314 Electrical Power Systems Technology
SCR Contactors
SCR contactors are electronic control devices designed to handle
large amounts of current. SCRs are triggered or turned on by pulses sup-
plied by the timing or sequencing circuits of the welder. The SCRs are
usually cooled by circulating water. The operating principles of SCRs are
discussed in Chapter 17.
ELECTRIC HEATING AND AIR CONDITIONING SYSTEMS
A very important type of electrical power conversion is that which
takes place in the heating and air conditioning systems of homes, indus-
tries, and commercial buildings. These loads convert a high percentage of
the total amount of electrical power that is furnished. Although natural
gas and fuel oil heating systems are still used, electrical heating is becom-
ing more prevalent each year. Air conditioning systems are also becoming
more commonly used to cool buildings. The use of electric heating and air
conditioning systems has made us even more dependent upon electrical
power. We now use electrical power to maintain a comfortable environ-
ment inside buildings.
Basics of Electric Heating
There are several important factors that you must understand in or-
der to have a knowledge of electric heating. Heat is measured in British
Figure 12-6. Block diagram of a typical electric welding system