protect the generator from power grid

[tareksabry]

we have a new plant in our factory it is a steam turbine which driven the generator,and it has it protection device,it`s done by Chinese engineers so they told me that the feeder of power grid should be connected always at same time with the generator while it is supplying the plant,some other peoples told me that we must have a protection device which protect the generator from the power grid like over voltage under voltage over freq. under freq. reverse power etc. so could any one help me in this issue.

 

[DanDel]

Generator protection as you mention is mandatory to prevent damage to your generator while it is connected to the grid. Typically, the generator has its own C/B connection which can be tripped for a issue such as motoring or a fault out on the grid which can damage the unit. This would be separate from the connection between plant loads and the grid.

 

[jimgineer]

I'm not too familiar with using a generator in this application, but typically with a generator that is paralleling (sourcing) into the grid, it's a big deal matching frequency and phase. With a generator operating as you describe, it sounds like you are more closely describing an alternator (ie: takes mechanical energy in, puts electrical energy out). In the parlance I'm familiar with, when you descibe a generator, you are describing not only the ability to take mechanical work and produce electrical work (alternator) but the ability to produce mechanical work in the first place --- for traditional 'generators' as I'm used to hearing, this usually means diesel fuel going into cyllinders, turning a rotor, etc.

I may be mincing words but long story short, yes you need protection, and yes, you need to ensure that the waveform produced by your 'generator' matches that on the grid. To do this, you often need some sort of controlling mechanism and the ability to 'lock out' your source until it reaches the rated voltage waveform.

As far as how EXACTLY this is accomplished in applications where you have a turbine, I look forward to some experts weighing in.

 

[jimgineer]

And keep in mind that a lot of the details will be covered ..or SHOULD be coverd.. in whatever utility's grid you're dealing with's interconnection guidelines.

 

[slavag]

Hi Tareksabry.
Isn't simple issue.
Of course it must be covered by utilities requerements.
Are connection to distribution or transsmision grid?
Firstly you must have LOSS OF MAIN protection
1. df/dt or F protections
2. Voltage step protection.
3. Maybe, out of step or pole slip protection.
4. Maybe reverse power protection or directional overcurrent+undervoltage protection.
Difficult case, if you have fast autoreclosere on your connection line. In this case maybe U1<, positive undervoltage will be used.
Hope that help.
Best Regards.
Slava

 

[cranky108]

From a utility perspective there must also be protection added to protect the utility's other customers, and utility's equipment.
For the best information I would refer you to the IEEE guides on generator protection. Or most utilities should have a write up on what is required for interconnection. Other guides can be found on the web sites of protective relay manufactures like SEL, ABB, Basler, or Beckwith.

Also several states have interconnection guides for interconnection to utilities within those states (also good information even if you are not in those states).

For larger generation, in the USA, the power pools may have guides for interconnection.

 

[TurbineGen]

Do you have any protection on your generator? Certainly your should have overvoltage/overcurrent protection at all times. When connected to the grid or paralleling any electrical system, reverse power protection is essential. Also you will need a synchronous check relay. As Jimengineer said, you need to be in phase and at the same frequency as the grid you are synching up to.

Basic devices you should have when connected all the time:
Ground fault protection
Over/undervoltage
Over current
Overspeed
Phase imbalance

Extra devices when connected to the grid:
Synchronous check (to get synchronized in the first place)
Reverse power
Instantaneous overcurrent - Possibly not needed
Frequency - This may not be required as well.

The best method of sychronizing would be to power your plant from the grid and synchronize only the generator. However, I agree it is ok be connected to the grid while it is also supplying the plant. In any case, you need to have a lockout device to be sure your generators voltage, frequency, and phase angle are in sync with the grid before it is closed on the line or it could damage your machine.

What size machine is the generator?



------------------------------------------------------------------------
If it is broken, fix it. If it isn't broken, I'll soon fix that.

 

[waross]

Is this a synchronous generator or an induction generator.
An induction generator is much cheaper and more forgiving and doesn't care very much about synchronization. It must/should be connected to the grid for voltage and frequency stability. It is not traditionally used for co-gen applications but if cost and simplicity is important it may be used for co-gen.
A synchronous generator or alternator will be able to supply all or part of your plant in the event of a grid failure. This would depend on the size of the generator relative to the plant load and the presence of suitable switching.
What size is the generator and what is the plant base load?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[BigIanH]

For more information on rules and regs for embedded power generation, check out G59/ETR113.
This will give lots of information.
Depending on the size of the alternator and also the requirements of the supply company, typically;

Under/over voltage.
Under/over frequency.
Vector shift.

These 3 are as a minimum in the UK.
Larger machines/HV alternators may require.

Neutral Voltage Displacement (NVD)
Directional overcurrent.
Rate of change of frequency (ROCOF).
Mains reverse power.

The genset should have a control system to protect against under/over voltage and frequency and preferably reverse power (motoring), the mains protection can be incorporated into the control system (such as a ComAp, Deep Sea or Woodward modular controller) but the majority of supply companys insist on a seperate stand alone protection module that has a direct trip contact to disconnect the generator from the grid within 0.5 seconds of a mains "disturbance".

I hope this helps, let me know if I can explain further.

Cheers.

 

[tareksabry]

it`s synchronous generator it`s power 15mw,also we have the device for auto synchronization,and also a protection device which have over voltage under voltage over freq. under freq. reverse power etc.but i want if anyone could tell me name or model no. of a certain device which protect the generator from power grid,when they are connected in parallel from any problem could happened in power grid then affect generator,

 

[davidbeach]

A 15 milliwatt generator, wow. Learn to write, please; proper capitalization, punctuation, complete sentences, etc. sure make it easier to read and understand what you might be trying to ask.

 

[slavag]

Hi.
for my pinion not bad relay for the LOSS OF MAIN protection

http://doc.seg-pp.com/doku.pdf/htl/mrg3/mrg3_gb.pdf

 

[cranky108]

davidbeach, give the guy some slack.
It's very common for non-native english speakers, so to speek, to misspell or understand the details in english.

 

[davidbeach]

I doubt there is any language that doesn't have rules of capitalization. Or, that does not have rules of sentence structure. Spell checkers (not particularly the problem at hand) are available for many languages. Quirks of idiom, verb/noun placement and the like are perfectly acceptable when working in a foreign language. Laziness in typing is not a useful trait when one is seeking specificity and reflects poorly on the thought processes of the writer.

 

[cranky108]

So how exactly does the spell checker work here?
Gee, the spell checker in word is much easer to invoke.

This is really a good forum, and I welcome reading about problems that I haven't stumbled into myself. And I perfectly understand that English can be difficult.

I also have problems with Kilo, is it with a "K" or "k". The lower case k just dosen't seem right.

 

[davidbeach]

Kilo as a prefix is always 'k', even though 'K' would be more in keeping with multipliers greater than 1 being upper case and multipliers less than 1 being lower case. Every rule has its exceptions.

I use Firefox and it has built in spell check as you type. There are add-on to allow spell checking if you is using IE. If I were trying to write in a foreign language I'd use Word and turn on the spell check for that language. It's not that difficult to spell check one's work if one actually cares about how things look.

 

[tareksabry]

i`m so sorry davidbeach what i mean it is 15 megawatt.(15MW)

 

[electricray]

Hi,

Siemens have a good protection relay Siprotec 7UM62 but there are a lot more. GE Multilin 789 is also a good and easy one. Futher there are relays from ABB and Beckwith.

And i can recommend you also a Rotor Earth Fault relay these things ar not so expensive and are easy and handfull.

 

[psprotection]

"A 15 milliwatt generator, wow. Learn to write, please; proper capitalization, punctuation, complete sentences, etc. sure make it easier to read and understand what you might be trying to ask."

I'm not sure why this type of criticism bugs me so much, but it does. Especially if it's from someone that doesn't really know what they are talking about, but likes the "image" of professionalism. I used to work for a mid to large electrical engineering consulting firm in which the president of the company was just this type. The more paper and "proper" termonology are the way to show how good you are. I read countless documents that basically said nothing or worse yet, were technically incorrect, but boy did they look professional.

For what it is worth, there is actually a document that specifies correct use of SI units. Check out this link if interested:

http://physics.nist.gov/cuu/index.html

 

[seymensaid]

Hi Tarek, I worked on a commissioning of a SEL 300G relay. You can download its manuel and find reasonable knowledge over protection of generators...

http://www.selinc.com/sel-300g.htm