Unit I – Introduction
1.What is relay?
The protective relaying is used to give an alarm or to cause prompt removal of any element of power system when that element behaves abnormally.The relays are compact and self contained devices.
2.What are the main reasons for main protection failure?
1.Failure in circuit breakers.
2. Failure in protective relay.
3. Failure in tripping circuit.
4. Failure in d.c tripping voltage.
5. Loss of voltage or current supply to the relay.
3.Name the methods of backup protection.
1.Relay Backup Protection
2.Breaker Backup Protection
3.Remote Backup Protection
4.Centrally Co-Coordinated Backup Protection
4.Give the essential quantities of protective relaying.
1.Reliability
2.Selectivity
3.Speed And Time.
4.Sencitivity
5.Stability
6.Adequateness
7.Simplicity And Economy.
5.Classify the protective relays.
1.Electro Magnetic Attraction Type Relays.
2.Induction Type Relays
3.Directional Type Relays.
4.Relays Based On The Timing
5.Differential Relays
6.Distance Type Relays.
6.Define plug setting multiplier.
The ratio of actual current in the relay coil to the pickup current is called plug-setting multiplier
P.S.M= fault current in the relay coil /pickup value
7.What are the advantages of electromagnetic relays?
1.It Can Be Used For Both A.C And D.C
2.Fat Operation
3.The Operating Time Varies With Current
4.High Operating Speed.
5.Compact, Reliable, Simple, Robust
8. What are the disadvantages of electromagnetic relays?
1.The Directional Feature Is Absent
2.Due To Fast Operation The Transients Can Affect The Working.
9. What are the applications of electromagnetic relays?
1.A.C And D.C Equipments.
2.Over/Under Current And Over/ Under Voltage Protection
3.Differencial Protection
4.Used As A Auxiliary Relays.
5.Earth Fault Protection
10.Name the types of induction type relays.
1.Shaded Pole Type
2.Watt Hour Meter Type
3. Induction Cup Relay
The Above Relays Are Classified Based On The Construction.
11.Define differential relay.
A differential relay is defined as the relay that operates when the phasor difference of two or more similar value electrical quantities exceeds a predetermined value.
12.What are the types of differential relay?
1.Current Differential Relay
2.Biaced Beam Relay Or Percentage Differential Relay
3. Voltage Balance Differential Relay
13.Define maximum torque angle.
The angle by which the current supplied to the relay leads the voltage supplied to the relay so as to obtain the maximum torque is called maximum torque angle.
It is denoted by .
14.Name the types of relay based on the voltage and current.
1.Impedance relay (measurement of Z)
2.Reactance relay.(measurement of X)
3.Admittance relay (measurement of Y)
15.Draw the operating characteristics of impedance relay.
X
ZR
R
16. Draw the operating characteristics of reactance relay.
X
XR
R
17. Draw the operating characteristics of mho relay.
X
ZR
R
18.Define static relays.
The relays do not use moving parts and use the solid state electronic components such as diodes, transistors are called static relays.
19.What are the advantages of static relays?
1.The moving parts are absent.
2.The Power Consumption Is Low.
3.The Response Is Very Quick
4.Maintenance Is Less
5.The Sensitivity Is High.
6.The Testing And Servicing Required Is Less.
20.What are the disadvantages of static relays?
1.characteristics are temperature dependent.
2.Reliability is unpredictable.
3.Additional d.c supply is required.
4.less robust compared to electro magnetic relays.
5.susceptible to the voltage fluctuations
21.Give the types of static relays.
1.Frequency Relay.
2.Negative Sequence Relay.
3.Microprocessor Based Relay.
4.Static Distance Relay.
5.Static Differential Relay.
6.Static Time Over current Relay and Directional O/C Relay.
22.What are types of frequency relays?
1.under frequency relay
2.over frequency relay
23.What are the components present in the static relays?
1.rectifier
2.filter
3.level dector
4.amplifier
24.What are the types of comparators used in static relays?
1.rectifier bridge type
2.hall effect type
25.What are the types of induction type relays?
1.induction cup type
2.induction disc type
POSSIBLE 16 MARK QUESTIONS.
- What are the essential quantities of protective relaying and explain it.
- Explain the symmetrical components for L-G fault and derive the expression for fault current.
- With a neat diagram, explain the zones of protection.
- Briefly explain the principle of protective relaying.
- What is fault? Explain the nature, types and causes of faults.
- What is meant by directional feature of a directional over current relay? Describe the construction and principle.(APR 04,AU).
- Explain the negative sequence currents for the operation of relays.(APR ‘04 ,AU).
- Explain the operation of directional and non-directional induction type over current relay.(APR’05 AU)
- Draw and explain the operating characteristics of the directional over current relay. .(APR’05 AU)
- Describe the principle of operation of microprocessor based static relays.
- How electromagnetic relays differ from static relays and describe the block diagram for static relays.
- What is meant by impedance, reactance &mho relay and differentiate it.
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