Download IAE – 3 Answer key EE2032 – HIGH VOLTAGE DIRECT CURRENT

IAE – 3 Answer key
EE2032 – HIGH VOLTAGE DIRECT CURRENT TRANSMISSION
1. Mention the performance criteria for selection of harmonic filter.
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Harmonic distortion
Telephone influence factor
Telephone Harmonic form factor
IT product
2. What are the effects of trouble caused by harmonics?
1. Resonance
2. Poor Damping
3. Efficiency of motor reduced
4. Overheating of cable
5. Trip of protection
6. Overheating at winding.
7. Increase magnetic losses.
3. Define Function of smoothing reactor.
A sufficiently large series reactor is used on DC side to smooth DC current and also
for protection. The reactor is designed as a linear reactor and is connected on the line
side, neutral side.
4. Write the effects of unbalanced voltages.
The presence of the negative sequence component in the AC voltages shifts the zero crossing
of the commutation voltages.
5. Define short circuit ratio (SCR).
6. What is HVDC simulator?
HVDC simulator is similar to transient network analyzer (TNA) which is Used to
determine over voltages in AC systems due to switching surges and load refection.
7. List some tools used for the simulation of HVDC simulation.
a.
b.
c.
d.
e.
Physical simulator
Parity simulator
Analog computer
Digital computer
Hybrid computer
8. Draw the of EMTP representation lumped inductor and capacitor.
9. State the advantages of parity simulator.
It avoids drawback of an analog computer simulation The advantages of an
analog computer in terms of change in Time scaling are retained while eliminating the
drawbacks The principle of parity simulation permits hybrid structure.
10. Compare the DC and AC cables from economic point of view.
DC is particularly applicable to long submarine cable transmission where the cost
ratio is high. The cost of DC cable is only a fraction of those for the AC cable and in
addition much less physical space tends to be required in the waterway involved. IN DC
cable the problems such as migration of impregnating compound, movement of the bales on
the sea-bed, under the effects of currents which may affect the economic considerations.
Part – B
11. (a) Illustrate in detail about the analysis of single and double tuned AC filters and
write the design criteria for AC filters
Negleting effects of variations due to frequency,L and C
Typical specified factors to be taken into account in filter design are the voltage distortion
caused by individual harmonics (FJ, the total voltagedistortion defined asand the telephone
influence factor (TIF)
∞
𝑉𝑡𝑑 = ∑ Vn2
𝑛=2
Two basic concepts in filter design are filter size and quality.
Size- defined as the reactive power
Quality- expresses the sharpness of tuning
The impedance of a single-tuned filter is Zf= R+j[coL- 1/icoQ] which at the resonant
frequency is a pure resistance R. The passband of the filter is defined as being bounded by the
frequencies at which thefilter's reactance and resistance are equal (i.e. when the impedance
angle is 45° and its modulus √2R).
Xo = 𝜔𝑛 L= 1/(𝜔𝑛 C) = √(L/C) = inductive or capacitivereactance at resonance
The quality factor Q can be expressed either as
Q= Xo/R
C = l/𝜔𝑛 RQ
(L=RQ/𝜔𝑛 )
The harmonic voltage Vn on the AC terminals is then given by
Vn=𝐼𝑛 /(Ysn+Yj )
11.
(b) Elucidate the characteristics and non- characteristics
harmonics in HVDC converter system.
Harmonic generation can be done in two ways. They are characteristics and
non characteristics.
Characteristics harmonics:
Harmonics present even under ideal conditions. DC current is assumed to be
constant.
h=np±1
Non characteristics harmonics:
Harmonics of order other than characteristic harmonics.
They are due to imbalance in the operation of two bridges, firing angle errors,
unbalance and distortion in SC voltages and unequal transformer leakage and
impedance.
Effect of firing angle errors:
Effect of unbalanced voltages:
12. (a)(i) Stability aspects of synchronous link.
12 (ii) Filters for harmonic elimination in HVDC-system
Explain
AC filters,
DC filters,
hybrid filters.
12. (b) Explain detail about the analysis of single and double tuned AC filters and write the
design criteria for AC filters.
The impedance of a single-tuned filter is Zf= R+j[coL- 1/icoQ] which at the resonant
frequency is a pure resistance R. The passband of the filter is defined as being bounded by the
frequencies at which thefilter's reactance and resistance are equal (i.e. when the impedance
angle is 45° and its modulus √2R).
Xo = 𝜔𝑛 L= 1/(𝜔𝑛 C) = √(L/C) = inductive or capacitivereactance at resonance
The quality factor Q can be expressed either as
Q= Xo/R
C = l/𝜔𝑛 RQ
(L=RQ/𝜔𝑛 )
The harmonic voltage Vn on the AC terminals is then given by
Vn=𝐼𝑛 /(Ysn+Yj )
13.(a) Discuss in detail about the passive and active DC filters with the design criteria.
DC filters do not carry fundamental-frequency power and therefore have sub-stantially
lower losses. Do not need to provide reactive power, their only function being harmonic
mitigation have, in their main capacitor, to withstand the full pole to neutral DC voltage.
interference effect on the telephone lines, i.e.
Ieq= √(∑𝑛=𝑚
𝑛=1 (𝐼𝑛 ∗ 𝐻𝑛 ∗ 𝐶𝑛 )^2
13 (b) Brief about the various types of system studies in design of HVDC system.
1. DC power transfer under various normal and contingency conditions.
2. Reactive power requirements
3. Post fault dc power recovery.
4. Stability improvements through power modulation or emergency controller.
5. Fundamental frequency over voltages.
6. Sub synchronous torsional interactions.
7. Insulation coordination.
8. Dc terminal arresters.
9. AC and DC filter design.
10. Controller requirements under normal and faulted conditions.
14 (a) Write short note on
(i)
Valve model
(ii)
Firing pulse generation
15 (a) (i) Describe the operation of parity simulator.
Principle of parity simulation is used in synchronous machines.
A voltage to current converter is employed together with a local feedback loop to establish
input current.
Advantages :
1. Avoids drawback of an analog computer simulation.
2. Permits hybrid structures.
(ii) Describe the operation of physical simulator.
HVDC simulator is similar to TNA used to determine over voltages and switching surges.
They are similar due the VA rating.
Problems that can be solved by DC simulator:
1. The development of concepts and equipment for control and protection of HVDC systems.
2. Analysis of various AC, DC system interactions.
Applications:
Insulation coordination, testing of controllers and operations etc.,
15 (b) Examine the thermal consideration and losses in dc cables.
Heating of cables
Factors:
1. Production of heat within the external periphery of the cable.
2. The conveyance of the heat as far as the periphery-that is upto the boundary of the
surrounding medium.
3. Medium should be away from the cable.
4. The current rating.
5. Nature of the load.
Losses in cable:
Dielectric losses and loss of tangent of a cable.
Dielectric loss is due to leakage and hysteresis effects whereas tan loss lies in the range of
0.002 to 0.003.