Measurement and control systems are vulnerable to transient surges and so require robust lightning and surge protection to avoid plant outages.
In addition to providing high-performance protection circuits and equipment status monitoring, it is especially important to ensure surge protection systems are easy to install and expandable.
Ensuring production plant availability is becoming increasingly important. Plant outages in any industrial sector generally entail substantial financial loss. Many demands are placed on surge protection devices (SPDs) in measurement and control systems.
In order for lightning and surge protection equipment to do its part in ensuring production facility availability, the SPDs must have high-performance protection circuits. Moreover, the protection systems also have to be monitored. It is not sufficient just to report an outage after it has occurred; preventive information about the status of the installed SPDs is also required.
The facilities to be protected are typically widely distributed, so it is helpful to be able to report and monitor the status of SPDs remotely, to avoid having to perform on-site inspections of the protection systems.
The new Plugtrab PT-IQ family of surge protection systems provides a status report when protection devices have reached their performance limit. A yellow LED indicates this status.
In large production plants or facilities that are difficult to access, such as remote wind power installations, performing on-site visual inspection of the surge protection equipment can be time-consuming and costly.
In such situations, it makes sense to use remote indication contacts to transmit the SPD status. The floating contact design of the Plugtrab PT-IQ allows users to select the transmission signal of their choice. Other components make it possible to integrate the remote indication contacts into intelligent reporting systems using the cellphone network or other wireless technologies.
The latest technology integrates the remote indication contacts into the housing design of the surge protection device. Doing this requires using connection terminals that could have been used for protecting other signalling lines. The obvious solution is to put the remote indication and auxiliary power equipment into a separate external controller.
Doing this is highly beneficial for the protection design, since controllers can be used to supply auxiliary power to multiple SPDs, making possible a group indication for the connected SPDs. This frees up all SPD connections to protect the signal lines.
Up to five signal lines can be connected to the SPD, providing space and cost savings. The new Plugtrab PT-IQ product family uses a T-Bus as a carrier rail connector to minimise the power supply and status indication installation costs.
If maintaining plant expandability is an important consideration, a surge protection system should be uncomplicated and expandable without requiring a great deal of installation effort. Such protection systems are also advantageous for handling last-minute planning modifications, which occur frequently nowadays.
The T-Bus design also allows the protection system to remain flexibly expandable in these situations. To integrate additional SPDs into the protection design, the T-Bus can simply be placed onto the carrier rail and connected to the other connectors. Additional SPDs can then be installed on it.
When selecting SPDs, it is important to consider not only the protection level but also the pulse discharge capacity. These properties, as well as many others, are established through standardised tests in accordance with the product standard. Users must differentiate between the types of standardised pulses that were used to determine the protection level.
For example, due to the internal design, the protection level for a C2 pulse of 10 kA is significantly higher than the protection level for a C3 pulse of 50 A. Since the expected pulse strength often depends on the installation location, well-documented SPDs ideally carry specifications for a number of standard pulses.
Measurement and control installations have small cable cross-sections, meaning that the resistance per unit of length (? / m) is relatively high. Comparatively moderate current pulse peaks of a few kA may therefore be assumed.
However, the devices to be protected against surges are more sensitive than line-powered devices. The protection level of the SPDs must be as low as possible. A good protection level can be achieved using voltage-limiting diodes (TVS – transient voltage suppressors). The current-carrying capacity of these devices is limited to several amperes. Gas discharge tubes (GDTs) provide good current-carrying capacity, but some require a relatively high trigger voltage of over 100 V. Two-stage surge protection devices combine the advantages of both components in one device: the low protection level of the TVS diode and the high current-carrying capacity of the GDT.
This makes it possible to protect not only devices having low rated currents such as sensors, but also typically low-resistance actuators such as valves, contactors, and motors. Smaller signal path losses make thermal management at the installation site easier and more economical. Since each current pulse causes wear to the gas discharge tube as a function of the pulse strength, the increased current-carrying capacity of the protective diode and the protective resistors help extend the service life of the SPD. This is possible because the diode covers a larger current pulse amplitude range.
The requirements for the highest level of production plant availability call for high-quality, high-performance surge protection products that are easy to install. These products must provide system-dependent advantages over standard products. Phoenix Contact’s new Plugtrab PT-IQ product family now offers a surge protection system for all current measurement and control application areas, which can be easily integrated into the plant’s protection equipment design and expanded as required.
• Phoenix Contact is a leading developer and manufacturer of industrial electrical and electronic technology and has been operating in Australia and New Zealand since 1996.