JPH0283907A - Device for detecting break of cooling oil flow - Google Patents

Abstract

PURPOSE:To prevent an erroneous alarm by the malfunction of a flow indicator at low temperature or at low revolution by installing an oil temperature detector to the cooling oil flow break detector of a transformer so as to change the lowest number of revolutions of an oil feed pump according to the temperature of the oil. CONSTITUTION:During variable speed operation, load currents are detected from a current transformer CT1, and through a current converter 2 by a first arithmetic unit 3, operation frequency signal in accordance with the characteristics of a transformer are obtained and are given to an inverter 5. At this time, the temperature of oil is detected by the use of a resistance bulb 6, etc., and is input into a second arithmetic unit 8 through a converter 7. In the arithmetic unit 8, the lowest frequency is set in advance so that it may be operation frequency above the operation sensitivity of an oil flow indicator. The output of this computing element 8 is added to the arithmetic unit 3 as the lowest limit and it given as the control signal of the inverter 5. Hereby, the lowest frequency can be set according to the temperature of the oil, and malfunction of the flow indicator can be prevented.

Description

Detailed Description of the Invention (Objective of the Invention) (Industrial Field of Application) The present invention is a method for detecting a cooling oil flow outage for detecting a cooling oil flow outage in a forced circulation type oil-cooled FJI system such as a transformer. Regarding equipment.

(Prior Art) In forced circulation oil cooling devices such as transformers, loss of oil circulation between a heat source such as a coil and a radiator has a negative impact on the lifespan of equipment such as transformers. It can also lead to big losses. For this reason, conventionally, a mechanical oil flow indicator has been installed near the oil circulation pump to enable monitoring from the outside, and at the same time, a micro switch that operates mechanically when the flow is below a certain level (m) is installed, and its contact point Therefore, a method of sending an alarm to a remote device has been adopted.

FIG. 2 shows an embodiment of a conventional cooling oil flow outage detection system.

In FIG. 2, a is the oil flow indicator contact closing condition,
b is the oil pump operating condition based on oil pump power supply voltage detection and the like. If the oil flow indicator contact closes when the oil pump operating conditions are met, an alarm will be displayed after the confirmation time of the time limit element d, and the MCCB for the oil pump will be cut off, etc., and the equipment will be shut off. was providing protection.

Here, the time-limiting element d has an initial lock function from when oil starts flowing after the oil feed pump is started until the oil flow indicator contact closes.

On the other hand, with the recent trend towards energy conservation, methods have been put into practical use that utilize variable speed control devices (hereinafter referred to as inverters) to achieve the minimum required cooling capacity without changing the rotational speed of the motor. In the case of this method, the flow rate of the insulating oil, which is a cooling medium, is varied according to the loss of the transformer, etc., so it is difficult to detect abnormalities by simply monitoring the flow rate at the rated frequency as in the conventional method. Therefore, a highly sensitive oil flow detector has been required. Generally, the minimum frequency of an inverter is set due to mechanical constraints,
Based on the oil flow rate at that operating frequency, the sensitivity was adjusted by increasing the area of the flapper of the curved flow indicator or changing the position of the microswitch, and the conventional system shown in Figure 2 was protected by.

(Problems to be Solved by the Invention) In the case of the variable speed control system described above, there is a limit to the improvement in sensitivity of the contacts of the oil flow indicator, and unstable operation is likely to occur. Particularly in the low frequency range where the flow rate is low, the difference between the normal flow rate and the abnormal flow rate is extremely small, and malfunctions are likely to occur. Furthermore, since the viscosity of the circulating oil changes depending on the oil temperature, there will be a difference in flow rate even if the motor rotation speed is the same. Therefore, even if the sensitivity is set at room temperature, malfunctions will occur if the device is operated at low temperatures.

FIG. 3 is an example showing the relationship between the oil temperature and the frequency at which the oil flow indicator contact closes when the operating frequency is changed by an inverter. At low temperatures, the contacts close at a relatively high frequency and an abnormality is detected, which is not good for maintenance.

Additionally, as substations become unmanned, unnecessary false detections create a large maintenance burden. Therefore, it is necessary to detect failures reliably.

Therefore, an object of the present invention is to prevent false alarms due to malfunction of the oil flow indicator in the low temperature and low frequency range.

(Structure of the Invention) (Means for Solving the Problems) The present invention provides an oil temperature detection device for detecting the temperature of circulating oil in a cooling oil cutoff detection device for detecting a flow cutoff of circulating oil in a cooling device of a transformer. and means for changing the minimum rotational speed of the oil feed pump (minimum frequency of the inverter) according to the temperature of the oil.

(Function) In the present invention, the oil temperature is detected by a resistance temperature detector, etc., and the minimum operating frequency of the inverter is changed according to the oil temperature, and the detection sensitivity of the oil flow indicator is always kept constant to prevent unnecessary malfunctions. It was designed to do so.

(Example) Hereinafter, an example will be described with reference to the drawings. FIG. 1 is a circuit configuration diagram showing an embodiment of a cold 19 oil outage detection neck according to the present invention.

During variable speed operation, the load current is generally detected by the current transformer CTI, passed through the current converter 2, and then obtained by the first computing unit 3 to obtain an operating frequency signal according to the characteristics of the transformer, which is then given to the inverter 5. . At this time, the oil temperature is further detected by the temperature measuring resistor 6 and the like, and is inputted to the second computing unit 8 through the resistance temperature converter 7.

The calculator 8 predetermines B2 as a function so that the operating frequency is higher than the operating sensitivity of the oil flow indicator shown in FIG. The output of this calculator 8 is added to the first performer 3 as a minimum limit, and is given as a control signal for the inverter. This allows you to set the minimum frequency according to the oil temperature, and even at low temperatures, the amount of oil flowing to the oil flow indicator can be the same as at room temperature, preventing malfunctions of the oil flow indicator. [Effects of the Invention] As explained above, according to the present invention, it is possible to compensate for changes in the sensitivity of the oil flow indicator due to high and low oil temperatures, and in particular, it is possible to compensate for changes in the sensitivity of the oil flow indicator at low temperatures. False alarms due to malfunctions can be prevented.

[Brief explanation of the drawing]

Fig. 1 is a circuit configuration diagram of a cooling oil flow detection device showing an embodiment of the present invention, Fig. 2 is a diagram of a conventional oil flow detection system, and Fig. 3 shows oil temperature and oil flow indicator contact closing frequency. This is a tag graph showing the relationship between. 1...CT 2...Current converter 3.
... Arithmetic unit 4... Diode 5... Inverter 6... Resistance temperature detector 7... Resistance-temperature converter 8... Arithmetic unit 9... Diode meter... Oil flow indicator contact Closing condition b...Oil pump operating condition C...A N D circuit d...Time limit ¥5 line e...M CCB new condition f...Alarm contact condition

Claims (1)

[Claims] In a cooling oil flow out detection device that detects a flow out of circulating oil in a cooling device for a transformer that drives an oil feed pump using a variable speed control method to circulate and cool oil in a transformer tank, the circulating oil The oil supply pump is characterized by comprising an oil temperature detection device for detecting the temperature of the oil feed pump, and a means for changing a preset minimum rotation speed of the oil feed pump according to the oil temperature in order to prevent misjudgment of flow interruption detection. Cooling oil flow outage detection device.