294 Electrical Power Systems Technology
Synchronous Capacitor
Balanced Three-phase Load
Unbalanced Three-phase Load
Line Voltage (VL)
Phase Voltage (VP)
Line Current (IL)
Phase Current (IP)
Power per Phase (PP)
Total Three-phase Power (PT)
LOAD CHARACTERISTICS
In order to plan for power system load requirements, we must un-
derstand the electrical characteristics of all the loads connected to the
power system. The types of power supplies and distribution systems that
a building uses are determined by the load characteristics. All loads may
be considered as either resistive, inductive, capacitive, or a combination
of these. We should be aware of the effects that various types of loads will
have on the power system. The nature of AC results in certain specific
electrical circuit properties.
You should review that portion of Chapter 2 that deals with resistive,
inductive, and capacitive effects in an electrical circuit. One primary factor
that affects the electrical power system is the presence of inductive loads.
These are mainly electric motors. To counteract the inductive effects, util-
ity companies use power factor corrective capacitors as part of the power
system design. Capacitor units are located at substations to improve the
power factor of the system. The inductive effect, therefore, increases the
cost of a power system and reduces the actual amount of power that is
converted to another form of energy.
Load (Demand) Factor
One electrical load relationship that is important to understand is
the load (or demand) factor. Load factor expresses the ratio between the av-
erage power requirement and the peak power requirement, or:
average demand (kW)
load demand factor = ——————————
peak demand (kW)