Posted on 6/12/2013 1:52 PM By Steven McFadyen
Capacitors are widely used in electrical engineering for functions such as energy storage, power factor correction, voltage compensation and many others. Capacitance is also inherent in any electrical distribution systems and can play a pivotal role in it's operation.
In order to fully understand capacitors and their use, it is essential that electrical practitioners have a good understanding of capacitor theory.
Posted on 4/25/2013 12:53 PM By Steven McFadyen
If two dissimilar metals are touching and an external conducting path exists, corrosion of one the metals can take place. Moisture or other materials acting as an electrolyte between the metals create an electrochemical cells (similar to that of a battery). Depending on the metals, one will act as a cathode and one as an anode of the cell.
Under this arrangement, stray d.c. currents will flow. In the same was a a normal cell, an electrochemical reaction takes place and there is a resulting corrosion of the anode.
Posted on 4/18/2013 1:12 PM By Steven McFadyen
While not as popular as it once was, frame leakage protection does still have some use in some circumstances. In essence frame leakage is an earth fault type protection. A current transformer installed in a connection from the frame to earth monitors any fault current and operates an instantaneous relay.
Posted on 4/11/2013 12:53 PM By Steven McFadyen
Ever wondered what kind of power an aircraft uses when parked at the airport stand.
Normally the aircraft generates it own power, but when parked with the engines switched off power provided by the airport would be connected to the plane. This connected power is typically 115 V at 400 Hz and is called ground power.
Posted on 4/4/2013 12:47 PM By Steven McFadyen
Photovoltaic (PV) systems are typically more efficient when connected in parallel with a main power gird. During periods when the PV system generates energy this can be utilized and the grid energy used at other times.
For large PV systems, any connection interface is likely to need discussion with the power network operator. For smaller systems (around 10 kVA), there are existing standards which will facilitate making a functional and safe grid connection. This note looks at some of the standards.
Posted on 3/27/2013 12:54 PM By Steven McFadyen
Per unit fault calculations is a method whereby system impedances and quantities are normalised across different voltage levels to a common base. By removing the impact of varying voltages, the necessary calculations are simplified.
To use the per unit method, we normalise all the system impedances (and admittances) within the network under consideration to a common base. These normalised impedances are know as per unit impedances. Any per unit impedance will have the same value on both the primary and secondary of a transformer and is independent of voltage level.
Posted on 3/27/2013 12:52 PM By Steven McFadyen
For unbalance conditions the calculation of fault currents is more complex. One method of dealing with this is symmetrical components. Using symmetrical components, the unbalance system is broken down in to three separate symmetrical systems:
Posted on 3/10/2013 11:50 AM By Steven McFadyen
We have a sister note to this (Robots - Interesting Video), in which I have posted some videos of interesting robots developed by commercial corporations and institutions. While these are great in themselves, there is a whole range of innovation carried out by hobbyist and amateurs. In this note, I intend to post videos of interesting robotics projects I come across which have not been developed by big institutions.
Posted on 2/28/2013 1:04 PM By Steven McFadyen
Multimeters are undoubtedly the most common item of electrical test equipment in use. Often it is the first piece of equipment people will turn to when trying to visualize and obtain data on an electrical system.
As the name suggests, a multimeter is an single meter with the ability to measure several electrical quantities. Nearly all multimeters will include the measurement of at voltage, current and resistance.
Posted on 2/18/2013 5:58 AM By Steven McFadyen
In the previous note we looked at the approach taken by the standard to the sizing of cables and illustrated this with an example. We then looked at one method of applying the standard and identified resources enabling the calculation of all the various parameters involved. In the note we are going to put everything together and reveal the necessary equations for actually calculating the cable maximum current rating.
Posted on 2/8/2013 11:17 AM By Steven McFadyen
Current transformers (CTs) are used to convert high level currents to a smaller more reasonable level for use as inputs to protection relays and metering equipment. Within electrical systems, current transformers are essential to ensure the correct functioning and control of equipment and for providing operational data and information.
This introductory note looks at the construction of current transformers and their specification
Posted on 2/6/2013 11:45 AM By Steven McFadyen
HTML supports a variety of entity symbols which can be entered using either numbers or an entity name. The number or name is preceded by the ‘&’ sign and ends in a semi-colon (;). To enter a symbol switch to HTML view in the editor and enter the number or name (Ω for example).