POWER TRANSFORMER PROTECTION USING FUZZY
LOGIC WITH DQ0 TRANSFORM
FIELD OF THE INVENTION
This invention relates to power transformation protection. In this invention, a different
algorithm was used for the protection of the power transformer has been proposed. This was
done by transforming ABC components to dq0 components.
BACKGROUND OF THE INVENTION
Modern civilization depends significantly on dependable electrical infrastructure; outages may
cease human activity. Protecting it is vital. Power transformers must be protected due to their
importance to the system. If power transformer protections fail, the whole power grid may
collapse. Transformers may be insulated in several ways. As shown in Fig. 1, differential logic
is the cornerstone for power transformer protection. The protection mechanism may detect
incorrect and healthy operations. Besides external causes, internal defects are conceivable.
Detecting differential current isn't enough to distinguish between internal issues and
operational conditions that cause an equivalent current. Over-excitation, magnetizing inrush
current, and sympathetic inrush current may yield equivalent current. Under certain conditions,
abnormal tripping may occur. It is challenging to create a protection system that can distinguish
between normal and abnormal functioning. Now the power transformer can be shielded in
many ways.
SUMMARY OF THE INVENTION
This innovation proposes an alternative algorithm for power transformer protection. ABC
components were changed to dq0. The fuzzy system uses these dq0 components to differentiate
between normal and fault circumstances. A fuzzy system contains rules for fault circumstances,
energization, and over-excitation. Overexcitation and energization didn't cause improper
tripping. Most power transformer failures were recognized within a half-cycle. This simple
solution eliminates erroneous tripping during energization and over-excitation. No additional
algorithms are needed to prevent improper energization and over-excitation. This approach
doesn't employ harmonic components to identify energization, which is a benefit. The simple,
easy-to-understand algorithm suggested.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1. Depicts the Differential relay diagram.
Figure 2. Depicts the Basic Flowchart of algorithm.
Figure. 3. Membership functions of Fuzzy. (a) Δd, (b)Δq, c) Δ0, (d) Output fuzzy for fault detection.
Figure 4. Depicts the Line diagram of the power system considered.
Figure.5 Depicts the LG fault in phase A on
primary of Transformer Primary and (b)
Secondary currents (c) Final Trip.
Figure.6 Depicts the LLG fault on Secondary
of Power Transformer(a)Primary and (b)
Secondary currents (c) Final Trip.
Description:The power system is very important for the modern world as its absence can halt almost everything. So the protection of the same is very essential. The power transformer is important equipment of power system, protection of the same is also essential to protect the power system eventually. Failure of power transformer protection can be interpreted as a failure of the power system itself. A number of protection methods are available for the power transformer. The basic technique used to protect the power transformer is percentage differential logic as shown in Fig. 1. The protection technique can differentiate between fault conditions and normal operation. Faults can be internal as well as external. But just detecting the differential current shall not be enough so that it can differentiate between internal faults and certain operating situations which produce almost similar currents. An operating condition which can produce similar currents is over- excitation, magnetizing inrush current (energization current), and sympathetic inrush currents. These operating conditions can lead to abnormal tripping. So to develop a protection system that distinguish between normal operation and mentioned operating situation is challenging. Many methods have been developed recently to protect the power transformer. Some methods to enhance differential protection, are implemented for the protection of power transformers. The wavelet transform and other transforms are used for protection purpose. The hybrid systems as well as restraint methods were also used for the same purpose. To differentiate between magnetization current and the internal fault is also required in the transformer to improve the reliability of the protection system designed.
Dissolved Gas Analysis, often known as DGA, is a technique that involves analyzing the gas that is created inside of the transformer. This approach has certain drawbacks, such as the fact that the quantity of gas generated is subject to variables such as loading, the age of the transformer, and even the thermal history of the transformer. Because of this, there is no set of standards that can be considered appropriate everywhere. Despite this constraint, DGA provides access to a variety of testing procedures. The dq0 transformation and fuzzy system have been used in the development of a technique that has been presented for the protection of transformers. Magnetizing inrush and overexcitation are taken into account by the protection system's design to ensure that they do not result in improper functioning of the trip signal. The fact that it does not offer erroneous tripping under an energization situations is one of the many key highlights of this approach. In many methods, a separate algorithm is there to prevent the energization alone; however, this method does not have such algorithm.
MATLAB Simulink has been used to create a working version of the approach that was suggested. Figure 2 depicts the primary outline of the flowchart. Primary and secondary current transformers, which are linked to the power transformer that has to be safeguarded, are responsible for collecting current signals. The dq0 transform is then applied to the current signals once they have been transformed. After that, these signals are sent to the fuzzy logic system so that it can differentiate between fault situations, abnormal circumstances, and normal operating conditions. The threshold value for this system is set to 0.5. Therefore, in the event that the value of the fuzzy is larger than 0.5, the circuit breaker is required to send a signal of the trip.
Data Acquisition: In the algorithm proposed, current data is acquired from the secondary of the CTs, connected for protection purposes, those present on the primary side and also a secondary side of the transformer being protected. This current is used for the protection algorithm. The current signals are collected from current measurement blocks.
Pre-processing- dq0 transformation: After the data has been collected, pre-processing will be commenced. This shall lead to obtaining desired signals for the input of the fuzzy system. The required signals are obtained by dq0 transformation done to ABC, three-phase currents present in secondary of the CTs present on primary and also secondary of the power transformer to be protected. The transform is effective for phasor values and instantaneous values as well. The dq0 transform is used to distinguish normal operation, over- excitation, energizing inrush current, and the internal faults.
Design of fuzzy system: Fault can be obtained by feeding all the data to the fuzzy system being used. The steps used for the same are as follows:
Fuzzification: Three fuzzy inputs: 1) ?d; 2) ?q and 3) ?0, are obtained for the fuzzy system designed. The value of inputs is given from equations (1) – (3). The membership functions can be observed in Fig. 3(a)- (c). The input variable ?d has a range between -150 to 150. The next variable ?q has a range between - 20 to 200. The last variable ?0’s ranges from -5 to10. The membership values of all the variables range from 0 to 1. The ranges of the fuzzy inputs have been amplified for better understanding and hence obtain accurate results. Fig. 3(d) shows the output variable that will determine the steady state and fault condition.

SIMULATED ELECTRICAL POWER SYSTEM:
The power system was simulated in MATLAB software. Fig. 4 gives the line diagram of the power system simulated to obtain data for the fuzzy system. This line diagram shows a differential protection scheme used for the transformer. The composition of the electrical system is given in Table 3. A power transformer with a delta connection on primary winding along with a star connection on secondary winding can be observed. By the winding CTs connected for protection is the star in the primary side and the delta in the secondary side. Few of the operations of the power transformer have been presented to better understand the protection algorithm proposed. The unloaded transformer was energized at zero crossing and during the operation, no trip signal was received. In the conventional method, false tripping is present during the energization of the transformer, which can avoid in the proposed algorithm. Next, the LG fault in the primary side of the transformer was developed to observe the performance of the algorithm. The current waveforms of the power transformer can be observed in Fig. 5. At 0.02 seconds the fault was developed and the same was detected at 0.0277 seconds i.e. within the half cycle itself, Fig. 6(c).
Primary and (b) Secondary currents (c) Final Trip: The other fault developed was the LLG fault on phase A and phase B towards the secondary side. The primary currents and secondary currents of the power transformer for this particular condition can be observed in Fig.6(a) and 6(b). Here as well the fault was developed at 0.02 seconds and the fault was detected at 0.02415 seconds, again within half the cycle itself. All the various faults were developed and detected within one cycle itself, which is fast in comparison to many algorithms, and also no false tripping was observed during the energization condition and over-excitation condition. False tripping usually occurs during energization and over- excitation conditions in conventional methods which are avoided by the algorithm proposed here which is an advantage. , Claims:1. Power system is very important for the modern world as its absence can halt almost everything, so the protection of the same is very essential.
2. Failure of power transformer protection can be interpreted as a failure of the power system itself. Several protection methods are available for the power transformer.
3. Dissolved Gas Analysis (DGA), a method in which the gas produced within the transformer is analyzed. This method has a limitation, the amount of gas produced depends on om facto like loading, age of the transformer, and even the thermal history of the transformer.
4. After the data has been collected, pre-processing will be commenced. This shall lead to obtaining desired signals for the input of the fuzzy system.
5. False tripping usually occurs during energization and over- excitation conditions in conventional methods which are avoided by the algorithm proposed here which is an advantage.
6. No incorrect tripping was obtained during over-excitation and energization. Most of the faults developed in the power transformer were detected within half cycle of the fault developed.
7. A method based on dq0 transformation and a fuzzy system has been presented to improve the efficiency of protection-used power transformers. The technique was tested, and a model of a power grid was created, in MATLAB.