TRANSIENT
Protection against transient overvoltages: very high voltage peaks (kV) of a very short duration (µs) which result from surges caused by lightning strikes or power network switching operations.
Surge Protection Devices (SPD)
SPD selection guide
According to IEC standards, depending on the installation's exposure to surges, protectors of different discharge capacities will be required.
Another point to be taken into consideration when selecting SPD is the equipment to be protected, as the level of protection (residual voltage) provided by the protector must be less than the value the equipment can withstand.
Depending on the discharge capacity or protection level (Up), protectors are divided into three classes.
Type 1
SPD capable of shuting high currents in waveform 10/350 µs. High Protection level (Up). These protectors must be installed at the main incomer expect the highest exposure to overvoltages and its protection level be only compatible with the equipments installed on it.
Type 1 protectors are required where a direct impact of lighting are expected or there is a LPS, as for example:
- Protection of rural houses with a lightning protection system.
- Protection of industries with a lightning protection system.
- Hospitals, public or cultural heritage buildings, etc. at a distance of less than 50 m. from an installation with an external protection.
Type 2
SPD capable of shuting high currents in waveform 8/20 µs. Medium protection level (Up). These are the most widely used as they provide a level of protection compatible with most equipment connected to the electrical network.
Its use is appropriate for medium protection where Type 1 surge protectors are installed or as a first step in homes, shops, etc. Type 2 SPD must always be installed downstream of Type 1 SPD in all installations with LPS, in the low voltage switchboard.
Installing it at the main incomer will be sufficient where the distance from an installation with an external protection is less than 50 m.
Type 3
SPD capable of shuting high currents in waveform 8/20 µs. Low protection level (Up). Must be installed to protect sensitive equipment for individuals and industrial equipments, and on equipments over 20 m. away from where the Type 2 SPD is installed.
Our SPD are based on varistor (MOV), gas discharge tube and spark gap technologies, and a combination of these, depending on the discharge capacity required.
Ideal method is to protect in steps, using different types of protector and selecting the devices best suited to the installation.
Our surge protectors are manufactured in accordance with IEC-61643-1, NFC 61-740, BS 6651 and DIN VDE 0675-6 standards.
Working principle of a SPD
SPD acts as a voltage-controlled switch. When the voltage is less than the nominal voltage, SPD acts as an infinite impedance element, and when the voltage is higher than the nominal value, it acts as a zero impedance element, shunting the excess voltage to ground.
Specialist in protection
Cirprotec family of surge arresters includes a full range of compact protectors for installation on DIN rail. The range is specially designed to provide complete and effective protection against surges, protecting equipment and property connected to the low-voltage network.
The range includes Type 1 35 kA to 100 kA surge arresters in 10/350 µs wave form, and Type 2 surge arresters with different discharge capacities: 15 kA, 40 kA and 100 kA in wave form 8/20 µs. Also Type 3 SPD's of different discharge capacities are available. The most suitable value will be selected according to the type of installation, premises and equipments to be protected (see the selection table). Four different formats one-pole, single-phase, two-phase and three-phase.
[Up] LEVEL OF PROTECTION
This is the paremetrer that characterises the action of the protection device against surges by limiting the voltage between its terminals. It must be less than the surge withstand capacity given by the category of the equipment to be protected. However, if the protector is far from the equipment to be protected it may be necessary to use additional protectors.
[Iimp] IMPULSE CURRENT
This is the peak current that the SPD can withstand without failing. The waveform of the applied current is normalised as 10/350 µs. Used in Class I SPD.
[Imax] MAXIMUM DISCHARGE CURRENT
This is the peak current it can withstand in a single pulse without failing. The waveform of the applied current is normalised as 8/20 µs. Used in Class 2 SPD.
[Uc] MAXIMUM CONTINUOUS OPERATING VOLTAGE
This is the maximum r.m.s. or d.c. voltage which may be continuosly applied to the terminals of the SPD.
[In] NOMINAL DISCHARGE CURRENT
This is the current that the device is capable of shnting to ground at least 20 times without failing.
[IR] REMOTE INDICATION
Models with remote indication (IR) have a voltage-free contact for remote signalling of the end of the protector's useful life.
Overvoltage propagation paths
Two are the paths for propagation of transient overvoltages. The first one is Common Mode propagation (or asymmetrical). This happens when the electrical disturbance takes place between the active conductors and ground (phase-to-earth and/or neutral-to earth), with risk of dielectric perforation. The second type of propagation is called Differential Mode (symmetrical). The disturbance takes place between the active conductors themselves (phase-to-phase and/or phase-to-neutral). This mode does especially affect computer and electronic equipment.
Coordination of protectors
It is intrinsically impossible to combine high discharge capacity along with low residual voltage (level of protection) in a single protector. It follows that an installation comprising sensitive equipment cannot be protected efficiently with just one protective device or step. Two or more protectors are needed and they shall be coordinated. The first one (P1) shall be installed at the main incomer and the rest (P2, P3, etc...) shall be installed at the distribution panels of the most sensitive lines according to the Up (level of protection), always as close to the devices as possible.
P1 is to be selected according to Iimp / Imax whereas secondary protectors must be chosen to assure the lowest Up. The rule to be followed in order to coordinate the operation of several protectors suggest to leave at least a 10 m. distance between them. The reason is that electrical wires delay the current associated to the overvoltage due to their inductive behavior. It is thus necessary to assure that P1 will have time to discharge the major part of the energy before the secondary protectors carry out their duty of reducing the residual voltage that the formers leave downstream. If two protection steps are installed in a single panel, coordination inductances will be used to obtain the same effect as the 10 m. cable stretch.
