CASE STUDY

PROJECTSince 2017, a large oil and gas E&P company have been conducting bi-annual Partial Discharge (PD) surveys by HVPD across a range of MV & HV assets, on multiple offshore production facilities in West Africa as part of a larger reliability campaign. The PD surveys included On-line and Offline PD spot testing and Motor Current Signature Analysis (MCSA).

ROTATING MACHINES

AFRICA

SOLUTIONAs part of this survey, Offline testing was conducted across the entire fleet of rotating machines on one site.

Prior to testing the operator conducted isolations at the main switchboard, and ensured the disconnection of sensors within the machines, ensuring safe HV energisation could be achieved using the VLF Generator

Tests conducted were:

• Insulation Resistance (IR)• Polarization Index (PI) • Partial Discharge (PD)• Tangent Delta (Tanδ)

By conducting this range of tests PD Inception Voltage, PD Extinction Voltage levels and PD values can be determined. Baseline Tanδ measurements can also be recorded. This combination of results can all be used to evaluate the insulation condition of the stator winding.

Offline Partial Discharge Testing of entire HV Motor and Generator Fleet as part of Reliability Campaign

EQUIPMENT USED:

VLF Generator

HVPD Australiawww.hvpd.co.uk

HVPD Chinawww.hvpd-china.com

HVPD USAwww.hvpdinc.com

HVPD Head Officewww.hvpd.co.uk

HVPD Middle East www.hvpd.co.uk

CASE STUDY

RESULTSA number of machines tested showed very high levels of PD. At 3860 mV, one 11 kV motor displayed extremely high levels of Peak PD.When the customer was made aware of this, the HVPD engineer was asked to conduct further internal inspection of the asset using a bores-cope.

This demonstrated clear evidence of electrical treeing on the windings which is an indicator of PD activity forming from internal voids.

A significant amount of contaminant was spread across the machine windings, as well as a large amount of oil sitting in the bottom of the machine which can cause PD activity on the insulation surface.The con-taminant was a combination of oil, metallic flakes (possibly from internal damage to the bearings) and paint particles where the coatings inside the machine and on fan blades has disintegrated.

RECOMMENDATIONS• HVPD recommended that a planned outage should be scheduled

as soon as possible in order to carry out a repair of the internal mechanical damage and remove the contaminant.

• It was also recommended by HVPD that permanent PD sensors be installed which would allow for future PD testing without the need for an outage, and accommodate future expansion plans for permanent On-line PD monitoring.

CONCLUSIONS• Due to the Offline tests conducted, and verified by the borescope

inspection, the customer was able to locate the cause of PD found and most likely prevent an unplanned outage.

• Following the results of the Offline PD testing, the customer was able to schedule an outage in order to conduct a full visual inspection and chemical clean of the stator with the rotor removed. HVPD wit-nessed the remedial work, carried out repeat offline testing and pro-vided consultation on the next steps regarding insulation condition.

• The customer will continue the PD survey across all West African offshore sites in order to maintain a comprehensive insight to the insulation condition of their HV network.

HVPD Australiawww.hvpd.co.uk

HVPD Chinawww.hvpd-china.com

HVPD USAwww.hvpdinc.com

HVPD Head Officewww.hvpd.co.uk

HVPD Middle East www.hvpd.co.uk