Insulation Class for Generator windings
Insulation Class for Generator windings
(OP)
For one of the Emergency DG set ( 1600 KW), the specification indicates Class F insulation and Overtemperature rise class B.
One of the vendor has offered for Class H insulation and Overtemperature rise class B.
Class H insulation will give better life than Class F . Is it OK to stick on to Class F insulation or based on the KW rating is it advisable to go for Class H insulation. How much will be approx cost impact between the two.
Thanks to clarify
One of the vendor has offered for Class H insulation and Overtemperature rise class B.
Class H insulation will give better life than Class F . Is it OK to stick on to Class F insulation or based on the KW rating is it advisable to go for Class H insulation. How much will be approx cost impact between the two.
Thanks to clarify






RE: Insulation Class for Generator windings
RE: Insulation Class for Generator windings
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RE: Insulation Class for Generator windings
I think that a higher class insulation material automatically meets that required for a lower class. (So a machine rated to Class F can used Class H material, and so on).
So a Class H material can be classified as Class F, as long as Class F temperature permitted rises are not exceeded.
But you cannot use class F material with class H temperature rise (except by agreement)
I say this with caution, since I do not have access at the moment to the latest Standards on this.
For your emergency diesel set, I assume that a mass produced generator is used. These are usually wound with Class H insulation material, for short term standby service.
If a user wants some margin, then they may specify a lower class of temperature rise.
Say Class F rise or Class B rise. The lower temperature gives a longer anticipated insulation life. The other benefit can be lower generator losses (better efficiency, because of the way the efficiency curve works) in relation to the lower rating.
The generator manufacturer does not use lower standard materials if you specify Class F insulation, he offers a standard, machine, wound with Class H materials, but selected for Class B rises for the KVA specified.
He can declare it Class F material, he is just using better material and does not have to tell.
I think your vendor has just offered his standard product, but rated for the lower temperature rise specified.
I hope this ramble is clear!
RE: Insulation Class for Generator windings
Yes, I agree that a class H machine is likely the standard design. A true class F machine would likely be a 'special' and would probably attract a price premium in spite of being a lower spec. If a vendor offered a class H winding with a class B rise I wouldn't be concerned - the chances are the other vendors are also offering a class H winding but have chosen to declare the rating so as to meet the class F spec you requested rather than be seen to exceed it.
There are plenty other things to worry about on a diesel set rather than whether the winding is class F or class H when you are so far below either limit - the quality and performance of the AVR and the engine for a start!
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If we learn from our mistakes I'm getting a great education!
RE: Insulation Class for Generator windings
Thank you very much hoxton for your detailed reply and I have clearly understood now.
ScottyUk, as rightly pointed by you , while reviewing the offer the cost aspect is also one of the main factor. As indicated by you , can you please give me the checklist to review the offer for an alternator and the diesel engine. This will be verymuch helpto me for reviewing the technical offers. Thanks to help.
RE: Insulation Class for Generator windings
Who's engine are you looking at and what model is it - there are couple of guys who frequent this forum who can likely comment on specifics of the engine design if you tell them what model it is.
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If we learn from our mistakes I'm getting a great education!
RE: Insulation Class for Generator windings
With regard to the make of the alternator and the engine there is no specific mark given. Different Vendors have quoted for Engines of MTU, Cummins & Mitsubishi and for alternators - Marelli & Leroy somer make.
Thanks to help and for your efforts
RE: Insulation Class for Generator windings
The rated temperature is variously quoted as 54, 55, and 57 Deg. C. Which one is it?
Control voltage of 110V DC is unusual for a small generator; I'd expected 24V DC. 24V DC for the starter at least gives you the chance to jump-start the generator from a truck / crane / forklift if you are in an emergency situtation (last time this happened at site we used a crane
Is the AVR a 3-phase averaging type and tolerant of non-linear loads? I expect it will be on a machine this size but worth checking.
Brushless excitation isn't as tolerant of transient loads as a PMG type. If the AVR draws upon the generator output for power then it will have (relatively) poor field forcing during fault conditions.
This is one reason for the poor recovery after a step load - 5 seconds to 95% voltage isn't a particularly impressive response for a small set.
No mention of the engine / governor arrangement. I would be concerned about the engine in such a hot and dusty environment: filters for combustion air and cooling air; fin-fan cooler for circulating water; etc.
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If we learn from our mistakes I'm getting a great education!
RE: Insulation Class for Generator windings
How do you field force in a brushless excitation ?
RE: Insulation Class for Generator windings
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If we learn from our mistakes I'm getting a great education!