JPS6226564B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for cooling electrical equipment such as a transformer using latent heat of vaporization of a condensable cooling medium.

In general, in electromagnetic induction devices such as transformers, cooling efficiency is high when a liquid-phase condensable cooling medium is sprayed on a heating element such as an iron core or winding, and the heating element is cooled by latent heat of vaporization during evaporation. Moreover, since it does not use mineral oil, it has attracted a lot of attention in recent years as an electromagnetic induction device that has many features such as being non-flammable, non-explosive, saving resources, and being compact and lightweight.

When this electromagnetic induction device, for example a transformer, is operated, the iron core, windings, etc. become heat generating bodies and the temperature rises. A cooling medium is sprayed to cool the heating element, and the heating element is cooled by latent heat of vaporization during evaporation. The evaporated condensable cooling medium fills the sealed container of the transformer, is cooled by a cooler provided in the sealed container, releases latent heat of vaporization, and becomes a liquid phase.

The relationship between the vapor pressure and temperature of the coolant gas in the vapor phase is such that when the transformer is operated, the temperature of the coolant gas increases, and at the same time, the pressure also increases.
However, when the transformer is at ambient temperature and immediately after the start of operation, the temperature and pressure of the cooling medium gas are low.

In general, a condensable cooling medium gas has good insulation properties, but the insulation properties change in proportion to the gas pressure, so when the gas temperature is low, the insulation properties also deteriorate. Therefore, when the transformer is under ambient temperature,
Immediately after the start of operation, the insulation of the transformer is threatened by overvoltage entering from the system line.

In order to maintain the insulation properties of the transformer at low temperatures and to sufficiently withstand overvoltages that enter from the system lines, it is necessary to connect live parts such as windings to grounded parts such as sealed containers and iron cores. It is necessary to strengthen the insulation by increasing the insulation distance or increasing the thickness of the insulator.

As a result, transformers have become larger and heavier, resulting in higher costs, and there have been major drawbacks such as increased installation space and larger buildings.

This invention was made to eliminate the above-mentioned drawbacks, and the purpose of this invention is to heat the condensable cooling medium before the electrical equipment is operated at ambient temperature, and increase the gas pressure to a level that can withstand the overvoltage entering from the grid lines. To provide a cooling method for electrical equipment, which can downsize the electrical equipment by starting the operation of the electrical equipment after the electrical equipment has cooled down.

The figures will be explained below. FIG. 1 is a characteristic curve showing the relationship between the temperature and pressure of a condensable cooling medium gas, and the pressure increases in proportion to the temperature.

FIG. 2 is a characteristic curve showing the relationship between the pressure of the cooling medium gas and the dielectric strength, and the dielectric strength increases in proportion to the pressure.

FIG. 3 is a characteristic curve showing the relationship between the temperature of the cooling medium gas and the dielectric strength, and the dielectric strength increases in proportion to the temperature.

In FIGS. 1 to 3, T ₀ is the lowest ambient temperature of the transformer, and the temperature of the transformer will never fall below T ₀ . The vapor pressure and dielectric strength at the temperature T ₀ are P ₀ and E ₀ , and the dielectric strength E ₀ is the dielectric strength value when it cannot withstand the overvoltage of the system line but can withstand the system line voltage. Dielectric strength E ₁ is the dielectric strength value that can withstand not only system line voltage but also system line overvoltage, and the vapor pressure and temperature at this time are P ₁ ,
Indicates that T ₁ .

The temperature T _M is the maximum temperature of the transformer, and the vapor pressure and dielectric strength at this time are P _M and E _M .

In order to connect a transformer to a system line and continue its operation safely, it is necessary to withstand not only the system line voltage but also the overvoltage of the system line.

Therefore, the temperature when the transformer starts operation is
Assuming that T is ₀ , the withstand voltage at this time is
E ₀ and steam pressure P ₀ cannot withstand overvoltage on the grid line, so in order to obtain a dielectric strength E ₁ that can withstand this, the transformer is connected to the grid line after increasing the temperature and vapor pressure to T ₁ and P ₁ respectively. Once connected, you can safely start driving. In addition, when the transformer starts operating, the windings and core become heating elements and the temperature rises.At the same time, the temperature of the refrigerant gas rises from _T1 to _TM , so the dielectric strength of the refrigerant gas increases. is always
Since E is maintained at ₁ or higher, operation can be continued safely.

To increase the temperature of the cooling medium gas from T ₀ to T ₁ , either operate a heater installed in the liquid phase of the cooling medium, or apply voltage from the load side of the transformer to supply no-load loss. The temperature of the refrigerant gas can also be easily raised by exciting the iron core and heating the refrigerant with iron loss heat generated in the iron core. In general, transformers have very few power outages, occurring once every few years. In addition, the power required to heat the condensable refrigerant liquid at the start of operation can be obtained by using surplus power from late at night, so it can be said that the time and effort required for heating and the required power are extremely small.

Although the above embodiments have been described using a condensable cooling medium, similar effects can be expected even if a mixture of a cooling medium gas and a non-condensable gas is used.

Although the above embodiment has been described as an example applied to a transformer, similar effects can be expected when applied to general electrical equipment.

According to this invention, before operating electrical equipment,
By heating the cooling medium and turning it into a vapor phase, and bringing the pressure of the gasified cooling medium to a predetermined value, the electrical equipment starts operating with the dielectric strength of the cooling medium improved, reducing the insulation distance. This makes it possible to downsize electrical equipment.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the relationship between the temperature and pressure of the cooling medium gas, Figure 2 is an explanatory diagram showing the relationship between the pressure of the cooling medium gas and dielectric strength, and Figure 3 is an explanatory diagram showing the relationship between the temperature and pressure of the cooling medium gas. FIG. 2 is an explanatory diagram showing the relationship between temperature and dielectric strength. Note that the same reference numerals in each figure indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] 1. A method for cooling electrical equipment in which a condensable cooling medium is brought into contact with the electrical equipment and the electrical equipment is cooled by the latent heat of vaporization of the cooling medium, before starting operation of the electrical equipment. . A method for cooling electrical equipment, characterized in that the cooling medium is heated to turn it into a vapor phase, and the pressure of the gasified upward cooling medium is brought to a predetermined value. 2. The method for cooling electrical equipment according to claim 1, wherein the cooling medium is heated by a heating means placed in the liquid phase of the cooling medium. 3. A patent claim characterized in that the electrical equipment is constituted by an electromagnetic inductor having an iron core, and a no-load loss is supplied from the load side of the electromagnetic inductor, and a cooling medium is heated by the iron loss heat of the iron core. A method for cooling an electrical device according to item 1.