As transformers age their internal condition degrades, increasing the risk of failure. When a transformer is new it has sufficient electrical and mechanical strength to withstand unusual system conditions. As transformers age, their insulation strength can degrade to the point that they cannot withstand system events such as short-circuit faults or transient over-voltages.
To prevent failures and to maintain transformers in good operating condition it is very important to perform preventative maintenance programs combined with regular testing.
In order to test for a transformer’s internal condition, it is necessary to remove it from its tank. However, this method can be tedious and take too much time. A more practical method is to use a sweep frequency analyzer. A sweep frequency response analyzer lets you diagnose the internal condition of a transformer by injecting an excitation signal and analyzing the spectrum bounced back by the windings. This is a more efficient way of detecting core and winding problems.
One of the most popular test sets used is the Doble M5400 Sweep Frequency Response Analyzer. The Doble M5400 has an output voltage of 20 Volts peak-to-peak at 50 Ohms output impedance.
With input circuitry that can analyze difference, cross-relation and sub-band at frequencies from 10 Hertz to 25 MegaHertz, the Doble M5400’s bandwidth is more than sufficient in analyzing common problems in transformers.
Features and Benefits of the Doble M5400
• Features a sampling rate of 100 MS/s with a dynamic range of >90 dB.
• Provides frequency-response measurement from 10 Hz to 25 MHz; the default range (20 Hz to 2 MHz) covers the most important diagnostic areas: core and magnetic properties; winding movement and deformation; and interconnections (leads and tap changers).
• Measures frequency response at logarithmically spaced intervals of 1.2% with a constant excitation level and can auto-scale each measurement, providing an overall dynamic range of 80 dB with ±1 dB accuracy, for the highest combination of dynamic range and accuracy.
• Frequency response measurements are highly repeatable; even subtle changes can be used for diagnosis.
• Rugged construction provides the accuracy of a laboratory instrument with the ability to withstand harsh field conditions and robust test leads to handle the rigors of site testing.