Posted on 1/31/2013 1:00 PM By Steven McFadyen
IEC 60287 "Calculation of the continuous current rating of cables (100% load factor)" is the International Standard which defines the procedures and equations to be used in determining the current carry capacity of cable. The standard is applicable to all alternating current voltages and direct current cables up to 5kV.
This note will introduce the concepts adopted by the standard, provide some guidance on using the standard and direct the reader to further resources.
Posted on 1/16/2013 10:33 AM By Steven McFadyen
The standard aims to consolidate AC and traction voltages within the industry and defines the following bands:
- band 1 - A.C. systems 100 V to 1000 V
- band 2 - A.C and D.C traction systems
- band 3 - A.C. systems above 1 kV to 35 kV
- band 4 - A.C. systems above 35 kV to 230 kV
- band 5 - A.C. systems above 245 kV
Posted on 1/9/2013 6:52 PM By Steven McFadyen
The image (reproduced from IEC 60909) shows a typical fault in an ac system. From the illustration it can seen that there is an initial dc component (id.c.). This initial dc component decays over time, eventually reaching zero. Addition of the dc component to the symmetrical short circuit current give the asymmetrical fault current.
Posted on 12/12/2012 1:26 PM By Steven McFadyen
IEC 60947 is the circuit breaker standard and covers the marking of breakers in detail. Any manufacturer following this standard should comply with the markings.
Posted on 11/29/2012 12:32 PM By Steven McFadyen
One of the fundamental requirements of an alternating current distribution systems it to have the ability to change the magnitude of voltages. It is more efficient to transmit power at high voltages over long distances, whereas it is safer and more practical to use a low voltage to drive appliances and equipment. Transformers are used to achieve this.
Posted on 11/11/2012 11:46 AM By Steven McFadyen
Over recent years the Lithium Ion battery has become popular in applications requiring high power densities with small weight and footprint. Today Lithium Ion batteries are commonly found in mobile phones, portable electronics, power tools, electrically operated vehicles and military applications. In addition to high power densities, Lithium Ion batteries are chargeable and have no memory effect. Charge/discharge mechanism of a Lithium Ion battery Image Source: http://batteryuniversity.com Developed in the early 1970's at Birmingham University in the UK, Lithium Ion batteries consist of a Lithium Metal Oxide positive electrode (cathode), carbon negative electrode (anode) and electrolyte of a lithium salt organic solution. During the discharge process, Lithium Ions move from the negative to the positive electrode, via the external circuit. During the charging the process is reversed by applying an over voltage. The Lithium Metal Oxide cathode is constructed using various ...
Posted on 8/17/2012 6:00 AM By Steven McFadyen
I've recently come across this question a couple times browsing the internet. Decided to give a quick answer here. A rectifier transformer is a transformer which includes diodes or thyristors in the same tank. Voltage regulation may also be included. Typically these are used for industrial processes which require a significant direct current (dc) supply. Typical processes would include dc traction, electrolysis, smelting operations, large variable speed drive trains, etc.
Posted on 8/1/2012 12:26 PM By Steven McFadyen
Over the past year or so I've been involved in on going discussions related to referring fault levels from the secondary of a transformer to the primary side. While this is easy for some people to grasp, for others it's not so straight forward. Here is a brief explanation of how to do this.
Posted on 7/10/2012 4:23 PM By Steven McFadyen
Electromagnetic compatibility (EMC) is the study of coordinating electromagnetic fields give off equipment, with the withstand (compatibility) of other equipment within the vicinity. In it's simplest form, we endeavour to ensure that the magnitude of any electromagnetic fields generated are less than the withstand level of adjacent equipment.
Within Europe there is the EMC directive (2004/108/EC), which is law in all European Countries. Equipment which bears the CE mark has been certified to comply with the relevant standards.
Posted on 7/10/2012 11:43 AM By Steven McFadyen
Power factor is the ratio between the real power (P in kW) and apparent power (S in kVA) drawn by an electrical load.
The reactive power (Q in kVAr) causes the real and apparent power to be displaced from each other. Reactive power provides the necessity for electric and magnetic fields to enable the power system to work.
In addition to being the ratio of real power to apparent power, the power factor can also be express as the cosine of the angle between the two.
Posted on 7/9/2012 10:48 AM By Steven McFadyen
Resistors are electronic components that oppose the flow of current. Manufactured in various types and ranges they have a wide application to electronics.
Posted on 7/3/2012 1:58 PM By Steven McFadyen
Installation of a UPS can help in reducing problems due to issues with the power supply. A lot of people relate this to nine key issues. Depending on the type of UPS installed it is possible to resolve some or all of the above issues. The simplest installation of an off-line UPS will resolve issues (1) to (3), while the installation of a full double conversion unit could potential resolve all issues.