33KV or 33 kV? 10 MVAr or 10 Mvar? 33/110 kV or 110/33 kV? .... there is a RIGHT way!

© Copyright 2012 Rod Hughes Consulting Pty Ltd

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It has got to the point where “enough is enough” ….
Or should I say perhaps “not enough is not enough” …  it appears that some of our engineers are just not professional enough at least in terms of the somewhat minor details!

For quite some time I have been reviewing all sorts of (national and international) documents about various electrical matters (letters, specifications, drawings, reports, papers, presentations, visual advertisements (printed/tv), press releases,  …. )
I would say “90%” of those documents are not written correctly in regards to showing quantities and units, or references to Standards!!  (sad) (error)
Not very "professional".

I have often had to correct things like “11kV”, or worse “11KV” (Kelvin Volts??), to “11 kV” .... lower case "k" AND with the space between the number and the units.
Or times of “20 mS” (milli-Siemens) to “20 ms” (milliseconds),    or “10 H” (Henry) to “10 h” (hours)
Or one of my favourites, reactive power as either “VAR” or “VAr” to “var”    - refer IEC 8000-6 ... the principle is it is a mathematically derived unit  with the derivation not directly related to only particular person(s)
Or “100 kB/s” to “100 kb/s”  ... one hundred kiloBytes is 8 times bigger than 100 kilobits
Or references to Standards like “IEC61850” to “IEC 61850”,     or “AS3000” to “AS 3000

… oh, and of course is the infamous reference breaking space or hyphen across lines such as
blah bah 11

or blah blah IEC 61850

Here is my writing guide which you are perfectly welcome to use. (big grin)(tick)(lightbulb)

Standards: these should always be referenced with a space between the organisation and the standard number, e.g. :
“AS3000” should be “AS 3000”
“IEC61850” should be “IEC 61850”

Under the ISO OSI rules (if you don't have a copy of those the easiest reference is https://en.wikipedia.org/wiki/International_System_of_Units), quantities should be referenced with a space between the numeric value and the quantity designation
There are also some key rules about the designation as per the examples below:

400V” should be “400 V” or “0.4 kV”  
11kV” should be “11 kV
1500A” should be “1500 A” or “1.5 kA
10MW” should be “10 MW
25000000VA” should be “25000000 VA” or “25 MVA” or "25000 kVA"
10MVAr” and "MVAR" should be “10 Mvar” (noting “var” is all lower case according to IEC 80000‑6 [2008] and IEEE 1459 [2010])
10ms” should be “10 ms

a bit is lower case b
a byte (8 bits) is upper case B
Capital "S" is for Siemens whereas as lower case "s" is for seconds e.g. m/s
Capital "H" is Henry, whereas lower case "h" is hour   e.g. MWh

Ratio numbers should all have a consistent designator
“33 kV/400 V” should be “33/0.4 kV”      or (less preferred) “33 k/400 V”
“1.5kA/1A” should be “1500/1 A”      or (less preferred) “1.5 k/1 A”

Power transformers always have the higher voltage first, even if it is a step-up transformer, i.e. "11/66 kV yn1D" should be "66/11 kV Dyn1".

IEC 60076-1:  Letter symbols for the different windings of a transformer are noted in descending order of rated voltage independently of the intended power flow.


https://en.wikipedia.org/wiki/Vector_group : In the IEC vector group code, each letter stands for one set of windings. The high-voltage (HV) winding is designated with an uppercase letter, followed by medium or low-voltage (LV) windings designated with a lowercase letter.

Note is it no longer correct to refer to consumer voltage levels as 240 V and 415 V supplies in such countries.  Some years ago now, these changed phase‑to‑neutral to 230 V, and correspondingly phase‑to‑phase changed to 400 V.

As referenced in https://en.wikip edia.org/wiki/International_System_of_Units, the "thousands" multiplier is a capital letter with the exception of 1000 which is a lower case "k" so as not to to be confused with the temperature measurement in degrees Kelvin designated as "K" (e.g. "22 KV" makes no sense!)

To note there are decimal and binary prefix symbols, the binary ones having a lower case i added to the similar decimal prefix letter e.g. https://en.wikipedia.org/wiki/Megabyte
100 Mb =100 x 10^6 bits = 100,000,000 bits
100 Mib = 100 x 1024^2 bits = 104,857,600 bits   
.... with one anomaly - "numeric" values use lower case k for 1000 whilst "digital" values uses Ki (with capital K) for 1024. 

Quite often technical drawings from electrical single line diagrams to construction manufacturing drawings for labels will write all the text in capitals. 
A drawing is no excuse not to follow international Standards.

When typing a unit as squared, cubed, degrees requiring sub/superscript and other symbols like ≥, use the appropriate symbol from the formatting tool bars rather than the number formatted as superscript - there is a difference when copy/pasting text for 300 m2 (superscript font) and 300 m² (symbol squared), or 75oC (superscript font) and 75°C (degrees symbol)  - try copy and paste this sentence as "plain text without formatting" and you will probably get that text as " 300 m2" vs "300 m²" and "75oC" and "75°C").

It is recommended to use the non-breaking space when typing these references so that the number and the quantity stay together on the same line: press Ctrl+Shift+Space. 
Non-breaking hyphens Ctrl+Shift+Hyphen are also useful for example IEC 61850‑7‑4 

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I provide a range of courses for company-specific in-house training and occasional public invitation courses.  Contact me for details.


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