Sentinel Power Quality, in partnership with leading manufacturers, offers a range of passive and active harmonics, power quality and EMI mitigation solutions, fully fit for purpose for challenging Industrial & Commercial applications worldwide.

We have the extensive knowledge and experience to help you engineer those solutions correctly, whatever the application.

Please use the tabs below to navigate to the appropriate product type or alternatively contact us direct with details of your PQ problem(s) and we will happy to assist you and/or provide advice.


Comsys AB, based in Lund, Sweden, are one of the market leaders in active harmonic technology with over 3000 ADF filters installed across the world; on ships, drilling rigs and industrial and commercial applications. Within the ADF range is the World’s fastest harmonic active filter (ADF P200) which also mitigates harmonics to the 120th order. Comsys's patented optional ADF sensorless control permits elimination of background harmonic voltage distortion and operation without current transformers.

For the Comsys ADF corporate brochure please click here.

Active filters are very low impedance (<1%), electronic harmonic current sources which provide non-linear loads the harmonic currents they require to function. Without such devices, the harmonic currents would be drawn from the generator or transformer often resulting in excessive harmonic voltage distortion in the power system.

Simplified block diagram of active harmonic filter

ALL active filters require at least 3% AC line (or DC bus reactance) in each VFD in order to meet the <5% Ithd (total harmonic current distortion) performance specification. The lack of additional reactance in a rectifier load results in significantly more harmonic current drawn from the active filter than previously from the transformer or generator. This is due to the < 1% source impedance for harmonics of the active filter.  For example, in VFDs, this additional current can be in the order of 50-100% for VFDs without additional reactance. With  3% AC line reactors installed, the ‘additional current’ is around 25% more but this additional harmonic current is usually designed into the current rating of the active filter.

If correctly dimensioned for VFDs with no additional reactance, the active filter will be substantially larger and significantly more expensive than required had suitable AC line (or DC bus) reactors been installed in the VFD. The active filter performance will be significantly degraded (~10-12% Ithd) and will not achieve the <5% Ithd often expected.

There are also issues when active filters are used with DC SCR drives where no AC line reactors are installed. Due to the inductive nature of the load (i.e. the DC motor armature) the additional current drawn when the active filter is connected is less compared to a VFD load (which is a capacitive load). However, if no AC line (or ‘commutation’) reactors are employed then high frequency energy in the DC SCR drive line voltage notches can potentially destroy the active filter’s passive carrier frequency suppression filter and render the active filter inoperative. Indeed, this was the biggest impediment to applying active filters to older rigs with mainly DC SCR drives. A combination of at least 4% AC line reactors and a fast response active filter can almost eliminate line notching, provide an excellent degree of harmonic mitigation resolve the carrier suppression filter problem and, if rated correctly, can also provide displacement power factor correction for systems with DC SCR drives.

Comsys ADF P100 Series

The Comsys ADF P100 series of relatively low-cost, compact active filters can be installed in their standalone IP21 enclosures on a wall in a factory, on a bulkhead or inside a switchboard. Their compensation ratings extend from 50A to 130A, all based on operating up to 50 deg C.

P100 series can be paralleled to a maximum of 15 units.

The P100N is a four wire (4W) device, available only in 100A per phase/300A neutral. However, paralleling up to 15 units is also possible.

In addition to harmonic current compensation, both P100 and P100N can provide simultaneous reactive power compensation as standard.

P100/100A and P100N (100A/300A for neutral)
Automated diagnostics across all ADF active filters

For the datasheet on Comsys ADF P100 please click here.

For the datasheet on Comsys ADF P100N please click here.

Comsys ADF P200 series

The P200, available in 100A ratings, is the fastest active filter in the World. Where most active filters compensate to the 50th order, the P200 compensates to 6kHz (120th order at 50Hz or 100th order 60Hz).

Up to 15 of P200's can be paralleled. Rated up to 50 deg C ambient.

The P200 comes with the option of sensorless (CT less control), wideband compensation and is often applied as an anti-resonant damper on applications which are subject to resonance (i.e. the P200 can be tuned in to prevent the resonance from occurring).

P200 – Fastest active filter in the World
P200 control panel – P200 can be used to prevent resonance and mitigate to 120th order

For the datasheet on Comsys ADF P200 please click here.

Comsys ADF P300 series

The P300 is the modular, high-performance harmonics and PQ workhorse of the Comsys ADF range. Available in voltages from 380V to 690V and compensation ratings from 90A to 360A, the P300 can operate in ambient temperatures up to 50 deg C. No matter how onerous the application, the P300 can handle it.

Up to 15 of P300's can be paralleled up. Simultaneous reactive power and harmonic compensation available as standard.

Both air cooled and liquid cooled P300 variants can be supplied.

Air cooled P300 cabinets can accept up to three 120A modules (360A)
P300 dashboard common across the ADF range
Door mounted display common across the ADF range

For the datasheet on Comsys ADF P300 please click here.

Comsys ADF PM300

The Comsys ADF PM300 is the P300 designed with OEMs and system integrators in mind. It allows them to install the filters into their own systems. It is supplied in component form as illustrated.

In common with the P300 series, the PM300 is available with air cooling or liquid cooling capabilities for operation up to 50 deg C.

Modular construction for ease of system integration
PM300 300A filter integrated with a 400kW VFD and other equipment

For the datasheet on PPM300, 90-120A ADF power processor modules please click here.

For the datasheet on PPM300v2B, 50A-150A ADF power processor modules please click here.

For the datasheet on PPM300W (liquid cooled), 140A-150A ADF power processor modules please click here.

For the datasheet on SCC2 ADF Controller for 1-6 PPM modules please click here.

Comsys ADF Sensorless Control

All active filters, including Comsys ADF series, attenuate the harmonic currents drawn by non-linear loads and indirectly reduce the harmonic voltage distortion due to the load(s) under mitigation. This requires the use of current transformers.

The range of Comsys ADFs also uniquely offer the option of ‘sensorless’ control, negating the requirement for current transformers. This can ensure that installation and commissioning is easier and quicker.

ADF Control set to voltage (sensorless)

Another exciting application of Comsys ADFs ‘sensorless control’ is compensation of background harmonic voltage distortion (Uthd) which effectively isolates it from loads downstream. This is essentially ‘voltage reconstruction’. This is of particular importance on drilling rigs and production platforms where large AC VFDs and or DC drives may result in excessive harmonic voltage distortion and other disturbances, which propagate through transformers to lower voltage consumers (including ROVs), disrupting or damaging susceptible or sensitive equipment.

If you, are your clients, have problems with LV equipment, possibly due to high background harmonic voltage distortion please contact us.

Important tool…

Active filters however, when applied correctly, are an important tool in the harmonic mitigation toolbox.   However, no form of harmonic mitigation is perfect. The secret of success is recognising the pros and cons of all types of active (and passive) mitigation and being able to apply the most appropriate form of mitigation for any given application.

We are in the process of updating our websites with high quality alternative products including series passive harmonic filters, du/dt filters and sinus filters.   Once all the details have been finalised, the ranges will appear in the websites of Sentinel Power Quality Group FZE and its divisions, Harmonic Solutions Oil & Gas and Harmonic Solutions Marine.


In the meantime, please forward any enquiries to us and we will respond accordingly.

We are in the process of updating our websites with high quality alternative products including series passive harmonic filters, du/dt filters and sinus filters.   Once all the details have been finalised, the ranges will appear in the websites of Sentinel Power Quality Group FZE and its divisions, Harmonic Solutions Oil & Gas and Harmonic Solutions Marine.


In the meantime, please forward any enquiries to us and we will respond accordingly.

The definition of a ‘transient’ or ‘spike’ is a temporary excess of voltage and current on an electrical circuit which has been disturbed in some way.

They can also be defined as a change in the fundamental (50Hz/60Hz) frequency. A transient ‘surge’ can contain thousands of volts and thousands of amperes with duration of nanoseconds to microseconds.

Example of transient voltage

Transients voltages can be due to lightning, faulty power factor correction switching, faults or other disturbances on the power line, for example.

Whatever the cause, transient voltages can have a devastating effect of unprotected electronic equipment, especially exposed equipment containing capacitors in their input circuitry including small variable frequency drives (VFDs), fluorescent lighting and switched mode power supply capacitors. The results are usually spurious tripping at best or total destruction with all the operational downtime which can result from such failures. Motor winding insulation can also be stresses due to excessive transient voltages.

Capacitor damaged on printed circuit board due to transient voltages

SineTamerTM is a type of TVSS (transient voltage surge suppression) device specifically designed to protect sensitive equipment including switchboards, computers, plcs and AC VFDs.  It is widely used extensively also to protect airport scanners.

Airport security scanners benefit from SineTamerTM
Two SineTamerTM TVSS units at input to switchboard

Damaging voltage spikes are not uncommon industry as can be seen.

Repetitive voltage spikes due to DC drive line notching and stray capacitance

The result is often disruption or the destroying of capacitor-based equipment such as switched mode power supplies, fluorescent light fitting and small VFDs.  SineTamerTM protects such equipment from the effects of the voltage spikes.

SineTamerTM protecting 11kW VFDs

SineTamerTM encompasses the development of a fourth-generation technology for surge and transient voltage protection. SineTamerTM is a lot more than a typical TVSS (transient voltage surge suppressor) which can be found in electrical panels worldwide. It is an engineered solution, specifically designed for the ultra-sensitive nature of electronic circuit boards (such as those used in VFDs, UPSs and PLCs) plus all variations of microprocessor-based control systems.

Please click at the appropriate place to obtain more information on :

SineTamerTM catalogue click here – sinetamer-catalogue.

SineTamerTM for VFD protection -  What exactly is a VFD? 

SineTamerTM for PLC protection - What exactly is a PLC?

SineTamerTM for petro-chemical industries click here – sinetamerpetroleum.

Information on “Unexpected downtime caused by electrical disturbances".