Lecture 8 - Electrical Transmission Systems and Service Drops PDF

Electrical Power Generation, Transmission, Service Drops and an introduction to small panel wiring IM115 Basic Electricity for the Industrial Technician  Electrical Generation ◼ Energy is transformed into electrical energy ◼ Rotation is required to cause a magn...

Electrical Power Generation, Transmission, Service Drops and an introduction to small panel wiring IM115 Basic Electricity for the Industrial Technician  Electrical Generation ◼ Energy is transformed into electrical energy ◼ Rotation is required to cause a magnetic field to be “cut” by conductors ◼ Rotational speed is controlled to provide an output sine wave at 60 hertz (cps) ◼ The magnetic field level (flux) is controlled by adjusting current flow in the field electromagnet Single Phase Generator N S N S N S N S  Two Phase Generator N S Three Phase Generator 120o N S 120o 120o 120o 120o  Three-Phase Induction Motor A C B B C A Three Phase Generator 120o N S 120o 120o 120o 120o Power Distribution ◼ Involves the transmission, transformation and distribution of electrical power from the power plant to the consumers ◼ Electrical energy is generated and distributed using Three phase power Power Transformation ◼ Consider a 25 MegaWatt power plant:  25,000,000 Watts  Inside the generating station: ◼ 11,000 volts ◼ 2270 amps ◼ 11,000 x 2270 ≈ 25,000,000 (25 MW)  Transform for distribution ◼ 200,000 volts ◼ 125 amps Power Plant Switch Station Switch opening under load High Voltage Pole Transformer Voltage in 120 & 240 volt circuits ◼ Connecting  Neutral (zero) to either hot – 120 volts  Hot to Hot – 240 volts Service drops – Service laterals Panel Meter Box Panel with circuit information House Panel Panel with additional information Panel – okay but questionable Grounding ◼ Protects people installing, testing or using the electrical system ◼ Protects the electrical system itself ◼ Typical high-voltage mishaps  Lightning strikes  Insulation degradation  Accidental contact between high voltage wires and service wires System Grounding ◼ The intentional connection of one conductor of the electrical system to the earth  A driven ground rod  A metallic water pipe  A buried metal ground plate ◼ Usually the neutral or “white” wire ◼ The neutral bus and ground bus are connected with a main bonding jumper System Grounding ◼ The neutral or ground should never be interrupted with switches ◼ Bonding involves the connection of all metallic parts of an electrical system to ground according to article 100 of the NEC ◼ All conduit connections should provide continuity System Grounding System Grounding Equipment Grounding ◼ Bonding the ground conductor to equipment enclosures and metallic equipment (boxes, etc) ◼ A permanent and unbroken path for stray current to flow to ground if ever contacted with a live conductor ◼ Never remove the ground lug from a grounded cord Grounding Conductor Markings ◼ AWG size ◼ Insulation type ◼ Voltage Rating ◼ Testing agency ◼ Number of conductors ◼ Outer finish or covering