Basic Electricity - 2 Flashcards
In what applications is a current transformer used
Steps down current of a circuit to a low value for instrumentation
Describe the relations between primary and secondary power in a transformer
Pprimary=Psecondary
Define feeder breaker
Circuit breaker used to receive power from a switchgear bus bar and direct the power to loads
What is the phase relationship between current and voltage in a conductive circuit
Current leads voltage (ICE)
Define bond
The permanent joining of metallic parts or circuits
What is the phase relationship between current and voltage in an inductive circuit
Voltage leads current (ELI)
Define frequency in relation to AC generation
The number of cycles completed per second
Define peak to peak voltage in relation to AC generation
The magnitude of voltage from maximum to minimum on the AC sine wave
Define period in relation to AC generation
The time required for the generator to complete one cycle
Define leg
A current carrying conductor intended to deliver power to or from a load
Define load center
Receives power from a substation and supplies power to motor control centers
Define conductor
Any wire, cable, or substance capable of carrying current
Define reactive power using the power triangle
Reactive power is the vertical component of the power triangle (Q=EIsinØ)
Define standby power
Power source that comes on line upon a loss of normal power
Define phase voltage
The greatest RMS difference of potential between any two legs of the circuit
Describe the development of a sine-wave output in an AC generator
The magnitude and polarity of the induced voltage caries as the conductor rotates in the field. Since the slip rings are continuously in contact with the same brush, the output varies between positive and negative as the conductor rotates.
Define switchgear
An assembly of circuit breakers electrically connected to a system of busses
Define normal power
Power received from the normal power supply
How does a capacitor oppose a change in voltage
As the voltage in a capacitive circuit decreases the energy stored in the plates of the capacitor are released to the circuit opposing the change in voltage.
How does an inductor oppose changes in current flow
As the current begins to change the established magnetic field starts to change which induces a CEMF which resist the change in current.
Define transformer efficiency
Power output divided by power input
Define neutral
A current carrying conductor normally tied to ground
Describe the construction of the iron core of a transformer
Magnetic material that the coils are wound around
Define true power using the power triangle
True power is the horizontal component of the power triangle (P=EIcosØ)
Define area substation
Receives power from the site distribution system for use in a facility