Medium Voltage V/S Low Voltage GENERATOR

[Sajid khan]

Dear Forum Members,

Please help me to know the major differences between MV & LV generator with regards to generator construction, fuel consumption, operating characteristics, efficiency and others.

Thanks in advance

 

[Sajid khan]

Dear Forum Members,

Please help me to know the major differences between MV & LV generator with regards to generator construction, fuel consumption, operating characteristics, efficiency and others.

Thanks in advance

Replies Please

 

[Tony S]

Have a look on the other forum you posted this same question

 

[Sajid khan]

Have a look on the other forum you posted this same question

Yes i posted the same to get replies..
Is it prohibited??

Sent from my GT-I9300I using Tapatalk

 

[ron]

From a high level, if the power ratings are the same, for example 3MW @ 480V vs 3MW at 13.8kV, the generator construction, fuel consumption, operating characteristics, efficiency and others will be essentially the same.

The MV alternator will have ungrounded conductors further spaced apart, but most other items will be the same.

Due to the leadtime of MV alternator delivery, or utility interconnection types, some will use resistance grounding vs solidly grounded systems.

 

[junkhound]

Replies Please

It would elicits more responses if more information was given, such as application, extent of load (feeder lengths), existing dist network.

e.g: oil field? shipboard? fixed comm installation?, number of gen sets to be paralleled, etc...

OP was too generic. That said, most installs I've been involved with are LV up to a few hundred kW, anything over a MW is MV.

Caveat: Assume that Saudi is mostly near sea level. Genset installs in high altitude areas often tend to stay LV due to possible degradation due to partial discharge at higher altitudes.

 

[Sajid khan]

From a high level, if the power ratings are the same, for example 3MW @ 480V vs 3MW at 13.8kV, the generator construction, fuel consumption, operating characteristics, efficiency and others will be essentially the same.

The MV alternator will have ungrounded conductors further spaced apart, but most other items will be the same.

Due to the leadtime of MV alternator delivery, or utility interconnection types, some will use resistance grounding vs solidly grounded systems.

The MV alternator will have ungrounded conductors further spaced apart, but most other items will be the same.

Thanks for the sentence.
you mean Ungrounded conductors further spaced apart similar to Medium voltage switchgear v/s low voltage switchgear due to voltage level.

 

[Besoeker]

From a high level, if the power ratings are the same, for example 3MW @ 480V vs 3MW at 13.8kV, the generator construction, fuel consumption, operating characteristics, efficiency and others will be essentially the same.

The MV alternator will have ungrounded conductors further spaced apart, but most other items will be the same.

Except the rating of the output conductors to the loads.

I think it would be helpful if the OP explains what he wants to power with his generator.

 

[Sajid khan]

Except the rating of the output conductors to the loads.

I think it would be helpful if the OP explains what he wants to power with his generator.

I have Seven MV Generator 3150kVA each, feeding the hospital load. These generators are located in Central Service building to feed the hospital loads. Emergency load as we calculate & fed by generators is 19000kVA. These generator are feeding mechanical pumps, AHUs, medical equipment, lighting power loads etc.

Actually i know a lot of difference between LV & MV gensets which are very common but it is my first time dealing with MV Generators, so want to know any major thing that is not with LV generator, before someone point me out.

Thanks

 

[junkhound]

....major thing that is not with LV generator.....


Insulation system damage over time due to Partial discharge and corona if all distribution components not properly designed and installed. A few web hits below for info:

http://www.hvpd.co.uk/technical/

https://irispower.com/services/online-testing-diagnostic-reports/?gclid=CPbarJaMmtQCFVVtfgodVfYA2w

http://ieeexplore.ieee.org/abstract/document/903131/

edit PS: which is one reason why MV conductors are 'farther apart' as previously mentioned.

 

[Besoeker]

I have Seven MV Generator 3150kVA each, feeding the hospital load. These generators are located in Central Service building to feed the hospital loads. Emergency load as we calculate & fed by generators is 19000kVA. These generator are feeding mechanical pumps, AHUs, medical equipment, lighting power loads etc.

Actually i know a lot of difference between LV & MV gensets which are very common but it is my first time dealing with MV Generators, so want to know any major thing that is not with LV generator, before someone point me out.

Thanks

So it would it be fair to say that most of the installed equipment runs on LV? If that's the case and you install MV generators and distribution you will also have to MV to LV transformers locally to the loads.
I have no experience of hospitals but arrangement is commonly used in industrial plants.

 

[Sajid khan]

So it would it be fair to say that most of the installed equipment runs on LV? If that's the case and you install MV generators and distribution you will also have to MV to LV transformers locally to the loads.
I have no experience of hospitals but arrangement is commonly used in industrial plants.

yes exactly the same case as you mentioned ,The installed equipment will run on LV and we have package substation to convert the MV generated voltage to Low voltage. The main reason to select the MV generator is the huge length around 300meter upto the equipments and doing so by LV generator will require two much cabling work.

 

[Sajid khan]

....major thing that is not with LV generator.....


Insulation system damage over time due to Partial discharge and corona if all distribution components not properly designed and installed. A few web hits below for info:

http://www.hvpd.co.uk/technical/

https://irispower.com/services/online-testing-diagnostic-reports/?gclid=CPbarJaMmtQCFVVtfgodVfYA2w

http://ieeexplore.ieee.org/abstract/document/903131/

edit PS: which is one reason why MV conductors are 'farther apart' as previously mentioned.

Thanks for sharing info...

 

[Sahib]

MV generator may have a lower reliability than a LV generator due corona problem and associated MV switchgear. It may not be possible to transfer power within 10 second if it rotates at medium speed rather than at high speed of LV generator.

 

[Besoeker]

MV generator may have a lower reliability than a LV generator due corona problem and associated MV switchgear. It may not be possible to transfer power within 10 second if it rotates at medium speed rather than at high speed of LV generator.

Drax, the largest UK power station, has six 660MW HV generators. They run at 3000 RPM 2-pole 50Hz.
LV (synchronous) simply can't run any faster.

 

[Sahib]

Drax, the largest UK power station, has six 660MW HV generators. They run at 3000 RPM 2-pole 50Hz.
LV (synchronous) simply can't run any faster.

If a MV gen set, of same capacity as a LV gen set, is designed to run at a lower speed, it may have a lower kinetic energy and as a result, it may not accept emergency loads within 10 seconds thereby failing an important code requirement to serve life support loads in a hospital.

 

[Besoeker]

If a MV gen set, of same capacity as a LV gen set, is designed to run at a lower speed, it may have a lower kinetic energy and as a result, it may not accept emergency loads within 10 seconds thereby failing an important code requirement to serve life support loads in a hospital.

I'm sure people with more expertise in that field than either you or I have thought that one through.

 

[Sahib]

I'm sure people with more expertise in that field than either you or I have thought that one through.

The question is whether a higher KVA capacity is always required if OP chooses MV generator of slower speed.

 

[Besoeker]

The question is whether a higher KVA capacity is always required if OP chooses MV generator of slower speed.

Not really the question.........

 

[Sajid khan]

The question is whether a higher KVA capacity is always required if OP chooses MV generator of slower speed.

The specification of the MV alternator is 2500 kW,4 pole, rated speed = 1800 rpm, over speed limit=2100 rpm.

IMO, The condition of slower speed will be momentary not persistent and it will not effect two much the KVA rating.