Transformers and Current Types

Study Notes

Dry type transformers are a common type
Askarel Insulated transformers use a synthetic non-flammable liquid for insulation
Oil Insulated transformers are installed in a fire rated transformer vault unless the capacity does not exceed 112.5 Kva

Direct current flows at a constant rate in the same direction
Alternating current periodically varies in time rate and direction
- A cycle is a complete set of changes in alternating current
- The frequency of the current is the number of cycles per second, measured in Hertz
- The frequency of lighting is typically 60 Hertz while motors may use 25 Hertz

Coulomb is the unit of electrical quantity, representing 6.25 x 10^18 electrons
Ampere is the rate of flow of one coulomb per second, or 6.25 x 10^18 electrons/second
- Ampacity is the current carrying capacity of a wire or cable measured in Amperes
Volt is the unit of electric potential difference between two points
Ohm is the unit of resistance, allowing one ampere of current to flow when one volt is applied
- Resistance is abbreviated as R in direct current circuits
- Impedance, abbreviated as Z, is used in alternating current circuits
Watt is the unit of electric power, which is the rate at which electrical work is done
- One kilowatt is equal to 1,000 watts
Watt-hour and kilowatt-hour are units of electrical energy, which is the capacity for doing work

Current (I) is directly proportional to voltage (V) and inversely proportional to resistance (R)
I (amp) = V (Volts) / R (Ohms)
Key equations:
- W (Watts) = I^2R or VI
- Whr = I^2R t
- KWhr = I^2Rt/1000

Effective utilization of energy by reducing peak loads and lowering demand charge
Load shedding control, peak demand control, peak load regulation, and power use control are all examples of load control systems

Electric loads are analyzed and scheduled to reduce demand by shifting large loads to off-peak hours and controlling the operation of loads

A duty cycle controller is used to continuously meter demand and issue an alarm when a predetermined level is exceeded

Also known as "rate control"
An automated version of the demand metering alarm system, which automatically disconnects or reconnects loads as needed
Controllable loads are separated into sheddable and unsheddable loads
- Sheddable loads include non-essential lighting, ventilation fans, space heating, and comfort cooling
- Unsheddable loads include essential lighting, elevators, and refrigeration

Compares the actual rate of energy usage to the ideal rate and controls kilowatt demand by controlling the total energy used within a metering interval

Electrical Systems

Electricity is a form of energy generated by friction, induction, or chemical change.
It is the motion of free electrons through a conductor
Electric current travels at the speed of light, meaning conduction is considered instantaneous.
William Gilbert is known as the "Father of Electricity" for his studies on electricity
Electricity is a property of basic particles of matter, including electrons, protons, and neutrons

A combination of two or more electric cells stores and supplies direct current through electro-chemical means
Primary batteries deliver electricity immediately upon being assembled
Secondary/Storage batteries require an external source of electricity to charge them before they can deliver a current

Converts mechanical energy into electrical energy
Alternating Current Generators (Alternators) produce most of the electrical energy used today
Direct Current Generators provide electricity for elevators, escalators, and certain signal systems

Convert one voltage to another:
- Step-up transformer converts lower voltage to higher voltage
- Step-down transformer converts higher voltage to lower voltage
Oil-insulated Transformers and Dry-Type Transformers are the two major types of transformers