In HVT (High Voltage Technology), any voltage above 11 kilo-volts is considered to be in the high voltage range. It can either be alternating or direct current. Majority of industries are supplied with this range of voltages from the national grid while some generates their own high voltage power using power generators. These high voltages are usually stepped down to some specific lower voltages, to run their electrical machinery such as motors, heaters, HVAC systems, among others. For these industries, regular checks must be conducted by authorized personnel to assess the condition of their equipment. Equipment testing is very crucial in determining the soundness of a machine so as to avoid equipment breakdown and massive production losses. These tests also assist in determining if a newly purchased equipment is worth, before installing it. Most manufacturers use high voltage testing to test the insulation of their equipment before supplying them to their customers.
The benefits of applying high voltage insulation testing are generally looked down upon by many industries, as a technique of finding out the conditionality of their electrical equipment. This can be greatly attributed to the fact that much pressure and emphasis is always put on production activities at the expense of proactive maintenance of the equipment. A reliable and effective insulation for an electrical machine is of utmost importance for its correct operation every time. Since insulation of equipment degrades with time, the respective electrical department for any industry must be regularly conducting regular check-ups for machines as part of their normal working schedule. This should be done to even low and medium voltage systems.
In most cases, a four stage process is followed. The stages are briefly described below:
This is the most basic process which can be done even on the readily installed equipment, so long as it is not running. This process involves the use of a meggering instrument to test the insulation integrity of the coils before it is connected to phases, neutral, and earth. In some cases, a multimeter can also be used. Inter-winding and winding-to-body resistances are checked at this stage. Therefore, the dielectric withstanding voltage and insulation resistance of the coil can be determined.
Ancillary Equipment Testing
This involves testing for insulation resistance and dielectric withstanding voltage for interconnecting cables, high voltage bushings, busbars, and terminations. This can be conducted when the components are interconnected or separated.
Generator Assembly Test
In this case the generator is visually inspected. Cleaning is done and the machine’s stability is also assessed. The pulse of the machine is closely monitored using a special display instrument. The equipment is also meggered for insulation resistance and dielectric withstanding voltage test.
Among the factors to consider in testing equipment are; voltage and right testing equipment. For the most dependable results testing voltage should be high enough to effectively measure the insulating resistance. However, it should not be too high to overstress the equipment insulation. The right testing equipment which can effectively store results enables them to be stored in a computer for archiving and analysis. This procedure saves time and reduces the risk of error.