Electrical installations may have the best conceptual design (redundancy, loops, etc ..) and even the best electrical equipment or being oversized and does not mean that they are valid for operation if the tripping values of their electrical protections are inadequate . Many times we have seen a major blackout in large public facilities or factories stops (with all the associated costs) due to improper firing of electrical protection installation. We have to consider that it is not sufficient for an electrical protection clearance defect, but must act solely the nearest protection problem to avoid leaving unserved other vital parts of the facility.
Another highlight, and not least, is that it is so critical selectivity in a system of medium voltage (hereinafter, MV) as a system of low voltage (hereinafter LV). We tend to underestimate the possible effects of non-selectivity between low-voltage switches and this can lead us very unpleasant surprises. How many times has not stopped the production of a factory due to stop an oil pump for lack of lubrication?
In Tecginia we are well aware of all the facilities hauled problems due to nuisance tripping. We have seen problems in large facilities (airports, factories, utilities, .. etc) and always the answer has been the same: It had not been considered all aspects of the regulation of protection or these regulations were not adequate or even did not exist.
The answer is conducting a study of selectivity or protection coordination both HV and MV and LV. To do that, it is advisable to use tools and software that enable appropriate calculations with the plant data for:
- Value the minimum and maximum levels of shortcircuit at each point of the installation.
- Knowing the philosophy of the installation to protect against overload and load imbalances and surges.
- Knowing the various elements of the electrical installation (cables, motors, capacitors, ... etc) make sure they are properly protected against overload and short circuit and (as to the most common event) earth faults.
- Recommend the best protection from the neutral point of the installation (grounding impedance, isolated, .. etc) to protect neutral line and (more important) protecting people too.
Only thorough a technical study including breaking capacity, protective equipment and their regulations may ensure adequate availability of our facilities and, therefore, minimize both the risks to people and the economic risks associated an electrical event.