Electricity Power/Energy Basics:
•In US household electricity is 120 volts AC –
60 cycles (therefore most appliances and
electronic equipment require this type of
Actual voltage with time in a 120 volt 60 cycle system
Effective voltage of the AC power system is 0.707 times
the peak voltage. Peak voltage is about 170 volts. Thus
the 120 volts is really an effective voltage. Effective
voltage is sometimes known as the rms (root mean
Reasons for Alternating Current:
•Electromechanical generators produce alternating
•Less energy loss in transmission lines if power (P) is
transmitted at higher voltages (V) and lower
current(I). Lower current yields less power loss (Pl).
Pl = I2 x R (R = resistance in transmission line).
•Voltage can be altered by transformers only for AC.
For example to lower transmission voltages
(e.g.,345Kv) to 120 v for household use.
The frequency of generation (60 cycles per
sec) is a function of the generator rotator
speed. Why 60 ? Why not 50 as in
Europe? Historians suggest that 60 was
selected so some clocks could be
synchronized with this frequency ( 60
sec/min, 60 min/hr???).
Converting DC to AC
Simple inverter (top = mechanical switch,
bottom = transistor switch)
Converting AC to DC
Full- wave rectifier:
Using capacitors and inductors we can
level the voltage output of a rectifier:
A capacitor opposes changes in voltage
An inductor opposes changes in current.
The following circuit can be used to level
the voltage output
A typical capacitor input filter consists of a filter
capacitor C1, connected across the rectifier
output, a choke L in series and another filter
capacitor connected across the load.
The capacitor C1 offers low reactance to the AC
component of the rectifier output while it offers
infinite reactance to the DC component. As a
result the capacitor bypasses an appreciable
amount of the AC component while the DC
component continues its journey to the choke L.
The choke L offers high reactance to the AC
component but it offers almost zero reactance to
the DC component. As a result the DC component
flows through the choke while the AC component
The capacitor C2 bypasses the AC component
which the choke had failed to block. As a result
only the DC component appears across the load.
Filtering the full-wave rectified signal using capacitors
(capacitor effect indicated by red lines) yields the
Existing electrical power sources:
2 - 68 kW Caterpillar generators
1 - 30 kW Detroit generators
Output = 480 volts
480 volts used for saltwater pump and reverse
osmosis, Voltage stepped down to 120/240 for other
For future comparison purposes average diesel
fuel consumption per capita by generators:
(This translates to $0.20 – $0.25/kW-hr)
Average Generator Capacity Utilization over a Day
Power Used (kW)
10:15 AM 4:15 PM 10:15 PM 4:15 AM 10:15 AM