Type test (design test) is defined as the series tests which are made upon the completion of the development of a new equipment design to establish representative performance and to demonstrate compliance with the relevant standard. Once made, these tests need not be repeated unless the design is changed so as to modify its performance. In such a case only the relevant tests need be repeated.Type testing is normally done by a testing authority independent from the equipment manufacturer. The test authority will be issuing Type test certification for the particular equipment.Switchgears and controlgears could be classified as type-test assembly (TTA) or partially type test assembly (PTTA).
Selecting the right equipment to perform the right task during design is a tedious job. A very good example is the variable speed drive (VSD) versus Soft Starter(SS).
On low capacity drives (<25kW), there is no significant cost difference between the two equipment. In high capacity drive application (rating above 1MW) and moving into the medium voltage (6.6kV - 11kV), there will be significant difference in the total cost of ownership between the two equipment.
Lightning is a high-voltage discharge (usually negative) within clouds (intra-), to each other (inter-), or to the earth. The cloud-to-ground (CG) flash is the one we are usually concerned with lightning protection. The charged cells in clouds normally attract charges of opposite polarity on the earth's surface or on high objects located directly below them. When the charge reaches a critical level causing the insulation between cloud and earth breaks down, it develops a stepped ionized path, frequently to the earth, resulting in a high current discharge (stroke) that neutralizes, for the moment, these cloud and earth charges. The discharge current increases from zero to a maximum of 1 us to 10 us, and then declines to half the peak value of 20 us to 1000 us. Lightning flashes usually consist of a sequence of individual return strokes that transfer significant electrical charge usually from the cloud to earth.
The best things in life are free. This is what I felt when I am doing this exercise, comparing results from InterPSS with ETAP.
To verify on how an open source software match up to an expensive commercial software like ETAP, I tried comparing the results side by side. I used ETAP 5.5.6 and InterPSS 1.4.04 in my comparison.
In any project, doing a simple short circuit verification and load flow analysis will save the electrical engineer headaches during testing, commissioning and system reliability testing of the project.
I know some electrical engineers who don't even bother doing a manual calculation because they assume that what they have experienced in their past projects will be the same as their current. This is totally wrong. Every project, despite having similarities have different electrical parameters. Making assumptions and not verifying it mathematically is totally unacceptable.
Short circuit calculation plays a very important role in determining the ratings of electrical equipment. Using software has the advantages, however, to ensure that the software results are correct, hand calculation could be done as a check. Depending on the complexity of the system, hand calculation may be very tedious and impractical.
To demonstrate a simple hand calculation, see the following tutorial at download section.
As the final article on voltage drop and cable selection series, I am now providing a complete worksheet for cable selection based on the IEC standards 60228 and 60364-5-54. I created the worksheet in such a way that it could be printed with your company name, logo, your project, your name, cable number, load description and many more.
Electrical design requires selecting the cable with the correct temperature rating. Designers tend to select the cable with the highest temperature rating, this is not acceptable as the first cost of the project will be affected considerably.
A cable temperature rating is based on the type of material used for its insulation. In this article, we shall be discussing how to correctly select the cable temperature rating for certain installation requirements based on the environmental condition.
In our example in Voltage Calculation - Part 2, we have only considered a single cable and checked only the voltage drop at starting. In actual practice, we shall be comparing several cable sizes, selecting the cable that provides optimum design consideration.
In this example, we shall be using several cables from 35 mm2 up to 120 mm2. Likewise, we shall be considering, not only the starting condition but the running condition of the motor as well. You might be asking, why we selected a motor in our example. The reason, a motor is a dynamic load. A motor circuit load varies from the starting to the normal running condition, thus there will be multiple considerations when selecting the cable for a motor circuit.
This article is the second part on the discussion about voltage drop calculation. We shall be providing real world example for you to be able to appreciate it better as it may have already been a part of what you have already done or currently doing in your design.
We shall be presenting an IEC standard equipment in our sample calculation.
A 120 mm2 3core XLPE insulated cable 120m in length supplies a 110 kW induction motor that has a starting current of 6 times the full-load current of 180 amps. The starting power factor is 0.25 lagging.
This article is the first of a series in the selection of electrical cables.
Cable selection is an important part of electrical installation design. Selecting the correct size of cable could lower initial cost, lower operating cost, better voltage regulation notwithstanding the safety factor.
The primary objective of earthing (or grounding as referred to in North American standards) is safety, to reduce risks to both human life and installations. The principles of electrical earthing are agreed upon internationally, though in practice, there are differences as to how these principles are best achieved.
Electrical systems were not always earthed. The first systems were unearthed ones with no earth reference at all. Even though such systems still exist in specific areas, they are the exceptions rather than the rule and by and large, some form of earthing is adopted for all power systems.
IEC 60079-0 specifies the general requirements for construction, testing and marking of electrical apparatus and Ex components intended for use in explosive gas atmospheres.
Unless modified by one of the parts in the IEC 60079 series, electrical apparatus complying with this standard is intended for use in hazardous areas in which explosive gas atmospheres, caused by mixtures of air and gases, vapours or mists, exist under normal atmospheric conditions of