Claims:1. A system for monitoring oil in a transformer, the system comprising:
a sensor disposed in an oil column adjacent to an oil sampling port of the transformer, the sensor configured to detect pressure of the oil column of the transformer; and
A control unit connected to the sensor and configured to determine the oil level of the transformer based on the pressure of the oil column detected by the sensor.

2. The system as claimed in claim 1, comprising an indicator for indicating the determined oil level.

3. The system as claimed in claim 1, wherein the transformer is a current transformer.

4. The system as claimed in claim 1, wherein the control unit is connected to the sensor through a shielded wire.

5. The system as claimed in claim 1, comprising a circuit breaker associated with the transformer wherein the circuit breaker is actuated if sudden increase in the level is determined by the control unit to prevent the transformer from distributing power.
, Description:FIELD OF THE INVENTION
[001] The invention relates to a system for monitoring oil in a transformer.

BACKGROUND OF THE INVENTION
[002] A current transformer generally comprises a hollow tubular insulated column, a top metallic housing mounted on the insulated column and a base connected to the insulated column. Primary winding, secondary winding and magnetic core are housed inside the top metallic housing. Such windings and core of the transformer generate a substantial amount of heat during operation which should be disposed off for proper working of the transformer. Accordingly, oil is provided inside the top metallic housing in which the windings and core are submerged and further runs through the tubular column. In this regard, an oil sampling port is provided at the base which is used for sampling oil for analysis.
[003] Oil in the transformer serves the purpose of insulation as well as maintains the temperature within a desired range. However, oil expands or contracts in response to varying temperature conditions inside the transformer. Accordingly, it is known to provide a bellow mounted on the top of the metallic housing which expands or contracts as the oil expands or contracts thereby providing ample space to the oil to expand or contract without damaging other components. Further, components degradation and failure may lead to leakage of oil which alters level inside the transformer.
[004] A hood having a transparent portion marked with maximum and minimum level is generally mounted over the bellow to allow an operator to check the bellow level which is indicative of oil level of the transformer. However, the bellow/ oil level inside the transformer has to be checked manually by visual inspection during operation of the transformer which is apparently dangerous. Further, continuous monitoring is not possible because of the requirement of site visit by the operator for manual inspection. The manual inspection is also a costly affair as it requires a huge number of man hours for timely inspection for ensuring proper working of the transformer.
[005] Further, since the transformer is mounted on a support structure, the overall height of the bellow from the ground level reaches upto 7 to 8 meters which makes it difficult for the operator of an average height to monitor the bellow level from the ground. Furthermore, accuracy of the oil level ascertained by manual inspection is questionable because of the parallax error.
[006] Therefore, there exists a need for a current transformer which does not require a manual inspection of the oil level inside the transformer.

SUMMARY OF THE INVENTION
[007] Accordingly, in one aspect the invention provides a system for monitoring oil in a transformer, the system comprising a sensor disposed in an oil column adjacent to an oil sampling port of the transformer, the sensor configured to detect pressure of the oil of the transformer, and a control unit connected to the sensor and configured to determine the oil level of the transformer based on the pressure of the oil detected by the sensor.

BRIEF DESCRIPTION OF THE DRAWINGS
[008] Reference will be made to embodiments of the invention, examples of which may be illustrated in accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.
Figure 1 shows a system for detecting an oil of a transformer adapted at an oil sampling port of the transformer in accordance with an embodiment of the present invention.
Figure 2 shows a schematic diagram of a circuit breaker fitted between a current transformer and a distribution line of power distribution system in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION
[009] The present invention is directed towards monitoring oil level in a transformer by detecting pressure applied by oil on a sensor, mounted at bottom of an oil tank.
[010] figure 1 shows, a system 100 comprising a sensor 110 and a control unit 120. As shown the sensor is disposed at an oil column adjacent to an oil sampling port 240 of a current transformer 200. As known, the current transformer comprises a hollow insulated column 230, a metallic housing 210 mounted on the top of the insulated column, a bottom portion 250 to fix the transformer to the ground and a bellow (not shown) mounted on the top of the metallic housing. Oil is provided for insulation and cooling purposes inside the metallic housing, the insulated column and the bellow. The bellow can expand/contract axially along a vertical axis when oil inside the current transformer expands/contracts as the ambient temperature inside the current transformer changes. A hood 220 having a transparent portion 222 marked with a maximum and minimum level is mounted over the bellow.
[011] The sensor is disposed in the oil column adjacent to the oil sampling port of the current transformer. The sensor continuously detects the pressure applied by the oil column on the sensor and sends the detected pressure of the oil column to the control unit. The control unit is configured to determine an oil level of the current transformer based upon the pressure of the oil column detected by the sensor. In an embodiment, the pressure of the oil column detected by the sensor is provided to the control unit and the control unit is preprogrammed to determine the corresponding oil level. The determined oil level is compared by the control unit with a predetermined maximum and minimum level and the control unit provides an indicator from a plurality of predetermined indicators based on the determined oil level. In this regard, a green indicator is provided when the determined oil level is within a predetermined range i.e. – between the maximum and minimum oil level. Further, a yellow indicator is provided if the determined oil level is less than the minimum level or more than maximum level and a red indicator provided is provided if the determined oil level is extremely high or extremely low. In this regard, if the determined oil level is more than an predetermined higher level or less than a predetermined lower level, the red indicator is provided by the control unit where the red indicator is indicative of dangerously high/low level of oil in the oil column of the transformer.
[012] In an exemplary embodiment of the present invention every indicator provided by the system is indicative of a condition of the current transformer. For instance, if the yellow indicator is provided then it indicates that either there is an leakage from the current transformer or gassing activity due to partial discharges/starting of insulation failure is taking place inside the current transformer. Advantageously, the oil level inside the current transformer can be monitored/ regulated remotely from a control room and requirement of manual inspection of bellow level of the current transformer is done away with in the current transformers adapted with the system as described hereinabove.
[013] In an embodiment of the present invention, an alarm connected with the control unit can be actuated by the control unit along with providing the indicator. For instance, if the determined oil is level is less than the predetermined higher level or predetermined lower level then the control unit can actuate an alarm unit connected to the control unit along with providing the red indicator.
[014] Figure 2 shows a circuit breaker 300 fitted in a power distribution system between a current transformer and a distribution line. In an embodiment if a sudden increase in the pressure of oil beyond a predetermined threshold cut off limit is detected by the sensor, which is indicative of bellow level going beyond the maximum level and touching the hood from inside, the circuit breaker associated with the current transformer is actuated to prevent catastrophic failure of the current transformer. In this regard, the circuit breaker can be actuated by the control unit to prevent the current transformer from distributing power. Type/ rating/ model of the circuit breaker connected to the transformer will depend upon scheme/rating of the transformer.
[015] In a preferred embodiment of the present invention, the control unit is placed at the control room and the sensor is connected to the control unit through a shielded wire. However, wireless connection between the sensor and the control unit is well within the scope of the present invention. Alternatively, a single unit which comprises of the sensor and the control unit can be adapted at the oil sampling port of the current transformer.
[016] Advantageously, as no physical inspection of the oil level is required in the transformers adapted with the system as described hereinabove, chances of operators coming into contact with high voltages are reduced thereby reducing threat to operator’s life.
[017] While the present invention has been described with respect to certain embodiments, it will be apparent to those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims.