WO2017089580A1

WO2017089580A1 - Cooling system for induction machines

Info

Publication number: WO2017089580A1
Application number: PCT/EP2016/078874
Authority: WO
Inventors: Andreas Gustafsson; Anders Backman; Håkan Jonsson
Original assignee: Abb Schweiz Ag
Priority date: 2015-11-26
Filing date: 2016-11-25
Publication date: 2017-06-01

Abstract

The present disclosure relates to a method of controlling a fan 5 in a cooling system for a fluid-filled electrical device 1. The method comprises obtaining information about a device temperature of the fluid-filled electrical device from an internal temperature sensor 3. The method also comprises, based on the obtained device temperature information, determining that there is no need to run the fan for cooling the fluid-filled electrical device. The method also comprises obtaining weather information about an ambient temperature and ambient precipitation from a weather sensor comprising an ambient temperature sensor 13 and an ambient precipitation sensor 11. The method also comprises, based on the obtained weather information, controlling the fan such that it is running, to avoid build-up of snow or ice on the fan.

Description

COOLING SYSTEM FOR INDUCTION MACHINES

TECHNICAL FIELD

The present disclosure generally relates to cooling of electromagnetic induction devices. In particular, it relates to a cooling system for cooling an electromagnetic induction device, such as a transformer and reactor.

BACKGROUND

Electromagnetic induction devices, such as power transformers or reactors, comprise windings, typically electrically insulated conductors, wound around a magnetic core. The windings are subjected to currents that result in heat development in the windings that would damage the electrical insulation of the conductors, and even the conductors, if cooling of the windings would not be provided. The windings of an electromagnetic induction device are cooled and insulated by insulating fluids e.g. transformer oils or esters or even gases, such as SF6. The heated fluid must then be cooled to maintain the

temperature of the induction devices. The typical induction devices are used in electrical transmission or distribution systems.

There are a number of ways in which the fluid may be cooled. Cooling may for example be performed by means of natural or forced convection of the fluids with a natural heat loss through the induction device tank walls. For higher voltages or power, it is common to utilize a dedicated cooling system comprising one or a number of motor-fan units that force cooling air through a heat exchanger. The fluid in the induction device flows through the heat exchanger, either by natural or forced convection, to be cooled and to maintain the fluid and winding temperature in the device within an

acceptable range.

Normally today, a control system controls each motor-fan unit in the cooling system by means of a relay which turns the motor-fan unit on/off based on the top fluid temperature, which has the highest temperature fluid in the device, this provides a fixed-speed operation of the motor-fan unit. The control of the fan is normally on/off i.e. either the fan is running or it is not. The Induction machines in an electrical power system can be located in remote locations, far from service or maintenance personnel.

In cool temperatures, the cooling need by forced air flow is lower, so the fan is operated with longer times of standstill. In cool or arctic areas there is always the chance of precipitation in the form of super cooled rain or snow. There is a risk that snow or subzero rain will blow into the fan and block the fan movement. If the fan is blocked the fan motor protection system will automatically stop the motor and cooling is impossible. If this happens it might lead to that the transformer will be shut down, which can be very expensive. Normally, if the fan motor protection is triggered an alarm is set to the operator of the transformer.

Service personnel have to be sent to the transformer to unblock the fan before the transformer is shut-down which can be expensive, especially on a remote placed transformer. There is a need to prevent the cooling fans on induction machines to be blocked by snow and rain.

Prior art includes building a mechanical snow cover over the fan. For an existing transformer, without cover, this requires to take the transformer off line. Mechanical snow cover might help with vertically falling snow but not with wind driven "horizontally falling" snow e.g. snow drift.

JP S57-49210 discloses an oil-filled electrical device, wherein the oil is cooled by means of air of an external fan. The running of the external fan is dependent on weather sensors with the objective of reducing power consumption. SUMMARY

An object of embodiments of the present inventive concept is to provide electrical devices such as electromagnetic induction devices which solve or at least mitigate the problems with existing solutions. The invention is based on the realization that if it is snowing and the fan is stationary there might be a build-up of snow that eventually will block the fan and trigger a fan motor protection and it is therefore better not to stop the fan if there is a risk of snow build-up. Hence, embodiments of the present disclosure provide a cooling system for an electrical device, wherein the cooling system comprises one or more fans each driven by an electric motor, a weather sensor that determines the weather; and a control system arranged to control each fan.

In a retrofit situation embodiment of the present invention may be easy to install. No stop of the operation may be needed and it may be cheaper than to install physical protection from snow falling on the fan.

According to an aspect of the present invention, there is provided a method of controlling a fan in a cooling system for a fluid-filled electrical device. The method comprises obtaining information about a device temperature of the fluid-filled electrical device from an internal temperature sensor. The method also comprises, based on the obtained device temperature information, determining that there is no need to run the fan for cooling the fluid-filled electrical device. The method also comprises obtaining weather information about an ambient temperature and ambient precipitation from a weather sensor comprising an ambient temperature sensor and an ambient

precipitation sensor. The method also comprises, based on the obtained weather information, controlling the fan such that it is running, to avoid build-up of snow or ice on the fan.

In some embodiments, the obtained weather information from the ambient precipitation sensor comprises information about ongoing raining, ongoing snowing and/or current snow level.

In some embodiments, the controlling the fan such that it is running comprises starting the fan or preventing the fan from stopping. In some embodiments, the controlling the fan such that it is running comprises controlling the fan such that it is running during a predetermined time period.

In some embodiments, the temperature of the fluid-filled electrical device is of the fluid, e.g. a top fluid temperature.

In some embodiments, the method is performed by a control system of the cooling system.

According to another aspect of the present invention, there is provided a cooling system for a fluid-filled electrical device. The cooling system

comprises a fan for cooling the fluid-filled electrical device, an internal temperature sensor configured to measure a temperature in the fluid-filled electrical device, a weather sensor comprising an ambient temperature sensor and an ambient precipitation sensor, configured to measure weather outside of the fluid-filled electrical device, and a control system. The control system is configured to obtain information about a device temperature of the fluid-filled electrical device from the internal temperature sensor. The control system is also configured to, based on the obtained device temperature information, determining that there is no need to run the fan for cooling the fluid-filled electrical device. The control system is also configured to obtain weather information about an ambient temperature and ambient

precipitation from a weather sensor comprising an ambient temperature sensor and an ambient precipitation sensor. The control system is also configured to, based on the obtained weather information, controlling the fan such that it is running, to avoid build-up of snow or ice on the fan. In some embodiments, the ambient precipitation sensor comprises a rain sensor, a snow sensor and/or a snow level sensor.

In some embodiments, the ambient precipitation sensor comprises at least a first and a second precipitation sensor positioned on either side of the fluid- filled electrical device. In some embodiments, the weather sensor is positioned on the outside of, and/or outside of, a tank enclosing the fluid-filled electrical device.

In some embodiments, the ambient precipitation sensor comprises at least one snow sensor comprising a heating element for melting snow collected by the snow sensor.

According to another aspect of the present invention, there is provided a fluid-filled electrical device comprising an embodiment of the cooling system of the present disclosure.

In some embodiments, the fluid-filled electrical device comprises an induction machine e.g. an electrical power transformer or an electrical motor.

In some embodiments, the fluid of the fluid-filled electrical device is a liquid e.g. an oil.

In some embodiments, the fluid-filled electrical device also comprises a heat exchanger arranged for exchanging heat between the fluid of the fluid-filled electrical device and ambient air from the fan.

It is to be noted that any feature of any of the aspects may be applied to any other aspect, wherever appropriate. Likewise, any advantage of any of the aspects may apply to any of the other aspects. Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. The use of "first", "second" etc. for different features/components of the present disclosure are only intended to distinguish the features/components from other similar features/components and not to impart any order or hierarchy to the features/components.

BRIEF DESCRIPTION OF THE DRAWINGS

The specific embodiments of the inventive concept will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure l schematically shows the prior art solution for induction machine cooling.

Figure 2 schematically shows an embodiment of the present invention for induction machine cooling.

Figure 3 schematically shows fan operation of the prior art.

Figures 4-5 schematically show fan operation according to the present invention in different embodiments.

DETAILED DESCRIPTION

The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplifying

embodiments are shown. The inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description.

Figure 1 shows a fluid filled induction device or machine Bi e.g. oil filled transformer. It has a temperature measurement, which could be a top fluid temperature measurement B3 and/or a winding hot spot temperature measurement. This measurement is communicated to a control system B2 which sends a signal B6 that switches on and off the fan B5 motor By. If the fan is operating, i.e. is on, it blows a stream of cool air on a heat exchanger B4 in which fluid from the induction device circulates. The flow of fluid in the heat exchanger B4 is either by natural convection or forced convection by e.g. a pump. The motor is controlled by a switch or relay which turns the motor on/off (a fixed speed operation) or the motor can be controlled by a variable frequency drive which enable variable speed operation.

Figure 2 shows a fluid filled electrical device 1 and associated cooling system in accordance with an embodiment of the present invention. Similar to the discussion in relation to figure 1, a fluid filled electrical (e.g. induction) device or machine 1 e.g. an oil filled transformer is shown. The cooling system of the electrical device 1 comprises an internal temperature measurement sensor 3, which may be a top fluid temperature sensor and/or a winding hot spot temperature sensor. The measurement of the internal temperature sensor 3 may be communicated to a control system 2 which may send a signal 6 that switches on and/or off (i.e. starts and/or stops) the motor 7 of the fan 5. If the fan is operating/running, i.e. is on, it blows or sucks a stream of cool air from outside of the fluid-filled electrical device on or past a heat exchanger 4 (e.g. a radiator) of the electrical device, in which heat exchanger fluid from the electrical device circulates. That the fan is "running" as discussed herein implies that the fan blades are turning and that thus build-up of snow and/or ice is reduced or prevented, regardless of whether the fan needs to be on in order to cool the electrical device. However, the fan may be running differently when the fan is needed for cooling the electrical device and when the fan is running to avoid build-up of ice or snow. When the fan is only running to avoid build-up of ice or snow, it may be running at a lower rpm and/or intermittently. The flow of fluid in the heat exchanger 4 may be either by natural convection or forced convection by e.g. a pump. The motor 7 may be controlled by a switch or relay which turns the motor on or off (a fixed speed operation), or the motor may be controlled by a variable frequency or voltage drive which enables variable speed operation. The fluid may be an electrically insulating gas or liquid such as an oil (e.g. mineral or vegetable) or ester liquid. The electrical device may be an electromagnetic induction device or machine l, e.g. a transformer or electrical motor. Preferably, the electrical device is an oil filled transformer. It may have a top fluid temperature measurement sensor 3. The control system 2 may also receive input 10 and/or 12 from a weather sensor 11 and/or 13. The weather sensor may try to determine the weather, especially if there is a risk of snow and/or ice on the fan 5.

The fan 5 is typically arranged in, or outside of, a wall or housing of the electrical device 1, or of a wall enclosing said electrical device, whereby the fan is exposed to the outside weather either directly or via the outside air which it draws in.

The term "weather sensor" should be interpret broadly. In the simplest form, it could include only one sensor, as for example an ambient temperature sensor 13 and/or precipitation sensor 11. Measurements from the weather sensor may be, or be part of, the weather information discussed herein, and may be inputted to the control system.

A more capable weather sensor could comprise more sensors for example any combination of; ambient temperature sensor, precipitation sensor, humidity sensor, wind measurements sensor, solar radiation sensor, barometric pressure sensor, current snow level, camera with digital image processing to detect snow etc. It may be an advantage to have more than one sensor of a type. Multiple same/similar sensor will make the measurements of a weather property (e.g. temperature, precipitation, snowfall, rain, wind etc.) more certain and will increase the redundancy, for example if one sensor fails.

The ambient precipitation sensor 11 may comprise any number of sensors, e.g. one or a plurality of sensors. The ambient precipitation sensor 11 may comprise at least one rain and/or snow sensor which physically measures precipitation, e.g. as moisture collected in a collector (cup) of the sensor, and/or a sensor comprising a camera, e.g. with image processing ability, for detecting rain and/or snow, e.g. ongoing raining or snowing at the site of the electrical device 1. Additionally or alternatively, the ambient precipitation sensor 11 may be configured for receiving input from, or weather information about measurements of, an external sensor (external to the cooling system), e.g. of a central control station or of a cooling system for another electrical device (e.g. in the vicinity of the electrical device 1). In some embodiments, the ambient precipitation sensor n may be configured to receive information about whether or not it is currently raining or snowing at the site of the electrical device l, e.g. as part of meteorological information from a weather station or a weather service provider.

The sensor information can then be combined and used, for example by a ruled based system, to estimate how likely the fall of snow or sub-zero rain is. The system could also estimate the likelihood of wind driven snow.

The weather sensor could also be a sensor less system where it relies solely on metrological forecasts. It is also possible to have a weather sensor that combines general metrological forecasts with locally measured sensor information of the type above.

In an embodiment the fan blades and the housing are arranged with a hydrophobic surface to prevent snow or ice to attach itself to the surface of the fan blades and/or the fan housing and thereby prevent blocking the movement of the fan. In some embodiment the weather sensor comprises at least two snow sensors, mounted on different sides of a tank or other housing enclosing the fluid-filled electrical device 1. To use at least two snow sensors may ensure a more reliable measurement, e.g. independent of snow drift due to different wind directions. The at least one ambient temperature sensor 13 may be used to indicate risk of ice build-up on the fan 5, e.g. if the temperature is below o°C while there is on-going raining or snowing, and/or while there is high humidity. The snow sensor 11 may have a built in heating element. Thus, when snow falls on the sensor it melts into water/moisture which may more easily be measured by the sensor.

The snow or rain sensor 11 may comprise a heating element to measure only ongoing snow or rain fall or snow drift the (melt) water/moisture may evaporate during time periods without precipitation (snow or rain).

The ambient temperature sensor 13 is arranged to measure the ambient temperature, outside of the fluid-filled electrical device 1, e.g. outside a tank or other housing enclosing the fluid-filled electrical device. Any part of the weather sensor, e.g. any part of the ambient temperature sensor 13 and/or of the ambient precipitation sensor 11 may be positioned outside of the fluid-filled electrical device 1, e.g. outside or on a wall of a tank or other housing enclosing the fluid-filled electrical device.

The combined signal from the ambient temperature sensor 13 and the ambient precipitation sensor 11, e.g. comprising a snow sensors, may be handled in the control unit 2, e.g. mounted in a control cabinet at or remote from the fluid-filled electrical device 1.

For instance, if the ambient temperature is below o°C and the snow sensor indicates moisture (melts snow). The control unit 2 may start the at least one fan 5 to keep it free from snow and prevent ice build-up.

To prevent too short run time of the fan 5, a time delay relay may prevent stopping of the fan during a predetermined time period (e.g. one hour) after it has been started. Figure 3 schematically shows fan operation of the prior art. The temperature B20 shown in a dashed line and the operation of the fan, in for example Rounds Per Minute (RPM), in a solid line. When the temperature reaches some determined value, the fan is operated (i.e. made to be running) B21, B22, i.e. switched on, and when the temperature reaches some determined lower value the operation of the fan is turned off. Figure 4 schematically shows fan operation according to one embodiment of the present invention. Similarly to the discussion relating to figure 3, the temperature 20 is shown in a dashed line (temperature on the Y-axis) and the operation of the fan, in for example Rounds Per Minute (RPM) on the Y-axis, in a solid line. In accordance with embodiments of the present invention, there is additional input to the control system 2 from a weather sensor 11 and/or 13. The weather sensor indicates that there is a risk for snow 24 during some time. The control system might prevent the fan from stopping operating 23 during this time. The device temperature might go below the determined lower value but the cooling and fan operating is still kept running. The fan motor stops only when the weather sensor indicates that the risk for snow is now very small.

Figure 5 schematically shows fan operation according to another

embodiment of the present invention. It is a similar situation as in figure 4 with the additional input to the control system 2 from a weather sensor 11 and/or 13. The weather sensor indicates that there is a risk for snow 24 during some time. The motor 7 of the fan 5 is controlled by variable frequency drive (VFD), which enables variable speed of the motor of the fan, or at least the motor is stably operated at two different speeds. If there is no need for cooling of the electrical device 1 but there might be risk for snow 24, the control system may operate the motor on a lower speed 25 than when it is cooling 21, 22. The temperature may not go below the determined lower value. The motor fan stops only when the weather sensor indicates that the risk for snow is now very small. The control system should be interpreted broadly. In the simplest form it switches the fan on when the internal (e.g. top fluid) temperature exceeds a set temperature and turns the fan off when the top fluid temperature goes below another set temperature. Normally, one would not want to turn the fan off and on with too high frequency so the set temperatures may not be the same. In addition, to prevent the fan from turning off and on with too high frequency there could be a time restriction on change of the state of the fan. For example, if the fan is operating it may operate during at least x minutes, e.g. 15 min and if the fan is stopped it may not start again until at least y minutes have passed, e.g. 10 min.

The present invention suggests that instead of solely relying on the internal temperature, to also include data from the weather sensor for the operating of the fan.

If the weather sensor may estimate that there will be a risk for blocking of the fan from snow or ice, the control system may then take appropriate measures, such as not stopping the fan.

If the fan motor control is more advanced, with for example a variable motor drive, the control signal 6 from the control system 2 could be, when there is no need for cooling of the electrical machine 1 but there is a risk for snow, made to not stop the motor but to more slowly turning the fan with the motor. Another option could be to fully use the full control of the motor speed that we get from the variable frequency drive and always run the motor. The varying speed of the motor and fan may then be adapted to the varying cooling need of the fluid filled electrical device. If the induction machine is hot, the motor speed may be high and if the induction machine is cool, the motor speed may be low but at no time may the motor be at standstill if there is a risk for snow. Below are presented some other embodiments of the present invention. Any embodiments presented in the present disclosure may be combined with any other embodiment if applicable.

An embodiment of the present invention relates to a cooling system for an electrical induction machine 1 comprising. The induction machine comprises a fan 5 with a fan motor 7, a weather sensor 11 and/or 13 and/or other weather sensor, and a control system 2. The control system controls the fan motor based on input from the weather sensor, e.g. in addition to input from a conventional temperature sensor 3 in the electrical induction machine 1. In some embodiments, the weather sensor comprises a precipitation sensor 11, a snow sensor 11, an ambient temperature sensor 13, a humidity sensor, a wind measurements sensor, a solar radiation sensor, a barometric pressure sensor, a current snow level sensor and/or a system to receive and evaluate metrological forecast data.

In some embodiments, the weather sensor comprises a system to receive and evaluate metrological forecast data combined with local sensors.

An embodiment of the present invention relates to a method of controlling a fan 5 with fan motor 7 in a cooling system for an electrical induction machine 1. The method comprises the step of using input from a weather sensor 11 and/or 13 and/or other weather sensor to control the fan motor.

In some embodiments of the method, the input from the weather sensor 11 and/or 13 and/or other weather sensor is the likelihood of snow, and if this likelihood is above a threshold value, the fan motor is left in operation, even if there is no cooling need.

The present disclosure has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the present disclosure, as defined by the appended claims.

Claims

1. A method of controlling a fan (5) in a cooling system for a fluid-filled electrical device (1), the method comprising: obtaining information about a device temperature of the fluid-filled electrical device (1) from an internal temperature sensor (3); based on the obtained device temperature information, determining that there is no need to run the fan (5) for cooling the fluid-filled electrical device; obtaining weather information about an ambient temperature and ambient precipitation from a weather sensor comprising an ambient temperature sensor (13) and an ambient precipitation sensor (11); based on the obtained weather information, controlling the fan such that it is running, to avoid build-up of snow or ice on the fan.

2. The method of any preceding claim, wherein the obtained weather information from the ambient precipitation sensor (11) comprises

information about ongoing raining, ongoing snowing and/or current snow level.

3. The method of any preceding claim, wherein the controlling the fan such that it is running comprises starting the fan or preventing the fan from stopping.

4. The method of any preceding claim, wherein the controlling the fan such that it is running comprises controlling the fan such that it is running during a predetermined time period.

5. The method of any preceding claim, wherein the temperature of the fluid-filled electrical device (1) is of the fluid, e.g. a top fluid temperature.

6. The method of any preceding claim, wherein the method is performed by a control system (2) of the cooling system.

7. A cooling system for a fluid-filled electrical device (1), the cooling system comprising: a fan (5) for cooling the fluid-filled electrical device; an internal temperature sensor (3) configured to measure a temperature in the fluid-filled electrical device; a weather sensor comprising an ambient temperature sensor (13) and an ambient precipitation sensor (11), configured to measure weather outside of the fluid-filled electrical device; and a control system (2) configured to: obtain information about a device temperature of the fluid-filled electrical device (1) from the internal temperature sensor (3); based on the obtained device temperature information, determining that there is no need to run the fan (5) for cooling the fluid-filled electrical device; obtain weather information about an ambient temperature and ambient precipitation from a weather sensor comprising an ambient temperature sensor (13) and an ambient precipitation sensor (11); based on the obtained weather information, controlling the fan such that it is running, to avoid build-up of snow or ice on the fan.

8. The cooling system of claim 7, wherein the ambient precipitation sensor (11) comprises a rain sensor, a snow sensor and/or a snow level sensor.

9. The cooling system of any claim 7-8, wherein the ambient precipitation sensor (11) comprises at least a first and a second precipitation sensor positioned on either side of the fluid-filled electrical device (1).

10. The cooling system of any claim 7-9, wherein the weather sensor (11, 13) is positioned on the outside of, and/or outside of, a tank enclosing the fluid- filled electrical device (1).

11. The cooling system of any claim 7-10, wherein the ambient precipitation sensor (11) comprises at least one snow sensor comprising a heating element for melting snow collected by the snow sensor.

12. A fluid-filled electrical device (1) comprising the cooling system of any claim 7-11.

13. The fluid-filled electrical device of claim 12, wherein the fluid-filled electrical device (1) comprises an induction machine e.g. an electrical power transformer or an electrical motor.

14. The fluid-filled electrical device of claim 12 or 13, wherein the fluid of the fluid-filled electrical device (1) is a liquid e.g. an oil.

15. The fluid-filled electrical device of any claim 12-14, further comprising a heat exchanger (4) arranged for exchanging heat between the fluid of the fluid-filled electrical device and ambient air from the fan (5).