Peter Hudson, Trabtech product manager, Phoenix Contact ANZ
The myth says, “Lightning never strikes the same place twice.” But if it was to strike even once, what would the repercussions on a modern manufacturing facility be?
Downtime cannot be tolerated in today’s just-in-time manufacturing environment. Competition is fierce and we need to stay competitive with the highest uptime possible. As the modern plant moves to more automation and electronics, we increase the sensitivity of components to high voltage surges that can damage or cause a malfunction in controllers, PCs, and other electronic peripherals.
Lightning and surge protection for the electrical panels is a very low cost protection method that is a must in the modern times. In the Main switchboard, it can divert lightning currents from nearby strikes, or transient over-voltages from the electrical grid away from the buildings electrical infrastructure. If not installed, these surge currents will travel throughout the building with a major cause of failures, or worst case a potential fire risk.
According to the lightning protection standard AS/NZS 1768, an Imax rating of 100kA to 40kA is suitable for the main switchboard dependant on the buildings lightning risk classification and electrical services delivery. A “C3” classification for high exposure, “C2” medium Exposure, “C1”; low exposure. If an event occurred, the majority of the transient is removed at the main switchboard, with only a portion of the transient voltage continuing within the building. This standard also discusses an IEC lightning values of IImp, where 10kA IImp loosely represents an Imax value of 100kA.
Secondary surge protection should be installed to reduce the residual voltage; but before we reach the sub-distribution electrical panels, the plant will now introduce its own transients within the building from items such as switching operations from Power factor correction units, generator change-over, Large Circuit breakers, motors, and large contactors. These all produce transients with moderate surge currents which need to be reduced at the sub-distribution panels, prior to progressing further into the building. Here; AS/NZS 1768, suggests for Category “B” installations, an Imax rating of 40kA down to 10kA is suitable. This also includes cables leaving the building from these panels for external power circuits but within close proximity to the building.
For panels housing Electronic equipment, surge protection should be a must, and installed on the feed to the electronic equipment. This could start with the AC supply to a power supply, UPS, a PC, or PLC. All these devices have small surge protection installed, but using a pluggable upstream surge protector will ensure longevity of the devices own transient components, and when the upstream SPD fails, it can be simply unplugged and replaced without interruption to the load. Just like using interposing relays on PLC’s, use an interposing SPD! A common question is; if protecting the 240V mains, do I need protection of the 24V side? The simple answer is yes; usually on the 24V input side to a PC, PLC, or electronic device. The reason for this is we now have 24Vdc switchgear connected to the same line as the PLC power supply. Collapsing fields of contactors when turned off, generate approximately 1,000V transients, and this can interrupt electronic controllers, and wear down their internal transient protection, thus reducing the potential lifespan of the devices.
Testing of the surge protection devices is recommended during the life of the plant, especially if the plant exists in a high lightning zone or has critical processes. An Alarm contact on SPD’s will notify maintenance when a module is spent. This is simply unplugged and replaced following electrical safety guidelines. But during maintenance shutdowns after years of operation, it is a great time to test your surge protection devices to determine if they full function. Testers like the Checkmaster 2 can determine if they are healthy, nearing design life, or have failed. This provides reassurance the plant is starting with the best possible protection in place.
Phoenix Contact is a leader in the design of Lightning and Surge protection equipment for electrical systems. Designed and tested for the highest safety to IEC61643-11, the Safe Energy Control range, provides powerful protection in a compact and pluggable Din Rail mount housing. The SEC range have compact pluggable arrestors for Lightning and Surge protection that suit the needs of Telecommunications, Mining, Water, Process, and general electrical installations.