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azril83 (Electrical) (OP)
7 Jan 08 4:32
Good Day Guys,
Simple question from me. What can caused reverse power to Turbine-Generator? Can anybody give some explanations.

ScottyUK (Electrical)
7 Jan 08 7:51
What can cause reverse power? Usually something which cuts off the energy input to the prime mover while the machine is synchronised to the grid. When the prime mover ceases to drive the generator, the generator behaves as a synchronous motor and drives the prime mover as a load. Some prime movers do not respond well to this, notably steam turbines and diesel engines.

If we learn from our mistakes I'm getting a great education!

burnt2x (Electrical)
7 Jan 08 8:22

Reverse power - power is coming into the generator and driving it like a motor; instead of feeding power out to the system.
Causes: prime mover of generator (diesel engine, steam turbine,hydro-turbine) is not driving the generator - lesser drive steam in turbines; lesser water turning the hydro-turbine, or lesser fuel into diesel engine.
slavag (Electrical)
7 Jan 08 12:20
Only one!!!! reason.
Good design/commissioning of our partners from turbine controlsmile
slavag (Electrical)
7 Jan 08 12:21
BTW, Azril.
32.2 is possible only in case of signal "Main Steam Valve Closed"
azril83 (Electrical) (OP)
9 Jan 08 3:07
Thanks to all,
I knew how reverse power concept at turbine-generator i.e instead of generator drive the turbine but turbine drive the generator. What i really want to know is how this reverse power can happen at turbine-generator? as slavag said : 'Main Steam Valve closed'. What is other caused?
waross (Electrical)
9 Jan 08 7:33
No steam reaching the turbine for whatever reason. Faulty relays or incorrect connections may indicate reverse power in error.

"Why not the best?"
Jimmy Carter

hasi (Electrical)
9 Jan 08 8:21
Hi Azril,
A reverse power from other source can cause windings failure in the alternator if there is no safty device i.e. reverse power trip relay.
hasi (Electrical)
9 Jan 08 9:03
Hi Azril,
When a reverse power is applied to the turbine, the turbine's alternator will not become a motor as the phase angles of both sources may not be the same at that time. In that case heavy circulating current will damage the windins of the turbine's alternator.
burnt2x (Electrical)
9 Jan 08 10:34
1. Boiler abnormalities can cause turbine losing drive steam even with MSV at full open. Boiler trips that fail to trip dedicated turbine (1 on 1 setup)
2. Turbine Controls failing; operators ignoring annunciators; etc..

BTW, we always get turbine/generator trips when these things occur.
slavag (Electrical)
9 Jan 08 12:34
Two Burnt2x's points exactly explained last FAULT OF TWO 500MW units in our area.
First unit was off by boiler problem, second by operators mistakes.
I'm not so joke about our partners from turbine control, lot of reverse power trips from turbine control systems.
Once I found reason of reverse power trip( 25MW steam turbine) : one wire of voltage circuit was diconnected.
One of "good" example: 9 trips on one night, after retrofit of turbine control ( was fun ).
ScottyUK (Electrical)
9 Jan 08 13:32
Is this confined only to steam turbines? Gas turbines: loss of fuel supply or failure of the main fuel valves.

A universal one is a unit trip due to suprvisory instruments on the turbine combining with failure of main breaker to open due to a protection failure or a tripping battery fault, etc. This is usually a very serious problem for the turbine.

If we learn from our mistakes I'm getting a great education!

dpc (Electrical)
9 Jan 08 14:55
Many large steam turbines routinely use a reverse power relay for normal shutdowns in order to prove that the main steam valve is indeed closed.

I saw a small steam turbine that almost flew out of the building when the generator breaker was opened on a normal shutdown, but the main stop valve wasn't actually closed, although its limit switch thought it was.  The insurance company bought them a new T-G.  

It's also fairly common to see a reverse power trip right after synchronizing if the operator doesn't pick up some load soon enough.  To protect the LP section of a steam turbine, the 32 device must be extremely sensitive and set to pick up at very low power levels compared to the normal forward power.  When using the normal Generator CTs and PTs, this power level requires an extremely low setting and CT ratio and phase angle error become an issue.     
slavag (Electrical)
9 Jan 08 15:07
For big steam turbine ( from 200MW), for reverse power functionality, we used only CT meas. class, it must. Seeting about 0.5% of Pnom.
DPC, remind very important point. I see in new turbine (w/o name), instead main steam valve limit switch some calculation of flow and data from several sensors, for my pinion not so good solution.
Against operators problem, we used " wait time"  solution, block of reverse power protection for some time after CB close position.
ScottyUK (Electrical)
9 Jan 08 15:10
Expanding a little on dpc's post, current flowing due to reactive load when there is very little real load on the generator may appear to the relays as real power due to phase shifts caused by the instrument transformers. This can make the reverse power relay mis-operate even though the actual power flow is zero or slightly positive.

If we learn from our mistakes I'm getting a great education!

slavag (Electrical)
9 Jan 08 15:16
I used this small reactive load for check direction of reverse power in case of generator-trafo block, of course in case of CT meas. class. Work fine.
burnt2x (Electrical)
9 Jan 08 19:51
We had one of our units, a 350MW (of a 2X 350MW plant) running afloat (not delivering power) for one hour! Guess how many heads rolled from the optn group! People doze off, they were sent home to sleep longer and never let back to work.
High inertia of the big unit just kept the thing turning with just a little incoming power. The equivalent in-house load was the only forward power flow from that unit, hence no reverse power.
dpc (Electrical)
9 Jan 08 19:55
The newer multi-function relays also have "Low Forward Power" function in addition to Reverse Power.
slavag (Electrical)
9 Jan 08 22:30
I can surprise you.
ABB REM543/5 made in Finland have 3 stage of underepower function,that possible config as low-forward and reverse power:
The primary application of the function block is the reverse power protection (Operation mode = reverse power) of the prime mover of a generator. The function is necessary for the following types of prime mover:
• steam turbines
• Francis and Kaplan hydro units
• gas turbines
• diesel motors
The function block can also be used for forward power monitoring (Operation mode = underpower). In case of parallel connected generators for example, the load of one generator may be so low that it is better to disconnect it and let the remaining generators feed the network.
And ABB Swiss series RE216/316, where possible add to relay
I don't know ten time power functions and free configurable each one for the:
• reverse power
• active power
• reactive power
• power direction
And new ABB SWeden REG670 relay with 4 stage of underpower functions.
slavag (Electrical)
9 Jan 08 23:42
DPC sorry,
I don't read your post right.
Don't pay attention on the my previuos post.
jamjaem (Mechanical)
10 Jan 08 15:47
Reverse power to a generator may also occur when a generator's breaker is closed inadvertently when aligned to an energized switchyard - of course proper procedure and protective devices should prevent this from occurring, but believe me, it does occur.   
slavag (Electrical)
11 Jan 08 3:49
I believe you.
Problem is reverse power operated in this case. 50AE ( or dead generator, or other terms) must be operated before.
ReidC (Electrical)
11 Jan 08 23:44
32-1 normally reserved for "sequential trip" meaning that the turbine generator breaker will open if the sequential trip is enabled, all steam turbine port stop valves are closed, time delay is met (3sec or so typ.)  As mentioned in another post, this is typically how a steam turbine is normally shut down

32-2 typically emergency trip of generator breaker after predetermined time delay after sequential trip is enabled.  I have seen around 30 sec however different sized machines should have different settings.
dapotiti18 (Electrical)
12 Jan 08 6:48
Hi Azril,
  Base on my own working experience,the causes of reverse power in turbine generator can be attributed to:
   1. improper position / incorrect polarity wiring of C.T
       in the generator or generator sychronization
       panel to reverse power relay( it happen in a   
        newly install generator or panel) can been experience if one of generator in   
      synchrization have a decrease voltage and frequency  
      discrepancy, which will resulted to the generator to
      work like motor, also affect direction of flow  
      current in primary and secondary side of c.t and it
      resulted to reverse power fault.
rovineye (Electrical)
15 Jan 08 16:48
I guess another cause of reverse power trip could be speeding up of a machine in parallel.
 I get that at times when commissioning diesel generator sets, and they are lightly loaded. One can speed up while adjusting governors and cause a reverse power trip (or reverse kVAR trip) on the other generator before the first reaches overspeed.
azril83 (Electrical) (OP)
5 Feb 08 3:00
thanks guys for very valuable info from each of you. very much appreciate.

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