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Posted on 1/23/2012 11:38 AM By Steven McFadyen
This post is quick introduction and overview to different railway electrification voltages used in answer to a question sent in via email. While there are numerous voltages in use through out the world (many dating back a hundred years), fortunately the number of voltages levels in common/widespread use is relatively few. To keep the post short, I will only list the more common voltages.
Both dc and ac systems are used. Direct current systems are generally used for metro lines and relatively commuter /regional systems up to around 100 km long. For longer and more heavily loaded routes, alternating current is generally used.
Posted on 1/17/2012 8:49 AM By Steven McFadyen
Reading is a bit of a hobby of mine and I"ve done a few off-topic posts in the past on this. Rather than continue doing the occasional post I thought I would create a master post, where it anyone (including myself) who wants to can add a comment on what they are reading can do. If you feel like sharing anything about what your busy reading, just add a comment. No particular requirements, it can be anything - top 10 books, favorite author's, what you are reading now, what you plan to read, etc.
Posted on 1/11/2012 4:03 PM By Steven McFadyen
In a previous article I looked at the dc resistance of conductors and in this article we turn our attention to ac resistance. If you have not read the previous article, now may be a good time to do so. The ac resistance of a conductor is always larger than the dc resistance. The primary reasons for this are 'skin effect' and 'proximity effect', both of which are discussed in more detail below.
Posted on 1/5/2012 2:14 PM By Steven McFadyen
This is the first of two posts on the resistance of conductors. In the next post I will look at the ac resistance, including skin effect and we deal with this. To get started, this post will look at the simpler case of dc resistance and how it can be calculated. The international standard for conductors is IEC 60287. The standard classifies conductors according to four classes. For each class of conductor, the standard defines the maximum allowable resistance at 20 oC.
Posted on 12/18/2011 12:20 PM By Steven McFadyen
I think this post is going to be helpful to several of our readers. While the IEC low voltage circuit breaker Standard [IEC 60947-2, Low voltage switchgear and controlgear - Part 2: Circuit-breakers] has been around for many years now, it's surprising how often fault ratings are misunderstood. Hopefully we should be able to clear some of the misunderstanding.
Posted on 12/12/2011 8:05 AM By Steven McFadyen
One of the comments on my Motor Starting Series was asking for something on duty cycles. Here it is.
As a purchaser of a motor, you have responsibility to let the manufacturer know the anticipated duty of the motor. To assist in the communication of this information, the standard IEC 60034-1 (Rotating electrical machines) defines several duty characteristics, denoted S1 to S10:
Posted on 12/6/2011 6:07 AM By Steven McFadyen
Straight forward list of some common motor faults. If I have missed any other common faults, please take a bit of time to add them in as a comment below.
Posted on 12/2/2011 4:56 AM By Steven McFadyen
Our IEE cable sizing was wrote a few years ago and had become rough around the edges. I thought it was time to give the tool a service. Unfortunately when I looked under the hood I found cracked cylinders, broken bell ends and worn cylinders. Rather than a quick service I had no choice be to do a major rewrite on the software. The only thing I didn't touch is the chassis [database], which while suffering from patches of rust, was still usable.
Posted on 11/24/2011 10:09 AM By Steven McFadyen
Some colleagues had an issue earlier in the week on sizing conduits to be cast in concrete for some power cables . It became clear that none of us had a clear idea on an approved method. In the end we agreed that selecting the conduit based on a 40% fill factor was a good idea. This may not be the best approach and if anyone has other ideas, please add below.
Before looking at the method, just want to make it clear we are looking at low voltage power cables, PVC or XLPE, single or multicore and armoured or unarmored.
Posted on 11/15/2011 2:00 PM By Steven McFadyen
Request to look at induction motor starting time have come up a few times on the site. Hopefully in this post, I give you guys some idea on how to calculate this. Failing that, hopefully at least some understanding that it is feasible.
Later in the article I'll give a formulae which you can apply to get an approximate starting time. Prior to that it is worth while looking at a few of the influences which make accurate calculation more difficult.
Posted on 11/11/2011 10:51 AM By Steven McFadyen
A quick post in connection with an email question:
Live Tank - the circuit breaker the switching unit is located in an insulator bushing which is live at line voltage (or some voltage above ground). Live Tank circuit breakers are cheaper than dead tank and require less space.
Posted on 11/7/2011 11:48 AM By Steven McFadyen
The correct sizing of current transformers is required to ensure satisfactory operation of measuring instruments and protection relays. Several methods exist to size current transformers. This note will look at several methods, with particular attention being paid to protection class CTs sized in IEC 60044, which is adopted internationally.