Safety Flashcards
(15 cards)
What are the four main reasons for the importance of protection systems in electrical and electronic applications?
- To isolate faulty circuits
- To prevent electric shock
- To provide good isolation for maintenance
- To prevent damage to equipment
Protection systems are critical for safety and equipment longevity.
What is prospective fault current?
It is the current that protection equipment should be capable of isolating under fault conditions to prevent explosion or risk of fire.
Prospective fault current can be significantly higher than normal operating current.
What are voltage and current transformers used for in large power systems?
They are used to safely measure large voltages and currents by proportionally reducing them to more manageable levels.
Transformers consist of two windings: primary and secondary.
How do distance relay protection systems operate?
They trip when the normal impedance (Z_normal) is greater than the fault impedance (Z_fault), indicating a fault has occurred.
This allows for determining the distance to the fault.
What is the behavior of inverse time overcurrent relays?
The operating time is inversely related to current; higher currents trigger the relay faster than lower currents.
This is useful for protecting circuits from overload.
What do Residual Current Devices (RCDs) measure?
They measure the difference in current between the live conductor and the neutral conductor.
RCDs trip the circuit if there is a small difference, such as when someone touches the live conductor.
What is required for lightning to occur?
The resistance of the air must be overcome, leading to a discharge in the form of a lightning strike.
This typically happens during thunderstorms.
What do lightning arrestors do?
They protect electrical equipment from high voltage surges caused by lightning strikes.
They consist of a spark gap and series non-linear resistors connected to earth.
What is the most common waveform in electrical distribution?
The sine wave.
Sine waves are fundamental in representing AC signals.
What defines an analogue signal?
It is a continuous time-varying signal characterized by amplitude, time period, and frequency.
Examples include temperature and pressure.
What is a digital signal?
A signal that represents data as a sequence of discrete values, typically in binary form.
Digital signals are represented by two voltage levels, commonly 0V and 5V.
What is signal conditioning?
It is the process of converting different types of signals to have the same type of analogue signal for interpretation.
This is important for systems measuring multiple variables.
What occurs after an analogue signal is converted into a digital signal?
Signal processing takes place, which can involve using a digital to analogue (D/A) converter.
This allows the processed information to be used in the real world.
What is a logic gate?
A series of transistors connected to provide outputs based on input combinations.
Common types include AND, OR, and NOT gates.
What do the terms ‘fan in’ and ‘fan out’ refer to in logic gates?
- Fan in: number of inputs designed for a single gate
- Fan out: maximum number of logic inputs a single output can drive
These factors are critical for the performance of digital circuits.
