Introduction
The testing of high voltage equipment is sometimes seen as a risky process as it can lead to loss of property and other damages. Thus, it is expected that the personnel that carries out the exercise do it with due care. The high voltage equipment testing usually includes two experiments; the first one is dielectric loss measurement and the second one is partial discharge determination. Each of this experiment has its own apparatus that is used so as to maintain the efficiency that is required in the exercise.
Dielectric loss measurement
The experiment is also referred to as dielectric dissipation factor. As noted above, this topic involves high voltage equipment. In this experiment, more emphasis is laid on the factor of thermo deterioration through the insulation materials. The materials that are used to insulate the high voltage material is expected to have a very low loss factor for it to be considered efficient. The calculation of the loss is gotten by the product of the power frequency, insulation capacitance and the square of the voltage of the equipment multiplied by the loss factor of the insulation (Yan, 2009). This is expressed as below:
PD = ω C V2 tan δ
The main purpose of caring out the experiment is to measure the normal and the abnormal insulation behavior of the insulating material at different environments. The ideal experiment comes up with the expected operation in every environment for various insulation materials. In the experiment, a bridge is used (Gdoutos, 2006). This bridge acts as the loss capacitor; measures the capacitance of the insulation material. The graph after the experiment looks as below
As noted elsewhere in the paper, the lower the loss factor the more efficient the insulation thus where tan δ = δ the insulation is at the best.
Partial discharges
Partial discharges are an experiment that is aimed at measuring the quality of the insulation through the measurement of the corona discharge due to the enlargement of the voids in the insulation material. It is note worth that, even though every manufacturer tries his best to produce a highly effective insulator, it is hard to avoid these voids. The deterioration of the insulation quality comes in when the voids carbonize and enlarge. This increases the corona loss which is being referred to as the partial loss (Yan, 2009).
An experiment to measure the partial discharges is done by monitoring the quantity of these breakdowns in the insulation material. The more the occurrence of the breakdowns the less effective the insulation material is considered. The repetition rate of the breakdown is also measured in this experiment (Gdoutos, 2006).
33kV current transformer
To carry out the above two experiments, the 33kV current transformer is used. In most organizations, this is one routinely. The ideal Dielectric loss for the insulation material in the above named transformer is 3 mill radians. This is at ambient temperatures. As noted earlier in this paper, the ideal dielectric loss is different at various environments. High temperatures result to high magnitude of the dielectric loss. The experiment on this transformer is tradition carried out using the Schering Bridge (Ushakov, 2004).
The 33kV current transformer is measured so as to confirm that the thermal failure that may result from the electrical stress does not occur. It has been proved that improper unearthing usually result to stray effects amounting to 50Hz. This effect is rarely eliminated.
11kV model bushing
The dielectric medium that is used in 11kV model bushing is either oil or air. The measurement of 11kV model bushing thus is aimed at valuing the change that may occur and see the extent at which it can increase the voltage level.
Conclusion
The above experiments are vital for any insulation product of high voltage equipment. It is paramount to note here that the persons who may be in the environs of the equipment after it is released may not be conversant with the use of such equipment. The producer should thus be keen to maintain low levels of dielectric loss and partial discharges. Routine tests on the equipment should also be carried out.
References
Gdoutos, E, Sixteenth European Conference of Fracture, ICI, New York, 2006 p.23- 26.
Ushakov, V, Insulation of high-voltage equipment, SAGE, New York, 2004 p.57- 61.
Yan, K, Electrostatic Precipitation: 11th International Conference, Cengage Brain, New York, 2009 p.100.