Question

1. When tests are performed on relay units which contain several components in a package, A. current test switches keep the current-transformer terminals short circuited. B. current transformers are disconnected by voltage test switches. C. the relay chassis should remain in the case to provide realistic operating conditions. D. the test plug, such as shown here, makes it possible to perform the tests without disconnecting the relay from service.

2. Why are current transformers important as parts of protective relaying systems? A. Current transformers reduce the supplied alternating current for application in relays. B. Current transformers provide low voltage for auxiliary contacts. C. Current transformers prevent relay current increases due to a fault. D. Current transformers decrease the relay current to become suitable for breaker coils.

3. Which of the following NEMA standard device numbers indicates a relay which operates when the impedance of the circuit changes sufficiently? A. 81 B. 46 C. 21 D. 51

4. When the circuit breaker and relays are taken out of service for testing, the A. tester does not have to exercise as much caution as when he is testing equipment in service. B. ground fault can be simulated by the aid of the load current and proper connections, C. results are more reliable than with in-service testing. D. tripping of the breaker does not provide a positive check for the whole trip circuit.

5. A compensating bimetal spring is used to oppose the action of the main spring in a thermal relay in order to A. mechanically strengthen the main spring. B. increase the temperature which activates the relay. C. make the relay action independent from the ambient temperature. D. reduce the delay of relay action.

6. A polarized d-c relay should be applied when A. it is important that the relay operate at any direction of current. B. high sensitivity is required for protection of a-c or d-c circuits. C. protection is needed on a-c circuits without a rectifier. D. a long delay in relay action is necessary.

7. If you were standing in front of a panel with the control circuits, shown in Fig. 5( a) and above, and you saw the red light suddenly go out and the green light go on, you should A. recognize that the breaker has just closed. B. tum quickly the handle to OPEN to prevent possible damage. C. conclude that the instant overcurrent relay did not operate properly. D. realize that the breaker has opened and remains open.

8. What type relay has a shorter reaction time when the overcurrent value is higher? A. Selected-time type B. Instantaneous type C. Inverse-time type D. Definite-time type

9. Which of the following relays will most likely detect a short circuit in a protected power circuit of a distribution line? A. Overcurrent relay B. Frequency relay C. Overvoltage relay D. Power relay

10. What is the range of burdens that can be tolerated for a current transformer class 2.5H20 when applied in relaying? A. From 0.1 to 0.4 ohm B. From 0 to 4 ohms C. From 1.25 to 2 ohms D. From 0.2 to 0.8 ohm

Answer 1

D, A, B, C, C, C, D, C, A, B.

Step-by-step explanation:

(1) The correct answer is D. When tests are performed on relay units which contain several components in a package, the test plug, such as shown here, makes it possible to perform the tests without disconnecting the relay from service.

(2) The correct answer is A. Current transformers reduce the supplied alternating current for application in relays. Current transformers are important as parts of protective relaying systems because they reduce the supplied alternating current to a level that is suitable for application in relays. This is necessary because the current levels that are typically encountered in power systems are much too high for relays to handle directly. By reducing the current level, the current transformer allows the relay to operate properly and protect the system from damage.

(3) The correct answer is B. 46. The NEMA standard device numbers are used to identify different types of protective relays. The number 46 indicates a relay that operates when the impedance of the circuit changes sufficiently. This type of relay is often used to protect circuits from short circuits, as the impedance of the circuit will change significantly when a short circuit occurs.

(4) The correct answer is C. When the circuit breaker and relays are taken out of service for testing, the results are more reliable than with in-service testing. This is because the tester can control the conditions under which the equipment is tested and can ensure that the test results are accurate.

(5) The correct answer is C. The compensating bimetal spring in a thermal relay is used to oppose the action of the main spring in order to make the relay action independent from the ambient temperature. This is because the bimetal spring changes its shape as the temperature changes, which in turn causes the main spring to be more or less difficult to compress. This allows the relay to operate at a constant temperature, regardless of the ambient temperature.

(6) The correct answer is C. A polarized d-c relay should be applied when protection is needed on a-c circuits without a rectifier. This is because a polarized d-c relay is designed to operate only when the current flows in one direction. This is important for protection of a-c circuits without a rectifier, because a rectifier would allow the current to flow in both directions, which could cause the relay to operate incorrectly.

(7) The correct answer is D. realize that the breaker has opened and remains open. When the red light suddenly goes out and the green light goes on, it means that the breaker has opened and remains open. This is because the red light is connected to the breaker's coil, and the green light is connected to the breaker's contacts. When the breaker opens, the coil is de-energized, which causes the red light to go out. The contacts also open, which causes the green light to go on.

(8) The correct answer is C. Inverse-time type relay has a shorter reaction time when the overcurrent value is higher. Inverse-time relays are designed to operate more quickly when the overcurrent value is higher. This is because they are intended to protect against short circuits, which are typically characterized by high current values. By operating more quickly, inverse-time relays can help to prevent damage to equipment and injury to personnel.

(9) The correct answer is A. Overcurrent relay will most likely detect a short circuit in a protected power circuit of a distribution line. Overcurrent relays are designed to detect and respond to excessive current levels, which are often associated with short circuits. When a short circuit occurs, the current level in the circuit will increase rapidly, which will cause the overcurrent relay to trip. This will disconnect the power circuit from the rest of the system, preventing further damage.

(10) The correct answer is B. The current transformer class 2.5H20 is a current transformer that is designed to be used in relaying applications. It has a secondary burden range of 0 to 4 ohms. This means that the transformer can be used with a variety of different relaying applications, as the secondary burden will not exceed the transformer's maximum rating.

Answer 2

Here are the answers to the questions provided:

1. D. the test plug, such as shown here, makes it possible to perform the tests without disconnecting the relay from service.
2. C. Current transformers prevent relay current increases due to a fault.
3. B. 46
4. D. tripping of the breaker does not provide a positive check for the whole trip circuit.
5. C. make the relay action independent from the ambient temperature.
6. C. protection is needed on a-c circuits without a rectifier.
7. D. realize that the breaker has opened and remains open.
8. B. Instantaneous type
9. A. Overcurrent relay
10. A. From 0.1 to 0.4 ohm