Field of the Invention

The present invention relates SYSTEM FOR TRANSFORMER PROTECTION / SAFETY. The present invention is mainly used for providing secondary back up protection in case of if any of the over current or differential relays fails to trips, in other words failure of any of inherent protection of transformer. The present system detects the possible hazard well in advance before the starting of decomposition of combustible coolant fluid / dielectric oil leading to Fire.

Background of the Invention

Electrical transformers exhibit losses both in the windings and in the core, which results in heat produced, which is required to be dissipated. So in order to cool down the winding, in High-power transformers cooling fluid such as oil is provided. The oils used are dielectric and can ignite above a temperature of approximate 140° C.

Any fault in insulation that generates a strong electric arc which prompts / activates the inherent electrical protection systems & in turn it will trip the supply relay of the transformer (circuit breaker). The electric arc also causes dissipation of energy, which generates / release of gas from decomposition of the dielectric oil, in particular hydrogen and acetylene. These gases get collected inside the enclosed chamber of transformer, which causes the pressure inside the chamber to increases very rapidly, thereby damaging the unit due to excessive pressure. The damage results in leakage of such gases & coming in contact with Oxygen in surrounding atmosphere, gases like acetylene can ignite very rapidly which results in Fire & will cause catastrophe. The fire can further spread to other units nearby. Reasons for explosions are many such as short-circuits caused by overloads, voltage surges, progressive deterioration of the insulation, insufficient oil level, the appearance of water or moisture or the failure of an insulating component, etc.

Fire protection systems for electrical transformers are known in the prior art, and these are actuated by combustion or fire detectors. However, these systems are implemented with a significant time lag, when the oil of the transformer is already burning. It then being necessary to make to with limiting the combustion to the equipment in question, and to prevent the fire from spreading to the neighbouring plant.

In certain cases, silicone oils may be used instead of conventional mineral oils in order to slow down the process of combustion of gases. However, explosion of the enclosure of the transformer due to the increase in the internal pressure is delayed only by an extremely short time, of the order of a few milliseconds. This length of time does makes it possible to engage means which can prevent the explosion.

The earlier inventions documented discloses a method for prevention against explosion and fire in an electrical transformer provided with an enclosure filled with combustible coolant / oil, by detecting a break in the electrical insulation of the transformer using a pressure sensor / rupture disc, depressurizing the coolant contained in the enclosure, using a valve, and cooling the hot parts of the coolant by injecting a pressurized inert gas into the bottom of the enclosure in order to stir the said coolant and prevent the oxygen from entering the enclosure of the transformer. This method is satisfactory and makes it possible to prevent the enclosure of the transformer from exploding up to certain extent.

However, the said method does not provide an indication in advance to take corrective measures. Also, by the time the corrective action takes place a significant amount of electrical insulation break down. Alternately other systems patented IN 189089 provides a method of preventing, protecting and/or detecting an electrical transformer from deterioration by way of protecting, preventing and/or detecting said electrical transformer against explosion and/or resulting fire, said electrical transformer having an enclosure filled with a combustible coolant fluid said method comprising the steps of detecting a break in the electrical insulation of the transformer, using a pressure sensor means; partial draining of the coolant contained in the enclosure using a valve and; cooling the hot parts of the coolant by injecting a pressurized inert gas into the bottom of the enclosure in order to stir the coolant and flush the oxygen located in proximity. The said patent particularly refers to a pressure means for prevention, protection and/or detection of transformer against explosion and/or resulting fire, which is different from this invention. The patent fails in clearly mentioning about the nature of the pressure means.

U.S. Pat. No. 6,804,092 discloses a device for prevention, protection and detection against explosion and/or resulting fire of an electrical transformer comprising an enclosure filled with combustible coolant fluid, and a means for decompressing the enclosure of the transformer. The decompression means comprises a rupture element with integrated explosion detector provided with a retention part including first zones which have a reduced thickness in comparison with the rest of the retention part and are capable of tearing without fragmenting when the said element ruptures, and second zones which have reduced thickness in comparison with the rest of the retention part and are capable of folding without tearing when the said element ruptures. The said rupture element is capable of breaking when the pressure inside the enclosure exceeds a predetermined ceiling. The signal from an explosion detector integrated with the rupture disc triggers a cooling system and prevents oxygen from coming into contact with the explosive gases generated by the electric arc in contact with the oil.

U.S. Pat. No. 6,804,092 briefly elucidates regarding “Decompression/Means” wherein a rupture element tears with an increase in pressure in the transformer tank beyond a predetermined ceiling, which is not a fool proof system for detecting and preventing an explosion in an electrical transformer. Both Prior Art systems discuss pressure developed and subsequent prevention measures through a rapture disc or “Pressure Means”. In both the Prior Art systems namely IN189089 and U.S. Pat. No. 6,804,092 there are inherent disadvantages such as tearing occurring after significant delay from the occurrence the internal electric arc. Therefore, it is likely that delay in detection of the pressure developed, explosion and or resulting fire in an electrical transformer take place. None of the prior art teaches the system or method which will detect or prevent occurring of tearing without delay.

The US Patent No. US 7869167B2, addresses the above shortcomings to certain level. The system uses one or more differential current sensing electrical relay for calculating the difference of input current and output current with the ceiling level and providing first input to the control unit, if ratio of input current to output current exceeding more than the predetermined limit one or more buchholz relay for sensing the excessive oil surge in the transformer and providing second input to the control unit, one or more circuit breakers for obtaining input signals from buchholz relay and/or other sensing means and proving third input to control unit, one or more control unit obtaining first, second and third input signals from the said electrical relay, buchholz relay and circuit breakers, generating control signal to energize lifting magnet for draining of the combustible coolant fluid through the drain valve and subsequently to inject inert gas from the bottom of the electrical transformer tank through a nitrogen release valve for stirring the coolant and bringing down oxygen contents for preventative measures against the explosion and/or resulting fire in the electrical transformer.

However, the above procedure / invention as mentioned in US Patent No. 7869167B2, does not address the situation in case if any of the three inputs to the controller namely the differential current sensing relay, Buchholz relay and/or other sensing means, fails to operate and gases / temperature of the transformer winding is rising, as the inputs to the controller are in series connection. Further the above system also fails to address the transformer fault wherein current relay is not required to operate & the pressure inside the transformer increases to the level wherein gases starts combustion, which can lead to any possible hazard.

Further referring to the report of Cigre (CIGRE 537),“Guide for Transformer Fire Safety”, classifies that 95% of the Transformer fires are due to On Line Tap Changers (OLTC) tank rupture, bursting of bushings, etc., (I.e. mainly due to hot oil spillage and coming in contact with Oxygen). The present invention also takes care of external fire by means of external fire sensors & external fire extinguishing system.

Hence looking to the above prior three systems & analyzing the failure of the components / relay’s / breakers & dependency on the feedback signals of the inherent components of transformer the present invention is developed to meet the criteria of failures in order to detect the rise into the temperature of the transformer oil / coolant & thereby taking a feedback of the increase in temperature coupled with the master breaker input to the microprocessor / relay based control circuit & thereby activating the nitrogen purging system by opening the drain valve & injecting the nitrogen gas from bottom of the transformer to stir & cool the oil / coolant through nitrogen release valve as well and bringing down oxygen contents for preventative measures against the explosion and/or resulting in fire in the electrical transformer along with external cooling by means of activating the external extinguishing / cooling system. Further the present system also takes care of any external fires due to reasons like Bursting of bushings, spillage of oil due to OLTC tank rupture, etc, thereby activating the Fire sensors fitted onto the outside of transformers & activating a command to External extinguishing system to operate & douse the fire.

Object of the invention

The objective of the present invention is to overcome the drawbacks associated with earlier systems & to provide a more stable & advanced method of detecting the possibility of explosion and / or resulting Fire at an early stage, i.e., before decomposition of combustible coolant fluid / dielectric oil into the transformer.

Another objective is to achieve the possible detection of the explosion and / or resulting Fire in case of failure / non operation of any of the primary or secondary current relay’s.

Yet another objective is to provide a full proof system & method of prevention, protection and / or detection of an electrical transformer against explosion and / or resulting fire with least delay.

Further the objective is also to detect the explosion and / or resulting Fire in case of external short circuit faults and / or excessive over load current.

Further the objective is also to detect the explosion and / or resulting Fire in case of any internal fault in transformer leading to flow of fault current in neutral line of the distribution transformers. Further one of the embodiment of the present invention is also to detect and / or extinguish the Fires due external failures of bushing, OLTC fire, tank rupture, etc.

Further one of the personification of the present invention is also to detect and / or extinguish the Fires due to hot oil spillage coming in contact with oxygen.

Statement of the Invention

For a better -understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be the accompanying drawings and descriptive matter in which there is illustrated the preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS The structure and the technical means adopted by the present invention is to achieve the above and other objects can be best understood by referring to the following detailed description of the preferred embodiments and the accompanying drawings.

Fig.1 represents the details layout diagram of the present invented system

Fig.2 represents the block diagram of pre-fire alarm system

(Case -1)

Fig.3 represents the block diagram of pre-fire alarm system

(Case -2)

Fig.4 represents the block diagram of fire alarm system

(Case -3) Detailed description of the invention

Before explaining the present invention in detail, it is to be understood that the invention is not limited in its application to the details of the construction and arrangement of parts illustrated in the accompanying drawings. The invention is capable of other embodiments, as depicted in different figures as described above and of being practiced or carried out in a variety of ways. It is to be understood that the phraseology and terminology employed herein is for the purpose of description and not of limitation. The present invention is based on possibility of Fire in transformer due to internal or external causes. While developing the solution guidance is taken from CIGRE 537,“Guide for Transformer Fire Safety”, which attributes 95% of transformer fire due to bushing or OLTC tank rupture, i.e., mainly due to hot oil spillage & coming in contact with oxygen. The present invention is broadly divided into three cases viz. a viz - Case 1 & 2 deals with internal failure and/or prevention of fire inside the transformer & Case - 3 deals with external failure such as bushing fires, OLTC fires, fires from surrounding equipment, etc., & protection of transformer in case of Fire. Case - 3 will come into action with external extinguishing system either water based or dry chemical powder based systems stored in a pressurized container as like nitrogen purging system which can also be considered as an alternate to the nitrogen purging system. There by the present invention can now have three different forms of detection with a combination of two different forms of extinguishing / cooling system.

As shown in Fig. 2 wherein Case - 1 - Case - 1 - Detection with Inherent protection equipment’s of the transformer along with external RTD sensors dipped inside the transformer oil with Internal coolant purging system and/or external extinguishing and/or cooling system -

Here in this case the system will sense sudden rise in temperature with the help of one or more RTD sensors (Item no.

11) immersed into the oil / coolant of the transformer. The sudden rise in temperature can be due to arching and/or any fault occurrence into the transformer windings, etc., thereby giving first input to the control unit (Item No.22), based on the increased temperature of the oil / coolant the liquid starts decomposition thereby releasing the gases as well as the pressure inside the transformer enclosed chamber increases, which triggers the Buchholz relay (Item no.3) and/or Pressure Relief Valve relay (Item no.10) for sensing the excessive oil surge / rapid rise of pressure in the transformer and generates second input to the control unit (Item No.22), resulting in generation of third input in the form of circuit breakers (Master Trip relay) (Item no.13 & 20) and proving third input to control unit(ltem no.22), which will generate a control signal to close the conservator valve (Item No.5) & simultaneously open the drain valve (Item No.29) resulting in energizing the internal fire prevention and/or external fire extinguishing and/or cooling system. As shown in Fig. 3 wherein

Case - 2 - Detection with Inherent protection equipment’s of the transformer with Internal coolant purging system and/or external extinguishing and/or cooling system -The system comprises of one or more differential current sensing electrical relay (Item No. 15) for calculating the difference of input current and output current with the ceiling level along with REF (Restricted Earth Fault) (Item No.18), IDMT (Inverse Definite Minimum Time) (Item no. 17), IDMT O/C relay (Item No.16), Winding Temperature Indicator (WTI) (Item No. 37) & Oil Temperature Indicator (OTI) (Item No. 36) and providing first input to the control unit (Item No.22), if ratio of input current to output current is exceeding more than the predetermined limit one or more Buchholz relay (Item no.3) and/or Pressure Relief Valve relay (Item no.10) for sensing the excessive oil surge / rapid rise of pressure in the transformer operates and thereby generating second input to the control unit (Item No.22), resulting in generation of third input in the form of circuit breakers (Master Trip relay) (Item no.13 & 20) and providing third input to control unit (Item No.22), thereby generating control signal to close the conservator valve (Item No.5) & simultaneously open the drain valve (Item No.29) resulting in energizing the internal fire prevention and/or external fire extinguishing and/or cooling system.

As shown in Fig. 4 wherein Case - 3 - Detection in the event of Fire due to external causes such as busing fire, OLTC fires, fires from surrounding equipment, etc. with Internal coolant purging system and/or external extinguishing and/or cooling system -

In case of Fires on external side of the transformer reasons may be due to bursting of bushes, OLTC fires, etc., the same will be detected by external fixed temperature / heat sensors (item No. 7) and/or other proven means of sensing fire and/or heat detectors (Item No. 23) wherein the threshold values are site adjustable with facility for cross zoning of the threshold parameters like the rate of rise per minute & max. temperature or pressure to avoid any false alarms. The bursting of bushes, OLTC faults, etc., causes enough energy to trigger the fault relays & thereby sensing the sudden rise in internal and/or external temperature will also trigger the sensors or detector & sense the Fire / Heat Signal generated which will generate an input to the control unit(ltem no.22) and / or feedbacks from one or more over load relays (item no 15/16/17/18) and/or PRV (item No 10) / Buchholz relays (item No. 3) will also generate input to control panel (item no. 22) which will generate the command to trigger the circuit breakers (Master Trip relay) (Item no.13 & 20) along with generation of a control signal to close the conservator valve (Item No.5) & simultaneously open the drain valve (Item No.29) resulting in energizing the internal fire prevention and/or external fire extinguishing and/or cooling system.

Internal Fire prevention (Inert Gas Purging System) and/or External Fire Extinguishing and/or Cooling system:

Inert Gas Purging System - The inert gas purging system operates on getting the signal from control unit (Item no.22). A pre filled pressurized nitrogen cylinder (Item No.28) is connected to the valves (Item No.27) which controls the flow and/or pressure of the inert gas flowing through piping network into the transformer from bottom of the transformer, thereby stirring & cooling the oil / coolant liquid of the transformer. It also forms a blanket on upper portion of the transformer, space created by draining of the oil / coolant liquid. The purging system will start only after the receipt of “Open” feedback signal of transformer oil / coolant drain valve (Item No.29) which will allow the oil / coolant to get drained thereby creating space for formation of inert gas layer to cool the residual oil / coolant liquid thus preventing the combustion of oil / coolant liquid & after receipt of “Closed” feedback signal from the valve (Item No.5) on the conservator tank, thereby blocking the addition of oil / coolant from conservator tank (Item No.1). The number of inlets for inert gas purging inside the transformer varies with different sizes of the transformer.

External Fire Extinguishing and/or Cooling system - The external cooling / Fire extinguishing system operates upon receipt of the command from the control unit. The system consists of a cylinder (Item No.35) either filled with water or premix solution of water + extinguishing media like AFFF, FFFP, etc., or Dry Chemical Powder & pressurized for effective purging of the stored media. The cylinder as per the extinguishing media is connected to external piping wherein through the nozzles (Item No.33) designed as per requirement of extinguishing media, the purging commences & thereby extinguishing the external fire and/or cool the transformer body. Before operating the external extinguishing / cooling system, a command to the master breaker is generated to trip the master trip relay (Item No.13 & 20) as a back up to the already existing logic for the inherent transformer protection devices. Post receipt of feedback for tripping of master relay (Item No.13 & 20), the external extinguishing system shall operate only after the receipt of “Open” feedback signal from the drain valve (Item No.29) of oil / coolant of the transformer, which will allow the oil / coolant to get drained thereby creating space for formation of inert gas layer to cool the residual oil / coolant liquid thus preventing the combustion of oil / coolant liquid& after receipt of “Closed” feedback signal from the valve (Item No.5) on the conservator tank (Item No.1)., thereby blocking the addition of oil / coolant from conservator tank (Item No.1). The number of nozzles required for external extinguishing / cooling system varies with different sizes of the transformer.

Alternatively, in cases wherein the fire is on the external surface of the transformer the external extinguishing and/or cooling system can also be activated immediately upon receipt of“Trip Command” from master circuit breaker (Item No. 13 & 20) as the case may be without activating the internal purging system. The valve (Item No.5) on the conservator tank (Item No.1) is electrical and/or pneumatically and/or mechanically operated valve. In case of electrical and/or pneumatic operation the valve receives the command for open or close from the control panel (Item No.22). In case of mechanical valve, based on flow rate of the oil / coolant liquid the valve will automatically shut off if flow rate of the liquid has increased drastically beyond set limits & simultaneously will send a signal feedback to the control panel (Item No. 22). In addition to the command as a backup based on the requirement the flow rate of the oil / coolant liquid can also be measured / monitored vide Flow Control Valve (Item No. 6) & input can be generated to the control panel (Item No.22) to generate a“Close” command to the valve (Item No. 5) and also alert the personnel in control room regarding the sudden increase in flow rate of the oil / coolant liquid traveling from conservator tank (Item No.1) to the main transformer tank (Item No.32). In this case the command to valve will be generated once the flow rate of the conservator tank (Item No.1) is increased beyond the specified acceptable limits. By monitoring the flow rate one can also monitor the oil / coolant circulation rate inside the transformer. Further it also helps in determining any leakages of oil / coolant liquid from any of the joints of the transformer as the case may arise. The flow rate monitoring (Sudden increase / decrease) will also be useful in case of determining any possible catastrophe which can be avoided at a very early stage. Also the monitoring data will help in carrying out detailed analysis post any unwanted incident. The permutation & combination of the valves can be decided upon the end client requirements.

Control Unit (Microprocessor / Relay based control Panel): The control unit (item no 22) can be relay based panel / microprocessor PLC based panel with provision to operate system manually and/or to take systems under maintenance mode as the case may arise.

All older inventions are all with conventional type of relay based panel. Conventional panels which are relay based panels are very difficult to troubleshoot & also the logics formation are very limited. Even the panels cannot store the required data like the history of various alarms, faults, etc., occurring into the systems which are very useful at the time of post disaster analysis of any kind of safety systems. Hence to overcome the shortcoming of the conventional panels & looking to the present need of automation & data record requirements the present invention calls for a robust panel with microprocessor based PLC systems to monitor & operate the logics through PLC’s & at the same time alert the personnel in control room. It also has provisions to poll all the data into the software & create the history & logs for Alarms, Faults, etc., in SCADA (Supervisory Control & Data Acquisition System).

The main unit of the control panel like the PLC’s & logics can all be installed in the field near transformer & only the feedback signals on SCADA can be transmitted to operator’s desk in control room, thereby saving huge space requirement inside the control room.

While, the invention has been described with respect to the given embodiment, it will be appreciated that many variations, modifications and other applications of the invention may be made. However, it is to be expressly understood that such modifications and adaptations are within the scope of the present invention, as set forth in the following claims.