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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?
- 210V
- 265V
- 240V (correct)
- 250V
Which of the following is a common cause of surge voltage?
Which of the following is a common cause of surge voltage?
- Load shedding
- Voltage regulation settings
- Lightning (correct)
- Faulty wiring
What device is typically used for protection against surge voltage?
What device is typically used for protection against surge voltage?
- Voltage regulator
- Surge Protection Device (SPD) (correct)
- Fuse
- Ground fault relay
What type of situation is indicated by a broken main neutral conductor?
What type of situation is indicated by a broken main neutral conductor?
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?
What is the typical duration of surge voltage?
What is the typical duration of surge voltage?
What causes overvoltage due to variations in load?
What causes overvoltage due to variations in load?
Which of the following occurs when photovoltaic cells are installed?
Which of the following occurs when photovoltaic cells are installed?
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?
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?
What is the primary function of an over and under voltage relay?
What is the primary function of an over and under voltage relay?
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?
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?
How is the Surge Protection Device (SPD) connected in a circuit?
How is the Surge Protection Device (SPD) connected in a circuit?
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?
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?
What is the purpose of a Type 1 SPD?
What is the purpose of a Type 1 SPD?
Where is a Type 2 SPD typically installed?
Where is a Type 2 SPD typically installed?
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?
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?
What recommendation is given regarding manufacturers of SPDs used together?
What recommendation is given regarding manufacturers of SPDs used together?
What does the SPD impedance do when a transient overvoltage occurs?
What does the SPD impedance do when a transient overvoltage occurs?
In a three-phase system, how should the SPD be connected?
In a three-phase system, how should the SPD be connected?
What is the maximum total lead length for connecting conductors to SPDs?
What is the maximum total lead length for connecting conductors to SPDs?
Flashcards
Overvoltage protection
Overvoltage protection
A safety feature that prevents electrical equipment from damage due to excessive voltage.
Over and Under Voltage Relay (O/U Relay)
Over and Under Voltage Relay (O/U Relay)
A device that monitors voltage fluctuations and triggers a response when voltage exceeds a pre-set range.
What does an O/U relay protect against?
What does an O/U relay protect against?
An O/U relay protects against voltage variations beyond +/-10% of the normal voltage level.
How does an O/U relay operate?
How does an O/U relay operate?
An O/U relay has an internal relay that activates when voltage exceeds the pre-set range. This activates a larger relay that controls the main power supply.
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Surge Protection Device (SPD)
Surge Protection Device (SPD)
A device that protects electrical equipment from damage caused by sudden voltage surges.
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Where does an SPD connect in an electrical system?
Where does an SPD connect in an electrical system?
An SPD is connected in parallel with the circuit it is protecting, typically on the power supply side of the load.
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What other locations can an SPD be used?
What other locations can an SPD be used?
SPDs can be used at various levels of the power supply network, from the main utility supply to individual appliances.
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Why is overvoltage protection important?
Why is overvoltage protection important?
Overvoltage protection is important to prevent damage to electrical equipment and ensure the safety of occupants.
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Overvoltage
Overvoltage
A situation where the voltage exceeds the acceptable maximum by 10% or more for a long period.
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Surge Voltage
Surge Voltage
A short burst of high voltage lasting for microseconds.
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SPD (Surge Protection Device)
SPD (Surge Protection Device)
A device that protects against surge voltage, a sudden spike in voltage.
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Causes of Surge Voltage
Causes of Surge Voltage
Surge voltage can be caused by lightning strikes, heavy current switching, or other sudden electrical events.
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Overvoltage due to Photovoltaic Cells
Overvoltage due to Photovoltaic Cells
Overvoltage can occur when photovoltaic cells generate a voltage higher than the supply voltage.
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Heavy Current Faults
Heavy Current Faults
Short circuits or other faults can cause overvoltage due to sudden changes in current flow.
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Overvoltage due to Load and Regulation
Overvoltage due to Load and Regulation
Variations in load and voltage regulation settings on the substation transformer can lead to overvoltage.
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Over and Under Voltage Relay
Over and Under Voltage Relay
A device that protects against overvoltage and undervoltage conditions, typically used in situations where the neutral conductor is broken.
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SPD Impedance
SPD Impedance
The SPD's impedance is initially high to allow normal operation, but it decreases when a surge occurs, diverting the surge current away from sensitive equipment.
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Type 1 SPD
Type 1 SPD
Recommended for industrial and service buildings with high risk of direct lightning strikes. It protects the entire electrical installation.
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Type 2 SPD
Type 2 SPD
The primary protection for all low-voltage electrical installations. Prevents overvoltages from spreading and protects loads.
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Type 3 SPD
Type 3 SPD
Provides secondary protection close to sensitive equipment, supplementing Type 2 SPD. Has a lower discharge capacity.
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SPD Connection
SPD Connection
SPDs are connected between the phase and neutral (or 3 phases and neutral for 3-phase systems). It should be installed between the main switch/breaker and RCD.
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Critical Conductor Length
Critical Conductor Length
Connecting wires to SPDs should be as short as possible to avoid voltage drops due to inductance.
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Maximum SPD Conductor Length
Maximum SPD Conductor Length
The total length of connecting conductors (a+b) should ideally be less than 0.5m, but never exceed 1.0m.
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SPD Coordination (Different Makes)
SPD Coordination (Different Makes)
When using multiple SPDs from different manufacturers, ensure they are compatible and will coordinate protection.
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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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