M.S. R E SI S T AN CE S
Rue du Crêt de la Perdrix
Zone Industrielle du Coin
42400 St Chamond / France
Tel :
Fax :
+33 477 29 39 80
+33 477 29 39 89
E-Mail: Sales@MSResistances.com
To whom it may concern
O/Ref:
Y/Ref:
Resistors Design
St Chamond / France – November 30, 2006
In order to be competitive, some Resistor Manufacturers have decided to deny all relevant standard and mainly IEEE-32 1972
(only Standard in world to strictly deal with Neutral Grounding Equipments such as Resistors). Those manufacturers have sold
Resistors which are not at all in line with standards.
IEEE-32 1972 specifies limits that shall not be over-passed in terms of Insulation, tolerances and Temperature Rise (Please see
below the temperature rise limit). Those limits are given to avoid any damage occurring on Resistor during any Earth Fault.
Those damages would result in destruction of Transformers and Generators they are attached to. But more important, they may
cause in some circumstances injuries to personnel… that would go up to Death cases and obviously would involve
Contractor’s Liability (Not Resistor’s Manufacturer’s one!!)
Moreover, we now have proofs (Photographs, Specifications & drawings) showing that those manufacturers do not hesitate to
lie, confirming they do have design in accordance with relevant standards.
We wish to point those out to you so that you do not take any risk in the future. We feel that you should ask, for any design
you wish to purchase, technical details such as Resistor active mass, Temperature Rise confirmed by Temperature Rise Test
carried out on same Design , or detail of design calculation showing that the temperature rise is under IEEE-32 (1972) limits
(amount of active parts in kg )
Furthermore, we found out that some manufacturers used to work on other applications such as Motor control, would like to
apply the same policy to Grounding Resistors, thus using the same kind of Alloys.
You should be aware that not all Alloys are suitable to Grounding Resistors. An alloy that has a very low Temperature
Coefficient (TCR), and thus that have a very low variation of Ohmic Value with Temperature is not suitable to grounding
Applications.
Indeed, main purpose of a grounding Resistor is to limit fault current to a maximum limit but trying to decrease that current to
a maximum. Very low TCR keeps that current level to its maximum defined by Ohmic Value!!
Recommended Alloys for Neutral Grounding Applications are:
- AISI 430 (mainly) with TCR of 14.5%/100°k
- AISI 304 (as an Alternative) with TCR of 9% / 100°k
Please, treat this letter with all care it deserves and do not hesitate to contact us for more information.
With our Best regards.
From IEEE-32 ~ ed. 1972 (mainly Table 5)
For NGRs, the allowed temperature rise after current flow should never exceeds:
Ö
760°K for Fault time (less than 10 minutes)
Ö
610°K for Extended time (stated as continuous Rating but with limitation in use per Year)
Ö
385°K for continuous rating
This also is applicable to Harmonic Filter Damping Resistor
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M.S. RESISTANCES S.A.S. ~ CAPITAL: 38 112,25 EUROS ~ A.P.E. 321A ~ SIREN / RCS ST ETIENNE: 429 035 355 ~ SIÈGE SOCIAL : Z.I. DU COIN – 42 400 ST CHAMOND / FRANCE
TVA Intracommunautaire: FR 79 429 035 355
FeCrAl is not a Stainless Steel Alloy.
Some Studies show corrosion problem at Temperatures Below 700°c See: http://publications.lib.chalmers.se/records/full_record/12107.html
Technical Specifications for NER
Rated System Voltage
Line –Neutral Voltage
Rated Current
Rated Time
Rated Frequency
Continuous Current
Resistance at 25ºC
Maximum element temperature rise
Element Type
Element Material
Temperature Coefficient of Resistance
Resistance change for 1000 ºC rise
Basic Insulation Level (to IEC-71)
Power Frequency withstand voltage shall be 28kV
Cable boxes
Incoming cable box to IP54
Enclosure
Service
Material
Thickness
Finish
Final Colour
Hardware
Ingress Protection
Resistor for
SCECO-C
13.8kV
8kV
800 Amps – 5 sec
As per IEEE-32 (1972)
5 seconds
760°c Temperature Rise max.
60 Hz
0
10Ω(+/-10%)
1000 ºC
Edge wound coils type ‘RP’
Stainless steel Fe-Cr-Al alloy
0.036 % Per ºC
36% approx
95kV (graded to earth)
Supplied
Means that Internal
Resistor Part is not
Outdoor use –IP – 23
fully insulated to
Aluminu – zinc treated mild steel
95kVBIL
2mm (1.5mm for removable covers)
Painted
RAL 7033
Stainless steel
IP23 to IEC 529 (BS EN60529)
Protected against Vermins & Rodents
Preliminary general arrangement
Please Advise
Net Dimensions (w x d x h)
800mm x 1420mm x 1100mm approx
17.5kV
Bushings
HIGH VOLTAGE
LOW VOLTAGE
17.5kV
1.2kV
Voltage class
95kV
30kV
Insulation Level (BIL)
Supplier’s
800 / 5A or 800/1A ( To be clarified
Name Hidden
after Base Design Approval ) 15VA,
CT’s
5P10
HV Bushing terminal shall be at a height of 2.5(Min) from floor level for HV outdoor
bushing.
Site test shall be carried out as per SEC-COA TCP # 5/8, Rev-1
Quality
Cressall Resistors are approved by LRQA to BS.EN.ISO 9001:2000
Testing Specification
Cressall NER are designed, manufactured and tested to IEEE-32 Standard Requirements.
Not Possible:
See above
As per IEEE-32 (1972)
760°c Temperature Rise max.
Supplier’s
Name Hidden
FeCrAl is not a Stainless Steel Alloy.
Some Studies show corrosion problem at Temperatures Below 700°c See: http://publications.lib.chalmers.se/records/full_record/12107.html
With Temp. Rise of 1000°c
& TCR of 0,0355%/°c
Variation of 35.5%!!
Resistor for
Oil & Gas
Supplier’s
Name Hidden