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Startup of gas turbine with Emergency lube oil pump
Application Questions and Problems topic
Posted by ICENGR on 13 May, 2006 - 4:59 pm
Auxiliary Lube oil pump is not available, Can we start the gas turbine with the emergency lube oil pump and how? Our Gas Turbine Model is 5341, control system Mark- V <I> .

Please share your experience.


Posted by Rahul P Sharma on 14 May, 2006 - 4:33 pm
To my mind, this is quite a risky scenario... Emergency Lube Oil Pump is a DC Pump that runs on batteries.... I am not sure, how long can you keep it running if the batteries are old... If the Auxillary Lube Oil Pump fails to start, the 63QL Switch should actuate and automatically start the Emergency DC Pump...

A nightmarish instance could be as follows: Suppose the Turbine Starts and reaches FSNL... It's sustaining itself on MHOP (shaft driven Main Hydraulic Oil Pump)... But something happens and GT trips... The EHOP will have to start when the pressure begins to fall, but just bcos all the battery power would have been used up in the start up cycle, it's likely that it may not start in the shutdown sequence... Now you wont have anything to maintain the pressure.... If there was enough time between the startup and shutdown cycles, the battries could be recharged but what if it happens almost very soon...??

In our plant, the battery bank can support the EOP for roughly half an hour...

Regards
Rahul


Posted by ICENGR on 18 May, 2006 - 11:41 pm
Agreed, very much risk involved to start the GT with Emergency Lube oil Pump (ELOP). So far we never experienced this type of startup. But in case of total power failure, gas turbine will have to start with ELOP which is DC motor driven.

As far as logic of this pump which I have understood that if we start the TG with ELOP then on acceleration speed (14 HA Pick up) the ELOP will stop automatically which shows that the MHOP (shaft driven Main Hydraulic Oil Pump) will take over.

In case of tripping of TG, pressure switch 63QL actuates which starts ELOP and this pump keeps on running until the speed of gas turbine reaches at 1~3 RPM (14 HR pick).

On zero speed the ratcheting sequence starts in which ELOP, Rachect Motor 88 HR and 20CS SOV will energize for approx. 15 sec. after every 3 Minutes.

Now, the question is when the machine is on rest (zero speed). How can ELOP be started without bypassing any security so that 63 QT switch reset and permissive to start can be achieved from the 4 circuits or P core. Manual operation Switch is not available for the ELOP. How will ELOP will be started in black startup.

Regards,

IC_ENGR


Posted by markvguy on 21 May, 2006 - 3:55 pm
So, you've examined the CSP and discovered the minimal protection afforded during shutdown and cooldown in the absence of AC is present.

Units sold with Black Start capability have sequencing to drive the Emergency Lube Oil Pump for starting. In some cases the Emer. Lube Oil Pump speed od these units must be increased above rated in order to reset the 63QT pressure switches during starting.

Another consideration you have not mentioned is how the ignitors will be powered during a Black Start. They require AC, and units sold with Black Start capability are also supplied with inverters to power the Mk V <I>, CRT, Logger (dot matrix printer), AND the ignition transformers. Your first post asked about starting the turbine without the AC L.O. pump; now you are asking about how to start the unit under Black Start conditions....

If your Emer. L.O. Pump does not have a TEST (Manual) push-button and you do not have Black Start sequencing for the Emer. L.O. Pump and do not wish to have someone come to site to make the necessary modifications or cannot or do not wish to do it yourself, the simplest solution would be to install a Manual push-button on the Emer. L.O. Pump. These are usually spring loaded, and must be manually pushed in and held during operation--this prevents "accidentally" leaving the pump running.

This would require someone to hold in the push-button until the Main Lube Oil Pump (NOT the Main Hyd. Oil Pump) discharge pressure is sufficient (probably around 10% speed). This may also require adjustment of the Emer. L.O. Pump speed to pick up the 63QT pressure switches.

But, there's still the issue of how you will power the ignition transformers/ignitors without AC during Black Starting.... Again, if you want to use the <I> during Black Starting, you will also need to have power for the <I>, the CRT, and the Logger (to have a printed record of alarms). If the <BOI> is properly configured and personnel are trained in its use and familiar with it, the <BOI> could be used to start the machine. Most <BOI>s lacked the ability to initiate an Auto Synch or permit a Manual Synchronization.

Lastly, most Black Start units had special hardware to allow one Cooling Water Pump and one Cooling Water Fan to run during Black Start conditions. This is to allow a unit to be Black Started after a trip from a running condition. Without Cooling Water for the L.O. system, the L.O. Temp may get too high during such a re-start attempt and actually trip the unit.

So, you need to consider all the possible ramifications which might occur during a Black Start condition--if that's what you're really trying to do. It's not clear if you just want to start the unit with a failed AC pump/motor, or you want to start the unit during black plant conditions.?.?.? However, in either case you will need AC power for the ignition transformers/ignitors.

markvguy


Posted by IC_ENGR on 15 June, 2006 - 9:37 pm
Thank you very much MarkVguy for detail reply. Lot of information and new points for consideration.

Regards,
IC_ENGR


Posted by markvguy on 21 May, 2006 - 3:56 pm
There's one more feature which a Black Start-capable machine must have: the ability to safely close the generator breaker onto a "dead bus" (called, unsurprisingly, Dead-Bus Breaker Closure). To suppy a black plant or grid which has gone black, the generator breaker must be able to close without a grid (voltage/frequency) to parallel with/to.

Most generator breaker closure circuits require a synch check relay to allow breaker closure--even Manual Synchronization. Most synch check relays require voltage on the "load" side of the breaker in order for the relay to operate (zero crossing, grid frequency). So most Black Start-capable units have a separate means to select Dead Bus Breaker Closure to bypass the synch check relay permissive in the generator breaker closure circuit.

So, being able to run the ELOP to satisfy the Master Permissive circuit, having AC to power the ignitor transformer(s) and operator interface components are not the only factors to be considered for being able to use a unit to provide power in the event of a black-out--there's also the need to be able to close the generator breaker, and close it safely. There's usually a permissive from the Bus Undervoltage relay(s) to prevent accidental closure on a live bus (which would most likely be out-of-synch!).

markvguy


Posted by markvguy on 14 May, 2006 - 4:34 pm
Before you start the unit using the Emer. L.O. Pump, consider what you will do if the unit trips and there is no Aux. L.O. Pump to supply L.O. flow to cool the bearings and for Cooldown (Ratchet) operation.

One of the most important functions of the Aux. L.O. Pump during cooldown--either after a trip or a normal shutdown--is to supply L.O. flow to the bearings to cool them. Without that flow, the bearings material can be damaged if they absorb too much heat from the surrounding area and the shaft.

It is possible to use the Emer. L.O. Pump to start a heavy-duty gas turbine; many Black Start-capable units do so.

However, the really important situation is that if the unit should trip or be shutdown without an Auxiliary L.O. Pump, there will be no Aux. L.O. pump pressure/flow to cool the bearings when the unit reaches zero speed--or for the Cooldown (Ratchet) operation.

Many units had some sequencing to cycle the Emer. L.O. Pump periodically in such situations, and the Emer. L.O. Pump will usually come on when the D.C. Hydraulic Ratchet Pump motor cycles on. Does yours? Be sure it does!

However, some units did not have a D.C. Hyd. Ratchet, requiring the Aux. L.O. and Aux. Hyd. Pumps for ratchet operation.

Think long and hard about before starting the unit with the Emer. L.O. Pump and no Aux. L.O. Pump for cooldown/ratchet operation. It's the stopping--not the starting--that could end up being the real problem....

markvguy


Posted by Anonymous on 10 March, 2007 - 3:24 pm
What ELOP are you using?

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