An acceptable level of harmonic voltage distortion and power quality is absolutely crucial to both the safety and operational integrity of all offshore or onshore oilfields.

The rationale for continuous power quality monitoring is clear. As well as satisfying current and future regulatory requirements with respect to harmonic voltage distortion levels, continuous monitoring can ensure that any signs of any degradation in power quality are recognized timeously and remedial action taken to resolve matters before equipment is adversely affected leading to/or disruption, equipment failure and downtime or worse, a breach of safety with possible catastrophic consequences. In addition, any ‘events’ leading up to, for example, a total blackout of power is captured and used to assist in any investigations as to the cause.

To address diverse requirements, Harmonic Solutions Oil & Gas offers two variants of PQGuard, our continuous harmonics and power quality monitoring system based on the following options:

PQGuard 605 – A conventional panel or switchboard mounted power and PQ analyser and recorder  which measures to the 63rd harmonic. Applications include monitoring of oilfield ESP VFDs either singularly or per oilfield field or single unit or multiple unit PQ monitoring on drilling rigs/ships, platforms and FPSOs.

PQGuard 4430 – A very advanced cycle by cycle recorder which records and captures every single cycle of voltage and current, almost 10,000 parameters and harmonics up to the 512th. These are applied in applications where significantly more PQ data is required and where deep analysis into for, example, the cause of a fault is crucial.

PQGuard 605 – Conventional analyser/recorder

A conventional type analyser has the following salient features :

  • Voltages (line and phase voltages)
  • Total harmonic voltage distortion both including Uthd (line voltages) and Vthd (phase voltages) up the 63rd order
  • Currents (A)
  • Current distortion (Ithd)
  • Frequency (Hz)
  • Energy – kW, kVA, kVAr
  • Displacement power factor (DPF) and true power factor (TPF)
  • Harmonic voltages and currents (tables and harmonic spectrums to or 63rd order)
  • Flicker (Pst)
  • Temperature (if PT 100s connected)
Panel or switchboard mounted PQGuard 605s

PQGuard 605 based local/remote power quality monitoring systems has powerful tools, including the following features :

  • Full set of trend recordings with date/time playback. PQGuard 605 provides magnification of parameter display to assist with analysis. The trend recording parameters are updated every second.  The accuracy is based on the sampling rate.
  • Adjustable event recording (e.g. “SCR 2 trip”) with two cycles before and after the event with playback. The limit values of each PQ parameter can be set and alarms initiated if required. On some more advanced monitors, emails can be sent to programmed address(s) to advise and event has occurred.
  • Waveforms of voltage and current for trouble shooting or monitoring. PQGuard can provide magnification of waveforms and spectrums to assist real time analysis.
  • Harmonic voltage and current spectrums at point of connection to 63rd harmonic. PQGuard allows for waveform magnification for analysis purposes.
  • If additional I/O installed, MCCBs and other equipment can be monitored (on some units).

Detailed below are some photographs and other illustrations of a recent PQGuard 605 based installation on a drilling tender:

One PQGuard 605 unit can be connected to the the main switchboard to continuous PQ monitoring of Uthd and total (summed) Amps, kW and other current based parameters.

Alternatively, PQGuard 605’s can be installed on each generator, as illustrated above, for optimum PQ monitoring. Details of the system is shown below based on local PQ monitoring and remotely to the company HQ 12,000km away.

PQGuard 4430 – Advanced cycle by cycle recorder

PQGuard 4430 is sophisticated ‘cycle by cycle’ power quality recorder (not analyser), which when combined with dedicated power quality analytic software, provides unarguably the world’s finest harmonics, power quality and events monitoring system.

The PQ recorder can accommodate current signals up to 5A per phase from conventional current transformer or via flexible Rogowski coils.

The complete system is available from Harmonic Solutions Oil & Gas, including industrial desktop or industrial computers and servers.

PQGuard 4430 PQ recorder with multi I/O module installed

The photograph shows the optional ‘multi I/O extension module installed.  This I/O module includes analogue and digital I/O in addition to a relay output.  This allows us to tailor the I/O to your precise application requirements.  With the PQGuard 4430 the operation, temperature and reliability of generators, transformers, circuit breakers and critical equipment can be monitored.

The PQGuard 4430 samples 1024 points per cycle and continuously records every single cycle for up to one year.   With the PQGuard 4430 it is simple to go from recordings of months to an event of milli-seconds or micro-seconds using a mouse.

Every single cycle of voltage and current are recorded plus almost 10,000 power and PQ parameters.  Harmonic voltages to the 512th and harmonic currents up to the 256th are captured.   No event is missed.  The example illustrated shows an event on an offshore platform.   The event illustrated was <2.7ms long.

Uthd, Urms and Irms at the instance an event (<2.7ms)
Physical features of the PQGuard 4430

Additional features PQGuard 4430 include :

  • Sampling : 1024 samples/cycle
  • Harmonics & Interharmonics : Up to 512th voltage/258th current
  • Internal memory : 16GB
  • Transient detection : 19.5/16.3μs (50Hz/60Hz)
  • Ethernet ports : 2
  • Ride through power loss : Up to 25 secs
  • Voltage channels : 4 off plus ground, 1000V rms continuously (8kV peak)
  • Current channels : Up to 5 off, up to 5A (50A peak)
  • Fundamental frequency : 42.5Hz to 69Hz
  • Power supply : 110-260VAC and 100-300VDC, 48 VDC auxiliary
  • Operational ambient : -20 deg to 70 deg C

Every single cycle of voltage and current, almost 10,000 power and power quality parameters are automatically captured and stored via PQZip, a patented process which compresses the data over 1000 times (all these parameters can be fully analysed and compared to others during investigations).  The data is de-compressed and displayed to permit analysis or used to provide manual and automatically produced standard or customised reports.

Samples of typical parameter trees, using InvestigatorTM, software is shown.

Examples of partial parameter trees for PQGuard 4430 cycle by cycle recorder

A selection of measurements captured and analysed follows :

PQGuard 4430 can be installed on each generator, if required, for optimum PQ monitoring.    Alternatively, one 4430 can be connected to the switchboard (as shown) to provide continuous monitoring of Uthd (with all other current derived parameters summed (e.g. kW, kVAr….)) as shown.

Typical application of one PQGuard 4430 to MODU switchboard with 4 generators to monitor Uthd

The simplified illustration depicts a typical single PQGuard 4430 application.  Note that the generator currents are summed and fed into the unit.   Conventional CTs or Rogowski coils (flexible current transducers can be used.

Visual and audible alarms are triggered, for example, in the event of the Uthd >8% (for example) being exceeded.  All events are logged and can also be communicated by email and SMS.    The PQGuard 4430 unit is usually installed in the main switchboard room and communicates with a dedicated local server (usually a desktop computer) in the Control Room (CR) and/or Maintenance Superintendent’s office.

As can be seen there is also the capability to being able to monitor the PQ remotely should a suitable internet connection be available.  This may be at the company Head Quarters or at a third-party company’s office, responsible for carrying out contract PQ monitoring.

Contract PQ Monitoring

Whatever the type of PQGuard system you wish installed, Harmonic Solutions Oil & Guard, can offer contract PQ monitoring.    Let us take the full technical responsibility from your company by continuously monitoring, analysing and reporting on your installation’s harmonics and power quality, whether on a MODU, FPSO or land-based oilfield.

This service can also entail detailed annual PQ audits, if applicable, including the systems downstream where the normal continuous PQ monitoring does not apply.

Note : Harmonics above the 50th                                                                                                                                                                       

Contrary to most standards and rules of marine classification societies, harmonics do not cease at the 50th order.  Indeed, there is officially a new class of harmonics called “supra-harmonics” in the range 2kHz to 150kHz.

The limit for harmonics at the 50th may be convenient for compliance with marine classification society rules and standards but can jeopardise the safety and operational integrity of the installation as the complete ‘harmonic and PQ picture’ is hidden when using conventional harmonic and PQ analysers which measure to the 50th (or 63rd).

Illustrated below is an example from a land-rig with three large DC SCR drives.  The 50th harmonic limit has been highlighted on the axis.  Note that the line voltage extends to the 141st order, but in fact, there are essentially three discrete spectrums;

  1. One spectrum to around 25th order due to the harmonic currents being drawn from the supply by the large DC drives interacting with the system impedances.
  2. Another spectrum (~33rd to 53rd order) due to a top drive 560kW VFD, not physically connected to the power system (it had its own generator 180m away). This is the VFD’s common mode voltage appeared on system busbars via the ground connection.
  3. Finally, the high frequency voltage harmonics (57th to 104th) due to the DC SCR drives’ line notching.
Line voltage harmonic spectrum due to mix of DC SCR and AC VFDs

It should be obvious from this example that anyone attempting to trouble-shoot harmonics, PQ and EMC (i.e. common mode) problems whilst looking up to the 50th harmonic only may be unsuccessful in their endeavours.

It should be noted that Harmonic Solutions Marine has been measuring harmonics to the 512th harmonic since 2010.  Some examples of those measurements can be seen in the previous section.  PQGuard 4430 also has the capability to measure to the 512th harmonic.  PQGuard 605 measures to the 63rd order at this time.