Question 1

GENERATOR POWER RATINGS EXPLAINED: PRP, LTP, ESP, COP

Accepted Answer

PRP – Prime Power is defined according to ISO8528-1 as the maximum power output that a generator set can produce continuously when connected to a variable load for an unlimited number of hours a year if the maintenance intervals and procedures are being carried out as prescribed by the manufacturer. A prime-rated generator set is limited to a 24-hour average load factor of 70%, if not stated otherwise by the manufacturer.

LTP – Limited Time Power is defined according to ISO8528-1 as the maximum power output that a generator set can produce for up to 500 hours a year if the maintenance intervals and procedures are being carried out as prescribed by the manufacturer.

ESP – Emergency Standby Power is defined according to ISO8528-1 as the maximum power output that a generator set can produce when connected to a variable load for a maximum of 200 hours a year if the maintenance intervals and procedures are being carried out as prescribed by the manufacturer. An ESP-rated generator set is limited to a 24-hour average load factor of 70%, if not stated otherwise by the manufacturer.

COP – Continuous Power is defined according to ISO8528-1 as the base load power output that a generator set can produce at a constant load for an unlimited number of hours a year, if the maintenance intervals and procedures are being carried out as prescribed by the manufacturer.

Question 2

EXHAUST EMISSIONS

Accepted Answer

According to legislation within the EU, all generator sets that are subject to movement at least once a year and are below 560kW of mechanical power output from the engine must fulfill the demands in EU Stage V emission requirements. If the generator set isn’t subject to movement, all stationary gensets as an example, the generator set doesn’t have to comply with EU Stage V.

Question 3

FUEL, FUEL CONSUMPTION AND FUEL SYSTEMS

Accepted Answer

The most used fuel in Sweden for backup power is environmental diesel HVO100. If you are to use any other type of diesel fuel for your backup power, please be careful and check with the vendor if that fuel type is approved, you may experience power deterioration and/or shortened service interval.

As a rule of thumb, a generator set uses 0.25 liters an hour and electrical kW produced.

When discussing the fuel system that you as a customer want to be installed with your backup power the first thing to consider is the running hours that you require, without the need for refueling.

If you have a small generator set and/or a low number of running hours needed, it is normally sufficient to install a day fuel tank within the room/container. If you have a larger generator set and/or require a high amount of running hours, we recommend installing a day fuel tank and an external fuel storage tank. The generator set is connected to the day fuel tank, which is filled from the external fuel storage tank. Filling of the day fuel tank is handled by a fuel transfer pump system. Our fuel transfer pump system is fitted with dual pumps and a control system making the system redundant.

Normally all our fuel tanks are installed with a spill tray or dual-walled.

Question 4

VENTILATION AND COMBUSTION AIR

Accepted Answer

The generator set requires larger openings for ventilation and combustion air than expected. A generator set with a direct-driven fan and radiator mounted to the base frame has been fitted with a fan big enough to produce enough cooling air both for the engine cooling and the ventilation of the heat rejection to the room.

The amount of air the fan pushes over the radiator plus the amount of combustion air the engine needs is the total amount of air that you must transport into the room/container over the air inlet openings.

Generally, when calculating the needed openings, we calculate using a maximum speed over the inlet grills and louvers set to 4 meters a second. By not exceeding this airspeed you will prevent snow, water and dust to be sucked into the room/container. You also must remember to adjust your numbers according to the grill's flow-dampering specifications. Normal grills reduce the free opening by 35% and a sound-proofed grill reduces the opening by 75%.

The outlet air opening is normally the same size as the radiator. The outlet air can have a higher air speed thus giving the advantage of smaller openings. But it always is necessary to calculate the back pressure over the fan. If you have a back pressure higher than approved by the vendor, you might experience a reduction in power output from the generator set.

When using coolant coolers with your generator set, the aspiration of the engine is important to have in mind. If you have a water-cooled aspiration you only have to fit that cooling circuit with a coolant cooler, but if you have an air-cooled aspiration you most likely will need to install a heat exchanger. A heat exchanger might be needed if the distance and/or the lifting height is too big to handle for the engine's internal water pump.

If you are using coolant coolers the heat rejection to the room still needs to be ventilated from the room and the engine still needs combustion air. The air inlet openings will be significantly smaller and the air outlet opening normally is small and fitted with a frequency-adjusted fan.

Question 5

TESTING THE GENERATOR SET

Accepted Answer

How often and how to test your generator set depends on the type of solution you have and which test function you have at your disposal. Some of the test functions will affect your daily operation and that might limit your opportunities to test your backup power.

The start test is the simplest test to perform. If you perform a start test the generator set will start but it will not control any breakers or connect the generator set to the load/grid. This test will make sure your generator set will start if needed and it checks the most common source of a failure, the batteries. Since you are not loading the generator set these tests should only be performed once a week and max. for a couple of minutes.

Load take-over is a test where the generator set starts and, if fitted with synchronization, will synchronize to the grid and disconnect the incoming feeder from the grid. The generator set is now feeding the load. This test will test all involved components, such as the generator breaker and the mains breaker, and since the generator set is loaded it will reach normal running temperature. Hence, everything will be tested, and your daily operations will most likely not be affected.

In parallel with the grid is almost the same as a load takeover, but instead of disconnecting the incoming feeder, the generator set stays in parallel mode. At this point, you can adjust the power output from the generator set. If the generator set produces more power than the load consumes the excess power will be fed out to the grid. Be sure to inform the grid owner that you will perform the test as you need approval from the grid owner.

Simulated mains failure is the best test to perform, if you can allow a short blackout on the load. The test is initiated from the control system, just like all the other tests, and it will simulate an error on the incoming mains. The generator set will start up, disconnect the incoming feeder from the grid and connect to the load. The complete chain of events will be exactly as an actual mains failure.

If you use the tests mentioned above and you perform your tests according to the recommended test interval instructions delivered with our solutions, you can be confident that your system will work when needed.

Question 6

CONTROL SYSTEM

Accepted Answer

The control system is the brain of your backup power system. In automatic mode, the control system will perform as expected in case of a mains failure and in manual mode you can control the chain of events. Today most control systems are based on a standard control panel from a vendor that has built and tested the panels to work as intended. The only thing we must do is to adjust it to fit the customer's needs and requirements.

When creating a control system, it's important for the end user to clearly state what type of solution they require and which functions and tests they need. For instance, do they need automatic mains failure start? Is it necessary to synchronize to the grid? Should the system communicate with a BMS (Building Management System)?

Please contact us for further help or information.

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