ETP-1 Power Transformer Maintenance

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The ETP-1 module determines the turn ratio on the three phases of power and distribution transformers and autotransformers of any type by applying a test voltage on the high-voltage winding and measuring the resulting voltage on the low-voltage winding. This method also provides the evaluation of other parameters:

• Excitation current I₁
• Phase angle between the test voltage V₁ and the excitation current I₁
• Phase angle between the test voltage V₁ and the measured V₂

The test is performed at low voltage and at the supply's frequency, which makes the ETP-1 adequate for field testing and for quality assessment in production lines.

The following problems can be detected with the ETP-1:

• Shorted turns
• Interrupted windings
• Magnetic core problems
• Dirty or damaged tap changer  

Database storage of results enables individual tracking of each transformer.
 

Complete three-phase system

The ETP System is composed by four independent measurement modules controlled from a common measurement & analysis software in a PC. Diagnostics are performed by co-relating the measurements done by each module:

• Turns Ratio: three-phase measurement of the turns ratio and the excitation current in ever y position of the tap changer. Results are compared with the theoretical values and the error is shown graphically.
• Recovery Voltage: evaluation of the solid and liquid insulation condition through electrical measurements.
• Winding Resistance: three-phase measurement of the resistance values in every winding and for every position of the tap changer.
• Short-circuit Impedance: evaluation at low voltage of the short-circuit impedance and voltage.
• The above measurements are used to evaluate the condition and then predict possible failures at the four main circuits in a transformer:
• Electrical Circuit: checking the continuity of the windings, the connections and the tap changer.
• Geometrical Circuit: checking the symmetry between the columns of the core, between the windings and the core and between these and the transformer's enclosure.
• Magnetic Circuit: checking the condition of the magnetic core (loose plates, short-circuits, detachment of the magnetic shunt, etc.).
• Dielectric Circuit: checking the degradation and the ageing of the solid and liquid insulation. Testing is a simple, automatic and fully software-guided task. The operation is divided into to main steps: 1) Measurement, wich guides the operator to the connections and wait operations, eliminating human errors and ensuring repeatability, and 2) Analysis, by immediately displaying the measured values on the screen as they are acquired by the software. The information can be immediately converted into a complete report and interpreted by an expert to determine whether maintenance operations should be planned or not.