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What is the difference between kW and kVA?

 

The primary difference between kW (kilowatt) and kVA (kilovolt-ampere) is the power factor.  kW is the unit of real power and kVA is a unit of apparent power (or real power plus re-active power).  The power factor, unless it is defined and known, is therefore an approximate value (typically 0.8), and the kVA value will always be higher than the value for kW. 

In relation to industrial and commercial generators, kW is most commonly used when referring to generators in the United States, and a few other countries that use 60 Hz, while the majority of the rest of the world typically uses kVA as the primary value when referencing generator sets.

To expand on it a bit more, the kW rating is essentially the resulting power output a generator can supply based on the horsepower of an engine.  kW is figured by the horsepower rating of the engine times 0.746.  For example, if you have a 500 horsepower engine it has a kW rating of 373. The kilovolt-amperes (kVA) are the generator end capacity.  Generator sets are usually shown with both ratings.  To determine the kW and kVA ratio the formula below is used.

0.8 (pf) x 625 (kVA) = 500 kW

What is a power factor?

The power factor (pf) is typically defined as the ratio between kilowatts (kW) and kilovolt amps (kVA) that is drawn from an electrical load, as was discussed in the question above in more detail.  It is determined by the generators connected load.  The pf on the nameplate of a generator relates the kVAto the kW rating (see formula above). Generators with higher power factors more efficiently transfer energy to the connected load, while generators with a lower power factor are not as efficient and result in increased power costs.  The standard power factor for a three phase generator is 0.8.

What is the difference between standby, continuous, and prime power ratings?

Standby power generators are most often used in emergency situations, such as during a power outage.  It is ideal for applications that have another reliable continuous power source like utility power.  It’s recommend usage is most often only for the duration of a power outage and regular testing and maintenance.

Prime power ratings can be defined as having an “unlimited run time”, or essentially a generator that will be used as a primary power source and not just for standby or backup power.  A prime power rated generator can supply power in a situation where there is no utility source, as is often the case in industrial applications like mining or oil & gas operations located in remote areas where the grid is not accessible.  

Continuous power is similar to prime power but has a base load rating.   It can supply power continuously to a constant load, but does not have the ability to handle overload conditions or work as well with variable loads.  The main difference between a prime and continuous rating is that prime power gensets are set to have maximum power available at a variable load for an unlimited number of hours, and they generally include a 10% or so overload capability for short durations. 

What does an Automatic Transfer Switch do?

An automatic transfer switch (ATS) transfers power from a standard source, like utility, to emergency power, such as a generator, when the standard source fails. An ATS senses the power interruption on the line and in turn signals the engine panel to start.  When the standard source is restored to normal power the ATS transfers power back to the standard source and shuts the generator down.  Automatic Transfer Switches are often used in high availability environments such as data centers, manufacturing plans, telecommunication networks and so forth.

Can a generator I am looking at parallel with one I already own?

Generator sets can be paralleled for either redundancy or capacity requirements.  Paralleling generators allows you to electrically join them to combine their power output.   Paralleling identical generators will not be problematic but some extensive thought should go into the overall design based on the primary purpose of your system.   If you are trying to parallel unlike generators the design and installation can be more complex and you must keep in mind the affects of engine configuration, generator design, and regulator design, just to name a few. 

How do I determine what size Generator I need?

Getting a generator that can handle all your power generation needs is one of the most critical aspects of the purchasing decision.  Whether you are interested in prime or standby power, if your new generator can't meet your specific requirements then it simply won't be doing anyone any good because it can put undue stress on the unit and even damage some of the devices connected to it.  Determining exactly what size of generator to get is please via professional electrician to give exact calculate.

Common Wattage Guide

Item

Running Watts

Starting Surge

100 watt light bulb

100

100

Radio AM/ FM stereo

50-200

50-200

Radio CB

50

50

Fan

200

200

Television

300-400

300-400

Microwave oven

700

1000

Air conditioner

3250

5000

Furnace fan (1/3 HP blower)

600

1800

Vacuum cleaner

600

750

Sump pump (1/3 HP)

700

2100

Refrigerator/ Freezer

800

2400

Freezer

500

1500

6" circular saw

800

1000

Floodlight

1000

1000

1/2" electric drill

1000

1250

Toaster

1200

1200

Coffee maker

1200

1200

Electric skillet

1200

1200

14" electric chain saw

1200

1500

1/2 HP water well pump

1000

3000

Hot plate

1500

1500

Electric range

10000

10000

10" table saw

2000

6000

Hot water heater

5000

5000



What is AMF ?

AMF or (Automatic Mains Failure) is Mains failure detection, Generators with AMF consist a means of monitoring the mains and start when it detects that the Main Power has failed. It can be setup different ways. The WALT GLOBAL POWER Range is fitted standard with an AMF Panel, manufactured by Deep Sea Electronics. This is a PLC that monitors not only the incoming power but also the generator.


What is the best, Petrol or Diesel Generators?

Petrol Generators is normally high speed generators, this means that it runs at 3000 rpm. With this it is smaller, and lightweight, and easy to move around, some bigger models also have wheels. Another positive look is it is cheaper than most diesel models to buy. It is good for use as a manual generator for short periods of time. Maintenance is not too expensive for renowned brands. Petrol generators downfall is fuel consumption, especially on the larger models, also fuel storage, and it is also not too good for a petrol generator to be stored for a long period with fuel still in the carburetor, as petrol tends to gel and block the main jet. The carburetor than needs to be cleaned by professional personnel.

 

Diesel generators is ideal for automatic use, especially because of the diesel fuel, it is fuel injection and this means that starting is not a problem in a longer period. Generators needs to be started often, petrol and diesel models. Diesel powered generators is expensive, even the high speed generators. Diesel generators is fuel efficient. My opinion, if you can afford it, and your requirements is power generation for long periods, than diesel is the answer.


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