Generation and Transport of Electrical Energy - Week 6

what are the generic voltage levels for the UK power system network

30kV (generator), 400kV, (step up via transformer), 132kV, (step down via transformer) , 33kv (step down), 11kV (step down), 440v (step down for consumer use)

draw the single line diagram for a simple small power system, with 4 zones

draw the two generic line diagram forms for a voltage transformer with two windings

draw the line diagram symbol for an AC power source

draw the line diagram symbol for an inductor

draw the line diagram symbol for a resistor

what are the advantages of the PU system

simplifies complexity as:

1. power network system is a system with single impedances only.

2. transformers are represented with an impedance only

3. all the qualities are expressed in terms of pu no different units.

4. good for computer simulations

5. transformer impedance is the same on both primary and secondary side proivided a good base is used. independent of winding connection(star, delta)

6. same pu for line to line and line to neutral

7. easier to use as manufactures often express impedances of machines in percentage pu

8. impedances for various equipment can be easily estimated since their per-unit impedances lie within a relatively narrow range (regardless of the equipment rating). Thus, per-unit impedance data can be checked rapidly for gross errors by someone familiar with the per-unit quantities. ( dont get this last point only learn if it comes up in a question)

write the equation which specifies the defintion of PU’s.

does the Pu have a unit or is it dimensionless

it is dimensionless

write down all the PU equations to remember

From the 4 quantities. I , S , V , Z how are they all calculated for a power unit system

1. S base is set the same for the whole power network then S(pu) can be calculated from that

2. V base is set for every voltage level in the system then separate V(pu) values can be calculated from that

3. I base and Z base values can be caculated from equations once you know V base and S base