Topic 01: Electrical Loads of the Past

All electrical loads prior to 1947 were non-solid-state loads – they used no electronic components in their designs. Basic electrical components were used. These components will be defined later in Lesson 1.

Four basic types of electrical loads were used in early electrical environments of customer facilities—residential, commercial, and industrial. These are listed below.

• Lighting loads – The first lighting loads were incandescent lamps which used a wire filament to covert electrical energy to light energy for illumination.
• Appliance loads – Appliance loads used electric motors inside the appliance to carry out the work: cooking, washing clothes, using a blender to make a cake. Some appliance loads also used heating elements if something needed to be heated like a stove eye to heat a pot of water and cold water to wash clothes. These loads were called linear loads because they had no electronic components. Many appliance loads contained on or more electric motors and one or more heating elements.
• Motor loads – Many appliances used simple electric AC motors that used brushes in residential electrical environments. Induction and synchronous AC motors were used in commercial electrical environments and industrial electrical environments. DC motors were used in some industrial environments. An example of a motor load used in all electrical environments is an electric fan.
• Communications loads – Communication loads were used by end users to listen to radio and television broadcasts and by fire departments, police departments, city / county / state governments to communicate between staff between offices and staff in the field. These loads used vacuum tubes for tuning and amplification. These loads typically used a large step-down power transformer to covert standard AC power (e.g., 120 volts) to lower and higher AC voltages that powered tube type rectifiers to covert AC power to DC power and tube type amplifiers to amplify audio and video signals. AC power at low voltage was used in the circuits to heat up the cathodes in vacuum tubes. DC power was used to bias (set) different parts of tubes to specific DC voltages needed to operate the tubes. These loads were called non-linear loads but did not use solid-state electronic components. All three electrical environments—residential, commercial, and industrial used vacuum tube-based communications loads.
  • Types of communications devices – all used vacuum tubes
    • Receivers – radios & televisions (TVs), starting with black & white TVs
    • Transmitters – radio & TV transmitters
    • Transceivers – devices that would transmit & receive

Definitions

Linear Load – an electrical load where the relationship between the voltage and current is constant, and the current at any time is proportional to the voltage. Additional information about linear loads will be introduced to you in Topic 2.

• These loads did not (and still do not) contain any electronic or solid-state components.
• One could predict how linear loads would operate when connected to building electrical systems (BES); thus, their behavior was predictable.

Non-Linear Load – an electrical load where the relationship between the voltage and current is not constant, and the current at any time is not proportional to the voltage. Additional information about non-linear loads will be introduced to you in Topic 2.

• These loads did not contain any solid-state electronic components.
• They did contain electronic components, because they used vacuum tubes[PK1] , which are considered electronic components. Most people didn’t think of vacuum tubes as electronic components, but they were since they controlled the flow of electrons in the tube and in a circuit with several tubes in it.
• One could also predict how non-linear loads (i.e., vacuum tubes) would operate for two reasons:
  • Energized components inside vacuum tubes were able to control the flow of electrons moving through the gas inside the tube. The gas inside the tube served as the “media” for the electrons to flow from one internal part of the tube to another internal part in the same tube. The gas also acted as a “cushion” for the electrons flowing through the tube. The “cushion” helped absorb changes in the AC and DC voltages and currents. Because of the gas, changes in the voltages and currents inside the tube didn’t cause the tube to experience damage and fail. Tubes were very rugged and could take quite a bit of “electrical abuse” from the electrical environment (i.e., customer facility) where they operated. 
  • A vacuum tube required a special heater (or heating coil) at the bottom of the tube to generate (or “boil off”) a lot of electrons, so they could flow easily through the tube.
  • Heating the coil required an AC voltage which was provided by a large step-down transformer which also helped protect the tube from disturbances in the BES that powered it.