EP2402698A1 - Method for monitoring the functions of and/or controlling a coolant system and coolant system - Google Patents

Abstract

The method involves performing a temperature difference process and a heat exchanger effectiveness process to monitor a function and operational safety of a cooling system. A temperature difference of vaporizable coolant in a condenser (20) and an evaporator (22) is formed corresponding to an equation. A global effectiveness of the thermosyphon is determined using a relationship, which is a ratio of a difference between temperatures at a condenser inlet (Tenv) and at a condenser outlet to a difference between temperatures at the inlet and at an evaporator inlet. An independent claim is also included for a cooling system comprising a thermosyphon.

Description

The invention relates to a method for monitoring or controlling a cooling system with at least one thermosyphon, in particular for transformers, preferably for dry-type transformers, wherein the cooling system is provided with at least one evaporator and at least one condenser and a vaporizable refrigerant and a gaseous medium, preferably air, used as a heat carrier, and a system for carrying out this method.

Cooling systems equipped with thermosyphon are known in principle from the prior art. In addition to water and air as heat transfer medium, they often also use refrigerant as an intermediate cooling medium.

The currently used air-to-air and air-to-water cooling monitoring technology is not sufficient to reliably predict and evaluate the operation of the thermosyphon.

It is not possible, for example, to make an early statement about the level of the system with heat transfer medium. The measured by sensors temperature and pressure difference alone are not suitable to provide this information. Only in the case of refrigerant leakage, these sensors can lead to the later detection of the error.

In cooling systems, in which the current technologies, for example, air-water heat exchangers, air-to-air heat exchangers and finned tube bundle heat exchangers, are used, there is a monitoring function and reliability through water leakage, pressure difference and temperature sensors.

Water leakage sensors are commonly used in marine applications to detect breakage in the air-to-water cooler and accordingly to prevent the ingress of water into electrical functional areas of the housing.

Differential pressure sensors monitor the fans or the air inlets and air outlets of the cooling system.

The temperature measurement is used to monitor the temperatures of the cooling air and the windings and, if necessary, to take corrective action.

From European patent application no. 09015185.3 is provided for the cooling of a transformer cooling system, which takes advantage of the thermosyphon principle, that is, the thermosiphon technology used.

However, a monitoring and diagnostic strategy for such a system is not yet available.

Based on this prior art, it is an object of the invention to provide a method and a cooling system of the type mentioned, which allows the simplest possible way to make reliable and meaningful statements about the current system state. For this, the development of a new logic and signal processing strategy for the early detection of errors is necessary.

This object is achieved by the characterizing features of claim 1.

Accordingly, the invention provides that for monitoring the function and the reliability of the provided with thermosyphon cooling system, the thermal difference method and / or the method of heat transfer efficiency can be used.

mit T^manifold _evap = Temperatur im Verdampfer und
mit T^manifold _cond = Temperatur im Kondensator
und beurteilt.In this case, in the thermal differential method advantageously the temperature difference DT of the refrigerant in the at least one capacitor and in the at least one evaporator is formed according to the equation $$\mathit{DT}\mathit{=}{\mathit{T}}_{\mathit{evap}}^{\mathit{manifold}}\mathit{-}{\mathit{T}}_{\mathit{condens}}^{\mathit{manifold}}$$

with T ^manifold _evap = temperature in the evaporator and
with T ^manifold _cond = temperature in the condenser
and judged.

• Der Druckabfall im Thermosiphon liefert normalerweise nur einen geringen Wert. Hierbei sind der Druck und die Temperatur bei Zweiphasen-Kältemittel (flüssig und gasförmig) miteinander gekoppelt, wie auch in Fig. 4 gezeigt ist. Da der Druck in den Behältern sich voneinander nur unwesentlich unterscheidet, ist auch die Temperaturdifferenz nahezu null (DT ~ 0).

In this method, therefore, the temperature difference of the refrigerant is formed in the condenser and in the evaporator container. The physical interpretation of this equation is as follows:

• The pressure drop in the thermosyphon usually provides only a small value. Here, the pressure and the temperature in two-phase refrigerant (liquid and gaseous) are coupled together, as well as in Fig. 4 is shown. Since the pressure in the containers differs only insignificantly from each other, the temperature difference is almost zero (DT ~ 0).

However, in the case of leakage, the temperature gradient along the thermosyphon is no longer negligible, since the thermal resistance between the evaporator (hot spot) and condenser (cold spot) is very high, that is $$\mathrm{DT}\mathrm{~}\left({\mathrm{T}}_{\mathrm{warm}}\mathrm{-}{\mathrm{T}}_{\mathrm{cold}}\right)\mathrm{,}$$

The monitoring of the cooling system functionality is carried out accordingly in accordance with the Fig. 2 specified logic.

A preferred development of the invention provides that the measurements are carried out sequentially in order to reduce the number of measurement channels required to acquire the temperature characteristics.

An advantageous embodiment of the invention is characterized in that the two temperatures are measured simultaneously on a thermosiphon element.

die globale Effektivität e des Thermosyphon-Systems aus dem Verhältnis der Differenz der Temperaturen am Kondensatoreintritt (T_env) und am Kondensatoraustritt (T_condens ^out ),zur Differenz der Temperaturen am Kondensatoreintritt (T_env) und am Verdampfereintritt (T_evap ⁱⁿ) gebildet wird.

So gilt beispielsweise

C_condens > C_evap mit C=cp*m

Hierbei sind

cp = Spezi. Wärmekapazität der Luft bei konstantem Druck
m = Luftstrom.

Für den Fall

C_condens < C_evap mit C=cp*m

As a second inventive - alternative or complementary - measuring and monitoring method, the method of heat transfer efficiency is provided. This method provides that according to the relationship $\epsilon =\frac{\left(T_{\mathit{env}}-T_{\mathit{condens}}^{\mathit{out}}\right)}{\left(T_{\mathit{env}}-T_{\mathit{evap}}^{\mathit{in}}\right)}$

the global effectiveness e of the thermosiphon system is calculated from the ratio of the difference between the temperatures at the condenser _inlet (T _env ) and the condenser _outlet (T _condens ^out ), the difference between the temperatures at the condenser _inlet (T _env ) and the evaporator _inlet (T _evap ⁱⁿ ) ,

For example

C _condens > C _evap with C = cp * m

Here are

cp = spec. Heat capacity of the air at constant pressure
m = airflow.

In the case

C _condens <C _evap with C = cp * m

The following applies: $$\epsilon =\frac{\left(T_{\mathit{evap}}^{\mathit{in}}-T_{\mathit{evap}}^{\mathit{out}}\right)}{\left(T_{\mathit{evap}}^{\mathit{in}}-T_{\mathit{env}}\right)}$$

With the respectively determined temperature values at the condenser _inlet (T _env ), at the evaporator _inlet (T _evap in) and at the condenser _outlet (T _condens ^out ), the global effectiveness of the thermosyphon system is formed according to the relationship given above.

If one or more thermosyphons fail, the condenser _outlet temperature (T _condens ^out ) and the temperature at the evaporator _inlet inevitably decrease (T _evap ^out ) increases. This leads to the reduction of the effectiveness number. This reduction can be correlated with a number of defective thermosyphons.

In order to cover this error case, it makes sense to determine a critical value of the effectiveness number (eff_I).

In the case of a reduction of the air volume flow at the condenser inlet, for example with a reduced inlet cross-section of the air inlets as a result of deposits, the air temperature at the condenser outlet increases. Accordingly, the effectiveness number increases - at a constant evaporator inlet temperature).

To cover this error case, it makes sense to set an upper limit of effectiveness (eff_u).

Effective efficiency limits (eff_I and eff_u), for example, are determined during the warm-up test along with the air temperatures within the enclosure. The logic for this method is in Fig. 3 shown.

According to an advantageous embodiment of the invention is characterized in that in the event of a fault, for example, the state "warning" (signals in Fig. 2 and 3 ) to remedy the flow of the gaseous heat transfer medium is at least temporarily interrupted or, if necessary, even the flow direction of the gaseous heat carrier is at least temporarily reversed.

A further advantageous embodiment of the method according to the invention is that the condenser as well as the evaporator are heated by heat from a heat source to avoid condensation in the condenser housing or icing of the condenser heat exchanger respectively, for example at the respective outlets.

As already mentioned above, the subject of the invention is also a cooling system, in particular a cooling system for transformers, preferably for dry-type transformers, wherein the cooling system comprises at least one thermosiphon, which is arranged in a housing and provided with at least one evaporator and at least one capacitor and a vaporizable refrigerant and a gaseous medium, preferably air, used as a heat transfer medium and is suitable for carrying out the method described above.

Such a cooling system is characterized in particular in that temperature sensors for determining the relevant temperatures for determining the required characteristic values for the thermal differential method and / or for the method of heat transfer efficiency are provided in the housing.

According to a preferred embodiment of the cooling system according to the invention, blower devices are provided which serve to generate a flow of the gaseous medium.

Here, according to an advantageous embodiment, it is provided that the delivery of the gaseous medium can be interrupted at least temporarily. It is also possible to make the flow direction of the gaseous medium reversible by changing the conveying direction of the blower device.

Another particularly advantageous embodiment of the cooling system according to the invention is characterized in that in which the at least one capacitor and the at least one evaporator receiving housing at least one heat source is arranged, wherein in a preferred manner, the heat source is formed by at least one heating element.

The surveillance strategy implemented with the invention uses only the information of temperature to diagnose the functionality of the thermosyphon. This leads to a significant reduction in the number of sensors in the system, for example by pressure or pressure difference sensors are not required.

These and other advantageous embodiments and improvements of the invention are the subject of the dependent claims.

Reference to an embodiment of the invention shown in the accompanying drawings, the invention, advantageous embodiments and improvements of the invention and particular advantages of the invention will be explained and described in detail.

Fig. 1

eine schematische Schnittdarstellung durch einen Transformator mit Thermosiphontechnologie;

Fig. 2

ein Logikschema für die Implementierung der Thermodifferenzmethode;

Fig. 3

ein Logikschema für die Implementierung der Wärmeübertragereffektivität-Methode und

Fig. 4

ein Druck-Enthalpie-Diagramm des inneren Kühlkreislaufs.

Show it:

Fig. 1

a schematic sectional view of a transformer with thermosiphon technology;

Fig. 2

a logic scheme for the implementation of the thermal difference method;

Fig. 3

a logic scheme for the implementation of the heat transfer efficiency method and

Fig. 4

a pressure-enthalpy diagram of the internal cooling circuit.

In Fig. 1 is a schematic sectional view through a transformer 10 with a housing 12 in which an iron core 14 with three winding assemblies 16 and separated therefrom in separate chambers 18, 19 each have a capacitor 20 and an evaporator 22 are arranged.

Furthermore, a total of five temperature sensors 24, 26 are arranged in the housing 12, of which on the one hand the sensors 24 for determining the required characteristic values for determining the effectiveness (method of heat exchanger efficiency) and on the other hand for determining the required characteristic values for determining the thermal difference formation between Refrigerant in the condenser 20 and refrigerant in the evaporator 22 (temperature difference method) are needed.

In addition, by arrows 28, 30, 32 (with hatching), the course of the inflowing cold cooling fluid into the housing 12 and within the housing 12 shown, while arrows 34, 36 (with dot matrix), the outflow of the waste heat laden cooling fluid from the housing 12 displays out.

Cold cooling fluid flows according to arrow 28 into the chamber 18 of the housing 12 and passes after flowing through the capacitor 20 to a part, taking along the heat absorbed in the capacitor 20 to the outside and to the other Part in the chamber 19, from where it flows into the area in which the actual transformer with iron core 14 and winding assemblies 16 is arranged. Here, the cooling fluid absorbs the heat radiated from the winding assemblies loss heat and then flows into the evaporator 22nd

In Fig. 2 a flow diagram for a schematic monitoring logic for the implementation of the temperature difference method is shown. The individual steps are indicated in each case. In the following, the individual steps or measures outlined therein are explained.

Description of the thermal difference method logic according to FIG. 3

1. 1. The monitoring (Monitoring) compares the temperature at the evaporator inlet (or the winding temperature) with predetermined design temperatures. If the threshold is not exceeded, the system is in standby mode; that means there is no action. The fans continue to run or fail to start if the winding temperature or evaporator inlet temperature is too low.
2. 2. If the threshold temperature in step 2 is exceeded and the fans are in accordance with Fig. 1 are turned off, they must now be started. Here, a control of the fan speed can be done.
3. 3. In this step, a steady state is awaited. The "manifold temperatures" at the condenser and at the evaporator are measured. The differences of the "n" thermosiphons are formed.
4. 4. The differences are compared with a threshold: DT threshold.
5. 5. If the threshold value is exceeded, the counter n _error (Diagnosis) increases.
6. 6. In step 6, the ratio of the defective thermosyphon is formed and compared with two thresholds (for example 0.6 and 1). If the ratio is in this range, many thermosyphon are defective and the functionality of the cooling system is at risk. Status service. Inspection and repair are necessary.
7. 7. If the ratio n _error / n is not greater than a certain, noncritical threshold value (for example 0.3), the thermosyphon system is not endangered. The status "OK" is then available. In the event that the critical threshold (eg 0.3) is exceeded, the status "Warning" is activated and an inspection is necessary.

In Fig. 3 a flow diagram is shown for a schematic monitoring logic for the implementation of the method of heat transfer efficiency. The individual steps are indicated in each case. In the following, the individual steps or measures outlined therein are explained.

Description of the logic for the heat transfer efficiency method

1. 1. The monitoring (monitoring) compares the temperature at the evaporator inlet or the winding temperature with predetermined design temperatures. If the threshold is not exceeded, the system remains in standby, that is, there is no action. The fans continue to run or fail to start if the temperature of the winding or at the evaporator inlet is too low.
2. 2. If the threshold temperature in step 2 is exceeded and the fans are in accordance with Fig. 1 are turned off, they must now be started. Here, a control of the fan speed can be done.
3. 3. In this step, a steady state is awaited. The effective number eff is determined by calculation.
4. 4. The effectiveness number is compared to a lower eff _low and upper eff _up threshold. Similarly, the winding temperature or the temperature at the evaporator inlet is compared with a threshold value T _{limit 1} . If the condition is met, the thermosyphon system is functional.
5. 5. If the conditions in step 4 are not met, the temperature winding temperature or air temperature at the evaporator inlet is compared again with a second threshold value T _{limit 2} . If the temperature and the effectiveness number of 4 remain in the range, a warning signal is indicated.
6. 6. If the temperature winding temperature or air temperature at the evaporator inlet over the second threshold, is an inspection or a repair necessary (service). If the efficiency number is above eff _up , the condenser or condenser fan must be inspected. If the efficacy number shows a value below eff _I , one or more thermosyphons will be damaged.

Fig. 4 shows a pressure-enthalpy diagram of the internal cooling circuit (refrigerant). The two-phase diagram (gas-liquid) with constant evaporation and condensation temperatures (pressures). The pressure drop in the thermosiphon is so small that a temperature difference is negligible.

LIST OF REFERENCE NUMBERS

10

transformer

12

casing

14

iron core

16

winding arrangement

18

first chamber

19

second chamber

20

capacitor

22

Evaporator

24

Temperature Sensor

26

Temperature Sensor

28

Arrow (with hatching)

30

Arrow (with hatching)

32

Arrow (with hatching)

34

Arrow (with dot matrix)

36

Arrow (with dot matrix)

Claims (13)

Method for monitoring the operation of a cooling system with at least one thermosyphon, in particular for transformers, preferably for dry-type transformers, wherein the cooling system is provided with at least one evaporator and at least one condenser and uses a vaporizable refrigerant and a gaseous medium, preferably air, as the heat carrier,
characterized in that
the thermo-differential method and / or the method of heat transfer efficiency is used to monitor the function and safety of the thermosyphon cooling system. A method according to claim 1, characterized in that in the thermal differential method, the temperature difference DT of the refrigerant in the at least one capacitor and in the at least one evaporator is formed according to the equation $$\mathit{DT}\mathit{=}{\mathit{T}}_{\mathit{evap}}^{\mathit{manifold}}\mathit{-}{\mathit{T}}_{\mathit{condens}}^{\mathit{manifold}}$$

with T ^manifold _evap = temperature in the evaporator and
with T ^manifold _cond = temperature in the condenser and is judged. Method according to claim 1, characterized in that in the method of heat transfer efficiency the global efficiency e of the thermosyphone system according to the relationship $\epsilon =\frac{\left(T_{\mathit{env}}-T_{\mathit{condens}}^{\mathit{out}}\right)}{\left(T_{\mathit{env}}-T_{\mathit{evap}}^{\mathit{in}}\right)}$

or $\epsilon =\frac{\left(T_{\mathit{evap}}^{\mathit{in}}-T_{\mathit{evap}}^{\mathit{out}}\right)}{\left(T_{\mathit{evap}}^{\mathit{in}}-T_{\mathit{env}}\right)}$

is formed from the ratio of the difference in the temperatures at the condenser _inlet (T _env) and at the condenser _outlet (T _condens ^out ), to the difference in the temperatures at the condenser _inlet (T _env ) and at the evaporator _inlet (T _evap ⁱⁿ ). A method according to claim 2, characterized in that the measurements are performed sequentially to reduce the number of required for the detection of the temperature characteristics measurement channels. Method according to one of claims 2 or 4, characterized in that the two temperatures are measured simultaneously on a thermosiphon element. Method according to one of the preceding claims, characterized in that in the event of a fault to remedy the flow of the gaseous heat carrier is at least temporarily interrupted. Method according to one of claims 1 to 5, characterized in that in the event of a fault to remedy the flow direction of the gaseous heat carrier is at least temporarily reversed. Method according to one of the preceding claims, characterized in that the capacitor as well as the evaporator are heated. Cooling system with at least one thermosyphon, in particular for transformers, preferably for dry-type transformers, wherein the cooling system comprises at least one thermosiphon, which is arranged in a housing and provided with at least one evaporator and at least one condenser and a vaporizable refrigerant and a gaseous medium, preferably air , used as a heat carrier,
characterized in that
in the housing temperature sensors are provided for determining the relevant temperatures. Cooling system according to claim 9, characterized in that blower devices are provided, which serve to generate a flow of the gaseous medium. Cooling system according to one of claims 9 or 10, characterized in that the flow direction of the gaseous medium by reversing the conveying direction of the blower device is reversible. Cooling system according to one of the preceding claims 9 to 11, characterized in that in which the at least one capacitor and the at least one evaporator receiving housing at least one heat source is arranged. Cooling system according to claim 12, characterized in that the heat source is formed by at least one heating element.

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