HVPD Oil, Gas and Offshore Services
HVPD Launch New Division, 'HVPD Offshore' in Aberdeen, Scotland
On-line partial discharge monitoring expert HVPD has launched a new division, 'HVPD Offshore' in Aberdeen, Scotland as part of a growth plan to extend its products and test services to the North Sea Oil & Gas industry.
Established in 2006 with over 30 years onshore and offshore experience in on-line partial discharge monitoring, HVPD has supplied On-line PD test technology and PD test services to a worldwide customer base in Europe, North America, the Middle East, South East Asia and Australasia.
HVPD Offshore is launched as a joint venture with Petrolec Ltd; an Aberdeen based electrical maintenance company to provide direct access to their shared expertise and support customers whilst expanding the local offshore market. HVPD Offshore is headed by John Milne (right) a principal engineer with over 25 years' experience in the power, oil and gas industries in onshore and offshore locations.
John's experience has been gained through supervisory and engineering roles within major organisations, providing electrical maintenance support for a global oil & gas exploration and production companies with North Sea assets. In John's role he is accountable for the safe, efficient management of all electrical operations and procedures onboard field installations.
Mr Milne said, "Petrolec are excited to be collaborating with HVPD in establishing HVPD Offshore. We will play a pivotal role in placing HVPD at the forefront as the supplier of choice for PD test services and further enhance their formidable expertise in the offshore marketplace. We look forward to 2010 being a busy and productive period with further opportunity to showcase to the industry the capabilities, knowledge and innovative technological developments within the HVPD portfolio."
Contacts
Mr John Milne
HVPD Offshore
9 Bucklerburn Wynd, Peterculter
Aberdeen, AB14 0XR
Tel: +44 (0)1224 733929
Mobile: +44 (0)7595 894583
E-mail:
HVPD Ltd
Manchester, UK
Tel: + 44 (0)161 877 6142
Fax: + 44 (0)161 877 6139
E-mail:
High Voltage Partial Discharge Ltd (HVPD) provides both On-Line and Off-Line Partial Discharge (PD) Test Services to an increasing number of electricity utility and industrial clients around the world.
PD Test Services are carried out by our team of highly trained Test Engineers who utilise the versatile HVPD Longshot™ Diagnostic PD Test Technology, PDGold© and ScopeControl© software and a range of On-line PD Sensors to provide the highest level of Partial Discharge assessment available in the marketplace.
Examples of HV Plant that have been PD tested by HVPD include:
- Cables and Cable Accessories (terminations and joints)
- Switchgear (AIS and GIS)
- Instrument Transformers (Voltage and Current)
- Power Transformers and Bushings
- Motors and Generators
- Surge Arrestors
- Capacitors
- Cable Sealing Ends
HVPD has performed Offshore and Onshore Partial Discharge (PD) Test Services to a range of domestic and international Oil companies as illustrated in the following examples.
BP Exploration, Angola
HVPD were instructed to visit BP Angola's FPSO Greater Plutonio to test the rotating machinery aboard the vessel for partial discharge. Eleven machines were tested in total over the course of a week. Four Gas turbine generators were tested along with five Compressor motors and two water injection pumps.
Aera Energy, USA
HVPD and Emerson Process Management were instructed by Aera Energy to perform On-line Partial Discharge testing of the subsea 12kV cable which connects the Offshore Platform 'Emmy' to the mainland at Aera Technology's processing facility at Golden West, Huntington Beach, California. HVPD were also instructed to test associated plant.
Background
The cable had been in service for many years, no information was available about the insulation condition of the cable. There had been previously a backup cable installed. This is no longer in service as the cable had been damaged by a ship's anchor. It had not been possible for Aera Energy to repair or replace this cable due to environmental restrictions on carrying out the work. This meant that the remaining cable to the Emmy platform has a very high 'criticality.'
It was recommended that the condition of the insulation in the cable is checked regularly using On-line test methods such as those applied by HVPD in the project.
Testing was first performed onshore at the 12kV main service substation. Initial testing was performed with HVPD PDSurveyor™ handheld device. The device located areas of interest within the substation. These were mainly found to be areas around the bus section of the switchgear.
Testing was then performed with the HFCT sensors connected to the HVPD Longshot™. The back of the switchgear panels were removed and HFCT sensors were placed around either the cable cores and drains or just the drains of the outgoing feeder cables to the circuits.
Further testing was performed at the far end of the Emmy feeder on the offshore platform and also at the far end of the Building No. 4 feeder so as to provide complete testing of these 2x circuits at both ends.
HVPD's recommendations to Aera Energy
For the 12kV Cables
The cables tested appeared to be clear of partial discharge at the time of testing. Regular monitoring and testing of cables was recommended important to ensure that this remains the case. Due to the very high criticality of these cables, particularly the sub-sea cable to platform Emmy, it was recommended that they are re-tested for PD using the HVPD On-line test method every 12 months.
For the 12kV Switchgear
Sources of Moderate 'Local' partial discharge were detected within the switchgear in the main substation at Huntington Beach. The results pointed to 2x locations of 'local' discharges in the switchgear, as follows:
- In or around the bus section of the feeder to Emmy cubicle, and,
- In the bus section of the Utility Switchgear cubicle.
The levels of Local PD detected were between 24 and 26dB.mV which puts the switchgear into the condition category of 15-30dB.mV: Amber - 'Some concern, regular monitoring recommended'.
Whilst these PD levels remain moderate it was recommended that the Switchgear is re-tested again in 3-6 months time. It was also recommended that, if possible, during a shutdown that some effort is made at locating and removing these sites of discharge. This was advised to be carried out by visual inspection with HVPD providing full instructions. Retesting after any remedial work has been performed to ensure the discharges have been removed was advised.
BP Exploration, Algeria
HVPD has been instructed to perform online partial discharge test services on behalf of BP Exploration. Testing has taken place at the Krechba site in Algeria.
Background
BP Algeria had suffered some insulation problems in areas of their high voltage plant. After analysis, the cause of the problem was found to be partial discharges occurring within the insulation.
PD testing was carried out on a compressor motor, two generators, one 10kV switchgear bus and two 10/5 kV transformers.
HVPD returned to Algeria to the Krechba site to perform an overview assessment of the plant insulation condition in May 2008 before travelling to Hassi R'Mel to assess the insulation of two transformers, two switchgear cubicles and associated cables.
A transformer had recently failed onsite due to partial discharge and it was decided that the other transformers present should have their insulation condition assessed. Partial discharges were located at the terminations to one of the transformers and one of the switchgear cubicles.
Saudi Aramco, Saudi Arabia
Saudi Aramco, instructed HVPD to undertake in-Service, On-Line Partial Discharge Testing Of 13.2kV Alstom Compressor Motors. Across their various sites in Saudi Arabia On-line partial discharge testing was carried out using previously installed capacitive PD couplers (IRIS 80pF HV Couplers) and the HVPD Longshot™ PD test unit.
Notes for On-line Partial Discharge Testing of Rotating Machine Insulation
HVPD utilised the HVPD-Longshot™ PD Test System to carry out both On-Line (in-service testing) and Off-line (factory testing) Partial Discharge (PD) Testing of Rotating High Voltage Machine Insulation. On-line PD testing is now widely accepted in the rotating HV machine industry as the best way to assess the condition of in-service HV motors and generators. To meet this market demand, the HVPD Longshot™ system and PDGold© software includes a dedicated 'Machines Software Module' which has been specifically designed for the PD Testing of HV motors and generators. The technology provides the user with the ability to carry out PD testing of HV machine insulation quickly and easily without the need for an outage.
- PD measurements can be made On-Line using split-core, High Frequency Current Transformers sensors around the supply cable.
- PD measurements in pico-Coulombs (pC's).
- PD activity is presented in simple colour codes based on the PD severity (PD magnitude x no. of pulses per power cycle).
- Automatic diagnostic of whether the discharge is in the Slot Section or the End Windings.
Background
Figure 5 shows a schematic of a rotating machine. Making PD measurements requires some access to the PD signals which emanate from the stator windings. The PD sensors normally fitted to an HV machine are either Coupling Capacitors, or High Frequency CT's (HFCT). Figure 5 shows the positions at which these sensors are usually fitted.
It is important to note that the HFCT's must be capable of working with the HV Machine's rated current passing through them as they are connected around the supply cable core(s). These load currents can be of several thousand amps in some machines and due to the fact that even specially-designed, high current Ferrite-Cored HFCT's saturate at around 1000 Amps this generally means that either Air-Cored Toriodal CT's (Rogowski coils) or Permanent Capacitive Coupler sensors are preferred for large HV machine PD testing i.e. machines with 1000A+ operating current. As Permanent Capacitive Coupler sensors have much higher sensitivity than Rogowski Coils they have become the preferred sensor for use in HV Machine PD Testing.
However, it should also be noted that ferrite-cored HFCT's can be used, provided that they do not saturate at the load current of the motor (the load current should be checked before testing for this reason). The large advantage of ferrite-based HFCT's are that they generally have much better sensitivity than the equivalent air-cored, Rogowski devices (of typically up to 20-30x better) and can thus be used to detect much lower levels of PD activity (HVPD supply a Ferrite-Cored HFCT which can be used without saturation up to 1000A). There are also occasions when the HFCT's can be fitted to the earth connection of the star point of the motor (this combines all the phase data together) and is normally only done when no other access to the cable or machine windings is feasible.
High Voltage Motor/Generator PD Testing
HV Motors and Generators with voltage ratings of 3.3kV and above have been successfully tested. If there are no built-in PD sensors in the motor then the PD test can be carried out with a split-core HFCT sensor fitted around the supply cables to the motor and the HVPD-Longshot™ PD Spot Tester with the PDGold© Software used to analyse the pulses.
It is recommended that the measurements are made as near to the motor as possible with short BNC co-axial cables to avoid any large signal attenuation along the measurement cables. The further you measure from the motor and the nearer measurements are made to other HV plant then the more electrical 'noise' signals will be introduced into the measurement circuit. If it is easier, or because of other constraints, it is decided to work near to the switchgear end of a motor supply cable, it is considered prudent to check the signal level for attenuation and interference at both ends of the cable using the PD Spot Tester Unit before commencing on regular testing from the switch gear end of the cable that is feeding the motor. This allows the user to take into account any PD signal attenuation which may occur along the HV Cable (this can be a few hundred metres in some cases).
When one considers that the normal PD levels produced by an HV Machine are significantly greater than the levels acceptable on bus bars and switchgear (typically an order of 10x higher) then there should be no problems with interference from other PD sources although RF Noise Interference can be seen in some cases.
With 3.3-6.6kV motors it is usual to use a 3-core, 'belted' supply cable between the switchgear and motor and thus when taking measurements with the HFCT transducer fitted around all three cores the instrument will see only the phase-to-ground discharge pulses from all 3x phases. This does not allow for observing any phase-to-phase discharge pulses but is normally acceptable if only the PD magnitude for the whole motor is required as part of a 'PD Trending' analysis. However if it is required to identify in which phase a particular large discharge is occurring it is necessary to gain access to a phase reference voltage signal which can be used alongside the PD Pulse Data to identify which phase is discharging.
For further details please visit our Applications Notes or download our On-Line Partial Discharge (PD) Testing of Rotating High Voltage Machine Insulation applications notes here.