Distance protection is a type of protection scheme used in power system transmission line protection. It provides good selectivity and sensitivity in identifying the faulted section of the line.
The main concept of distance protection is to compare the voltage and current of the protected line and calculate the distance to the fault. This protection is widely used in Extra High Voltage (EHV) transmission lines. Design of three-stepped distance protection: Three-stepped distance protection for the EHV transmission line can be designed using the following steps:
Step 1: Zone 1 protection For the first step, we use the distance relay to provide Zone 1 protection. This relay is located at the beginning of the transmission line, and its reach is set to cover the full length of the line plus the length of the adjacent feeder. The relay uses the phase-to-phase voltage (Vab, Vbc, Vca) and the three-phase current (Ia, Ib, Ic) to measure the impedance of the line. If the calculated impedance falls below a set threshold, the relay trips the circuit breaker. The circuit diagram of Zone 1 protection is as follows:
Step 2: Zone 2 protection For the second step, we use the distance relay to provide Zone 2 protection. This relay is located at a distance from the substation, and its reach is set to cover the full length of the transmission line plus a margin. The relay uses the phase-to-phase voltage (Vab, Vbc, Vca) and the three-phase current (Ia, Ib, Ic) to measure the impedance of the line. If the calculated impedance falls below a set threshold, the relay trips the circuit breaker. The circuit diagram of Zone 2 protection is as follows:
Step 3: Backup protection For the third step, we use the overcurrent relay to provide backup protection. This relay is located at the substation and uses the current of the transmission line to measure the fault current. If the fault current exceeds a set threshold, the relay trips the circuit breaker. The circuit diagram of the backup protection is as follows:
Constraints: There are some constraints that we need to consider while designing three-stepped distance protection for the EHV transmission line. These are as follows:• The reach of each zone should be set appropriately to avoid false tripping and ensure proper selectivity.• The time delay of each zone should be coordinated to avoid overreach.• The CT ratio and PT ratio should be chosen such that the relay operates correctly.• The trip contact configuration of the circuit breaker should be considered while designing the protection scheme.
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Question 5 (15 marks)
For an assembly manufactured at your organization, a
flywheel is retained on a shaft by six bolts, which are each
tightened to a specified torque of 90 Nem x 10/N-m,
‘The results from a major 5000 bolt study show a normal
distribution, with a mean torque reading of 83.90 N-m, and a
standard deviation of 1.41 Nm.
2. Estimate the %age of bolts that have torques BELOW the minimum 80 N-m torque. (3)
b. Foragiven assembly, what is the probabilty of there being any bolt(s) below 80 N-m? (3)
¢. Foragiven assembly, what isthe probability of zero bolts below 80 N-m? (2)
Question 5 (continued)
4. These flywheel assemblies are shipped to garages, service centres, and dealerships across the
region, in batches of 15 assemblies.
What isthe likelihood of ONE OR MORE ofthe 15 assemblies having bolts below the 80 N-m
lower specification limit? (3 marks)
. Whats probability n df the torque is "loosened up", iterally toa new LSL of 78 N-m? (4 marks)
The answer to the first part, The standard deviation is 1.41 N-m.
How to find?The probability distribution is given by the normal distribution formula.
z=(80-83.9)/1.41
=-2.77.
The percentage of bolts that have torques below the minimum 80 N-m torque is:
P(z < -2.77) = 0.0028
= 0.28%.
Thus, there is only 0.28% of bolts that have torques below the minimum 80 N-m torque.
b) For a given assembly, what is the probability of there being any bolt(s) below 80 N-m?
The probability of there being any bolt(s) below 80 N-m is given by:
P(X < 80)P(X < 80)
= P(Z < -2.77)
= 0.0028
= 0.28%.
Thus, there is only a 0.28% probability of having bolts below 80 N-m in a given assembly.
c) For a given assembly, what is the probability of zero bolts below 80 N-m?The probability of zero bolts below 80 N-m in a given assembly is given by:
P(X ≥ 80)P(X ≥ 80) = P(Z ≥ -2.77)
= 1 - 0.0028
= 0.9972
= 99.72%.
Thus, there is a 99.72% probability of zero bolts below 80 N-m in a given assembly.
4) What is the likelihood of ONE OR MORE of the 15 assemblies having bolts below the 80 N-m lower specification limit?
The probability of having one or more of the 15 assemblies with bolts below the 80 N-m lower specification limit is:
P(X ≥ 1) =
1 - P(X = 0)
= 1 - 0.9972¹⁵
= 0.0418
= 4.18%.
Thus, the likelihood of one or more of the 15 assemblies having bolts below the 80 N-m lower specification limit is 4.18%.
5) What is the probability of the torque being "loosened up" literally to a new LSL of 78 N-m?
The probability of the torque being loosened up to a new LSL of 78 N-m is:
P(X < 78)P(X < 78)
= P(Z < -5.74)
= 0.0000
= 0%.
Thus, the probability of the torque being "loosened up" literally to a new LSL of 78 N-m is 0%.
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Compute the Fourier Series decomposition of a square waveform with 90% duty cycle
The Fourier series decomposition of the square waveform with a 90% duty cycle is given by: f(t) = (a0/2) + ∑[(an * cos((2πnt)/T)) + (bn * sin((2πnt)/T))]
The Fourier series decomposition for a square waveform with a 90% duty cycle:
Definition of the Square Waveform:
The square waveform with a 90% duty cycle is defined as follows:
For 0 ≤ t < T0.9 (90% of the period), the waveform is equal to +1.
For T0.9 ≤ t < T (10% of the period), the waveform is equal to -1.
Here, T represents the period of the waveform.
Fourier Series Coefficients:
The Fourier series coefficients for this waveform can be computed using the following formulas:
a0 = (1/T) ∫[0 to T] f(t) dt
an = (2/T) ∫[0 to T] f(t) cos((2πnt)/T) dt
bn = (2/T) ∫[0 to T] f(t) sin((2πnt)/T) dt
where a0, an, and bn are the Fourier coefficients.
Computation of Fourier Coefficients:
For the given square waveform with a 90% duty cycle, we have:
a0 = (1/T) ∫[0 to T] f(t) dt = 0 (since the waveform is symmetric around 0)
an = 0 for all n ≠ 0 (since the waveform is symmetric and does not have cosine terms)
bn = (2/T) ∫[0 to T] f(t) sin((2πnt)/T) dt
Computation of bn for n = 1:
We need to compute bn for n = 1 using the formula:
bn = (2/T) ∫[0 to T] f(t) sin((2πt)/T) dt
Breaking the integral into two parts (corresponding to the two regions of the waveform), we have:
bn = (2/T) [∫[0 to T0.9] sin((2πt)/T) dt - ∫[T0.9 to T] sin((2πt)/T) dt]
Evaluating the integrals, we get:
bn = (2/T) [(-T0.9/2π) cos((2πt)/T)] from 0 to T0.9 - (-T0.1/2π) cos((2πt)/T)] from T0.9 to T
bn = (2/T) [(T - T0.9)/2π - (-T0.9)/2π]
bn = (T - T0.9)/π
Fourier Series Decomposition:
The Fourier series decomposition of the square waveform with a 90% duty cycle is given by:
f(t) = (a0/2) + ∑[(an * cos((2πnt)/T)) + (bn * sin((2πnt)/T))]
However, since a0 and an are 0 for this waveform, the decomposition simplifies to:
f(t) = ∑[(bn * sin((2πnt)/T))]
For n = 1, the decomposition becomes:
f(t) = (T - T0.9)/π * sin((2πt)/T)
This represents the Fourier series decomposition of the square waveform with a 90% duty cycle, including the computation of the Fourier coefficients and the final decomposition expression for the waveform.
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ie lbmol of pentane gas (C₅H₁₂) reacts with the theoretical amount of air in a closed, rigid tank. Initially, the reactants are at 77°F, 1 m. After complete combustion, the temperature in the tank is 1900°R. Assume air has a molar analysis of 21% O₂ and 79% N₂. Determine the heat transfer, in Btu. Q = i Btu
The heat transfer, Q, can be calculated using the equation:
Q = ΔHc + ΔHg. To determine the heat transfer in Btu for the given scenario, we need to calculate the heat released during the combustion of pentane and the subsequent increase in temperature of the gases in the tank.
Where ΔHc is the heat released during combustion and ΔHg is the heat gained by the gases in the tank due to the increase in temperature. To calculate ΔHc, we need to determine the moles of pentane reacted and the heat of combustion per mole of pentane. Since pentane reacts with air, we also need to consider the moles of oxygen available in the air. The heat of combustion of pentane can be obtained from reference sources. To calculate ΔHg, we can use the ideal gas law and the given initial and final temperatures, along with the molar analysis of air, to determine the change in enthalpy. By summing up ΔHc and ΔHg, we can obtain the total heat transfer, Q, in Btu. It's important to note that the actual calculations involve several steps and equations, including stoichiometry, enthalpy calculations, and gas laws. The specific values and formulas needed for the calculations are not provided in the question, so an exact numerical result cannot be determined without that information.
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