Loading Document1- A 3-phase, 4-wire distributor supplies a balanced voltage of 400/230 V to a load consisting of 30 A at P.F. 0·866 leading for R-phase, 30 A at P.F. 0·866 lagging for Y phase and 30 A at unity P.F. for B phase. The resistance of each line conductor is 0·2 Ω. The area of X-section of neutral is half of any line conductor. The phase sequence is RYB.
VSY=VY+IYRY+INRN
VY=230∠−120°
IY=30∠−150°
IN=30∠30°+30∠−150°+30∠120°=30∠120°
RNRL=ALAN⟹RN=2RL=0.4Ω
VSY=230∠−120°+30×0.2∠−150°+30×0.4∠120°=229.58∠−123.34°
2- A central station is supplying energy to a community through two substations. Each substation feeds four feeders. The maximum daily recorded demands are:
POWER STATION ------ 12000 KW
Substation A ----- 6000 kW Sub-station B---- 9000 kW
Feeder 1 ----- 1700 kW Feeder 1------ 2820 kW
Feeder 2 ----- 1800 kW Feeder 2 ------ 1500 kW
Feeder 3 ----- 2800 kW Feeder 3 ------ 4000 kW
Feeder 4 ----- 600 kW Feeder 4 ------ 2900 kW
Calculate the diversity factor between (I) substations (II) feeders on substation A and (III) feeders on substation B.
3- Draw a single line diagram of a typical AC power supply scheme. What is the effect of load power factor on regulation and efficiency of a transmission line?
For lagging P.F. loads: P.F.⇊=Regulation ⇈efficiency ⇊
For leading P.F. loads: P.F.⇊=Regulation ⇊efficiency ⇈
* Here regulation refers to how much voltage is dropped during transmission
4- Deduce an expression for voltage regulation of a short transmission line, giving the vector diagram.
%Reg=VRVS−VR×100=VRIR(RLcosϕ+XLsinϕ)×100
5- How will you determine the economic transmission voltage?
I'd go for the highest voltage possible but there's a catch:
higher voltage means less current for the same amount of power which mean we can save big on conductors,
however, it'd need higher towers for good insulation.
so I'd find a sweet spot between the two!
6- Discuss the disadvantages of a low power factor.
1- Large kVA rating of equipment.
2- Greater conductor size.
3- Large copper losses.
4- Poor voltage regulation.
5- Need for Compensation equipment.
7- What is the effect of power factor on the cost of generation?
The lower the power factor, the higher the current required to deliver a given amount of power. This leads to higher losses in the transmission and distribution system, which in turn leads to higher costs for generation.
8- Explain the terms load factor and diversity factor. How do these factors influence the cost of generation?
The load factor is the ratio of the average load to the maximum demand occurring in a given period.
Diversity factor is the ratio of the sum of individual maximum demands to the maximum demand of the whole system.
The cost of generation inversely proportional to the load and diversity factors.
A low load factor means that maximum demand is relatively high, which increases the cost of generation.
A low diversity factor means that maximum demand is relatively high, which increases the cost of generation.
9- The values of demand factor and load factor are always less than 1. Why?
Load factor is always less than 1 because average load is smaller than the maximum demand.
Demand factor is always less than 1 because maximum demand is generally less than the connected load.
10- What are the effects of diversity factor on the maximum load of a distribution transformer?
Diversity factor is the ratio of the sum of individual maximum demands to the maximum demand of the whole system.
A low diversity factor means that there is less variation in demand across different parts of the system, which increases the load on the transformer.
11- Explain only with drawing the following systems of distribution:
