Hi all,
I have a 4-wire level gauge installed on a storage tank and connected to a control panel in the control room about 600m apart. The gauge power and communication boards have been damaged previously perhaps as a result of Lightning surge. The Level gauge is rated 15-24vdc. Now, we want to repair the level gauge and set it into operation. In order to prevent future damage to the device or the gauge, we have gotten a DC surge protector that we intend to install on the DC power line very close to the gauge. Please find attached snap shot of the Surge protector we intend to use. Please we want to know if this Surge protector will work and protect the level gauge from future surge. Considering the Uc rating of this surge protector, is this the ideal surge protector for the gauge or is there any alternative? Your response will be highly appreciated.

 

I am not specialised in surge protection, but at one glance the proposed device doesn't fit in your application.

Your instrument rated at 24VDC, Uc rated 670VDC is continuous rated voltage of SPD, and it's Up 2.2 KV certainly far too high for the intended protection.

May by I am wrong, suggest you consult the vendor for proper selection of SPD.

 

As stated above, the surge protector above is intended to protect at 670vDC. A surge would have already destroyed 24volt device by then.

The nearest I can find is by Furse for telephone applications - see if the spec. is suitable for your application:
IP66 Telephone Line Protector - Furse ESP 15D/2BX
https://www.farnell.com/datasheets/1821392.pdf

 

You don't want a surge protector - you need an isolator. There are literally thousands of off the shelf options for electrical or optical isolation. For lightning isolation I recommend optical - via fibre optic if your budget and install allows.
If you are trying to avoid damage from shifts in the ground plane due to nearby strikes then 10kV electrical should be enough.

 

Please explain how the instrument and it's 24vDC power supply is protected from lightning surge with just an isolator ?

 

Hi oneye14,
The damage to the instrument & power supply & control panel is caused by excessive current in the instrument loop and/or power supply loop. Unless your cable & end devices are fully isolated a change in potential at one end (caused by a nearby lighting strike or simply a different earth potential) will result in current flow in the cable. In general using isolated instrument and comms loops are good practise all the time.
Screens are tied to earth at one point only - all instrument cables must be paired (not cored) - all control panel PLC/DCS inputs must be fully isolated (i.e.; instrument loops should not use a common 24VDC / 0VDC - as typical for cheaper high density PLC's & DCS etc).
For a 600m cable run in a lighting prone area I would use an individual isolated DCC converter for your power supply, and a "loop isolator" at your control panel. Make sure your screen is connected at one end only. Check your 4-wire instrument to determine whether it internally "grounds" either the power supply or instrument loop (yes some do this). Work around it.
If your instrument uses comms rather than 4-20mA - use the correct respective comms isolators for serial / DSL / ethernet etc.
I use Moxa for comms isolators, and Pheonix for power, and MTL for 4-20mA loop isolators - but there are many options - pretty cheap.
Look for high levels of isolation. At the worst the isolator will take the damage rather than the expensive instrument OR control panel comms.
When using comms, always use fibre optic cables for longer runs especially between different earth potentials (i.e.; buildings / substations / load centres).
Cheers, PB

 

I meant DC to DC converter ... although happy face is good too ...

 

You appear to be mixing up current [loop] protection with storm created voltage protection, including high static voltages, which is a very different scenario. We have in the past used barriers, not only for isolation but knowing they would protect from high voltage spikes.

A DC to DC converter would offer little from voltage surges, allowing insulation breakdown to affect power supply and instrument being powered. Surge Protectors such as those quoted by the op detect high voltage spikes and suppress the very high transient currents down to earth. Isolators are not designed to do this.

Lightning protection is a subject on it's own needing specialised knowledge and experience; several of my past clients would have rejected without hesitation the replacement of surge protectors with isolators.

 

Hi Oneye,
I have found nothing survives voltage surge from a direct lighting strike - and the damage is extensive and unambiguous. The comment in the first post "damaged previously perhaps as a result of Lightning surge" suggests you are unclear - which is why I encourage selecting isolation equipment designed for HV levels of isolation.
If the isolation fails - then surge protectors are your friend and can protect your expensive equipment.
Unfortunately surge protectors are often single use - i.e.; they self destruct absorbing the surge or the equipment.
Consider whether the surge protector needs to monitored or will fail in a way that forces maintenance.
I can't seem to find the manual for the proposed IPT PV40/600 - though I think Uc=670 suggests this is designed for LV devices and is well above your target 24VDC.
Pheonix contact have a good range of surge & isolation devices for instruments.
Good luck, PB

 

This is where the study of Lightning protection becomes useful. Fortunately direct lighting strikes even on high ground is very rare; it is the summer storms that create cloud to cloud lightning strikes that are completely silent set the scene for Corona discharge.

Once a field instrument is within range of discharge, surge protection discharges safely to ground. Isolating devices offer no protection at this point. If discharge does become excessive then more often than not the surge protector will become damaged still doing the job it was designed to do.

It is not only a matter of technical expertise but can affect asset insurances.
https://en.wikipedia.org/wiki/Corona_discharge