Troubleshooting onsite problems caused by power quality issues

July 4, 2017

 

 

Often in the lighting industry, there are cases where an onsite power quality problem can be misidentified as a reliability issue with old/worn onsite breakers [where nuisance tripping occurs and is attributed to old faulty breakers] If such a site issue is not correctly identified, the resultant non-compliant power supply, could lead to product failure of solid state [LED] lighting units and other onsite machinery.

 

When a non-compliant supply damages onsite lighting equipment – the chances are that this scenario may be misinterpreted as a product reliability issue, if the site manager is unaware of the supply issue [just as with the breakers]

 

In this situation, the lighting product supply company should examine faulty/returned units - in order to determine the cause, and make the right call with regards to immediate corrective action. 

The product may be at fault or unsuitable and needs replacing – or they may be a need to investigate site conditions further.

 

However –there are many box shifting companies will simply replace the faulty products, only to find the same fault occurring all over again!  Without sufficient technical knowledge, the lighting company may then dismiss a second failure, as being a reliability issue with the product, and then replace the product make/type – without knowing the same issues will still occur on any replacement product selected.

 

Guessing at a solution- for what could be a complex onsite EMC issue [without technical support/knowledge] could lead to an ongoing situation [with rising costs] which could damage the site’s own heavy machinery as well as having the potential to cause a legal dispute - which would require a third independent party being called in, to have experts analyse the power quality- in order to determine whether the site conditions ,or the installed product are at fault [with even more additional costs]

 

Bear in mind, that an onsite power quality issue can be an indicator of an onsite energy hazard – not identifying the onsite cause, could be very costly- or even dangerous for the site –if more onsite machinery/wiring is also being damaged/overheated it could produce a fire hazard!

 

When to use a power logger onsite

 

To ensure the sites operation is safe, as well as saving time/inconvenience and money, we always recommend a power quality check if there is any suspicion that there an on-site problem – and when no cause of failure can be found on a returned faulty lighting product. A power quality analysis is often the only way forward, to determine the cause – in such cases, speed is of the essence, as equipment onsite may be in the process of being damaged and quick action could avert an even greater problem from occurring.

 

We understand that hiring an analyzer with the additional cost of shutting the site down during its installation +equipment hire, is not the preferred option for site manager – power loggers should be called in, when a sufficient explanation and remedy has not been found for sure – and there is reason for concern with regards to site safety and/or product reliability or re occurrence of site problems.

Note: Sometimes, what appears to be an onsite supply problem [causing product failure] could actually be the result of momentary damage to equipment, which caused by a brief non-re-occurring event. In these cases, a power logger can only be useful if the momentary cause is re-created while collecting data.

 

Regarding onsite conversions from HID to LED technologies.

 

As mentioned before in our blog-misjudgments can be made, when trouble shooting a mixture of technologies used in parallel – such as a combination of magnetic or HF HID with SELV LED products, the industry has seen cases where old HID lighting units are emitting non-compliant current harmonics – which has damaged new compliant solid-state LED lighting gears AC input filter and rectifies stages.

 

Worn out HID lamps /fittings can create a number of power quality issues – such as ringing harmonics/dips/swells and fast transient voltage spikes – all of which can make the onsite supply non-compliant to the expected limitations set by EN50160:2000 [Voltage characteristics of electricity supplied by public distribution systems] – in such cases, solid state products such as LED lighting units wired in parallel, may have their AC input stages damaged – leading to product failure.

We would advise when switching over from HID to LED, that the LED fittings swapped over in one go – or that during ongoing stages of switchover –that attention is paid to balance of the three-phase system. Remember- converting to LED from HID reduces the load- so if the conversion is only done on one phase first it can create an imbalance that can damage the LED drivers internal components – and as the damage may not show up right away, it could result in a lengthy time wasting investigation [including a logger being unnecessarily installed+ time delay + cost + inconvenience] with no solid proof at the end!

 

Such damage may not be immediately apparent/visible – the electrical characteristics of internal components may have been changed [reducing driver life span –or specification]. In these cases, the cause is much harder to determine later, as the initial site condition changes- leaving no evidence. For this reason, we advise getting as much information about the installation methods used as possible.

 

We write these blogs- to help installers avoid such costly situations –so they can maximise their productivity and success rate.   

        

When power quality issues, such as surges or excessive current harmonics occur – we expect to see many units on the same power feed experiencing the same fault condition – where the AC input stages of the luminaire driver are damaged in the following ways:

 

1. The AC input filter stages are overheat/burnt out [with no load fault on the fitting]

2. The driver’s AC input bridge rectifier’s stage is damaged – with no load fault on the fitting to cause this.

3. The driver’s AC input stage fuse is blown – with no load fault further down the line.

4. The spike suppressing MOVs [metal oxide varistor] are blown –or the copper circuit track to the MOV has experienced overcurrent- or the MOV has blown the main AC fuse [to protect the luminaire from an energy hazard]

5. The drivers internal MOVs connecting between Neutral and Earth are blown [or the copper track between then has received overcurrent damage]

What clues to look for?

There are site indicators, which may provide valuable clues as to the source/location and nature of the onsite problem- such as:

1. When what looks like a rare fault condition affects a large number of drivers which were running from the same feed.

2. When drivers connected to one phase goes faulty – but the units on other phases work fine.

3. When the units which are faulty are all wired at closest to the distribution point, or are the most further away [or suing very long cable lengths].

4. When a mass failure occurs after a site alteration or service shutdown maintenance - where changes are made to the site which could affect the balance of the phases/ harmonics and voltage spike levels.

5. When other equipment onsite has been damaged or interrupted - such as computers – or other solid-state equipment including RF digital communication equipment.  

6. When old HID lighting units wired in parallel, is seen to flicker or have an unstable light output.

 

Very Important- Please note

 

When using onsite electricians to install a power quality analyser onsite – it is vitally important that the power logger is capable and set to record the following data in event mode.

 

Grid frequency

  • Voltage sags and dips - on all three phases.

  • Interruptions- on all three phases

  • Transient over voltage [fast transient voltage spikes] -on all three phases

  • Over voltages – on all three phases

  • Voltage Harmonics -on all three phases

  • Current harmonics –on all three phases

  • Voltage imbalance -on all three phases

  • Dc offsets- on all three phases

Note: current harmonics data, can time-indicate which piece of machinery may be generating offensive harmonics

 

Please note –very important: be warned – if the wrong power logger is chosen [one without full event recording ability] or if the user has no previous experience using that particular model and setting it up, the result could be a frustrating waste of time – especially if the logger was placed on site for a month –with no data to show.

 

If in doubt – we recommend hiring an engineer with their own power logger –who knows how to get the required results, it is tempting to save money by using onsite electrical staff and hiring a logger – but only if they can program the right type of logger the right way. If delays are caused, it could lead to more failures onsite and increasing costs [as well as damage to reputation]

 

If you are looking for a good/reputable UK hire company for a suitable logger- we would highly recommend SIS [Specialist Instrument Services] at http://www.sis-calibration.co.uk/hire

 

We would recommend with any logger hire company, that you fully discuss your requirements with their advice team first. When working on such problems- try to get the site manager /luminaire supplier/logger installer working together by sharing relevant information – it is in everyone’s interests to work as a team and resolve the issue ASAP.  

 

If you are working alongside a lighting company –consult the supplier for additional technical support, before hiring/installing the logger- ask the lighting supplier –if there is any other data that the logger needs to record.    

 

Note: We would recommend leaving a logger on for two weeks or more [depending on site usage and cycle of routine time] with any particular maintenance routines that have occurred previously re-enacted – such as the on/off switching of site machinery in the same sequence as when the fault condition occurred.

 

Simulating maintenance work previously done onsite.

 

Sometimes maintenance work involves isolating the power and switching back on again – the manner in which this is done can affect solid state devices more so than old magnetic gear.

 

For example: If breakers and wall switches are not switched off individually, and all power to the site is restored at the same time [so all site machinery +lighting creates an enormous current inrush+ voltage dips], we could see damage to LED the drivers [they could be inrushes which cause 3 phase imbalances – leading to overvoltage]

 

You may think in this scenario that the breakers will trip before any damage occurs – but if the site has any wiring issues –such as poor earth bonding or raised impedances on cable runs, or if the breakers are rated for the old HD lighting gear – additional unforeseen problems can possibly occur. Bearing in mind, that it is standard practice to isolate breakers and switches when working on a mains circuit, simply because it is good safe practice.

       

An unstable erratic supply, could lead to toggling between voltage drops and spikes -which would then cause the drivers to rapidly switch on/off [which increases the frequency of inrush currents in the driver’s rectifier stages] this can cause the drivers to constantly attempt a re start – extending the start-up time of – thus making the voltage dips on the supply even more complex as well as increasing the time period these supply conditions.

 

The result is an interaction between multiple pieces of equipment – creating voltage distortion/current harmonics, which hinders equipment start-up and creates an extended start up time- exposing equipment to supply conditions which can lead to product failure.  

 

Make note and take into consideration, if any maintenance work has been performed onsite- which may have affected the lighting products, for example –if maintenance of power factor correction capacitor banks requires a discharge test, which involves the possibility stray voltages running through the site wiring system.  

 

As site conditions vary, there many potential complex EMC problem scenarios that can occur – dependent on each particular site. This guide is only for general use to help you get started, as each site may have a different/configuration or cause.

 

Collecting information

 

Note: in view of the possible fault conditions that can occur – we advise getting as much information about the site as possible- ask the site manager the following:

 

1. Are there any previous logger reports for the site? [And if any alterations have been made since]

2. Has the site had any such problems before – if so, what is the site’s history? Has any other equipment onsite failed at any time in its history – this could be another clue, indicating an equipment/supply or wiring issue. 

3. Has any new equipment been introduced/installed recently [was the phase balance checked during and afterwards]?

4. Has maintenance work been done which involves a shutdown/reboot?

5. When did the problems start to occur – does this coincide with any alterations or change in site conditions?

6. What heavy machinery is used onsite -such as large motors /air compressors etc.?

7. Does the sites OEM manual show anything unconventional or bespoke about the site – there may be corrective work done in the past which highlights problematic areas onsite.

 

Ask for any other information [no matter how irrelevant it may seem] – sometimes there may be combination of an EMC issue, with the product running close to its maximum rated ambient temperature onsite [where the EMC fault lowers the ambient temperature handling of a product by overheating it]  

 

Interpreting collected data

 

When looking at the data collected from the logger –it should be read taking the following into consideration: 

1. State/condition/age of the si