DESC:FIELD OF THE INVENTION
[001] The invention relates to transformers, more particularly to diagnosing faults in transformers.

BACKGROUND OF THE INVENTION
[002] A transformer is one of the most important and vital component in a power system. Faults in transformers are usually due to over voltages, overloading, insulation degradation, core and winding thermal defects, short circuit faults, lightening impulses, loose connections, vibrations, operating incorrect procedures and breakdown of electrical structure etc. Such faults may affect winding, core, any phase or mechanical part associated with the core and windings, transformer core, winding, OLTC, bushings, insulation, clamping, etc.
[003] Fault in the transformer or part of the transformer affects the power system resulting in outage of the power station. Thus it is required for the transformer to be reliable and to be in service for a long time. Therefore there is a necessity to develop methodology to diagnose and detect mechanical faults and failure tendencies in a transformer from time to time so that required maintenance can be performed such that power outages are averted.

SUMMARY OF THE INVENTION
[004] Accordingly, the present invention in one aspect provides a method to diagnose mechanical faults in a transformer, the method comprising the steps of: obtaining parameters associated with the transformer by a test instrument connected to at-least one winding of the transformer, the parameters include at-least one of frequency (Fq), magnitude (MdB); resonance at frequency (Rfq); turns ratio (TR); tap position (Tprq); winding resistance (Wr) and magnetic balance (MB) of the transformer; analysing at-least one of the parameters to determine operating condition of transformer; and identifying at-least a core related fault or a winding related fault or a tap winding related fault or a lead related fault of the transformer based on the obtained parameters in response to determining that a fault condition exists in the transformer.

BRIEF DESCRIPTION OF THE DRAWINGS
[005] 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 flowchart of method to diagnose mechanical faults in a transformer in accordance with an embodiment of the invention.

DESCRIPTION OF THE INVENTION
[006] The present invention provides a diagnostic method for identifying faults in a transformer. The diagnostic method determines the operating condition of the transformer, and in case of faulty condition, the method determines nature of the fault including the faulty component/part which is causing the transformer to be in the faulty condition.

[007] Figure 1 shows a flowchart of a method to diagnose mechanical faults in a transformer. According to the present invention, the transformer is monitored at regular intervals by the method of the present invention to verify operating condition of transformer. As shown, the method from step 100A to step 100F, first determines operating condition of the transformer, and in the case of fault condition of the transformer the method proceeds to step 150 for identifying the faulty component/part of the transformer. According to the present invention, the method determines at-least core related faults, winding related faults, tap winding related faults or winding lead related faults.

[008] At step 100A, the method obtains parameters associated with the transformer, the parameters include at-least one of frequency (Fq), magnitude (MdB); resonance at frequency (Rfq); turns ratio (TR); tap position (Tprq); winding resistance (Wr) and magnetic balance (MB) of the transformer. The parameters are measured by a test instrument connected to at-least one winding of the transformer. The test instrument is connected to start of a winding and to other end of the respective windings. While measuring the parameters, all other windings are kept open and transformer is disconnected from supply. At step 100B, the method processes the input variables for low frequency (LF), medium frequency (MF) and high frequency (HF) range. At step 100C, the method determines covariance factor Vfby correlating magnitude (MdB) of the transformer with a reference value of the magnitude (MdB). Thereafter at step 100D the method obtains deviation dB, and at step 100E, the method calculates/computes output error based upon deviation values. At step 100F, the method determines the operating condition of the transformer based upon the output error. If the transformer is unhealthy, the method proceeds to step 150 to determine whether the faulty condition is due to any of core related faults, winding related faults, tap winding related faults or lead related faults.

[009] To determine core related faults, the method proceeds to step 150A where the method receives parameters -frequency (Fq), resonance at frequency (RFq), magnitude (MdB), turns ratio (TR) and magnetic balance value (MB), and thereafter at step 152A the method applies an analysis logic on frequency (Fq), and magnitude (MdB) , wherein frequency (Fq), and magnitude (MdB) of the transformer are correlated with pre-set reference values of frequency (Fq), and magnitude (MdB). Further at step 152A, it is determined whether there is a deviation to ascertain if the transformer is in the faulty condition due to core related fault.

[010] To determine winding related faults, the method proceeds to step 150B where the method receives parameters - frequency (Fq), magnitude (MdB); resonance at frequency (Rfq); turns ratio (TR); winding resistance (Wr), and thereafter at step 152B the method applies an analysis logic on the parameters, wherein magnitude (MdB); resonance at frequency (Rfq); turns ratio (TR); winding resistance (Wr) of the transformer are correlated with pre-set reference values of magnitude (MdB); resonance at frequency (Rfq); turns ratio (TR); winding resistance (Wr). Further, identifying winding related fault further includes measuring geometrical parameters such as thickness, width, conductor dimensions, and correlating such measured geometrical parameters with pre-set reference values. Further at step 152B, a variation pattern for different frequency from 10 kHz to 100 kHz is generated. The variation pattern ascertains any deviation/difference from the reference values, and accordingly determines whether the transformer is in the faulty condition due to winding related fault.

[011] Further, in the event, the analysis logic at step 152A and step 152B are not conclusive, the method proceeds to step 154A, whereby method applies an analysis logic on the parameters, wherein correlated values of magnitude (MdB) and resonance at frequency (Rfq) from step 152A and 152B are compared with another set of pre-set reference values of magnitude (MdB) and resonance at frequency (Rfq). From the comparison, if there is any deviation, the method determines whether the transformer is in the faulty condition due to core related fault or winding related fault.

[012] To determine tap winding related faults, the method proceeds to step 150C. In this regard, tap winding related fault is identified in response to a healthy condition of winding. At step 150C, the method receives parameters - frequency (Fq), resonance at frequency (RFq), magnitude (MdB),tap position (TpRq) and thereafter at step 152C the method applies an analysis logic on the parameters, wherein magnitude (MdB); resonance at frequency (Rfq); turns ratio (TR); tap position (Tprq); winding resistance (Wr) of the transformer are correlated with pre-set reference values of magnitude (MdB); resonance at frequency (Rfq); turns ratio (TR); tap position (Tprq); winding resistance (Wr). Further at step 152C, a variation pattern for different frequency from 40 kHz to 200 kHz is generated. The variation pattern ascertains any deviation/difference from the reference values, and accordingly determine whether the transformer is in the faulty condition due to tap, insulation related fault.

[013] To determine winding lead related faults, the method proceeds to step 150D. In this regard, winding lead related fault is identified in response to a healthy condition of tap winding. At step 150D,the method receives parameters frequency (Fq), resonance at frequency (RFq), magnitude (MdB), winding resistance (Wr), Z, Dn and thereafter at step 152D the method applies an analysis logic on the parameters, wherein magnitude (MdB); resonance at frequency (Rfq); turns ratio (TR); tap position (Tprq); winding resistance (Wr) of the transformer are correlated with pre-set reference values of magnitude (MdB); resonance at frequency (Rfq); turns ratio (TR); tap position (Tprq); winding resistance (Wr). Further, at step 152D, a variation pattern for different frequency from 200 kHz to 600 kHz is generated. The variation pattern ascertains any deviation/difference from the reference values, and accordingly determines whether the transformer is in the faulty condition due to winding lead related fault.
[014] Further, in the event, the analysis logic at step 152C and step 152D are not conclusive, the method proceeds to step 154B respectively whereby method applies an analysis logic on the parameters, wherein correlated values of magnitude (MdB) and resonance at frequency (Rfq) from step 152C and 152D are compared with another set of pre-set reference values of magnitude (MdB) and resonance at frequency (Rfq). From the comparison, if there is any deviation, the method determines whether the transformer is in the faulty condition due to tap winding or winding lead related fault.

[015] According to the present invention, the method of the present invention can be integrated with other online monitoring systems.

[016] Advantageously, the present invention provides a method for fault detection which is accurate and effective. Additionally, the method does not require human expertise for transformer core and winding fault detection, and the decision making is faster. Further, the method can be configured to monitor the transformer at regular intervals, thereby providing operating condition/health status of transformer at regular intervals.

[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.
,CLAIMS:WE CLAIM:
1. A method to diagnose mechanical faults in a transformer, the method comprising the steps of:
obtaining parameters associated with the transformer by a test instrument connected to at-least one winding of the transformer, the parameters include at-least one of frequency (Fq), magnitude (MdB); resonance at frequency (Rfq); turns ratio (TR); tap position (Tprq); winding resistance (Wr) and magnetic balance (MB) of the transformer;
analysing at-least one of the parameters to determine operating condition of transformer; and identifying at-least a core related fault or a winding related fault or a tap winding related fault or a lead related fault of the transformer based on the obtained parameters in response to determining that a fault condition exists in the transformer.

2. The method as claimed in claim 1, wherein for determining operating condition of the transformer, magnitude (MdB) of the transformer is correlated with a reference value of the magnitude (MdB).

3. The method as claimed in claim 1, wherein for identifying core related fault, frequency (Fq), and magnitude (MdB) of the transformer are correlated with pre-set reference values of frequency (Fq), and magnitude (MdB).

4. The method as claimed in claim 1, wherein for identifying winding related fault, magnitude (MdB); resonance at frequency (Rfq); turns ratio (TR); winding resistance (Wr) of the transformer are correlated with pre-set reference values of magnitude (MdB); resonance at frequency (Rfq); turns ratio (TR); winding resistance (Wr) to generate a variation pattern for different frequency from 10 kHz to 100 kHz.

5. The method as claimed in claim 4, wherein the step of identifying winding related fault further includes measuring geometrical parameters such as thickness, width, conductor dimensions, and correlating such measured geometrical parameters with pre-set reference values.

6. The method as claimed in claim 1 or 3, wherein tap winding related fault is identified in response to a healthy condition of winding.

7. The method as claimed in claim 1 or 6, wherein for identifying tap winding related magnitude (MdB); resonance at frequency (Rfq); turns ratio (TR); tap position (Tprq); winding resistance (Wr) of the transformer are correlated with pre-set reference values of magnitude (MdB); resonance at frequency (Rfq); turns ratio (TR); tap position (Tprq); winding resistance (Wr) to generate a variation pattern for frequency range from 40 kHz to 200 kHz.

8. The method as claimed in claim 1, wherein for identifying winding lead related magnitude (MdB); resonance at frequency (Rfq); turns ratio (TR); tap position (Tprq); winding resistance (Wr) of the transformer are correlated with pre-set reference values of magnitude (MdB); resonance at frequency (Rfq); turns ratio (TR); tap position (Tprq); winding resistance (Wr) to generate a variation pattern for frequency range from 200 kHz to 600 kHz.