Reference no: EM13986748
Question 1. Define briefly:
(a) the fault level of a system or unit in a system
(b) base MVA.
State:
(c) the equation for percentage impedance or impedance voltage
(d) the relationship between X% and X pu
(e) the units of X% and X pu
(f) X pu in terms of the fault level. MVA and the base MVA.
Question 2. Draw the individual and combined impedance (X pu) diagrams to a base of 10 MVA for the units and system shown in FIGURE 1. Determine the system fault MVA and fault currents at the 11 kV and 3.3 kV busbars. Show all working.
Question 3. For the system shown in FIGURE 2, using a 10 MVA base, calculate the fault MVA levels through each unit and the base "voltage" MVA across each unit for a fault at F. Draw the impedance diagrams showing the fault levels and the base "voltage" MVA across each unit for:
(a) bus section switch B open and A open
(b) bus section switch B closed and A open.
Other circuit breakers are closed.
The generators have the same rating and characteristics.
Question 4. FIGURE 3 shows part of an electrical supply system. Draw the impedance diagrams reducing to a single impedance. Calculate the fault MVA levels in each unit for a fault on the left 3.3 kV bus with the bus-section switch B open and A closed. Use a base MVA of 10 and show the fault MVA levels on a diagram. Comment on the result and suggest a method of improving the system to limit the fault MVA through T1 to approximately 5 x FL current. (It is not necessary to recalculate.)
Question 5. Given the relationships:
X pu = MVA base/MVA fault
= (MVA base/MVA rated) x X%/100
fault MVA = √3VIfault
XΩ = V/√3 Ifault
show that (a) Fault MVA = MVA rated/X% x 100
(b) X pu = MVA base V2 x XΩ
and hence calculate the pu impedance of 100 m of 3 single core 415 V cables in trefoil. Take the cable impedance to be 90 microhms per metre. Use a 1 MVA base. Neglect the resistance of the cables.
Question 6. (i) For the system shown in FIGURE 4, determine the fault level for a fault on the cable at the 3.3 kV unit shown when the bus section switch is closed. The cable impedance is 90 microhms per metre. Neglect cable resistance and use a base of 10 MVA.
(ii) What would be the effect on the fault level of replacing the unit shown in FIGURE 4 with a running motor?
Question 7. Determine the pu impedance and the reactance of the interbus reactor for the system shown in FIGURE 5, if generator G2 is to be used. The switchgear rating is 500 MVA. Use a 10 MVA base and assume all circuit breakers are closed, except' the 11 kV bus section circuit breaker, and the inter bus reactor is in service.
|
Intense seasonal demand for loans
: As the executive of a bank or thrift institution you are faced with an intense seasonal demand for loans. Assuming that your loanable funds are inadequate to take care of the demand, how might your Reserve Bank help you with this problem?
|
|
Simple balance sheet of assets and liabilities
: Assume that Banc One receives a primary deposit of $1 million. The bank must keep reserves of 20 percent against its deposits. Prepare a simple balance sheet of assets and liabilities for Banc One immediately after the deposit is received.
|
|
What will be the net charge of the ball
: How many excess electrons can be counted in a rubber rod of -8* 0.00001 nano coulombs of charges? A metal ball has -1 coulomb of charge. If it receives 0.50*10^20 number of electrons , what will be the net charge of the ball?
|
|
How far has the milk travelled in your frame of reference
: How far has the milk travelled in YOUR frame of reference. What is the minimum speed at which the milk must be travelling such that it is still good when it returns to you in 10 days?
|
|
Draw the individual and combined impedance diagrams
: Draw the individual and combined impedance (X pu) diagrams to a base of 10 MVA for the units and system - What would be the effect on the fault level of replacing the unit - Determine the pu impedance and the reactance of the interbus reactor for th..
|
|
Find the acceleration and the stopping distance
: A bus running along a straight street at 30m/s is slowed uniformly to stop in 5sec. Find the acceleration and the stopping distance.
|
|
What is the percentage error in the value of g
: You measure the Gravity constant which is g= 9.8 m/s2. If your experiment yields a value for g=8.85 m/s2, what is the percentage error in the value of g?
|
|
What is its length from your vantage point on a fixed planet
: A bus moving with speed 0.96c is 65 feet long according to its passengers and driver. What is its length from your vantage point on a fixed planet?
|
|
What is the potential of plate a
: A large capacitance of 1.01 mF is needed for a certain application. Calculate the area the parallel plates of such a capacitor must have if they are separated by 4.11 μm of Teflon, which has a dielectric constant of 2.1.
|