Power quality Flashcards
What is power quality and what does it attempt to achieve
Study of characteristics of voltage and current to determine if it is suitable up supply electrical loads
What are the 7 power quality problems
1) transients
2) short duration voltage variations
3) long duration voltage variations
4) voltage imbalance
5) waveform distortion
6) voltage fluctuation
7) frequency variations
What are 2 high tolerance loads
Heading and motors
What are 2 mid tolerance loads
Vsd (variable speed drives) PLC (programmable logic computers)
What are 2 low tolerance loads
Signal and data processing equipment
How long do short duration voltage variations last
Less than 1 minute
What is a voltage swell
Anything over 110% of rated voltage
What is a voltage sag
Any voltage between 10 and 90%
What is a voltage interruption
Voltages that are less than 10% of rated
How long is an instantaneous variation
0.5 to 30 cycles
How long is a momentary variation
30 cycles to 3 seconds
How long is a temporary variation
3 seconds to 1 minute
What is a common cause for a voltage sag?
Startup of loads with large startup current
What is the difference between non-periodic impulse transients and periodic impulse
transients?
Non periodic occur once, periodic regularly occur
What is used to protect against transients
Surge suppressors
3 common causes of voltage surge
Loads being switched out
Lightning
Switching of pf correction caps
What is BIL
basic impulse level- amount of vintage and quick DC impulse level a device can be subjected to without damage
When installing surge arresters their conduction voltage should be less or more than the BIL
rating of the equipment they protect?
Less than BIL
What is station class arrester
3 to 612kv
What is intermediate class arrester
3 to 144kv
What is distribution class arrester
1 to 36kv
What is secondary surge arrester
Less than 1kv
Most common surge arrestor used
MOV metal oxide varistor
What are 4 tires of arrestors
Rod gap surge
Expulsion type
Silicon carbide multiple gap
Horn gap
