Portfolio Stufy Flashcards
Draw a power triangle clearly labelling reactive power, apparent power and true power include units
True power watts, apparent power VA, reactive power VAR
State 3 effects of operating an installation with low or poor power factor and explain how to improve it
Higher cost, low efficiency, wasted power
Connect capacitors in parallel
The power that actually does work in a circuit is called
True power
The power that is a product of line voltage and current is called
Apparent power
The power stored and returned to a circuit is called
Reactive power
The ratio between true power and apparent power is called the
Cos - power factor
The common name for either the angle of leaf or lag is called
Phase angle
Name the instruments used to measure
Single and tree phase power
Energy consumption
Maximum demand
Power factor
Wattmeter
Kilowatt meter
Maximum demand meter
Power factor meter
Does operating a circuit with a low power factor significantly increase costs associated with running installation
Yes
State two methods to improve power factor
Operate motors at full load
Connecting capacitors
Name an instrument to measure resistance
Ohmeter
Name three measuring instruments required to enable the calculation of the power factor of a single phase circuit
Voltmeter, ammeter, wattmeter
Where on the manufacturers piece of equipment would you find the power factor requirements
Name plate
Do question 13
Check
Name one purpose for providing a neutral in an unbalanced three phase, four wire system
A return path for unbalanced current
State one effect of an open circuit neutral on an unbalanced three phase four wire MEN installation under load
It will creat unbalanced load voltages across the 3 phases
Harmonics can be defined as
Multiples of the fundamental frequency
State one effects of harmonics
Distortion of electricity supply voltage
Name an instrument used to test harmonics
Harmonic analyser
State the dangers of operating a series circuit at resonance
XL and XC cancel each other out allowing high levels of current and voltage to flow across reactive components
Name two common sources of harmonics
Electronic lighting equipment, computers
Under what conditions will resonance occur in a series or parallel circuit
If inductive reactance and capacitive reactance are the same in a ac circuit
State the dangers of operating a parallel circuit at resonance
Current will increase extremely high
Name method used to reduce the problems caused by harmonics
Harmonic filters
