Transmission and Distribution

Question 1

Impedance due to a capacitor equation

Answer 1

Handbook (p. 36) - Xc=(-)1/(wc)

Remember that w = 2(pi)*f

So Xc = 1 / (2(pi) f C)

Don’t worry about the negative

Question 2

The inductance of a 3ph transmission line is NOT dependent on which of the following?

Conductor permeability
Distance between conductors
Conductors thickness
Conductor permittivity

Answer 2

Conductor permittivity

Handbook p.62 says that inductance depends on area, permeability, and mean path - so the first three are out

Question 3

3 types of busses in power flow analysis

Answer 3

Load bus
Voltage-controlled bus
Slack bus

Question 4

Voltage-controlled bus

Answer 4

One that maintains a constant voltage to the system

This is accomplished with a generator

Question 5

Current flow in transformers in parallel with different impedances

Answer 5

More current will flow through the transformer with lower percent impedance

(Path if least resistance)

Question 6

Leading power factor angle

Answer 6

Negative (-)

Question 7

Lagging power factor angle

Answer 7

Positive (+)

Question 8

Zero sequence flow through transformer

Answer 8

ZERO SEQUENCE CAN ONLY FLOW THROUGH WYE-WYE TRANSFORMER grounded on both sides)

Question 9

Compensation

Answer 9

Typically refers to the addition of reactive devices to a transmission line in order to improve system stability, voltage drop, power factor, or power transfer

Question 10

Shunt (parallel) compensators

Answer 10

Mostly used to help supply reactive power to an inductive circuit

Question 11

Series (in line) compensators

Answer 11

Mostly used to help balance the overall impedance of the transmission line conductors so that it is less inductive

Question 12

Typical advantages of compensation

Answer 12

• improve (increase) the available voltage mag other at the receiving end due to less (decreased) voltage dropped along the line
• improve the system stability by decreasing the angle difference between the sending and receiving voltage
• improve (increase) the available transmission power transfer by decreasing the angle difference between the sending and receiving voltage and by decreasing the overall line reactance
• improve power factor of the trans line by reducing the amount of reactive power required to be supplied by the transmission line due to supplemental reactive power supplied by shunt compensation