Power Quality Site & EMI Services

Power Quality Site & EMI Services

In addition to the provision of mitigation to the industrial and commercial sectors, Sentinel Power Quality Group provides a range of harmonic, PQ services and conducted EMI services in the United Arab Emirates, GCC and internationally.

We offer a complete range of PQ and conducted EMI consulting services, audits, troubleshooting, investigations, and compliance testing to national harmonics and PQ standards.

PQ services include :

• Harmonics, power quality and conducted EMI audits.
• PQ and conducted EMI investigations into marine equipment malfunction/failure
• Diagnosis and monitoring of common mode voltage and current (due to VFDs) and other EMC issues
• Studies (including harmonic modelling) on harmonics and related topics for power systems
• Consulting services regarding all aspects of PQ
• Pre-purchase PQ and EMI site measurements to ensure proposed mitigation equipment is correct and to identify that there are no hidden issues which could adversely affect the equipment performance and reliability. Note, this service is also available when considering equipment from other manufacturers.

Advanced harmonics, PQ and conducted EMI measuring equipment

For investigations, Sentinel Power Quality Group utilise advanced, cycle by cycle PQ recorders which capture every single cycle, harmonics to 512^th (voltage) and 256^th (current), capture every PQ event and record over 5000 power and PQ parameters automatically. The data captured is then analysed by powerful, investigative software.

EMC & EMI site measurements

Note that “Power Quality” is usually associated with the interaction of the utility supply, their network consumers and their facilities. Any concerns or problems between, for example, the VFD output to a motor, can be classed as EMC/EMI. These can be associated with excessive du/dt, common mode voltage and current and cable resonance (‘standing waves’).

An example of the interaction between the line and common mode voltages, phase and common mode currents on a PWM VFD is illustrated below.

Excessive common mode voltage can adversely affect susceptible and sensitive control and monitoring equipment and including other VFDs connected to the same ground. The associated common mode current is renowned for destroying motor bearings via high frequency micro-arcs of current.

Examples of some PQ & EMC problems

Food manufacturer – Continual failing of VFDs, their power supplies and disruption of process and monitoring equipment.

Cause : Poor VFD-motor installations from an EMC perspective.

Chiller plant resonance – Large chiller plant operated for 5 years with regular MV PFC capacitor failures. During that time, four PQ companies visited, none could find resonance as each event lasted <8ms (< half an ac cycle). SPQ captured first event within 41 mins and fourteen more in next three days.

Cause : Incorrect PFC design.

Pump drive – AFE VFD  (low harmonic drive) driven centrifugal pumps had direct spurious trips. In addition, regular trips were recorded on other equipment locally.

Cause : The lack of a proper L-C-L filter was the cause of the excessive 10kHz components. This, plus poor system quality control and lack of compliance with regard to EMC resulted in excessive common mode voltage directly and indirectly attributing to the VFD and local spurious trips.

Large kW chillers with integrated active filter(s) – Advanced healthcare facility A number of large capacity chillers with integrated active filter(s) but considerable localised PQ problems included the failure of a number of very expensive medical scanners.

Cause : The 15kHz CMV travelled through the ground (around 280m) and destroyed the scanner power supplies, disrupted medical monitoring and other equipment The serious problem on this site was that the installation was incompliance with IEEE 519-1992 at the PCC (with the utility) but was well above those limits with the facility IEEE 519 at that time was limited to 50^th order. It does not cover EMC, of which common mode voltage and common mode current are important components.

Large DC drives – DC (SCR drives have been largely overtaken over the last 20 years by VFDs However, in many industries, they are still as used. The waveforms below are facility with 3 x 1200kW and 2 900kW DC drives. The client purchased an active filter from reduce the THDu. However, within 11 days, the active filter failed and was repaired under warranty Almost three weeks later, the active filter failed again.

Cause : The active filter failures were directly attributed to the lack of AC line reactors. The resultant high frequency notching voltage harmonics damaged/destroyed the active filter’s passive L-C-L carrier suppression filter. If no AC line reactors are present, special measures have to be employed to prevent damage to crucial filter components.

Pumping system – Two 200kW “low harmonic” VFDs resulted in the catastrophic failure of a 2000kVA transformer. Shortly beforehand, the client complained of very hot metalwork and very hot cables. Two large international companies took measurements and measured to the 13^th and 50^th orders. Both stated the compliance with IEEE 519-1992. Two days later, the transformer burned out at light load.

Cause : The failure of the 2000kVA transformer was the combination of greatly increased copper and iron losses, proximity effect and skin effect, all due to the high frequency voltage and current components to 10.4 kHz injected by the active filters were direct or contributory factors in the failure of the transformer. However, the majority of the overheating was likely due to significantly increased iron (transformer core) and copper losses (windings), especially due to the former, as a result of the high frequency emissions from the so called “low harmonic VFDs”!

Repetitive voltage dips – Client, a large facility, was contacted by the utility due to large and continual service voltage dips. A local “specialist PQ company” was employed to undertake detailed measurements and provide equipment to resolve the problem. The company quoted a mix of active filters and SCR based PFC. The client asked SPQ for a second opinion due to content of the report and the cost of the proposed mitigation equipment.

Cause : Full analysis was carried out by Sentinel Power Quality Group The source of the repetitive voltage dips was positively identified as historically incorrectly set-up of a large number of soft-starters on numerous pumps. The soft-starters were set to energise the bypass contactors at around 300V instead of the correct 400V. This would have been realised had the ‘specialist’ PQ company carried out a proper investigation rather than sell a “solution”, the cause of which they were totally aware of. Sentinel Power Quality Group reset all the soft-starter controls and problems were resolved. Had the client purchased the proposed active filters and PFC units, the severe voltage dip problems would have remained.

Our clients include:

To contact Sentinel Power Quality Group for PQ and EMI site services click here…