Electrical Power Systems Flashcards
Most electrical loads are not pure resistive, and involve ____ (conversion to magnetic energt) which impactss the AC power system.
Reduces power factor
Inductive Loads
__ __ cause currents to be drawn that are not in phase with that of the applied voltage. The higher currents increase
Magnetic Loads
the __ currents increase the energy lost in the distribution system and require large wires and other equipment
higher
We seek to reduce the reactive power, which will reduce the apparent power and increase the __ __
kW / kVA
Power Factor
Power factors below __ __ require a utility to generate more than the minimum volt-amperes necessary to get the work done.
5%
Inserting a ___ to correct the power factor and need less apparent power you will need
kVAR needed = Real power (kW) - Table Factor
capacitor
Billed kW =
Metered kW * .9 over measured PF during month
__ __ is related to how well a bus voltage (usually our facility) maintains a pure sinusoidal waveform at rated voltage and frequency
Issues include - spikes, notches, outages, harmonics, and power factor
Power Quality
Voltage imbalance between three phases
Reduced motor efficiency, potential damage to motors, increased losses, increased neutral current
__ __ __ is found as the rate of the largest phase to phase voltage difference from average, divided by the average voltage
maximum deviation from average / average voltage
Percent voltage imbalance
steps to deal with power problems
- Inspect wiring and and grounding
2. clean and tighten all connection
Loose electrical connections come from what four things?
vibration, oxidation, corrosion, and age
multiples of the fundamental frequency
Harmonics
A measure of power quality
Limits are_
General systems - 5%
Special applications (hospitals MRI machines) - 3%
Total Harmonic Distortion (THD)
provides recommended practices and requirements for harmonic control in electrical power systems
IEE 519 Power Quality Standards
How to assess harmonics
Power Quality meters provide the ability to see what harmonics exist
Low order cause more power type issues
higher order cause more interference type issues
p = V * I * PF (watts)
Single Phase AC system
Power = Volts - average phase to phase voltage * Ampere - average phase current (Volts) * power factor in watts (watts / Volt Amps)
P = 1.732 * V * I * PF
Three-phase AC system
Power = square root of three * Volts - average phase to phase voltage * Ampere - average phase current (Volts) * power factor in watts (watts / Volt Amps)
PF =
V =
I =
Power Factor
V - Volt - average phase to phase voltage
I - ampere or current
kW (given electrical info) = 1.732 * kV * I (ampere) * PF (power factor)
kW (given mechanical info) = HPnameplate * .746kW/HP * LF OVER Efficiency
three phase motor equations
kW
The real/working and useful power (work done)
kVAR
reactive power, kilovoltamps reactive - we need some reactive power to create and maintain the magnetic field which rotates the motor
kVA
Total apparent power
How much value for money we’re getting for the power we consume
kilovolt amperes
In power factor management, we seek to __ the kVAR reactive power, which will __ the total apparent power and __ the power factor. The real working power remains __.
Reduce
Reduce
Increase
Unchanged
Why is it bad to have a low Power factor and what is this number?
industrial plants are increasing the current flow through the electricity network and causing voltage drops which reduces the suppliers distribution capacity and has a knock on effect for other customers.
Below 1 is bad
What are the formulas for Power Factor for a 3 phase motor
kW / kVa
kW / (kVI1.732)
an expression of how much energy was used in a time period, versus how much energy would have been used, if the power had been left on during a period of peak demand. It is a useful indicator for describing the consumption characteristics of electricity over a period of time.
What is load factor?
If a power factor correction capacity is installed on a motor, the power factor __ of the capacitor is increased.
The current (amps) upstream of the capacity is __
increased, decreased
A facility has properly installed a power factor correction capacitor on a motor. The power factor upstream of the capacitor has been improved. What is the impact on the real (working) power used by the motor?
It is unchanged because the motor still does the same amount of work downstream.
