1. "Overload" refers to the condition when a load draws more current than its rated capacity. Overload relays are protective devices designed to protect electrical equipment from damage caused by overload conditions. The normal setting of overload relays is typically 125% to 150% of the equipment's rated current.
2. A short circuit occurs when there is an unintended low resistance path between two conductors of different potentials. Short-circuit faults can develop in a generator when there is a breakdown in the insulation between the windings or between the winding and ground. External short-circuit faults can occur if conductors become damaged or insulation fails, causing a low resistance path between the conductors.
3. Undervoltage relays are used to protect equipment from damage caused by low voltage conditions. Some common types of undervoltage relays include overvoltage relays, underfrequency relays, and voltage imbalance relays.
4. Surge refers to a transient voltage or current that can occur in an electrical system. Surges can be caused by lightning strikes, switching transients, or other events. Surge protective devices (SPDs) are used to protect electrical equipment from damage caused by surges.
5. The advantage of a thermal relay over a magnetic relay is that it can provide more accurate protection against overcurrent conditions. Thermal relays use a bimetallic strip or other temperature sensing device to detect changes in temperature caused by current flow, while magnetic relays use a magnetic field to detect overcurrent conditions.
6. "Reverse current" refers to current flowing in the opposite direction of normal current flow, while "reverse power" refers to power flowing back into the source. A directional overcurrent relay is used to protect against these conditions.
7. Protective devices such as circuit breakers and fuses are typically provided on distribution boards to protect against faults and overloads. These devices are designed to interrupt the flow of current in the event of a fault, preventing damage to equipment and minimizing the risk of fire.
8. A fuse is a protective device designed to interrupt the flow of current in the event of a fault or overload. There are several types of fuses, including blade fuses, cartridge fuses, and resettable fuses such as circuit breakers.
9. Single-phasing refers to the condition when one of the three phases in a three-phase system is lost. This can cause equipment to malfunction or fail. Single-phasing can be avoided by using protective devices such as phase failure relays.
10. When the temperature rises, insulation can become damaged or degraded, reducing its ability to protect against electrical hazards. Overheating can also cause insulation to soften or melt, leading to equipment failure or fire. It is important to ensure that electrical equipment is designed and installed to operate within safe temperature limits.
