Power System Protection: Qualities and Characteristics

What are the two primary qualities that a protective relay must possess to ensure reliable operation in a power system?

Dependability and Security

What is the primary purpose of a protective relay in a power system, and how does it achieve this?

To detect and isolate equipment failures, and it achieves this by tripping when a fault is detected, thereby isolating the faulty equipment and preventing further damage.

What is the difference between dependability and security in the context of protective relays?

Dependability refers to the correct operation of a protective relay when needed, while security refers to the avoidance of incorrect operation.

What is the formula to calculate the dependability of a protective relay, and what does it represent?

Dependability % = (Number of correct trips / Number of desired trips) × 100, and it represents the percentage of times the relay operates correctly when needed. Signup and view all the answers

What is the primary benefit of a protective relay's speed in terms of safety and system protection?

The primary benefit is that it minimizes damage to the surroundings and ensures safety to personnel. Signup and view all the answers

What is the relationship between reliability, dependability, and security in the context of protective relays?

Reliability is the overall performance of a protective relay, which encompasses both dependability (correct operation) and security (avoidance of incorrect operation). Signup and view all the answers

What are the two types of disturbances that can affect the power system?

Small disturbances and severe disturbances Signup and view all the answers

What is the primary purpose of a protection system in a power system?

To prevent the entire power system from being jeopardized in the event of a severe disturbance Signup and view all the answers

What are the two types of protection used in a power system?

Primary relaying and back-up protection Signup and view all the answers

What are the essential skills required of a Protection Engineer to ensure the reliable operation of a power system?

Calculate power system currents and voltages during fault conditions, check that breaking capacity of switchgear is not exceeded, determine the quantities which can be used by relays to distinguish between healthy and fault conditions, and appreciate the effect of the method of earthing on the detection of earth faults Signup and view all the answers

What is the significance of ensuring that load and short circuit ratings of plant are not exceeded in a power system?

To prevent damage to the power system and ensure its reliable operation Signup and view all the answers

Why is it necessary for protection equipment to cover 100% of the protected network?

To ensure that all parts of the power system are protected from faults and disturbances Signup and view all the answers

What is the primary limitation of electromechanical relays in terms of their functionality?

Limited functions Signup and view all the answers

What is the primary advantage of numerical relays over static relays?

Many protection functions integrated in one relay Signup and view all the answers

How do digital relays address the issue of variation in parameters of individual components?

Immune to variation in parameters of individual components Signup and view all the answers

What is the primary consideration when connecting CTs and VTs to protective relays?

Correct connection Signup and view all the answers

What is a key benefit of digital relays in terms of maintenance and operation?

Less Maintenance Signup and view all the answers

What feature of digital relays enables the storage of historical data?

Permit Historical data storage Signup and view all the answers

Why should CT secondary circuits never be open-circuited?

To prevent damage or faults Signup and view all the answers

What is the recommended wire gauge for CT and VT circuits for mechanical strength?

Greater than 2.5mm2 Signup and view all the answers

What is the primary advantage of digital relays in terms of communication and data exchange?

Fiber optical communication with substation LAN Signup and view all the answers

What type of protection is widely used in all power systems and is voltage-dependent?

Overcurrent and Earthfault protection Signup and view all the answers

What type of protection is used for transmission lines and is characterized by high-impedance and restricted earth fault (REF) or low-impedance biased pilot wire digital types?

Differential protection Signup and view all the answers

What type of protection is used for under and over voltage, as well as under and over frequency?

Miscellaneous protection Signup and view all the answers

What are the future generations of protective relays expected to be based on?

Intelligent (ANN, ES based, GA, etc…) Signup and view all the answers

How do digital relays differ from electromechanical relays in terms of sensitivity and accuracy?

Digital relays have high sensitivity and accuracy, whereas electromechanical relays have low sensitivity and accuracy. Signup and view all the answers

What is the primary advantage of µP-based relays over old electromechanical relays?

µP-based relays are more versatile and can be used for different applications. Signup and view all the answers

What is the significance of self-diagnostics in digital relays?

Digital relays have self-diagnostics, which is not available in electromechanical relays. Signup and view all the answers

What is the purpose of the IEC 60617-series and IEEE C37.2 standards in relation to relay symbols and device numbers?

These standards provide a sample list of relay symbols and device numbers for use in electrical systems. Signup and view all the answers

What is the function of device number 50 in the abbreviated list of commonly used relay device function numbers?

Device number 50 is used for instantaneous overcurrent or underpower protection. Signup and view all the answers