Bostjan et al,
The original ideas that led to insulation coordination were
conceived in the early days of electricity when it was clear that failures
in the system should be forced into the smaller, cheaper components and not
the larger expensive components. Best not to have to replace the generator
due to a failure.
The long term experience in all of this was captured in IEC 60664 -
Insulation Coordination - requirements and was based upon the experience
with the extensive power grid in place worldwide.
Now a goodly portion of this power grid is being replaced with local
sources - such as the windmill or solar panel sources being installed.
There are now many more players (such as the ones that you are dealing with)
in this business. Not many of them have the same level of experience as
the traditional suppliers and, as such, aren't watching all of the same
issues in getting into this market.
The safety standards for products have been built upon the
traditional network practices and should be acceptable in this new
electro-space but difficult to apply, as you have found.
There will be a lot of pushing and shoving to get the correct set of
requirements smoothly running here.
From your description the extreme voltage is not an external
transient but an expected startup condition of the generator. If it cannot
be kept from the dc/dc smps you are designing then you must consider
accommodating it. Or, alternatively, since the difference is relatively
small between the max tolerance and the occasional peak, you may consider
ignoring it and put up with the difficulty it may cause occasionally.
None of this provides direct standards guidance but should give you
a place to start discussions with the customer and the test house folks.
You are going where no man has gone before - to repeat a familiar
saying.
:>) br, Pete
Peter E Perkins, PE
Principal Product Safety Engineer
PO Box 23427
Tigard, ORe 97281-3427
503/452-1201 fone/fax
[email protected]
_ _ _ _ _
Hello Rich,
I understand your point.
Unit is DC/DC converter supplied from generator or windmill. There is a 3
phase rectifier in front of the unit. Wind mild has rated phase voltage 230V
tolerances of -15%/+30% (e.g. 195,5-299V). For short period (at start)
output voltage can achieve 343V~ (up to 1 min). When you rectify this values
you get rated voltage 563Vdc and with considered ac tolerances 480-730Vdc.
If you check IEC 60950-1 standard, it says you need to consider for dc mains
tolerances of -15%/+20% unless otherwise specified by the manufacturer. For
clearances and creepage distances you only need to consider rated voltage
(not tolerances) of the product (only 560VDC will be marked on the unit). In
this particular case manufacturer specified a bit higher tolerances. There
is nothing mention about value of tolerances.
I know many products have rated voltage 220-240V and operational voltage
range 180-276V. For clearances and creepage distances only 240V was
considered.
Therefore I am a bit confused what should we consider for determination of
working voltage. Is it rated voltage (marked on the unit) or we need to
consider also tolerances or even short-term voltage?
Best regards,
Bostjan
-----Original Message-----
From: Richard Nute [mailto:[email protected]]
Sent: Thursday, September 10, 2015 12:28 AM
To: [email protected]
Subject: Re: [PSES] requirement for spacings
> I can't understand how a 'rated voltage' can be
560 V
> +30%/-15%. It must
> mean something other than what is normally understood as 'rated
> voltage'
> in safety standards.
In the IEC, rated voltage is a value assigned by the manufacturer.
For years, standards committees have attempted to specify one or more
formats for the voltage rating. Each standard is different, and sometimes
each edition is different.
The problem is when a manufacturer uses a single, nominal value. We know
that line voltages vary, so standards committees choose, say, +6%, -10%.
We have commonly seen wide-ranging power supplies rated 90-250 volts. But,
we cannot fault a manufacturer for rating his wide-ranging product as 150
volts, +166%, -60%. With your i-Phone, you can easily calculate whether the
equipment will operate on your power line!
In this case, the manufacturer has rated his product to operate from 470 to
728 volts. What is wrong?
Best regards,
Rich
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