Fire service switch
A fire brigade switch is a switch that enables photovoltaic systems to be disconnected from the rest of the direct current installation quickly and as close as possible to the modules in the event of danger or to avert danger .
Different strategies are pursued depending on the field of application; in the simplest case, triggering is followed by an interruption in the energy-carrying line. The module circuits (strings) can also be short- circuited in order to reduce the voltage to a safe level.
construction
As an interruption switch, the fire service switch safely separates the live part of the modules from the rest of the installation through an air gap between the contacts in the fire service switch. As a short-circuit switch, it short-circuits the circuit between one or more modules so that the voltage is lowered to a safe level. As a rule, fire brigade switches are designed as remotely operated switches that, for. B. from the entrance area of a house or the fire alarm center with a switch (z. B. key switch ).
The fire brigade switch is usually a remotely operated switch with at least two normally open contacts to safely disconnect both the plus and minus lines, as there is a risk of the contacts "sticking" when switching under load. In practice, a three-pole, remotely operated switch is therefore often used in which either the plus or minus line is routed in series via another contact. Electronic switches (e.g. from Optimizing Performance) are not safe switches and cannot be used reliably as fire service switches.
function
As with all electrical systems, photovoltaic systems can, for example, interrupt their operation or damage cables . This can endanger people, and under certain circumstances an electric arc can occur . This applies in particular to the lines between the modules and the inverter , as these are usually not secured. In contrast to the on-board electrics of vehicles or boats, the risk of a short circuit is low, since the short-circuit current of a photovoltaic system is only slightly higher than the operating current and the components used can easily take over this permanently.
In order to prevent high voltages from being applied to the lines in the event of a hazard (e.g. house fire), which may pose a risk to the people or emergency services to be rescued, fire service switches are installed in certain design variants of photovoltaic systems. These switches are suitable for currents up to approx. 30 A and for high nominal voltages (up to 1000 volts DC ). The manufacturer of the switch or the authorities regularly demand a safety reserve of 20% of the maximum switchable current (a fire brigade switch with a maximum current rating of 30 A may then only be operated with a maximum of 24 A, taking into account the short-circuit case).
Fire brigade switches are switched to interrupt the power supply or to generate a short circuit in the modules combined to form a "string". For this purpose, the fire brigade switch is installed as close as possible to the photovoltaic modules , in any case before or shortly after the cables enter the building.
The fire brigade switch can in case of danger
- manually triggered via a main switch or emergency stop switch or
- triggers automatically as soon as the connection line to the main switch z. B. in a fire, is interrupted (closed- circuit principle ) or
- triggers automatically if the main power supply to the building is interrupted.
Fire brigade switches can switch on again automatically as soon as all previously defined safety parameters are met (fully automatic fire brigade switch), since there is usually no dangerous operating state when the main voltage supply returns.
For maintenance work, fire brigade switches can be mechanically secured (e.g. with a padlock) to prevent them from being switched on again.
Types of fire service switches
Fire service switches must be designed as load switches in such a way that they can switch the maximum rated currents that occur.
Semi-automatic fire brigade switch
Semi-automatic fire service switches trigger automatically. These must be switched on again manually to switch the photovoltaic system on again. In the case of semi-automatic fire brigade switches, e.g. B. stepped on a roof in order to switch it on again, which can endanger people.
Fully automatic fire brigade switch
Fully automatic fire brigade switches trigger automatically. As soon as all the intended safety parameters are available, they automatically switch the photovoltaic system back on.
SolarEdge has developed its own concept in which the safety shutdown was built into the power optimizers .
security concept
Since photovoltaic systems can cause dangerous conditions for emergency services with regard to the possible hazards and effects in the event of failure of a safety device (e.g. fire service switch) (voltage in the building, although the main power supply is switched off), a safety assessment must be carried out in advance. The result of the safety assessment is documented and implemented in a written safety concept.
Example: After the safety analysis carried out, it emerges for a specific system that the switching status of the fire brigade switches should be reported to the control center in such a way that a control lamp only signals this safe switching state (no voltage) when all fire brigade switches are switched off. If only one of the fire brigade switches does not trigger or if the control line for the signaling has been interrupted, it cannot be assumed that the photovoltaic system is safe and switched off according to this specified safety requirement ("light on - all fire brigade switches off"). Therefore, the to meet the safety requirements established for this signaling circuit principle apply.
Function check
According to the information provided by the manufacturer of the photovoltaic system, the fire brigade switches must be checked regularly by the person responsible for the system or the system operator to ensure that they are working properly. The shutdown should not take place when the system is fully loaded, but rather when the load is low (low solar radiation) to protect the contacts of the fire service switch. The result of the function test must be documented.
safety instructions
- Switching photovoltaic systems and fire service switches is basically quite simple. Nevertheless, the installation, removal, repair or maintenance of a fire service switch may only be carried out by a specialist.
- Work on an electrical DC voltage network may only be carried out by a specialist. There is a risk of personal injury and property damage in the event of improper handling or incorrect installation or use.
Alternative measures
In addition to installing a fire brigade switch, other measures can also effectively prevent a danger to people and property from photovoltaic lines in the building. These are e.g. B.
- Concealed installation of the lines,
- other fireproof laying of the lines (e.g. with fire protection tape),
- Installation of the inverter outside the building.
See also
literature
- Patrick Gehlen: Functional safety of machines and systems. Implementation of the European Machinery Directive in practice. 2nd Edition. Publicis Corporate Publishing 2010, ISBN 978-3-89578-366-1
- Alfred Hösl, Roland Ayx, Hans Werner Busch: The electrical installation in accordance with regulations, residential construction, commercial industry. 18th edition, Hüthig Verlag, Heidelberg 2003, ISBN 3-7785-2909-9
- Günter Boy, Horst Flachmann, Otto Mai: The master's examination in electrical machines and control technology. 4th edition, Vogel Buchverlag, Würzburg 1983, ISBN 3-8023-0725-9
Web links
Individual evidence
- ↑ SOLTEQ fire brigade switch ( memento of the original from June 26, 2015 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. .
- ↑ See Anton Schäfer , Structure of a fire brigade switch .
- ↑ a b See Anton Schäfer, Necessity of fire brigade switches .
- ↑ If several main or emergency switches are in use, which switch off the same system, each of these switches must put the entire system out of operation.
- ↑ See e.g. B. DIN EN ISO 13850 (successor standard to DIN EN 418).
- ↑ See Anton Schäfer, Function of fire brigade switches .
- ↑ Example: EATON fire service switch .
- ↑ Example: ETA fire brigade switch ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. with arc detection.
- ↑ Use is e.g. B. EN ISO 13849 or safety requirement levels according to DIN EN 61508 or the international standard IEC 61508 . Here are risk graphs created to quantify the risks. The higher the risk, the higher the requirements for the fail-safe safety of the shutdown device.
- ↑ See Anton Schäfer, Functional Control of Fire Service Switches .
