Blackstart Generator

[Belshazzar]

Hello everyone. I'm a newbie here. I am currently studying the possibility of inserting a blackstart generator to the existing system as shown in the photo.In doing this , I will be back-powering the aux transformer through its secondary winding and at the same time supplying the AUX BUS for the plant startup when the grid is not available. The delta winding goes to the plant's main generator transformer delta (not shown) and during blackout , is at high impedance state (open HV). The tertiary Y goes to an 11.5MW unity power factor consumer that is required during startup. Granting that my new generator can meet the required startup power, what is the impact on the existing protection at the secondary side (BSDG side)? Any modifcation required on the existing or shall I just define a new set of protection together/coordinated with that of the blackstart generator? Thank you.

 

[ATSman]

Sketch

Sketch

Can you send a revised dwg?
Cannot read it even after zooming 200%

 

[Belshazzar]

 

[Bugman1400]

Your wye system seems to be resistive grounded while your BSDG is not. You'll need to change that and ensure you have OV protection or sensitive ground protection. Secondly, you'll need to ensure your BSDG breaker can handle the full fault availability and that it is coordinated with upstream protection for a fault in the BSDG. You'll also need to check that your existing breakers on other ckts can handle the added BSDG fault current.

 

[topgone]

Your wye system seems to be resistive grounded while your BSDG is not. You'll need to change that and ensure you have OV protection or sensitive ground protection. Secondly, you'll need to ensure your BSDG breaker can handle the full fault availability and that it is coordinated with upstream protection for a fault in the BSDG. You'll also need to check that your existing breakers on other ckts can handle the added BSDG fault current.

Do you mean to say the units will be connected in parallel for some time?
IMO, if the emergency unit is small compared to the system capacity, I doubt the fault current available will be larger.

 

[Bugman1400]

Do you mean to say the units will be connected in parallel for some time?
IMO, if the emergency unit is small compared to the system capacity, I doubt the fault current available will be larger.

The idea is that, in absence of any onsite (station service) power, you can bring the unit up on the BSDG and then xfer over to the unit aux xfmr. Perhaps the xfer is done with a break-before-make switch and the two would never intertwine but, the OP did not clarify that. In absence of that important note, I assumed the BSDG could potentially run in parallel with the main unit for a short time.

 

[ATSman]

The idea is that, in absence of any onsite (station service) power, you can bring the unit up on the BSDG and then xfer over to the unit aux xfmr. Perhaps the xfer is done with a break-before-make switch and the two would never intertwine but, the OP did not clarify that. In absence of that important note, I assumed the BSDG could potentially run in parallel with the main unit for a short time.

Short Time ? can you be more specific? With closed transition ATS's we are talking in the range of hundreds of millisecs,
surely less than a sec.

 

[Belshazzar]

Thank you all for a very wonderful discussion. I am just collecting ideas/scenarios and yes the discussion already provided some. This plant (CCGT) has the capability to run in island mode but lacks the facility to boot itself in the event that the HV system (230kV) is not available , hence the idea of a blackstart generator. I am planning to put a 25MVA package generator and sorry I used BSDG in the figure as I assume its a generic system, but it is actually a package gas turbine generator unit and not a diesel engine driven one. Bugman1400's assumption to run the main generator in parallel with BSDG/BSTG is right.The transfer of load is supposedly glitch-free because we will utilize bus sychronization techniques. The plant is huge such that the auxiliaries alone requires around 10MW and roughly 21.5MW during startup (the 11.5MW alone is for the Static Startup Device) . Once the transfer from BSDG is complete and the main generator already supplies the whole plant, it can be quickly synched back to the grid once the 230kV becomes available. I didn't mention what we have two points for the main generator to be synchronized to the grid. One is thru the 230kV breaker with the GCB already closed and plant is running (as in my case) the other is through the GCB where the 230kV side is closed and available , which is the default.

 

[Bugman1400]

Short Time ? can you be more specific? With closed transition ATS's we are talking in the range of hundreds of millisecs,
surely less than a sec.

Why would you think we're talking about an ATS for 4160V? I'm sure they probably make them but, I've never seen one in a plant at that voltage. I typically see some type of relaying or other control scheme that makes the switch.

 

[Bugman1400]

Thank you all for a very wonderful discussion. I am just collecting ideas/scenarios and yes the discussion already provided some. This plant (CCGT) has the capability to run in island mode but lacks the facility to boot itself in the event that the HV system (230kV) is not available , hence the idea of a blackstart generator. I am planning to put a 25MVA package generator and sorry I used BSDG in the figure as I assume its a generic system, but it is actually a package gas turbine generator unit and not a diesel engine driven one. Bugman1400's assumption to run the main generator in parallel with BSDG/BSTG is right.The transfer of load is supposedly glitch-free because we will utilize bus sychronization techniques. The plant is huge such that the auxiliaries alone requires around 10MW and roughly 21.5MW during startup (the 11.5MW alone is for the Static Startup Device) . Once the transfer from BSDG is complete and the main generator already supplies the whole plant, it can be quickly synched back to the grid once the 230kV becomes available. I didn't mention what we have two points for the main generator to be synchronized to the grid. One is thru the 230kV breaker with the GCB already closed and plant is running (as in my case) the other is through the GCB where the 230kV side is closed and available , which is the default.

Would like to know more about the Static Starter. I've seen a 4160 motor used to start the CT via the accessory drive but, not sure what a Static Starter is. Perhaps the alternative to a BSDG or BSTG is to use a 454 big block w/ a Holley 4 barrel carb like we did in the old days for simple cycle CTs. All you needed for that was a couple of car batteries and a few gallons of gas!

 

[ATSman]

Why would you think we're talking about an ATS for 4160V? I'm sure they probably make them but, I've never seen one in a plant at that voltage. I typically see some type of relaying or other control scheme that makes the switch.

Bugman
This could be a matter of semantics.
Stand alone vs contactor design. Up to 12KV transfer schemes are very common. The only difference is that at higher voltages they employ typically MV vacuum breaker pairs ( air switches in some cases) instead of the contactor type to switch the load used by ASCO, Russelectric,Cummins, Kohler, GE-Zenith, etc
Some utilities use solid state ATS systems that I hear are in the 34.5KV range.

 

[Belshazzar]

Would like to know more about the Static Starter. I've seen a 4160 motor used to start the CT via the accessory drive but, not sure what a Static Starter is. Perhaps the alternative to a BSDG or BSTG is to use a 454 big block w/ a Holley 4 barrel carb like we did in the old days for simple cycle CTs. All you needed for that was a couple of car batteries and a few gallons of gas!

Ok, there is actually no need to modify anything on the current startup system, All I need is a startup power as it does not only address the startup device requirement but also the power required by the auxiliaries. The static startup device is a Static Frequency Converter , its a gigantic VFD. Huge thyristors are connected to my tertiary -Y, rectify the 3-phase voltage into DC and filter it with another gigantic forced air-cooled inductors. After smoothing, the filtered DC is converted back to a 3phase AC using Pulse Width Modulation technique and another set of thyristors to accomplish switching - at a desired frequency . That's it. It drives the Synchronous generator as a motor (of course I need the static excitation system also). The speed of the "motor" is dependent on the frequency and as required by the gas turbine. If I am not mistaken , ours is the biggest class (11.5MW) manufactured by ABB , so far.

 

[Belshazzar]

Bugman
This could be a matter of semantics.
Stand alone vs contactor design. Up to 12KV transfer schemes are very common. The only difference is that at higher voltages they employ typically MV vacuum breaker pairs ( air switches in some cases) instead of the contactor type to switch the load used by ASCO, Russelectric,Cummins, Kohler, GE-Zenith, etc
Some utilities use solid state ATS systems that I hear are in the 34.5KV range.

I agree. besides, vaccum breakers, etc. are nothing without the relays that actuate them when necessary. Workplaces have different terminologies but connote the same function for a given equipment. In our case for instance, the BUS COUPLER performs the function of the ATS such that when one bus losses power as long as it is not Bus fault, it will be transferred to another bus through the BUS COUPLER but this is actually a vacuum CB @ 6.6kV