Proactive Differential Transformer Protection as a Means of Promoting Personal Safety - Thesis Example

In power systems, transformer protection is crucial and is dependent on precise and quick discrimination of internal fault current from magnetizing inrush current. Previously, differential protection has been the most preferred technique of protecting transformers but with its tendency to falsify faults, this technique has been coupled with wavelet transform and artificial neural networks to reinforce classical protection principles while facilitating faster, secure, and reliable differential protection for power transformer.

The role of the wavelet transform is to extract components of a transient signal while the neural network was trained to extract the components of the transient signal and precisely differentiate between internal faults and inrush current. Three-phase transformer rating 315 MVA, 220/400kV, and 50Hz was modeled in PSCAD/EMTDC software. For the resulting algorithm, a simulation was done using MATLAB. The results indicated that the conventional differential protection was less accurate, less reliable, and slower compared to the proposed differential transformer.

Transformers are classified as stationary electrical devices. They are used in electrical power systems to transmit power-linking circuits using electromagnetic induction or ordinary magnetic field. The functioning of transformers occurs when an alternating current runs through a conductor and creates a magnetic field around itself. By introducing a second conductor in the resulting field influx lines connect the subsequent conductor. In this case, the latter conductor also has a voltage induced into it through the principle of transformers.

There are different forms of transformers all of which operate under the principle of transformers despite their differences in sizes and their design for use in different electric and electronic applications. Some types of power systems transformers include three or two winding electrical power, earthing transformers, regulating transformers, and rectifier transformers. 

For all these transformers, protection is crucial as a way of controlling or avoiding damage arising from abnormal voltages/currents. Transformer protection scheme ensures that the overcurrent and overvoltage withstand limits are not surpassed. Different transformer protection schemes exist for different transformers. However, the choice of protection scheme depends on factors such as normal service condition, type of transformer faults, tap changing scheme, and the extent of present overload among others.

According to Rockerfeller[Roc07], the common influencers of the kind of transformer scheme to use are transformer’s MVA and primary kV as well as issues regarding personal safety issues and the extent of risk reduction linked to the chosen scheme. In addition, the capability of a given protection scheme to reduce the occurrence of a given catastrophe, and the general economic impact of transformer fault and the measures needed to combat such risk like financial impact of repair and maintenance, time needed for repair, and accessibility to backup power.

Given the costs associated to dealing with catastrophes or incidents of transformer fault, this paper proposes proactive differential transformer protection as a means of promoting personal safety, reducing dangers to nearby structures, and as a mean of reducing costs incurred as a result of transformer failure. The transformer protection is the critical nature of the balance between transformer protection scheme and the costs of arising from the consequences of depending on other forms protection or forfeiting the transformer.

The engineer has to understand the different forms of transformer failure classifications and focus on proactively implementing transformer protection. Winding to core transformer faults result from weakened insulation resulting to short-circuiting. These faults occur on transformer terminals[Pai10]. On-load tap changing or OLTC gear is also type of transformer fault. In addition, it is common for transformers to suffer from enormous inrush currents rich in harmonic content during switching particularly if transformer is unloaded.

In addition, transformers experience hot spots within windings due to inter turn faults, or experience over fluxing because of operating at rated voltage. Another transformer fault is oil leakage due to transformer immersion into oil. There are numerous forms of transformer protection like protection against overheating and over fluxing, over current protection, restricted earth fault protection, and voltage differential protection. These protection measures are crucial especially in ensuring that any fault condition is cleared within the fastest possible time to facilitate harmonization between shielding devices upstream and downstream the apparatus being protected.

The implication here is that despite there being numerous protecting devices, any occurring fault detection has to include only one must detect the problem. The fault detection devices may be relays or fuses[Sch131]. Relays react on the circuit-breaker coil indirectly while fuses offer direct faulty circuit clearance. Additionally, fuses work in conjunction with mechanical tripping attachment to open linked three-phase load-break switch. 1.2Objectives The research focuses on transformer protection particularly dealing with transient inrush current when the generator is energized.

The inrush is current is uniquely characterized by a huge second harmonic and may as well occur during transformer faults that most digital differential protection transformers do not effectively contain given that it is expressed as a ration of fundamental component of differential current. Consequently, mal-operation occurs because of to second harmonic component of inrush current not being distinguished from internal faults. To investigate the role of d1 level wavelet signal co-efficient as an input to artificial neural network that establishes a novel approach to online detection method that discriminates magnetizing inrush current and inter-turn fault, and fault location. 1.