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Intelligent surge protection device monitoring

Applicable DIN standards demand the regular inspection of surge protective devices, and many users also want additional monitoring during operation. But what options are there for monitoring, diagnostics, and the electrical testing of devices? To be able to react quickly to device overloads or failures, the status of surge protective devices is transmitted and evaluated throughout the system or between systems.

Sensitive electronic devices are increasingly being installed in areas where high system availability is required. Surge protective devices (SPD)  are used as effective protection against man-made surge voltages and against weather-related surge voltages and lightning currents.

SPDs are designed such that typical man-made or weather-related surge voltages or lightning currents do not lead to appreciable premature aging of the devices. Frequent man-made surge voltages and high-energy lightning events can, however, lead to the SPDs themselves aging prematurely. At the end of their service life, SPDs are automatically switched to a safe state and are normally disconnected from the protected circuit.
To ensure high system availability, SPD aging must be detected as early as possible – prematurely damaged SPDs should be replaced as part of a preventive maintenance program. Premature SPD aging can be easily detected through smart monitoring functions and qualified electrical testing.

Surge protective devices with simple status indicator
Many SPDs are equipped with a simple status indicator. On varistor-based SPDs, for example, the temperature of the varistors is monitored, and the status of the thermal disconnect device is displayed on the front of the SPD. Thermal disconnect devices are not just used in SPDs for energy technology applications. They can also be used in signal or data-related applications to detect overloads in SPDs due to impermissibly high external voltages – for example through the unintentional connection of a higher voltage to a circuit with a lower dielectric strength.

Smart status monitoring
In SPDs for signal and data-related applications, monitoring electronics integrated into the devices have been used increasingly in the past few years. Such smart SPDs can measure leakage currents, detect short circuits and register surge voltages and lightning currents.
Smart SPDs often need an auxiliary voltage supply – 24V DC, for example. User-friendly SPDs are designed in such a way that the supply of auxiliary voltage and the acquisition of status information is possible without the need for additional wiring or configuration work – for example via a DIN-rail-integrated bus system.

Acquiring and processing status information
SPDs are often equipped with remote indication contacts for transmitting status information. Users often want a group message to be issued if one or more SPDs are defective. A group message can be realised through the series connection of remote indication contacts. Some more technically sophisticated SPDs enable the generation of optoelectronic group messages, for example. One vendor, Phoenix Contact, offers its TERMITRAB complete product range, while the PLUGTRAB IQ product range is available for group messages via DIN-rail-integrated bus systems.

In some cases, SPDs are installed in remote locations – for example in elevated water tanks, well systems and pumping stations. Wireless modems are a suitable option for such applications, enabling status information to be transmitted to superior automation and signaling systems.

The status information of surge protection devices is displayed, transmitted and processed by:
• Local display (lamp, signaling panel);
• acoustic signaling equipment (horn, buzzer);
• input of a PLC or automation system;
• remote input of a fieldbus system or TCP/IP based network;
• field multiplexer;
• analogue modem;
• GSM/GPRS wireless modem (SMS, e-mail, smartphone app, ODP protocol); and
•     trusted wireless networks.

Regular SPD testing
The regular testing and maintenance of lightning and surge protection devices is required by various parties. These include legislative, regulatory and professional bodies, and also applicable DIN standards, such as DIN EN 62305-3 Appendix E.7. The test interval for visual inspections and for comprehensive testing depend on the type of system and the lightning protection levels to be used in accordance with DIN EN 62305-3 Table E.2. Comprehensive testing for lightning protection levels I and II must be performed at the latest every two years, and at least every four years for lightning protection levels III and IV.

Many SPDs have a simple function display. Some smart SPDs have additional monitoring functions which enable extended SPD monitoring and diagnostics. Comprehensive testing of the devices, as stipulated in DIN EN 62305-3, is not possible during ongoing operation of an electrical system. A suitable high-voltage test device is therefore necessary for testing SPDs comprehensively. The measurement results obtained during the tests are then compared with reference values and evaluated. For meaningful testing, SPDs must thus be designed such that it is possible to test all relevant SPD components.

Monitoring SPDs is essential for high system availability. SPDs with smart monitoring functions can detect complex error states, therefore going far beyond the function of a simple thermal monitoring system. The status information of SPDs can now be acquired conveniently and then displayed and processed throughout the system and between systems. Furthermore, intelligent high-voltage test devices enable the comprehensive electrical testing of SPDs within the scope of test intervals specified in standards and by legislative bodies.

Standards for surge protection are:
•     DIN EN 62305-3 and VDE 0185-305-3 (2011): Protection against lightning – Part 3: Physical damage to structures and life hazard
•     DIN EN 62305-4 and VDE 0185-305-4 (2011): Protection against lightning – Part 4: Electrical and electronic systems within structures.

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