Underload Generators?
Underload Generators?
(OP)
We have 3 gensets used as back up in a high rise building. 2 gensets were tagged as prime power at 1.6MW each rated capacity. The other is at 1MW rated capacity and plated stand by. Our billing from the power utility suggested a 3.5 MW demand (max) last month and the building is 80% occupied. Our technical group has audited the power system and concluded that the generators are not sufficient in running the building, which is quite contradicting with the utility provider's billing. We have synchronization panels & load sharing equipment to evenly distribute the load. My questions are:
1. Can we run the prime power to 110% its capacity? Is this be possible? Dowe need to purchase another generator based on the details above?
2. Is it safe to assume that our utility provider has left some switchgears unmetered (i know this sounds funny)? Can we rely on their billing or just ask them to make an audit themselves to verify our findings?
3. How do we go about a full scale power audit in a typical building? Has anyone done this? Any tips?
Thank you.
1. Can we run the prime power to 110% its capacity? Is this be possible? Dowe need to purchase another generator based on the details above?
2. Is it safe to assume that our utility provider has left some switchgears unmetered (i know this sounds funny)? Can we rely on their billing or just ask them to make an audit themselves to verify our findings?
3. How do we go about a full scale power audit in a typical building? Has anyone done this? Any tips?
Thank you.






RE: Underload Generators?
Standby rated sets may be identical to prime rated sets except for the ratings. However in the larger sizes the prime rated sets may have options fitted to the engine to facilitate continuous running at high loads. Some common options may be larger oil sumps and oil coolers.
The engine will be over sized to allow loading above nameplate rating. The same engine may, in some instances, be used for standby sets. The engine may have the power output "turned down" during the manufacturers load test.
Metering.
Utility metering is commonly done at one point of the supply, rather than on individual feeders.
However, if the tenants are metered individually there is a possibility that some feeders may have been accidentally or intentionally missed on the metering scheme.
3.5 MW demand on an 80% occupied building suggests a demand of 4.375 MW with full occupancy, but such a simple extrapolation is very unreliable. Based on an admittedly unreliable extrapolation the 1.6MW+1.6MW+1Mw=4.2
MW capacity is low.
Prime rated sets allow 10% overload for defined durations. Typically one hour in ten hours.
Standby rated sets do not allow overloading.
Your numbers are so close that a complete power survey is probably required. The survey should include an allowance for full occupancy.
You may consider a N+1 scheme. This may be 3 x 1.6 MW sets for a total capacity of 4.8 MW. A fourth 1.6 MW set would be installed for reliability. In some plants the "+1" set is available, in some plants all 4 sets will be operated together so that the failure of any one set will not cause an outage.
respectfully
RE: Underload Generators?
RE: Underload Generators?
RE: Underload Generators?
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Underload Generators?
1. If they cook something they should turn of air conditioning and water heat boilers.
If you take those 3 consumers you will see that they are taking 60% or more of each flat consumption. If people are aware of problem and know what to do they will comply willingly. Even if there is % of people that will not comply you will have your load at 80% or less in emergency if you send each tenant a bulletin that costs 1cent or less
RE: Underload Generators?
RE: Underload Generators?
Power factor correction
thread238-195278: Power factor correction
its recent.
And you can get the reading with power meter, you measure, active and reactive power from consumers, than you get angle from that calculus P/Q=S*ctg(f) -> arc(ctg(f)) is a phase angle you need to know, after that you just calculate cos(f) genset power factor should be known from SCADA system, and maybe it can even calculate consumer consumption. If you have any measurement for power company for few MV object you should get that data about pf from that device (Simeas P for instance has that monitorings built in)or from power company.
RE: Underload Generators?
Typically, the demand determined by the engineers will be considerably higher than actual because not enough diversity is considered. Utilities sometimes use a factor of 30% - 50% of service entrance size to size transformers for commercial customers.
Providing full backup power for a calculated maximum demand could be very expensive. Better to leave some interruptible loads off of the backup system or use some load shedding scheme on selected feeders. Leaving some loads off may not be feasible without extensive changes in switchgear. Maybe underfrequency relaying could be applied to some feeders for load shedding, coordinated with the generator protection.
RE: Underload Generators?
Our average demand is at 3.2MW spread over a year. It is still safe to say that it is within capacity. But with tenants moving in at a faster phase, we might hit 100% occupancy by mid 2008, which is our worry right now. We can do load shedding, great idea, but you know tenants. They just get in your nerves when they see a small portion of their units not being lit. In any case, we need to identify areas where we can shed some in case of emergency.
Any methodology and checklist for power audit... anyone? Thanks.
RE: Underload Generators?
RE: Underload Generators?
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Underload Generators?
110% is possible, but not suggested. Most generators have some headroom, but you may have warranty issues.
2. Is it safe to assume that our utility provider has left some switchgears unmetered (i know this sounds funny)?
You can put a recorder on the service and get a better idea of your power useage. Most people don't understand utility billing (kwh) and instant kw fluxuations.
3. How do we go about a full scale power audit in a typical building? Has anyone done this? Any tips?
I would put a KW recorder or electronic metering package that will track this information for you.