## Electrical Engineering

### DEFINITION’S:

The sum of all the loads connected

to the electrical system.

The ratio of the maximum operating load to the load connected to a
system. The demand factor is usually less than and cannot be
greater than unity.

The actual operating load in kilowatts of a system.

The demand load may be measured using a watt meter or calculated
by multiplying the connected load by the Demand Factor. For
electrical energy suppliers revenue metering purposes maximum
demand is averaged over a small increment of time, usually 30
minutes or sometimes 15 minutes.

The ratio of the sum of the demands on a system to the maximum
demand. The diversity factor is always greater than or equal to unity.

Load factor is the ratio of the average demand to the maximum
demand over a defined interval.

In most commercial office buildings, for example, between the
hours of 9.00 a.m. to 6.00 p.m. the load factor is usually close
to unity.

Active power is the time average of instantaneous power when the
average is taken over a complete cycle of an A/C waveform.

The active power when the voltage and current waveforms are
sinusoidal can be calculated by either:

- P = El cosΦ (single phase)
- P = El cos√3Φ (three phase)

Φ is the angular displacement between the voltage and current
waveforms and is known as the power factor angle. Cos Φ is
the power factor.

Apparent power is the product of RMS voltage and current - either:

- AP = El (single phase)
- AP = El Φ3 (three phase)

It is often the basis for rating electrical requirement. This
traditional definition is based upon sinusoidal waveforms. For
non-sinusoidal waveforms other characteristics of the voltage
and current waveshape may need to be considered when rating
equipment. For example, the peak voltage levels or current
levels may be considerably higher than for a sinusoid of the
same rms. value. These voltages and currents can contribute
to excessive insulation stress, thermal stress, etc.

Power factor can be defined as the ratio of active power,
(watts), to apparent power (volt amperes).

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