How to implement protection for multi-winding transformer?

S

sankui

#1
Hi Forum,

Our multi-winding transformer failed the short circuit and overload test. I would like to ask for your kind help.

It is a toroidal transformer (Class B) with eight (8) output windings. The primary winding is equipped with an internal thermal cut-out of 130 C.

The tests are made on each winding in turn, the other windings being loaded as in the normal use. Unfortunately, the output winding burnt during the testing, because of each of these outputs contributes little to the total power and cannot render the primary fuse and thermal cut-out operative.

In order to solve the failure caused by short circuit, I would like to add a fuse to each output winding. The fuse is in-line mounting type (i.e. in the transformer output lead) so as to achieve the 2 MOOP (between the output contacts of the transformer up to the protective device) easily and avoid redesigning the PCB.

But should we add internal thermal cut-out into each output winding (in my case, eight thermal cut-outs) for protection against the overheating?

Thank you!
 
Elsmar Forum Sponsor

Peter Selvey

Staff member
Super Moderator
#3
Both options are OK, secondary fuses or thermal fuses in each winding, or at least in each low power winding. Often the main power winding can still be protected by the primary device, so the main concern are the small low power windings.

There is a test in the standard which applies 5x voltage 5x frequency (e.g. 1200V 300Hz for 240V 60Hx rating). One of the purposes of this test is to verify that the secondary is unlikely to short inside the transformer itself, i.e. equivalent to 2 MOOP internally. That means you only need to worry about 2 MOOP external to the transformer.

If the fuse is in-line mount, then there is no cr/cl to measure, and the wiring should meet 2 MOOP.

If you decide later to move the fuse to the PCB (for easier manufacturing), there might be some theoretical problems. The limits in the standard for 2 MOOP are quite high for small voltages. In the 3rd edition, the basic limit would be 2.4mm, which is more than 20 times a reasonable limit as taken from IEC 60664-1 (0.08mm). IEC 60664 allows very small gaps for a PCB I guess because there won't be any movement or production variations. IEC 60601-1 has no special limits for PCBs, resulting in a huge gap in limits.

The good news is, most test labs don't measure this distance ;)
 
S

sankui

#4
According to 15.5.1.3, windings with more than one protective device could require multiple overload tests. When a winding is protected by a fuse and a thermal cut-out, it seems that the test (a) should be performed because of the first (minimum) operative current cannot be determined based on the data. Is it right?

I am a bit confused about the purpose of test (a). Test (a) does already require some steps to reach thermal stability when determining the minimum current at which the protective device operates. But why test (b) is still required after the operation of the protective device in (a)? I would think the overload test is finished if thermal stability is achieved.

I am also confused about the rationale of 15.5.1.1.
Output windings are required to be “tested in turn” because under overload conditions, testing all windings simultaneously can cause over temperature devices to operate which would not operate if only one winding was being overloaded.
It seems to me that the reason explained in the standard to do the test in turn is not because of the single fault philosophy. I always think that more than one winding overloaded simultaneously should be regarded as multi-fault conditions. Someone told me that overloading is different from the short circuit (SFC definitely) and belongs to normal condition. Is this correct?
 
Thread starter Similar threads Forum Replies Date
placebo_master Verification Protocols - when to implement them (and when to skip in lieu of a report) 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 4
G How to implement H&S and Quality Control Requirements in Contract for Potential Supplier? Contract Review Process 6
R Using R package to implement Bayesian phase I/II dose-finding design for three outcomes ISO 13485:2016 - Medical Device Quality Management Systems 6
R AS5553 Clause 3.1.7 f - "Implement a returns process....." AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 5
Q AS9100:2016 D - Intent of 8.4.3 (K) - Implement QMS AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 5
Y When will Notified Bodies require MedDev manufacturers to fully implement ISO 14971:2019? ISO 14971 - Medical Device Risk Management 1
S How to Implement COSO 2017 Framework Various Other Specifications, Standards, and related Requirements 0
M How to implement the 4M Change Management System Lean in Manufacturing and Service Industries 3
M Can I audit processes I've established but do not implement or maintain? Internal Auditing 6
S How to address and implement OH&S opportunities in ISO 45001:2018? Occupational Health & Safety Management Standards 12
J ISO 9001:2015 Cl. 8.1 - 'and to implement the actions determined in clause 6' ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 7
I How to implement ISO 9001:2015 for Construction Field ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 1
Q Is it worth the effort to implement ISO 31000 Risk based on ISO 9001:2015? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 5
A How do we implement a Process Approach ISO 13485:2016 - Existing GMP QMS Other ISO and International Standards and European Regulations 2
Crusader Can I Implement AS9100 in 1 Department only? AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 4
L How many working hours to required to implement ISO 14001 ? ISO 14001:2015 Specific Discussions 6
A Do we have to implement customer specific requirements? Customer and Company Specific Requirements 13
L Roadmap to implement Business Excellence by department Misc. Quality Assurance and Business Systems Related Topics 11
B How to implement a Nonconformance System in a Service Industry ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 3
R Does "establish, implement and maintain a procedure" require a Document - OHSAS 18001 Occupational Health & Safety Management Standards 1
W Working in a company where we try to implement ISO 27001 IEC 27001 - Information Security Management Systems (ISMS) 9
T What type of industries or companies that should implement PAS 55? Other ISO and International Standards and European Regulations 2
A What is QSB? How do you implement? What are your documents? IATF 16949 - Automotive Quality Systems Standard 4
B How to implement 4.2.4 - Disposition of Records in Electronic Files ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 2
T Metrics and Statistics for Improvement - Easy to implement Statistical Analysis Tools, Techniques and SPC 4
M My company wants me to implement ISO 17025 in our laboratory ISO 17025 related Discussions 7
C Which of these 2 ways would you implement a Quality System? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 6
B How to define and implement Configuration Management Document Control Systems, Procedures, Forms and Templates 5
K How Can I Implement the Process Approach in AS9100C AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 9
D Implement ISO 22000 or E-Cristal System. Food Safety - ISO 22000, HACCP (21 CFR 120) 2
R How to implement Six Sigma within an IT-driven organisation? Six Sigma 14
A How to Develop and Implement 5S +1 Program Lean in Manufacturing and Service Industries 3
L Time Required to Implement ISO 27001 if ISO 9001 certified & SOX compliant? IEC 27001 - Information Security Management Systems (ISMS) 3
R What I have to do to implement ISO 9001:2008 till Registration and Certification? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 9
M How to Implement QMS for an Information Solutions company Quality Management System (QMS) Manuals 2
S Planning and Costs to Implement ISO / IEC 27000 - Where to start? IEC 27001 - Information Security Management Systems (ISMS) 2
K How to start Implement SPC for Injection Molding Process? Statistical Analysis Tools, Techniques and SPC 24
C Do you implement real SPC not just a paper work? Statistical Analysis Tools, Techniques and SPC 18
2 Trying to Implement a Manufacturing Engineer Concept to my Company Manufacturing and Related Processes 5
R How does my firm implement hybrid system? ISO 13485:2016 - Medical Device Quality Management Systems 5
M How to implement ISO/TS 16949:2009 when customers do not require PPAP? IATF 16949 - Automotive Quality Systems Standard 7
E Why to Implement or Not to Implement ISO 26000 (Social Responsibility) Other ISO and International Standards and European Regulations 14
bobdoering The CORRECT steps to implement an SPC chart Imported Legacy Blogs 16
J When to implement the Development and Design Clause 7.3? Design and Development of Products and Processes 18
M Want Help to Implement IMS (Integrated Management System)? Occupational Health & Safety Management Standards 7
M How to Implement the QHSE Integrated Management System Easy Steps? Occupational Health & Safety Management Standards 1
E Should FDA implement 3rd party (PMAs) reviews? What are the pros and cons of doing so Other US Medical Device Regulations 2
N Implement the Best Format and Set of Tools for Design For Six Sigma Six Sigma 7
K Which Australian Standard will help me implement OH&S in my business ? Occupational Health & Safety Management Standards 8
D How to implement Control of Employee Access to Client Data IEC 27001 - Information Security Management Systems (ISMS) 2

Similar threads

Top Bottom