Electrical Engineering


Connected Load:

The sum of all the loads connected to the electrical system.

Demand Factor:

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.

Demand Load or Maximum Demand:

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.

Diversity Factor:

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:

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 (Real Power):

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:

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:

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

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:

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


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