Electrical Power Systems

Question 1

Most electrical loads are not pure resistive, and involve ____ (conversion to magnetic energt) which impactss the AC power system.
Reduces power factor

Answer 1

Inductive Loads

Question 2

__ __ cause currents to be drawn that are not in phase with that of the applied voltage. The higher currents increase

Answer 2

Magnetic Loads

Question 3

the __ currents increase the energy lost in the distribution system and require large wires and other equipment

Answer 3

higher

Question 4

We seek to reduce the reactive power, which will reduce the apparent power and increase the __ __

kW / kVA

Answer 4

Power Factor

Question 5

Power factors below __ __ require a utility to generate more than the minimum volt-amperes necessary to get the work done.

Answer 5

5%

Question 6

Inserting a ___ to correct the power factor and need less apparent power you will need
kVAR needed = Real power (kW) - Table Factor

Answer 6

capacitor

Question 7

Billed kW =

Answer 7

Metered kW * .9 over measured PF during month

Question 8

__ __ 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

Answer 8

Power Quality

Question 9

Voltage imbalance between three phases

Answer 9

Reduced motor efficiency, potential damage to motors, increased losses, increased neutral current

Question 10

__ __ __ 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

Answer 10

Percent voltage imbalance

Question 11

steps to deal with power problems

Answer 11

1. Inspect wiring and and grounding

2. clean and tighten all connection

Question 12

Loose electrical connections come from what four things?

Answer 12

vibration, oxidation, corrosion, and age

Question 13

multiples of the fundamental frequency

Answer 13

Harmonics

Question 14

A measure of power quality
Limits are_
General systems - 5%
Special applications (hospitals MRI machines) - 3%

Answer 14

Total Harmonic Distortion (THD)

Question 15

provides recommended practices and requirements for harmonic control in electrical power systems

Answer 15

IEE 519 Power Quality Standards

Question 16

How to assess harmonics

Answer 16

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

Question 17

p = V * I * PF (watts)

Answer 17

Single Phase AC system
Power = Volts - average phase to phase voltage * Ampere - average phase current (Volts) * power factor in watts (watts / Volt Amps)

Question 18

P = 1.732 * V * I * PF

Answer 18

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)

Question 19

PF =
V =
I =

Answer 19

Power Factor
V - Volt - average phase to phase voltage
I - ampere or current

Question 20

kW (given electrical info) = 1.732 * kV * I (ampere) * PF (power factor)

kW (given mechanical info) = HPnameplate * .746kW/HP * LF OVER Efficiency

Answer 20

three phase motor equations

Question 21

kW

Answer 21

The real/working and useful power (work done)

Question 22

kVAR

Answer 22

reactive power, kilovoltamps reactive - we need some reactive power to create and maintain the magnetic field which rotates the motor

Question 23

kVA

Answer 23

Total apparent power
How much value for money we’re getting for the power we consume
kilovolt amperes

Question 24

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 __.

Answer 24

Reduce
Reduce
Increase
Unchanged

Question 25

Why is it bad to have a low Power factor and what is this number?

Answer 25

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

Question 26

What are the formulas for Power Factor for a 3 phase motor

Answer 26

kW / kVa | kW / (kV*I*1.732)

Question 27

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.

Answer 27

What is load factor?

Question 28

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 __

Answer 28

increased, decreased

Question 29

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?

Answer 29

It is unchanged because the motor still does the same amount of work downstream.