For the three-bus power system shown in the figure, the trip signals to the circuit breakers  to  are provided by overcurrent relays  to , respectively, some of which have directional properties also. The necessary condition for the system to be protected for short circuit fault at any part of the system between bus 1 and the  -  loads with isolation of minimum portion of the network using minimum number of directional relays is

The most commonly used relay, for the protection of an alternator against loss of excitation, is

The total impedance of the secondary winding, leads, and burden of a 5A CT is . If the fault current is 20 times the rated primary current of the CT, the VA output of the CT is_____________.

In a 132 kV system, the series inductance up to the point of circuit breaker location is 50 mH. The shunt capacitance at the circuit breaker terminal is 0.05. The critical value of resistance in ohms required to be connected across the circuit breaker contacts which will give no transient oscillation is __________.

A power system with two generators is shown in the figure below. The system (generators, buses and transmission lines) is protected by six over current relays  to . Assuming a mix of directional and non directional relays at appropriate locations, the remote backup relays for  are

A 3-phase transformer rated for 33 kV/11kV is connected in delta/star as shown in figure. The current transformers (CTs) on low and high voltage sides has a ratio of 500/5. Find the currents  and, if the fault current is 300 A as shown in figure.

The over current relays for the line protection and loads connected at the buses are shown in the figure.

The relays are IDMT in nature having the characteristic

The maximum and minimum fault current at bus B are 2000A and 500A respectively. Assuming the time multiplier setting and plug setting for relay  to be 0.1 and 5A respectively, the operating time of  (in seconds) is _______________.

A negative sequence relay is commonly used to protect

A three-phase 33kV oil circuit breaker is rated 1200A, 2000MVA 3s. The symmetrical breaking current is

Consider a stator winding of an alternator with an internal high-resistance ground fault. The current under the fault condition are as shown in the figure. The winding is protected using a differential current scheme with current transformers of ratio 400/5 A as shown. The current through the operating coil is

Match the items in List-I with the items in List-II and select the correct answer using the codes given below the lists

A two machine power system is shown below. Transmission line XY has positive sequence Impedance of   and zero sequence impedance of .

An 'a' phase to ground fault with zero fault impedance occurs at the center of the transmission line.  Bus voltage at X and line current from X to F for the phase 'a', are given by  Volts and  Amperes, respectively. Then, the impedance measured by the ground distance relay located at the terminal X of line XY will be given by

Voltage phasors at the two terminals of a transmission line of length 70 km have a magnitude of 1.0 per unit but are 180 degrees out of phase.  Assuming that the maximum load current in the line is 1/5th of minimum 3-phase fault current, which one of the following transmission line protection schemes will NOT pick up for this condition?

A lossless single machine infinite bus power system is shown below:

The synchronous generator transfers 1.0 per unit of power to the infinite bus. The critical clearing time of circuit breaker is 0.28s. If another identical synchronous generator is connected in parallel to the existing generator and each generator is scheduled to supply 0.5 per unit of power, then the critical clearing time of the circuit breaker will

Consider the protection system shown in the figure below. The circuit breakers, numbered from 1 to 7 are of identical type. A single line 10 ground fault with zero fault impedance occurs at the midpoint of the line (at point F), but circuit breaker 4 fails to operate ("stuck breaker"). If the relays are coordinated correctly, a valid sequence of circuit breaker operations is

Keeping in view the cost and overall effectiveness, the following circuit breaker is best suited for capacitor bank switching.

In a biased differential relay, the bias is defined as a ratio of

The transmission line distance protection relay having the property of being inherently directional is

The interrupting time of a circuit breaker is the period between the instant of

A list of relays and the power system components protected by the relays are given in Group I and Group II respectively. Choose the correct match from the four choices given below:

Consider the problem of relay co-ordination for the distance relays R1 and R2 on adjacent lines of a transmission system (Figure). The Zone 1 and Zone 2 settings for both the relays are indicated on the diagram. Which of the following indicates the correct time setting for the Zone 2 of relays R1 and R2

In the protection of transformers, harmonic restrain is used to guard against

In an inverse definite minimum time, electromagnetic type over-current relay the minimum time feature is achieved because of

In a 3-step distance protection, the reach of the three zones of the relay at the beginning of the first line typically extends up to

The plug setting of a negative sequence relay is 0.2A. The current transformer ratio is 5:1. The minimum value of line-to-line fault current for the operation of the relay is

Three sections of a feeder are provided with circuit breakers CB1, CB2, CB3, CB4, CB5 and CB6. For a fault F as indicated in fig.

Determine the required MVA rating of the circuit breaker CB for the system shown in fig. Consider the grid as infinite bus. Choose 6 MVA as base.  

Transformer: 3-phase, 33/11 kV, 6 MVA, 0.01+j0.08p.u. Impedance

Load: 3-phase, 11 kV, 5800 MVA, 0.8 lag, j0.2p.u. Impedance

Impedance of each feeder 9+j18 Ω

The neutral of 10MVA, 11KV alternator is earthed through a resistance of 5 ohms. The earth fault relay is set to operate at 0.75A. The CT’s have a ratio of 1000:5.

What percentage of the alternator winding is protected?

Reactance relay is normally preferred for protection against

Resistance switching is normally employed in

If the fault current is 2000A, the relay setting is 50% and CT ratio is 400:5, the plug setting multiplier will be

If the inductance and capacitance of a power system network upto a circuit breaker location are 1H and 0.01μF respectively, the value of the shunt resistor across the circuit breaker, required for critical damping of the re-striking voltage is _________________

The distance relay with inherent directional property is known as ________________  relay.

Match the following

A three-phase delta-wye connected 30MVA, 33 kV/11 kV transformers is protected by a simple differential relaying scheme. The CT ratio on the primary side is 500: 5 and that on the secondary side is 2000: 5. Sketch the CT connection diagram for the relaying scheme. Also calculate the relay current setting for faults drawing upto 200% of the rated current.

The distribution system shown in figure is to be protected by over current system of protection.

For proper fault discrimination directional over current relays will be required at locations

A Buchholz relay is used for

Match the following

In a 4 bus system the circuit breakers and the various zones of protection are shown in figure. If the circuit breakers E, F and G trip, the location of the fault is on ___________

A 50 MVA, 132/66 kV, , three phase power transformer is protected by percentage differential relays. If the current transformers (CTs) located on the delta and wye sides of the power transformer are 300/5A and 1200/5A respectively.