"vector shift relay" or "rate of change of frequency relay" 1

[kobavr]

Hi everyone,

There is a cogeneration plant synchronized with the grid and there is coupling circuit breaker for connection to grid.
When grid further breaker opens, we want to trip the coupling breaker.
Which one of "vector shift relay" and "rate of change of frequency relay" can overcome this protection, or two of them?

Thanks in advance..

 

[MAS2000]

Your question is not clear. I believe you can have an inter-trip scheme to achieve this.


M.A.Sh.
Elect. Engr.

 

[iceworm]

How about just using a UV trip on the coupling breaker?

ice

 

[jghrist]

Phase displacement and rate of change of frequency can be used to detect islanding. See

http://www.supergen-amperes.org/Lib...nerators - A Comprehensive Survey Report.pdf.

The success rate depends on how close the islanded load is to the generator power output.

 

[iceworm]

How about just using a UV trip on the coupling breaker?

What was I thinking? The OP clearly said Cogeneration. Ignore my last

ice

 

[ScottyUK]

I believe that a correctly set vector shift relay can provide faster disconnection than a ROCOF relay, but that the latter is generally simpler to set up, especially if the system conditions are not accurately known.

An inter-trip is not appropriate because a loss-of-grid condition may occur as a result of numerous possible breaker trips and it is unrealistic to arrange an inter-trip from every breaker. Additionally not every breaker would necessarily require the embedded machine to trip in every circumstance, so the tripping logic would be come enormously complex.

 

[kobavr]

ScottyUK,

Once the grid shuts down, does any vector shift appear with generator voltage?
Somewhere I read that ROCOF relay is better for this situation

 

[Marmite]

The attached paper may be of interest. As JGhrist stated, the protection is usually used to prevent islanding, ie prevention of backfeeding the utility network. For this reason it is usually stipulated by the utility. Do you need your generator to trip when you lose the utility infeed, or remain connected servicing your site load?
Regards
Marmite

 

[ScottyUK]

That is a good paper Marmite. I'm much less familiar with protection of embedded machines on the distribution system than with the large central plant feeding the transmission system; large generating plant is generally expected to remain connected to the grid during severe disturbances, so the protection applied is very different. Thanks for the link.

 

[kobavr]

Marmite,

Generator will remain connected servicing the site load.

 

[iceworm]

There is a cogeneration plant synchronized with the grid and there is coupling circuit breaker for connection to grid.
When grid further breaker opens, we want to trip the coupling breaker.
Which one of "vector shift relay" and "rate of change of frequency relay" can overcome this protection, or two of them?

Once the grid shuts down, does any vector shift appear with generator voltage?

I can't help, I'm not familiar with either of the two relays. However, I watch over two plants with generation as well as a utility connection - so I'm very interested. So, a couple of questions that will make it easier for me to follow:
1. Does your plant always import power from the grid? Always export?
2. Are there operating scenerios where there is no power transfer across the grid connection CB - just floating - probably only for short periods?
3. When the grid goes down, is it normally open circuit (their CB direct to you opens)? Or short circuit (they open the line way up stream)?

ice

 

[DiscoP]

The voltage vector shift protection is faster than ROCOF, but normally less sensitive.

There are a few multifunction relays that include both protection elements - I have used the Alstom P341, but there is one from Basler and probably others too.

We use both elements of this relay on our generator tie circuits.

 

[slavag]

Siemens and Woodward/Seg protective terminals are included a both function.
Voltage shift is faster..about 40ms, ROCOF about 100-120ms, but voltage shift in not easier for setting.