Field of the invention

The invention relates generally to the field of power transmission networks, and in particular to fire protection within such networks.

Background of the invention

Power transmission networks sometimes utilize backup power systems, for example in order to compensate for varying power generation or load, or in the case of loss of power. This can for example be the case in wind- or solar power systems. The backup power system provides power during fluctuations of the generated wind or solar power and even during power outages. Such backup power systems rely on a bank of batteries to store enough energy to even out the power fluctuations.

In power transmission networks such battery storage systems may consist of a large amount of battery cells connected in series and parallel to reach sufficiently high voltage levels and high power and energy. The voltage levels may be in the order of several tens of kV and power capability up to several 10 MWs or even in the order of 100 MW. To achieve this, such battery energy storage systems will comprise several thousands battery cells.

The batteries of the backup power thus contain high amount of energy, and a failing battery cell, e.g. by external or internal short circuit or overload, will quickly become very hot. The heat emitted from the failing cell will heat up an adjacent battery cell, which in turn will heat up the next cell and so on, and this of course constitutes a huge fire hazard. As an example, Li-ion battery cells exceeding a critical temperature may result in opening of the cell, known as venting of the cell, with a release of highly inflammable gases that can easily catch fire. If this happens there is a large risk of the whole battery storage system being destroyed. The gases released from Li-ion battery cells may contain a mixture of hydrogen, carbon monoxide, carbon dioxide, methane, ethane, methylene, propylene, organic carbonates and also carbon powder. The battery backup systems are therefore usually protected by temperature sensors detecting heat of a fire and by fire extinguishing means, for example argonite based fire extinguishers. Argonite gas is injected rapidly into the storage room within which the battery backup is stored, when the temperature sensors detect an abnormal temperature.

However, such fire protection systems aim in the first place at extinguishing fires once they have started. Although there are different kinds of fire prevention in the form of overload protection circuits, circuits detecting abnormal currents etc., it would be desirable to be able to fight fires at an early stage, as safety aspects are very important in power transmission networks. It would in particular be desirable to be able to fight fires at the verge of breaking out.

Summary of the invention

It is an object of the invention to provide an improved way of detecting, preventing and extinguishing a fire within a battery storage of a power transmission network.

It is another object of the invention to provide a system and a method for fire protection, wherein possible fire hazards are detected at an early stage.

It is yet another object of the invention to provide a system and a method for fire protection, wherein fires are extinguished locally at the fire centre, and in particular without filling the whole storage room within which the battery backup is stored with the fire extinction means.

It is still another object of the invention to provide a system and method for fire protection, able to regress an arising fire before actually catching fire.

These objects, among others, are achieved by a system and by a method for fire protection as claimed in the appended claims.

In accordance with the invention, a system is provided for fire protection of a battery storage comprising at least one battery module, which battery module in turn comprises one or more battery cells. In accordance with the invention, the battery storage comprises a housing, which is connected to an inlet arrangement for injection of a fire extinguishing means into the housing. By means of the invention it is possible to inject the fire extinguishing means, preferably carbon dioxide, into the housing containing the failing battery cell. The injected gas sweeps away gases released from the failing cell into the housing and also cools down the one or more battery cell (s) , thereby preventing avalanche effects of the failing battery cell heating adjacent battery cells and thereby regressing the arising fire before it actually catches fire. By transporting away the highly inflammable gases the risk of fire is greatly reduced. The system thus provides means for preventing fire and also means for quickly extinguishing a fire that still has occurred. Further, by means of the invention, it is possible to extinguish fires at the precise seat of fire.

In accordance with an embodiment of the invention, the housing of the battery storage is further connected to an outlet arrangement comprising means for collecting and discharging gas released by the one or more battery cells. The outlet arrangement preferably comprises gas-detecting means for detecting gas released by the one or more battery cells. An early detection of a possible fire hazard is thereby provided. A gas released by a failing battery cell, for example hydrogen gas, is detected very early. Upon detection, the fire extinguishing means is injected. The system thus provides an early detection, means for preventing fire and also, as mentioned, means for quickly extinguishing a fire that still has occurred.

In accordance with another embodiment of the invention, the system further comprises temperature sensors arranged at the at least one battery module. A battery cell soon to break will be heated up, and by detecting such temperature increases of the battery cells, an early detection of a battery cell very soon to break is enabled.

In accordance with another embodiment of the invention, the system further comprises additional fire extinguishing means, for external cooling of the battery chassis. Conventional fire extinguishing means is thus used as a backup, should a fire still occur. Such situation could occur, for example if the previous fire extinction did not work properly or due to the human factor or sabotage, external fires or the like.

Further features, defined in further dependent claims, of the invention and advantages thereof will become evident when reading the following detailed description.

The invention also relates to a method for fire protection of a battery storage, whereby advantages similar to the above are achieved.

Brief description of the drawings

Figure Ia illustrates a system for fire protection in accordance with the invention. Figure Ib illustrates a battery module comprising a number of battery cells and inserted into a battery cabinet.

Figure Ic illustrates the battery cabinet of figure Ib in a side view.

Figure 2 illustrates in a different view the fire protection system of figure 1.

Figure 3 illustrates an inlet connection of figure 2.

Figure 4 illustrates steps of the method in accordance with the invention.

Detailed description of embodiments of the invention

Figure Ia illustrates a system for fire protection in accordance with the present invention. The fire protection system 1 comprises a battery storage 2 to be protected, located within a suitable storage room. The storage room can be any suitable building or container. The roof, in the following denoted top, and floor of such storage room are indicated at reference numerals 3 and 4, respectively.

The battery storage 2 comprises any number of battery modules 5, in turn comprising any number of battery cells. One battery cell is schematically illustrated at reference numeral 7. The battery module 5 may for example comprise a number of series- connected and/or parallel-connected battery cells 7 housed within a chassis 6, also denoted housing, of the battery module 5. The battery modules 5 are, for example, series- connected to each other and constitute a battery string housed within a housing, in the following denoted battery cabinet 8 (see figures Ib and 2) .

One Li-ion battery cell may, for example, contain 2 MJ of combustible energy in case of fire, the energy content depending for example on battery cell design and type of battery cell. As an example, assuming that a battery module 5 comprises 14 battery cells 7 and that a battery string comprises 13 battery modules 5, this would mean that an energy of as much as approximately 360 MJ could be released in the battery string. In a large storage system having several thousands of battery cells the total combustible energy will be even larger. One single battery cell 7 may release up to 250 litres of gas having a temperature ranging up to 300- 400 ⁰ C. The gases are highly combustible and may cause a chain reaction in that a vented battery cell 7 is heated up, and in turn heats up the adjacent battery cell which in turn ventilates and so on. It is thus realized that a failing battery cell 7 may cause an avalanche effect rather swiftly.

The battery cell 7 comprises a housing, in the following denoted casing. The casing has, for example, a welded upper or lower part. Such battery cell 7 casing has a known weak point, for example the welding or some other intentionally made weak point. If the battery cell 7 would fail, gases resulting from such failure would escape at the weak point, e.g. the welding. The present invention utilizes this knowledge by providing means for capturing and detecting possible gases discharged from the battery cells 7 of the battery modules 5. In particular, assuming that the bottoms are the weak points of the battery cells, they are placed in contact with a chimney construction, which will be described in the following. If other parts of the battery cells 7 are deemed to be the weakest point, the chimney construction is connected accordingly, so as to collect gases released from the weak point.

Figure Ib illustrates one battery module 5 comprising a number of battery cells 7, wherein dashed lines schematically illustrate one battery cell 7. The chassis 6 of the battery module 5 is inserted into the battery cabinet 8. The battery cabinet 8 may for example comprise a number of fastening devices 24, such as brackets, for holding the battery module 5. The chassis 6 of the battery module 5 may further comprise handles 25 for facilitating insertion and removal thereof.

With reference again to figure Ia, the fire protection system 1 comprises a chimney construction, which comprises an outlet arrangement 9 for detecting gases discharged from the battery cells 7. The outlet arrangement 9 may comprise a hollow pipe connected to the battery cabinet 8, or other battery storage housing, in such a way as to capture and lead gases discharged from the battery cells 7 through the top 3 of the storage room. The outlet arrangement 9 should thus be suitable for leading gases discharged from the battery cells 7 arranged in battery modules 5, in turn arranged in the battery cabinet 8, through the top 3 and out to the atmosphere.

Figure Ic illustrates the battery storage 2 of figure Ib in a side view. The battery modules 5 _X are inserted into the battery cabinet 8, leaving an air gap 22 between the rear side of the chassis 6 of the battery module 5 and a wall 23 of the battery cabinet 8. As illustrated in figure Ic, the outlet arrangement 9 is connected between the top 3 of the storage room and the battery cabinet 8, and in particular connected so as to collect gases released by the battery cells 7. In the illustrated example, the battery cells 7 are located in the chassis 6 in such a way that when a battery cell 7 fails, the gases released from it are submitted into the air gap 22 and led upwards to the outlet arrangement 9. The air gap 22 can thus be considered as part of the chimney construction. The outlet arrangement 9 thus captures gases released within the battery cabinet 8 and led through the air gap between the wall 23 of the battery cabinet 8 and the rear side(s) of the chassis of the battery module (s) 5. It is noted that the air gap can be created between any side of the chassis 6 of the battery module 5 and the battery cabinet. In fact, the air gap can be arranged in any suitable manner within the battery cabinet 8.

The outlet arrangement 9 further comprises a valve 10, in the following denoted outlet valve 10 that can be opened and closed in an automated manner. The outlet valve 10 is opened when gases are to be released to the atmosphere and closed otherwise. Alternatively, the outlet valve 10 may be a non- automated valve, opened by the gas pressure within the chimney construction, e.g. a flip valve.

The outlet arrangement 9 comprises a gas detector 12, for detecting gases that are released by broken battery cells 7. A broken battery cell 7 may release, for example, hydrogen gas H ₂ and/or carbon monoxide CO. Other gases that may be released by the battery cells 7 comprise carbon dioxide, methane, ethane, methylene, propylene, organic carbonates and/or carbon powder. The gas detector 12 may thus comprise, for example, a hydrogen detector. Hydrogen is very light and easy to detect and detection of the released hydrogen gas therefore provides an early detection of possible fire hazards.

An oxygen meter 20 may further be arranged in connection to the outlet valve 10 for measuring the oxygen level of the gases. If, in case of a fire, the oxygen level is above an oxygen threshold value Th _oxygen , the outlet valve 10 is closed. Thereby any upcoming fire is stifled and extinguished. In an alternative embodiment the storage room in which the battery storage 2 is arranged, may comprise a single oxygen meter, arranged to measure the oxygen level of the storage room.

The chimney construction of the fire protection system 1 further comprises an inlet arrangement 11 for injection of a fire extinguishing means, preferably carbon dioxide CO ₂ . As soon as the gas detector 12 has detected a release of gas from the battery cells 7, the carbon dioxide is injected through the inlet arrangement 11. The inlet arrangement 11 is connected through suitable connection pipes 14, 15 to a supply of fire extinguishing means, in the following exemplified by a rack of carbon dioxide supply 13a. The connection pipes 14, 15 lead the carbon dioxide gas from the carbon dioxide supply 13a to the respective inlet arrangement 11 of the battery cabinets

Carbon dioxide CO2 is particularly suitable in the present invention. When gas (e.g. hydrogen gas) released from the battery cells 7 has been detected, the carbon dioxide is injected into the chimney construction through the inlet arrangement 11, and the gases, i.e. the carbon dioxide and the gases released from the battery cells, are led through the air gap 22 and outlet at the outlet arrangement 9. The released, ignitable gases will thereby be swept away along with the carbon dioxide gas before it catches fire. At the same time, as a further advantage of the invention, all the battery cells, including the vented battery cell, will be cooled down by the injected carbon dioxide gas. Solid carbon dioxide, also known as dry ice, converts directly from a solid to a gas at -78 ⁰ C or above. The carbon dioxide gas may thus have a temperature of about -78 ⁰ C when injected into the chimney construction.

Further, if the oxygen level as measured by the oxygen meter 20 arranged at the outlet valve 10 is above the mentioned threshold value Th _oxyge n more carbon dioxide can be injected, thereby cooling down the battery cells 7 as well as sweeping away the gases released from the battery cells 7.

Figure 2 illustrates the fire protection system of figure 1 in a different view, showing five battery cabinets 8. With reference now to figures 2 and 3, the inlet arrangement 11 comprises the suitable connection pipes. The part of the inlet arrangement 11 between an inlet valve 16 and the battery cabinet 8 could for example be made of glass fibre or any other material suitable for high-voltage applications, as the battery cabinets 8 will be on high potential, possibly several kVs . Further, the connection pipes 14, 15 are preferably made of electrical conducting steel or stainless steel due to gas pressure reasons, and therefore the part of the inlet arrangement 11 that is in contact with the battery cabinet 8 should be made of a material that can withstand high voltages as well as the required gas pressure.

The inlet valve 16 is arranged at the inlet arrangement 11 for letting the carbon dioxide gas into the battery cabinet 8. The inlet valve 16 may for example be a magnetic valve actuated by a control signal transmitted from a control device 17, schematically indicated at reference numeral 17. Control signals transmitted by the control device 17 for controlling e.g. different valves within the system, are indicated in figure Ia by dashed lines.

The control device 17 is used for controlling the fire protection system 1 and could be any suitable processing means, for example computer means comprising software for performing the desired functions. For example, the control device 17 comprises means for opening and closing the different valves 10, 16 of the system 1, means for receiving signals from the gas detector 12 and the oxygen meter 20 and means for responding to such signals by suitable action, for example to release carbon dioxide into the battery cabinet 8 and/or to close the outlet valve 10.

In accordance with the invention, battery cells 7 soon to break may also be detected. The battery modules 5 may comprise temperature sensing means, such as a temperature sensor schematically illustrated in figure Ib at reference numeral 28, for measuring the temperature of the battery cells 7. Although illustrated only for one battery module 5, it is noted that each battery module 5 preferably comprises such temperature sensor 28. If the temperature sensor 28 detects that the temperature of a battery cell 7 exceeds a predetermined value, the battery module 5 communicates this information to the control device 17, which in turn activates the inlet arrangement 11. The temperature of the battery cells 7 and/or battery module 5, as well as other data measured by the battery module 5, may be communicated to the control device 17 on a regular basis. The data is then processed in a suitable manner, for example in order to detect abnormal values. The control device 17 may thereafter take appropriate action, for example disconnecting the battery storage 2, and/or transmitting an alarm.

In an embodiment of the invention, the control device 17 is arranged to open the inlet valve 16 at regular intervals and injecting the carbon dioxide. The intervals may be chosen so that the oxygen level, for example as measured by the oxygen meter 20, is kept at an acceptable level. As an example, the oxygen level is chosen so as to minimize the risk of the vented gases inflaming and/or exploding.

In still another embodiment of the invention, the fire protection system 1 further comprises temperature sensors, schematically indicated at reference numeral 21a, 21b,..., 21n, located in connection to the respective battery cabinet 8 of each battery storage 2. The temperature sensors 21a, 21b,..., 21n are arranged to measure the temperature of the battery cabinets 8. The temperature sensors 21a, 21b,..., 21n may for example comprise IR-sensors, and each battery cabinet 8 has preferably its own temperature sensor 21a, 21b,..., 21n measuring the temperature of the particular battery cabinet 8. The temperature sensors 21a,..., 21n comprises means for conveying data to the control device 17. By means of this feature, the control device 17 is able to receive signals indicative for the temperature of each battery cabinet 8. A particular battery cabinet 8 having an abnormal temperature, for example in the range of 70-90 ⁰ C, should be cooled down.

To achieve the cooling of the battery cabinet 8, the fire protection system 1 comprises a second rack of carbon dioxide 13b. A pipe 18 is connected from the second rack of carbon dioxide 13b to the vicinity of the battery cabinets 8. The pipe 18 comprises a suitable number of nozzles formed and directed so that dry ice is formed around the individual battery cabinets 8, whereby an effective cooling of the battery cabinet 8 having an increased temperature is accomplished. Valves 26a, 26b,..., 26n are arranged in the pipe 18 close to a respective nozzle so as to enable the supply of fire extinguishing means from the second rack of carbon dioxide 13b at a particular location, i.e. so as to enable pumping of carbon dioxide on a specific battery cabinet 8 by opening the valve 26i arranged over that battery cabinet 8. The pipe 18 and second rack of carbon dioxide 13b is similar to known fire protection means, and provides an external cooling of the battery chassis 6 or 8.

In particular, if the control device 17 receives a signal from the temperature sensor 21i of a specific battery cabinet 8 indicating a temperature higher than an expected temperature, a particular valve 26i and corresponding nozzle is activated for cooling down the specific battery cabinet 8.

In another embodiment of the invention, the fire protection system 1 further comprises temperature sensors, schematically indicated at reference numeral 19, located within the storage room wherein the battery storage 2 is located, and arranged to measure the temperature within the storage room. If the temperature as measured by the temperature sensors 19 reaches a predetermined value, for example within the range of 70-90° Celsius, carbon dioxide should be released. The above- described second rack of carbon dioxide 13b can be activated. It is noted that the pipe 18 can extend along the entire storage room, not only around the battery cabinet 8. Thus, if a fire should start anyway, for example although a battery cabinet 8 having an increased temperature is cooled down, the carbon dioxide gas CO2 is injected rapidly into the storage room within which the battery storages 2 are located.

In still another embodiment, a smoke detector, schematically illustrated at reference numeral 27, is arranged in the storage room comprising the battery storage 2. Upon detection of smoke within the storage room, the supplies of fire extinguishing means 13a and/or 13b are/is activated.

In yet another embodiment, the supplies of fire extinguishing means 13a and 13b are interconnected by a pipe 29. If either one of the racks of carbon dioxide 13a, 13b is depleted, the control device 17 can open a valve 37, whereby the provision of fire extinguishing means can be provided from one of the supplies of fire extinguishing means 13a and 13b, as if being from both of them.

In the above description, carbon dioxide is used as an example of a gas suitable for sweeping away gases released by the battery cells 7 and for cooling down the battery cells 7. However, other gases could alternatively be used, for example a fire extinguishing means comprising argon gas or a mixture comprising argon gas.

In the above description, the chimney construction comprises the inlet arrangement 11, the outlet arrangement 9 and the air gap 22. However, the outlet arrangement 9 could alternatively be arranged at a per battery module 5 basis or at a per battery cell 7 basis. That is, although illustrated as an outlet arrangement 9 per battery cabinet 8, there could be an outlet arrangement 9 per battery module 5 or even per battery cell 7, with suitable connection means to each respective housing, i.e. to the battery cell casing, or to the battery module chassis. A chimney construction could then comprise one inlet arrangement and one outlet arrangement per battery module, the chimney construction comprising no air gap.

With reference to figure 4, the present invention also provides a method 30 for fire protection of the battery storage 2 having a housing, wherein the battery storage 2 comprises a battery module 5, which in turn comprises at least one battery cell 7. The method 30 comprises the first step 31 of detecting gas emitted from the at least one battery cell 7. The detection of gas can be done in any suitable manner, for example by means of the earlier mentioned gas detector 12. The method 30 comprises the next step of injecting 32 fire extinguishing means into the housing (for example the battery module chassis 6 or the battery cabinet 8) of the battery storage 2. The fire extinguishing means is injected through the inlet arrangement 11 of the housing 6 or 8 upon detection of gas emitted from the one or more battery cell 7.

The method utilizes fire extinguishing means that is suitable for sweeping away gas emitted from the at least one battery cells 7, for cooling of the at least one battery cell 7 and for extinguishing fire, as described earlier.

The method may comprise additional, optional steps, illustrated with dashed line in the figure 4. The method 30 may for example comprise the step of detecting 33 the oxygen level of gases released through the outlet arrangement 9, by means of an oxygen meter 20 arranged at the outlet arrangement 9 of the housing 6, 8 of the battery storage 2. The method 30 then preferably comprises the further step of injecting 34 or increasing the amount of fire extinguishing means through the inlet arrangement 11 when the oxygen level exceeds a threshold value Th _oxyg en.

The method 30 may comprise yet further steps, for example the step of activating 35 an additional supply of fire extinguishing means 13b if a temperature sensor 19 indicates a temperature exceeding a predetermined threshold value Thtemperature • The method 30 may comprise yet additional steps, for example sending an alarm upon detection of gases emitted from the battery cells 7. Still other optional steps comprise measuring the temperature of the individual battery cabinets 8 by their respective temperature sensor 21a, 21b,..., 21n and activating the additional supply of fire extinguishing means 13b for a particular battery cabinet 8 having an abnormal temperature .

Further, it is noted that, for all embodiments of the invention, the supplies of fire extinguishing means 13a and

13b can be activated simultaneously or, alternatively, only one of them may be activated, for example upon detection of an abnormal temperature, as sensed by any of the described temperature sensors 21a, 21b,..., 21n and/or 19 and/or 28. In particular, if the temperature sensors 21a, 21b,..., 21n of a particular battery cabinet 8 and/or temperature sensor 19 of the storage room and/or temperature sensor 28 of a particular battery module detect an increased temperature, then both supplies of fire extinguishing means 13a, 13b or only one of them may be activated.

The battery storage 2 described above is suitable for use in high-voltage power transmission networks, for example connected a load, such as a voltage source converter. The battery storage 2 can be arranged to provide active power to the power network.