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Questions and Answers
What is the accepted maximum voltage for a nominal voltage of 230V before it is considered overvoltage?
What is the accepted maximum voltage for a nominal voltage of 230V before it is considered overvoltage?
Which of the following is a common cause of surge voltage?
Which of the following is a common cause of surge voltage?
What device is typically used for protection against surge voltage?
What device is typically used for protection against surge voltage?
What type of situation is indicated by a broken main neutral conductor?
What type of situation is indicated by a broken main neutral conductor?
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What should be used to protect against overvoltage caused by a broken conductor?
What should be used to protect against overvoltage caused by a broken conductor?
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What is the typical duration of surge voltage?
What is the typical duration of surge voltage?
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What causes overvoltage due to variations in load?
What causes overvoltage due to variations in load?
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Which of the following occurs when photovoltaic cells are installed?
Which of the following occurs when photovoltaic cells are installed?
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What voltage fluctuation level must be protected against according to S.L.545.24?
What voltage fluctuation level must be protected against according to S.L.545.24?
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Where should an over voltage protective device be installed according to the regulations?
Where should an over voltage protective device be installed according to the regulations?
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What is the primary function of an over and under voltage relay?
What is the primary function of an over and under voltage relay?
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What is a key feature of the recently introduced units of O/U relays?
What is a key feature of the recently introduced units of O/U relays?
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What is the role of a Surge Protection Device (SPD) in an electrical installation?
What is the role of a Surge Protection Device (SPD) in an electrical installation?
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How is the Surge Protection Device (SPD) connected in a circuit?
How is the Surge Protection Device (SPD) connected in a circuit?
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What should be done with over and under voltage relay protection for new installations?
What should be done with over and under voltage relay protection for new installations?
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What type of current can the internal relay of an over and under voltage relay typically handle?
What type of current can the internal relay of an over and under voltage relay typically handle?
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What is the purpose of a Type 1 SPD?
What is the purpose of a Type 1 SPD?
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Where is a Type 2 SPD typically installed?
Where is a Type 2 SPD typically installed?
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Which type of SPD must always be installed in conjunction with Type 2 SPD?
Which type of SPD must always be installed in conjunction with Type 2 SPD?
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What is a critical factor in the installation of SPDs to ensure maximum protection?
What is a critical factor in the installation of SPDs to ensure maximum protection?
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What recommendation is given regarding manufacturers of SPDs used together?
What recommendation is given regarding manufacturers of SPDs used together?
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What does the SPD impedance do when a transient overvoltage occurs?
What does the SPD impedance do when a transient overvoltage occurs?
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In a three-phase system, how should the SPD be connected?
In a three-phase system, how should the SPD be connected?
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What is the maximum total lead length for connecting conductors to SPDs?
What is the maximum total lead length for connecting conductors to SPDs?
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Study Notes
Overvoltage Protection
- Two main types of overvoltage:
- Surge voltage: Short bursts of high voltage lasting microseconds. Caused by lightning and heavy current switching/faults. Surge Protection Devices (SPDs) protect against these. Impulse voltage, typically 100µs duration. Operating impulse type has a frequency of 100kHz to 1MHz.
- Overvoltage (excess voltage +/- 10%): Voltage exceeding nominal voltage (230V) by 10% for an extended period. Causes include:
- Higher voltage generation (e.g., photovoltaic cells).
- Load variation combined with substation transformer voltage regulation.
- Broken neutral conductor causing voltages across phases.
- Over and under voltage relay used for this type of overvoltage protection.
Surge Protection Devices (SPDs)
- Used to protect against surge voltage.
- Connected in parallel with the circuit to protect loads.
- Have high impedance, which decreases during a surge, allowing surge current to pass through the SPD, bypassing the installation and sensitive equipment.
Over and Under Voltage Relay
- Used to protect against voltage fluctuations exceeding +/- 10%.
- Primarily a voltage sensor.
- Operates an internal relay when voltage falls below or rises above a set value.
- The internal relay can handle a smaller current than that handled by the whole installation.
- Some units include a power relay for high currents.
- Can be installed as a single unit in the consumer unit between main switch and RCD.
Types of SPDs
- Type 1: Recommended for service-sector and industrial buildings with lightning protection systems. Protects against direct lightning strikes.
- Type 2: Main protection system for low-voltage installations, installed in switchboards. Prevents over-voltages from spreading, protecting equipment.
- Type 3: Low discharge capacity, supplementary to Type 2, installed near sensitive loads.
Critical Length of Connecting Conductors
- Keep connecting conductors short (ideally under 0.5m, but no more than 1m) for minimal inductive voltage drop.
- Refer to manufacturer instructions for optimal installation.
- If multiple SPD types are used, they should be of the same make/manufacturer if designer is not sure of compatibility.
SPD Wiring
- Always connect SPDs across the phase and neutral (or phases and neutral for 3-phase systems).
- Connect between the main switch or circuit breaker and RCD.
- SPDs can be damaged by high surges (e.g. from overhead lines), so additional protection is recommended if necessary.
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Description
This quiz covers the fundamentals of overvoltage protection, focusing on surge voltage and the types of devices used to mitigate risks associated with electrical surges. Key components such as Surge Protection Devices (SPDs) and their functions will be explored, alongside explanations of overvoltage scenarios. Test your understanding of these crucial electrical safety concepts.
