Powerfact Book - Electrical Terminology Basics

Voltage Current & Power

Electricity

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There are basic several components that need to be clearly understood in order understand electricity and how to quantify it.

Voltage and Current

VOLTAGE:
- Also known as electromotive force (EMF), is electrical “pressure”, measured in Volts with the symbol V or E.
CURRENT:
- Electrical “flow”, measured in Amperes and has the symbol I (for intensity of charge flow)
DIRECT CURENT (DC):
- Where the voltage and current are uniform and do not change direction.
ALTERNATING CURRENT (AC):
- Where the voltage and the current alternate regularly in direction and value.
FREQUENCY:
- Measured in Hertz, it is the number of cycles the voltage makes in one second.

Power

POWER (DC):
- Measured in watts, it is the amount of electrical work. It is equal to the voltage times the current. P = V x I
POWER (AC):
- There are 3 components of ac power:
  - Apparent power or total power supplied is measured in VA.
  - Active power, power used, or “real” power is measured in Watts.
  - Reactive power or “imaginary” power is measured in VARs (Volt Amp Reactive).
POWER FACTOR:
- Ratio of the active power to apparent power. (Power used divided by power supplied). Since the power used can never be more than the power supplied, the power factor can never be greater than 1.

The difference between installed capacity and generation is critical to understanding how to quantify electricity.

elec term basic 02a

Installed capacity

Installed capacity is measured in kW, MW, GW or TW

Installed capacity refers to the amount of electricity a power station can supply at any given point in time.
- A 600MW coal power station can deliver up to 600MW of electricity when it is at full power. If demand drops, then the power station can reduce the amount of electricity delivered.
- A 600MW solar farm can deliver up to 600MW in full sunshine, no clouds & at their optimum angle.

Demand

Demand (or load) is measured in kW, MW, GW or TW

Demand is the amount of electricity required or being used at any given time.
- If one air conditioning (AC) unit is 5kW when at full power, its demand is 5kW.
- 20 5kW AC units all on at the same time would have a demand of 1,000kW or 1MW. The grid would need to deliver that capacity.

Electricity generation

Electricity generation is measured in kWh or MWh or GWh or TWh

Generation is measured as the amount of electricity produced (and therefore consumed) per hour over a period of time.

Electricity consumption

Electricity consumption is measured in kWh or MWh or GWh or TWh

When a user consumes, or “demands” energy, the generators must make sure that capacity is available.
- One 100-watt light bulb turned on for 10 hours consumes 1,000 watt-hours or 1 kWh. The entire time it is on, it demands 100 watts or 0.1 kW from the Utility.
- That means the utility must have that 0.1 kW ready whenever the user turns the light on.
- Similarly, ten 100-watt light bulbs on for 1 hour consume 1,000 watt-hours or 1 kWh.

Terminology