15-01-2013, 02:22 PM
MODELLING OF TRANSFORMER
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ABSTRACT
Modelling of transformer with Incipient fault detection in transformers can provide early warning of electrical failure and could prevent catastrophic losses. To develop transformer fault detection technique, a transformer model to simulate internal incipient faults is required. This paper presents a methodology to model internal incipient winding fault in distribution transformers. These models were implemented by combining deteriorating insulation models with an internal short circuit fault model. The internal short circuit fault model was developed using finite element analysis. The deteriorating insulation model, including an aging model and an arcing model connected in parallel, was developed based on the physical behaviour of aging insulation and the arcing phenomena occurring when the insulation was severely damaged. The characteristics of the incipient faults from the simulation were compared with those from some potential experimental incipient fault cases. The comparison showed the experimentally obtained characteristics of terminal behaviours of the faulted transformer were similar to the simulation results from the incipient faults models.
TRANSFORMER INTERNAL INCIPIENT FAULT MODEL
The transformer internal incipient fault computer model is a combination of a two-dimensional nonlinear finite element analysis internal short circuit fault model and deteriorating insulation model consisting of an aging and an arcing component. These models are briefly reviewed in this following section. More details about these models can be found in [2, 4].
Transformer Non-Linear Model
The transformer two-dimensional nonlinear finite element model presented in [5] applies finite element analysis to calculate the parameters for an equivalent circuit of a transformer with an internal short circuit fault. A soft Maxwell® software package was used to perform calculations. The transformer model can be exported as a SPICE sub-circuit and imported to the SIMPLORER® simulation environment as a black box with a set of interface terminals. These terminals are appropriately connected to the voltage source, load, and incipient fault model to simulate an incipient fault scenario.
Arcing Model
A persistent fault in a transformer would eventually involve an arc which is defined as a continuous
luminous discharge of electricity across an insulating medium, usually accompanied by the partial volatilization
of the electrodes the arcing characteristics can be illustrated as in Fig. 3. This is a simple case where arcing
happens in a resistive load circuit. The arc ignites only after sufficient voltage is across the gap. This period is
called the burning period. Arcing voltage is almost a square wave, except for the transient near current zero. In
addition, arcing is a random and stochastic phenomenon. The arc extinguishes when voltage drops below that