opened when the energizing current of the cooler motor exceeds a predetermined threshold value Ip compared with a predetermined value Ip, the cooler motor will be restrained even at frequencies below the rated frequency _fN . It is possible to prevent overheating and burnout due to abnormalities.

In addition, by adding a condition that cuts off the motor power when the motor current exceeds a predetermined threshold for a predetermined period of time, it is possible to reduce the Or comparative judgment device 1 using transient current during deceleration
9 unnecessary operations can be prevented.

Note that the comparison and determination device 19 may have any configuration as long as it has the above-mentioned functions. FIG. 10 is a block diagram showing an example of the configuration of the comparison/judgment device 19.
In the figure, 20 is a multiplexer for sequentially switching and inputting load current detection signals of a plurality of cooler motors, 21 is an analog-to-digital conversion circuit, 22 is an arithmetic processing circuit such as a microprocessor, and 23 is a memory. It is a circuit. In the apparatus configured as shown in FIG. 10, the detection signal detected by the detection device 17 is selected by the multiplexer 20, the signal digitized by the analog-digital conversion circuit 21 is inputted to the arithmetic processing circuit 22,
Calculating the level and frequency of the detection signal, and
By performing a comparison calculation process with a threshold value stored as a function of frequency in the storage circuit 23, it is possible to determine whether the cooler motor is overloaded. Also the 11th
The figure is a block diagram showing another example of the configuration of the comparison and determination device, in which 24 is a level determination circuit;
25 is a frequency discrimination circuit, 26 is a function generator, 27
is a comparison circuit. In the device configured as shown in FIG.
The output of the frequency discrimination circuit 25 is further input to a function generator 26 to obtain a threshold value Ip corresponding to the frequency as the output of the function generator. Level discrimination circuit 2
Comparison circuit 27 compares the output of function generator 26 with the output of
and compare the two, level discrimination circuit 2
When the output of function generator 26 is greater than the output of function generator 26, it can be determined that there is an overload.

Further, although FIG. 8 shows an example in which the comparison and determination device 19 is provided independently of the control section 15, the function of the comparison and determination device 19 may be included in the control section 15.

In the above embodiment, an oil-feeding air-cooled transformer was described, but cooling devices such as oil-feeding natural cooling type or oil-filled air-cooling type that have only either an electric oil feeding pump or an electric cooling fan, Similar effects can be expected even if the present invention is applied to a cooling device using another cooling medium, such as an oil-fed water-cooled transformer.

As explained above, in a transformer cooler operating device in which a cooler electric motor is driven at variable speed by a variable frequency power supply device, the present invention includes a detection device for detecting the current flowing through the cooler electric motor, and a detection device for detecting the current flowing through the cooler electric motor, and Equipped with a comparison judgment device that compares the energizing current with a predetermined threshold value, and cuts off the motor power when the energizing current of the motor exceeds a predetermined threshold value as a function of the power supply frequency, thereby determining whether the drive frequency is below the rated frequency. Even in this state, it is possible to detect and eliminate a restriction abnormality in the cooler electric motor.

[Brief explanation of the drawing]

Figure 1 is a block diagram centered on the cooling system of a conventional oil-feeding air-cooled transformer, Figure 2 is a block diagram of the cooling system in Figure 1, and Figure 3 is an example of the main circuit configuration of one cooler. Figure 4 is a block diagram of the improved cooling system, Figure 5 is a diagram showing an example of the characteristics of the drive frequency of the cooler motor and the auxiliary equipment loss per cooler cooling capacity, and Figure 6 is A diagram showing an example of the driving frequency and current characteristics of a motor for a cooler, FIG. 7 is an explanatory diagram of the operating state of the cooling device in FIG. 4, FIG. 8 is a block diagram of the cooling device according to the present invention, and FIG. FIG. 10 is a diagram showing a configuration example of a comparison and determination device according to the present invention, and FIG. 11 is a diagram showing another configuration example of a comparison and determination device according to the present invention. In the figure, 1 is the transformer body, 2 is the cooler, and 3
1 is an electric oil pump, 4 is an electric cooling fan, 5 is a detection unit, 14 is a variable frequency power supply device, 15 is a control unit, 1
6 is an electromagnetic contactor, 17 is a detection device, 18 is an electromagnetic contactor, and 19 is a comparison determination device. Note that the same reference numerals in the figures indicate corresponding parts.

Claims (1)

[Scope of Claims] 1. A cooler that forcibly sends a cooling medium necessary for cooling the transformer using an electric motor, a variable frequency power supply device that drives the electric motor at variable speed according to the load condition of the transformer, and a current flowing through the electric motor. a detection device for detecting, and a motor current detected by the detection device;
Transformer cooling equipped with a comparison/determination device that compares the motor with a predetermined threshold value as a function of the power supply frequency and cuts off the motor power when the motor current exceeds the predetermined threshold value as a function of the power supply frequency. device operating device. 2. A cooler that forcibly sends a cooling medium necessary for cooling the transformer using an electric motor, a variable frequency power supply device that drives the electric motor at variable speeds depending on the load condition of the transformer, and a detection device that detects the current flowing through the electric motor. and a motor current detected by the detection device,
Compare the motor power supply frequency with a predetermined threshold value as a function of the power supply frequency, and when the current flowing through the motor exceeds the predetermined threshold value as a function of the power supply frequency for a predetermined period of time or more, the motor power supply is switched off. A transformer cooler operation device equipped with a comparison judgment device for shutting off.