UNIT 1
1. What are the functions of a protective relay?
2. What are the essential quantities of protection?
3. Write the types of over current relays? With the help of neat sketch, explain the
operation of IDMT relay.
4. What is an impedance relay? Explain it principle of operation. Show its characteristic
on R-X diagram?
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1. With neat sketch, explain the operation of induction type over current relay
2 Describe briefly the following terms as applied to protective relaying
i.
Pickup value
ii.
Current setting
iii.
Plug setting multiplier
iv.
Time multiplier setting
3. Give the constructional features, principle of working of directional over current
relay. Draw its characteristics?
4. A relay is connected to a 400/5 current transformer and set at 150% with a primary
fault current of 1200A.Determine its plug setting multiplier.
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1. What is universal torque equation? Using this equation derive the following
characteristics?
i.
Impedance Relay
ii.
Reactance Relay
iii.
MHO Relay
Draw the characteristics and indicate clearly the zones of operation and no operation.
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2. Explain the basic principle of operation of a differential relay. Describe the working
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of this type of relay
i.
An internal fault
ii.
A through fault
3. A relay operates with rated current of 5 Amps has a relay setting of 150%.It is
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connected to a power system thought current transformer of ratio 400/5.If the fault
current is 6000A.Calculate the plug setting multiplier of the relay.
4. What is the principle of a differential relay? What are its drawbacks and how they are (7M)
over come?
1. Discuss what you understand by selectivity and stability of a protective relay
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2. Discuss how saturation affects the accuracy of C.Ts .Explain the accuracy limit
factor or saturation factor.
3. What are the different types of faults? Which type of fault is most dangerous?
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4. Discuss briefly the role of protective relay in a modern power system.
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UNIT 5
1. Discuss the effect of asymmetry in fault current on active recovery voltage
2. Write about arc extinction/arc interruption? What are the various methods used for
arc interruption?
3. For a 132KV system, the reactance and capacitance upto the location of the circuit
breaker is 3 0hms and 0.015µF respectively. Calculate the following
a. The frequency of transient oscillation
b. The maximum value of restriking voltage across the contacts of the circuit
breaker
c. The maximum value of RRRV
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4. Write the ratings of the circuit breaker
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1. Explain the construction, principle of operation of SF6 circuit breaker.State its
applications
2. Write short notes on any two of the following
i.
Current chopping phenomenon
ii.
Capacitive current breaking
iii.
Resistance switching
3. Define active recovery voltage
4. What is resistance switching? Derive the expression for critical resistance in terms
system inductance and capacitance which give no transient oscillation
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1. A 3 phase 10MVA 11KV generator is connected to a power system, the system
inductance and capacitance per phase are 5Mh and 0.4µF respectively. Calculate
i.
Maximum restriking voltage
ii.
Frequency of restriking voltage
iii.
Average rate of restriking voltage
2. Write about the testing of circuit breakers.
3. Explain how the arc is extinguished in air blast circuit breakers?
4. Explain the terms:
i.
Restriking voltage
ii.
Recovery voltage
iii.
RRRV
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1. How does a circuit breaker differ from a switch
2. What is meant by making capacity of a circuit breaker?
3. Discuss the recovery rate theory and energy balance theory of arc interruption in a
circuit breaker
4. Discuss the operating principle of SF6 circuit breaker. What are the advantages over
other types of circuit breakers?
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UNIT 4
1. What is static relay? Explain with the help of block diagram.
2. Explain duality principle? How an amplitude comparator can be converted into
cosine phase comparator?
3. What is phase comparator? Describe coincidence type phase comparator.
4. What is hall effect? Explain sine comparator? State its applications.
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1. Draw the operating characteristics of mho relay on impedance plane. Logically
determine the signal inputs to amplitude comparator for the design of mho relay.
2. Explain quadrilateral characteristic relay by using cosine phase comparator.
3. Draw the operating characteristics of distance relay used for the protection of
medium length lines. Design the relay using cosine phase comparator.
4. Show that the polar curve of a biased differential relay using a static comparator is a
circle, why does the area outside the circle represent the operating zone.
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1. What do you understand by amplitude comparator and phase comparator? Prove the
duality between them with the help of phase comparator.
2. State the merits and demerits of static relay over electromagnetic relay?
3. What are the different types of phase comparators? Explain the phase splitting
technique employed to measure the period of coincidence
4. What is meant by duality related to comparators?
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1.
2.
3.
4.
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Basic elements of static relay.
Briefly discuss principle of duality
What is static relay?
What is meant by duality related to comparators
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