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.