Surge Protection Devices
Lightning as a source of harm is a very high energy phenomenon. Lightning flashes release many hundreds of mega-joules of energy. When compared with the milli-joules of energy that may be sufficient to cause damage to sensitive electronic equipment in electrical and electronics systems within a structure, it is clear that the additional protection measures will be necessary to protect some of this equipment.
The need for this international standard has arisen due to the increasing cost of failures of electrical and electronic systems, caused by electromagnetic effects of lightning. Of particular importance are electronic systems used in data processing and storage as well as process control and safety for plants of considerable capital cost, size and complexity (for which plant outage are very undesirable for cost and safety reasons.)
The part 4 of IEC 62305 therefore provides information on protection measures to reduce the risk of permanent failures of electrical and electronic systems within structures.
Permanent failure of electrical and electronic systems can be caused by lightning electromagnetic impulse (LEMP) via.
- Conducted and induced surge transmitted to apparatus via connecting wiring;
- The effects of radiated electromagnetic fields directly into apparatus
Surges to the structure can be generated externally or internally;
- Surges external to the structure are created by lightning flashes striking incoming lines or the nearby ground and are transmitted to electrical or electronic system via these lines;
- Surges internal to the structure are created by lightning flashes striking the structure or the nearby
The coupling can arise from different mechanisms.
- Resistive coupling (e.g. the earth impedance of the earth termination system or the cable shield resistance );
- Electrical field coupling ( g. caused by rod antenna reception ).
Radiated electromagnetic fields can be generated via
- The direct lighting current flowing in the lightning channel
The partial lightning current flowing in conductors (e.g. in the down conductors of an external LPS according to IEC 62305-3 or in an external spatial shield according to the standards).
(Source from SS 555 part 4: 2018)
A surge protector (or spike suppressor, surge suppressor, surge diverter, surge protection device (SPD) or transient voltage surge suppressor (TVSS) is an appliance or device intended to protect electrical devices from voltage spikes in alternating current (AC) circuits.
(Source from Wikipedia)
Our SPD Standards for power and data line:
- IEC61643-11 Low-voltage surge protective devices – Part 11: Surge protective devices connected to low-voltage power systems – Requirements and test methods (replaces IEC 61643-1)
- IEC 61643-21 Low Voltage Surge Protective Devices – Part 21: Surge Protective Devices Connected to Telecommunications and Signalling Networks – Performance Requirements And Testing Methods
** Note: Many failures of SPDs and damages to equipment are due to improper selection of SPDs and improper installation methods.
Surges to the structure can be generated externally or internally;
- Surges external to the structure are created by lightning flashes striking incoming lines or the nearby ground and are transmitted to electrical or electronic system via these lines;
- Surges internal to the structure are created by lightning flashes striking the structure or the nearby
The coupling can arise from different mechanisms.
- Resistive coupling (e.g. the earth impedance of the earth termination system or the cable shield resistance );
- Electrical field coupling ( g. caused by rod antenna reception ).
Radiated electromagnetic fields can be generated via
- The direct lighting current flowing in the lightning channel
The partial lightning current flowing in conductors (e.g. in the down conductors of an external LPS according to IEC 62305-3 or in an external spatial shield according to the standards).
(Source from SS 555 part 4: 2018)
A surge protector (or spike suppressor, surge suppressor, surge diverter, surge protection device (SPD) or transient voltage surge suppressor (TVSS) is an appliance or device intended to protect electrical devices from voltage spikes in alternating current (AC) circuits.
(Source from Wikipedia)
Our SPD Standards for power and data line:
Varistor (MOV):
- Voltage dependable (limiting) resistor.
- Normally 10 MΩ to 1GΩ
- In a surge of lightning situation, current will flow through the MOV and the resistance will fall to about 10Ω
- Because of the high inside resistance and at the time with lightning or surge current that is flowing through it, a high electrical energy is transferred to heat.
– Because this high heat in the MOV, it can only take low impulse current like transient surges.
– Typical application class II (C) SPD
Gas Discharge Tube (GDT):
- No resistor, isolated
- Normally 5 to10 GΩ
- In a surge of lightning situation, current will flow through the GDT and the resistance will fall to only few mΩ
- Because of the very low resistance of plasma at the moment of current flow a very low electrical energy is transferred to heat.
-Because of low heat, GDT can take high impulse current like direct strike from lightning .
-Typical application class I (B) SPD
Apart from lightning and surge current the SPDs also can be used in application of switching surges.
A surge arrester is a device to protect electrical equipment from over-voltage transients caused by external (lightning) or internal (switching) events. Also called a surge protection device (SPD) or transient voltage surge suppressor (TVSS), this class of device is used to protect equipment in power transmission and distribution systems.
( Source from Wikipedia )
The reason switching surges exist is because of the inherent inductance and capacitance of power systems. The lines and transformers are major contributors of inductance. The lines are also very capacitive relative to earth and other phases.
When a surge occurs during a thunderstorm, it is usually caused by direct strike, nearby lightning strike or distanced lightning strike. The high energy generated by impulse current and voltage are extremely dangerous and it is imperative to protect these electrical/electronic systems and equipment from the danger they are exposed to.
Taking into consideration that there is an earth impedance, a direct or nearby lightning strike will cause a high voltage drop from the earth impedance from a building to the surrounding earth distance. This voltage drop from the earth impedance from the building to the remote earth or potential difference will create an electromagnetic wave which will cause a surge into the electrical/electronic systems and equipment.
Distanced lightning strike can happen at a faraway distance and propagated to the point of protected devices. Lightning strikes at distanced overheard power lines, discharging at cloud to cloud are also causes of surge current to be induced into the electrical/electronic systems and equipment.
Industrial Surges
An industrial surge covers a phenomena caused by switching electrical power sources on or off.
Industrial surges are caused by:
- Starting motors or transformers
- Neon and sodium light starters
- Switching power networks
- Switch “bounce” in an inductive circuit
- Operation of fuses and circuit breakers
- Falling power lines
- Poor or intermittent contacts
| LPL | Maximum Current KA | Maximum Type I SPD current KA per mode (10/350us) |
| I | 100 | 25 |
| II | 75 | 18.75 |
| IIII/IV | 50 | 12.5 |
Reference to IEC 62305-1 table 3 / SS 555-1 clause 8.2 table 3
IEC 62305-4 clause D.3.2 / SS 555-4 clause D.3.2 Installation factors affecting current distribution
SPD Standards:
- IEC 61643-11 Low-voltage surge protective devices – Part 11: Surge protective devices connected to low-voltage power systems – Requirements and test methods (replaces IEC 61643-1)
- IEC 61643-21 Low Voltage Surge Protective Devices – Part 21: Surge Protective Devices Connected to Telecommunications and Signalling Networks – Performance Requirements And Testing Methods
Surge Protection Devices
| LPL | Maximum Current KA | Maximum Type I SPD current KA per mode (10/350us) |
| I | 100 | 25 |
| II | 75 | 18.75 |
| IIII/IV | 50 | 12.5 |
Reference to IEC 62305-1 table 3 / SS 555-1 clause 8.2 table 3
IEC 62305-4 clause D.3.2 / SS 555-4 clause D.3.2 Installation factors affecting current distribution
SPD Standards:
- IEC 61643-11 Low-voltage surge protective devices – Part 11: Surge protective devices connected to low-voltage power systems – Requirements and test methods (replaces IEC 61643-1)
- IEC 61643-21 Low Voltage Surge Protective Devices – Part 21: Surge Protective Devices Connected to Telecommunications and Signalling Networks – Performance Requirements And Testing Methods