Ch 5 & 6 Flashcards
Coil of a transformer energized from AC source.
Primary Winding
What causes an expanding and collapsing field in the core?
AC voltage applied to primary windings
The expanding and collapsing magnetic field induces voltage in what?
Secondary windings wrapped around the core
The output from the secondary windings is the same frequency as what? And goes where?
Primary windings. Load.
Transferring energy to an electrically isolated circuit.
Mutual Inductance
Coil that delivers AC to the load.
Secondary Winding
When voltage is increased, Current is?
Decreased and vice versa
Inductor produces self induced EMF that opposes applied voltage.
CEMF
Functions of Transformers?
Step up step down AC voltages
Provide isolation between source and load.
Primary distribution that connects load breakers to power source.
Electrical Bus
Device that consumes electrical power.
Electrical load
Electrical component that is essential to operation of a system that performs a vital function.
Vital/Essential Load
Centralized distribution and control point for 480 vac loads.
Motor Control Center
What helps prevent accidents to personnel?
Equipment Grounding
Reduces voltage and functions as centralized pt for distribution of power.
Substation
Transforms high voltage power to a level that can be used by loads in the system.
Distribution Transformer
Removal of any part of a power system that suffers an electrical fault by energizing the trip circuit.
Protective Relays
Protects component from overcurrent.
Fuse
3 Purposes of Circuit Breakers
Maintenance isolation
Open circuit for protection and provide normal switching without damaging circuit.
Starter for large motors
Low voltage breaker components
Operating mechanism Main contacts/arching contacts Arc extinguisher Tripping mechanism Terminal connectors
Breaker positions
Racked in
Racked out
Test
Breaker Indicators
Circuit breaker positioning indicating lights
Circuit breaker positioning indicating flag
Breaker Safety Features
Rack in out / test positions Arc extinguisher Automatic trip Trip free operating mechanism Quick make quick break Open/closed tripping indicators
Control and protect the operation of a motor.
Motor Controllers
Deenergize motor during low voltage condition and prevent it from starting automatically upon restoration.
LVP Controller
Deenergize motor during low voltage condition and restarts motor upon restoration.
LVR Controller
Maintains motor across the line at all times.
LVRE Controller
3 features of manual controllers for small loads
Small size
Automatic restart upon power restoration
Low cost
Magnetic controller protective devices
Low voltage
Over current or overload
What proves overload protection?
Manual controllers
Two position switches used for isolation of power to loads.
Disconnect Switches
Automatically transfers essential loads from normal power source to an alternate power source when normal power lost.
Automatic Transfer Switches
Designed to prefer one power source over any other.
Normal seeking transfer switch
This switch does not make the distinction between power sources.
Power seeking transfer switches
480 v distribution system indications
- Transformer Voltmeter - voltage on the line.
- Transformer Ammeter - Current output of transformer.
- Transformer demand watt-hour - displays highest output power.
- Switchgear bus voltmeter - voltage on switch gear bus bar.
Small distribution panels that provide power at either 120 v or 208 v.
Panel Board
Electrical problems such as overloads, short circuits and open circuits.
Electrical Fault
Assembly of circuit breakers that are electrically connected to a system of buses.
Switchgear
Power from the normal source, 115 kv at site.
Normal Power
Furnished power to all vital/essential loads.
SDG Power
Conducting connection between a circuit and the earth. Human body can serve as the earth and complete connection.
Ground
Protective Relays
Differential relay Over voltage relay Under voltage relay Thermal overload relay Instantaneous OC relay Instantaneous ground OC relay
