We were asked to investigate a possible fault with a Voltage Optimisation unit installed at a Gym south of London. The site reported that the load started to flicker and eventually the VO unit went into bypass mode increasing the voltage back to its original levels.

Upon further investigation, it was found that the L2 phase terminal on the voltage transformer had failed and caused damage to the L2 transformer winding. The unit had not been serviced since installation and we suspect a poor connection was the cause of the terminal overheating and ultimately failing.

Therefore, we  recommended a new 400A VO unit connected to the existing 400A-rated bypass device along with the removal and disposal of the failed equipment.

The work was to be done out of hours to prevent any disruption to the Gyms customers and keep downtime to a minimum. upon completion the site voltage was reduced from 429V per phase to 398V per phase, helping them save money on their electrical bills.


We were asked to carry out a survey with the intention of replacing 1000kVAr worth of failed PFC equipment at a large office building in central London. Upon our initial visit to the site we found that the existing Power Factor Equipment had suffered some major component failures due to lack of servicing which had consequently led to a small fire and the units being isolated by the site.


The two PFC units on site, each on one supply, were split into a Master/Slave configuration with the existing mains cables coming into an expansion box on the side. These cables were still satisfactory and to help the customer keep costs down it was decided that they were to be re-used for the new equipment.


The new units would be from our FSi Deep range and consist of 2 stages of 30kVAr and 7 stages of 60kVAr each with its own 189hZ detuning reactor all controlled by a 10-stage Lovato Digital control relay.


Due to the location of the LV panels being on the roof of the 12-story building, once the new PFC panels had been built and tested the detuning reactors were removed to help reduce the total weight of the units making them more manoeuvrable for our engineers. Once the units were positioned the reactors were re-installed and the panel re-tested.


The installation took 4 engineers 2 days during normal working hours with no disruption to the site, and all waste was removed and disposed of as required. On the 3rd day, an engineer returned to commission the new panels and carry out some final tests.




This Power Factor Correction unit was found to be unsuitable for site during an annual maintenance inspection along with multiple failures. It was also noted that the capacitor stages for too coarse for the load and the site would benefit from a mixture of smaller and larger stages to allow the PFC to fine-tune its correction.

As such a new 5 stage 100kVAr Power Factor Correction unit was quoted to be installed with a mix of 13.5kVAr and 25kVAr capacitor banks all controlled via a Lovato DCRL5 digital control relay.

Utilizing the existing power and C.T cables kept the cost down for the customer and meant our engineer could carry out the work during normal working hours without any disruption to site supply.



An example of one of our FSi100 Power Factor Correction units with the addition of illuminated Hand/off/auto selector switches. These switches allow the manual operation of the capacitor stages without the use of the digital control relay.

The selector switches also illuminate when the capacitor bank comes into circuit providing another form of indicating separate from the control relay display. This style of switch can be added to any of our PFC equipment upon request.


Here we see the unit following its testing carried out in-house by our workshop team. Once all testing is completed and approved the unit is either delivered and installed by one of our electrical engineers at PFC Engineering or when requested as supply only, delivered to site.




We are contacted by an insurance business that occupies a large commercial building in central Ipswich regarding the failure of an Active Harmonic Filter on one of the LV supplies.

We already carry out the annual Power Factor maintenance on site and were familiar with the site’s electrical installation. Following a week-long Power Quality Analysis we were able to provide a quotation to supply and install 2 new 100A 4-wire Active Harmonic Filters to be wall-mounted in the same location as the failed unit. These 2 new filters were designed to go on one LV supply with the filters working in a Master/Slave configuration.


Due to the additional AHF being connected a new 4 core cable was also run to a spare switch on the LV panel and the original C.T circuit was reutilized.


All works were completed during normal working hours without the need for a shutdown.


The fuse switch built into this old-style Power Factor unit had failed in such a way that the rotary handle mechanism no longer functioned.


The unit was luckily fed via another MCCB in the LV panel so it was able to be isolated safely. The fuse switch was then removed and a new 200A load break switch was installed in its place using the original power cables.

A new interlocking handle and shaft were installed and then the unit was put back in service.


Unit replacement on baggage line at large UK airport.


Due to a change in the load, this existing single-stage 50kVAr unit was too large for accurate correction so it was to be replaced with a unit that still had a total kVAr output of 50kVAr but split into 4 smaller stages of 13.5kVAr.


Utilising the existing power cables and C.T cable the unit was swapped out with a standard FS100 PFC unit with built-in local isolation and the remote control relay was moved from the LV panel into the PFC unit itself for easier access.



This 100kVAr Power Factor Correction unit installed at a high street supermarket had not been fully serviced since its installation in 1992 and as such we recommend an ‘End of Life’ replacement for all components.

This FS style of PFC unit built by us at PFC Engineering is still in use today, however with a more updated style. This meant that our workshop was able to build and pre-test the whole tray assembly and then one of our site engineers was able to replace the old ‘SBA Tray’ like for like.

The new SBA tray assembly consisted of all new 480V rated Frako capacitors, IMO MC32 soft switching contactors and subfusing.



A recent installation of two Power Factor Correction units at a large recycling facility in north London.

Due to the nature of the site, the switchgear was extremely dirty and the original Power Factor Units installed, one stand-alone unit and one panel-built unit, had to be disconnected and removed ready for the new equipment to be installed.


The larger of the two panels was a fully detuned 400kVAr FSi Deep PFC unit with 8 stages of 50kVAr, each with its own 189Hz detuning reactor, soft switching contactor and sub-fusing.


The smaller unit was also a fully detuned 250kVAr FSi PFC unit with 5 stages of 50kVAr each with its own 189Hz detuning reactor, soft switching contactor and sub-fusing.


Once the old equipment was removed and the new units positioned, additional cable trunking was installed for cable management and a shutdown was scheduled for final connections.


Finally, the area was cleaned up and the units were commissioned. All the works were carried out over 3 days by 2 of our engineers with minimal disruption to the site.



Harmonic levels at a large grain storage and drying factory had, over the past few years, crept slowly up in distortion eventually leading to some major equipment failures. This increase was also having a detrimental effect on the Power Factor Equipment already installed on site. Though this was detuned PFC equipment, which is designed to prevent the capacitors from increasing the harmonics when the capacitors come into circuit, it too was struggling with the high levels of distortion on the site load.

Following a week-long Power Quality Analysis, it was concluded that the best way to reduce these harmonics would be with a 125A Active Harmonic Filter on each supply in place of the existing PFC Equipment installed in a Master/Slave configuration. The new AHF would also be able to correct the Power Factor with its built-in capacitor banks.

The new AHF Units would utilise the existing power cables feeding the PFC Equipment, and a new multi-core C.T cable would be run along with new Current Transformers on the main LV tales for the filter to see the site’s loads and correct accordingly.

Once the new filters were installed a full commissioning was carried out on by our engineers along with a connection of a remote monitoring device as standard to provide remote access to the Active Harmonic Filter from any desktop PC.


Upon completion of the works, the new AHF lowered site’s average voltage distortion down from 6% to 2% across multiple harmonic ranges and corrected the Power Factor from 0.89 inductive to 0.99 inductive.



Original Power Factor Correction Equipment on site.


  Active Harmonic Filter

Active Harmonic Filter Active Harmonic Filter


Active Filter – Off


Active Filter – ON 

A large engine manufacturing plant that had multiple failures inside their panel-built Power Factor Correction unit including welded contactor coils, heat-damaged cabling and capacitor failures. Due to the age of the equipment and the wide range of failures, it was decided that an end-of-life replacement of all components would be required.

Load tests taken on-site showed that the full 300kVAr of the original install was not required and the site would operate with a healthy power factor of only 200kVAr. As such the units were rebuilt with 4 stages of 50kVAr detuned capacitor banks utilising the existing framework.

There are 2 supplies in the Switchroom each with its own PFC section so both sets were replaced with new equipment. The reduction in the total amount of kVAr installed in each unit also allows for better access during future maintenances as the LV panel has no rear access.

All the work was carried out by one engineer over 2days without any disruption to the site.


Above – Original 300kVAr PFC Equipment


Below – New 200kVAr PFC Equipment rebuilt in LV Panel


Following an annual maintenance check at a large grain storage and drying facility found that there are high harmonic distortion levels on the sites load and as such the standard FS200 Power Factor equipment installed was now elevating the harmonics even more. As such a replacement fully detuned FSi200 Power Factor Unit was now required.

As the units output rating stayed the same all the original power cables were able to be re-used from the standard PFC unit along with the MCCB feeding the unit. This also meant all the work could be completed during normal working hours without the need for a shutdown.

Ventilation for the unit was also installed due to the heat produced from the reactors. An over temperature safety circuit was also installed as standard to cut the power to the relay should the heat in the unit reach an unsafe level.


Above – Original Standard FS200 PFC Unit


Below – New Fully detuned FSi200 PFC Unit