PDSurveyor™

Universal, Hand-Held On-Line Partial Discharge (PD) Surveying Tool for Insulation Condition Testing of High Voltage Plant.

The PDSurveyor™ is a handheld, portable device suitable for the measurement of Partial Discharge (PD) activity in high voltage equipment (partial discharge activity is produced by incipient faults in high voltage insulation and is widely regarded as the best indicator of HV insulation condition). The unit is suitable for the PD testing of a wide range of in-service High Voltage (HV) plant including HV cables, switchgear, transformers, CTs / VTs and rotating machines.

The PDSurveyor™ has been developed to meet the market demand for a simple, low-cost PD surveying unit which can be used as a 'first-line' PD test and screening device by all operational staff. The required time for a pre-screening survey on an HV plant item with the PDSurveyor™ is around 10 seconds per test, thereby enabling large numbers of HV plant items to be screened quickly and easily.

The PDSurveyor™ is unique in that it is the world's first handheld PD test technology which combines 3x Types of PD Sensor Technology (ultrasonic, electromagnetic (HFCT) and transient earth voltage (TEV)) into one, simple-to-use test unit. The unit has been carefully designed to meet the present requirements of high voltage plant owners across the world and has been developed further to customer requests for a simple, portable and easy-to-use PD test device which can be used by all operational staff in the substation.

The PDSurveyor™ is thus intended to be used as a first-line PD 'checker' for HV plant, providing the user with the ability to test the insulation condition of the equipment in seconds. The unit's simple, 7-level, colour-coded PD level indications (displayed as a range of LEDs from green (OK) to yellow to orange to red (high PD)) allows the user to quickly identify potential insulation defects and incipient faults. By using the PDSurveyor™ in this way, large numbers of HV plant items can be scanned for PD activity in a fraction of the time required by other commercially available systems.

In the event of moderate PD activity (Orange LED) or high PD activity (Red LED) being detected by the PDSurveyor™, the next stage of the insulation condition assessment process is to utilise a high-specification diagnostic PD test and/or monitoring technology such as the OSM-Longshot© PD Test Unit from IPEC Engineering Ltd.

The PDSurveyor™ meets the market need for a simple, low-cost PD surveying device which can override the main impediments to date in the widespread uptake of PD surveying of assets by the power industry. These impediments have included the combined influence of the price of high-level diagnostic PD test equipment, the complexity of its use, the need for skilled technicians to operate the equipment, and the sheer lack of productivity possible from present hardware when testing all assets. All of these have collectively contributed to the inescapable problem of marginally acceptable survey costs per item inspected. All that has now changed with the advent of the IPEC Engineering PDSurveyor™ hand-held PD surveying device!

The Design Philosophy guiding the development of the PDSurveyor™ is in itself revolutionary in the field of hv plant asset management. This can be summarized as follows:

• Firstly, experience from On-Line PD Testing has shown that of all hv assets surveyed for PD, typically only 5 to 10% will have significant levels of PD activity. This draws the conclusion that a device that could pre-screen all assets quickly and cheaply would greatly appeal to plant owners. Once assets had been identified as having concern then these can be prioritised for a targeted investment, including a comprehensive, diagnostic PD survey and/or remedial action.
• Secondly, the fact that the required time for a pre-screening survey on an hv plant item with the PDSurveyor™ is around 10 seconds per test, compared with 5-10 minutes presently for a full PD survey, leads to much higher testing productivity.
• Thirdly, and significantly, companies simply do not have a significant resource of technical staff with the qualifications and time on hand to conduct full-time, specialist PD surveys in larger networks. The PD Test technology has been designed and packaged in a form whereby it can go into the hands of a substation fitter with a few hours of training. This has the dual benefit of reducing testing costs and, by virtue of the fitters being out and about in substations all day, of ready access to gear for surveying as part of normal site visits.
• Fourthly, the PDSurveyor™ has a selling price of around 10% of that of the average specialist PD Diagnostic Test kit, making PD Testing much more affordable and accessible to any high voltage plant owner.
• Lastly, and very importantly, those who have ever been close to the aftermath of an explosion of either a piece of metal-clad MV switchgear or a cable termination in the confines of a substation would need no convincing that we are talking here of one of the worst possible of electrical accidents. From a Health and Safety viewpoint, the concept of the logical combination of a simple PD screening device that can be used by fitter staff as a quick pre-screening tool for safety checking in the sub prior to doing any necessary work in the building is an inescapable one.

The PDSurveyor™ can be used to test High Voltage Cables, CTs, VTs, Switchgear, Rotating HV Plant and Transformers in the following modes:

1. As a Safety and Security Device - the unit provides an immediate indication to the user as to whether switchgear or other 'local' HV plant in the substation is safe to approach and/or to work in close proximity to. This function can be used by all operations and technical staff to ensure the HV Plant in their working area is safe from dangerous levels of Partial Discharge Activity which could produce catastrophic failure, explosion and personal injury.
2. As a First-Line Screening/Diagnostic Device - the unit provides a quantified, colour-coded PD Level indication as to the Partial Discharge Level in cables, switchgear, transformers CTs/VTs and rotating HV plant. This data can then be used to 'screen' large numbers of HV plant items for PD activity as a prelude to using the high-specification diagnostic PD test and/or monitoring technology (such as the OSM-Longshot© PD Test Unit from IPEC Engineering Ltd).

With the PDSurveyor™ costing around 10% of that of the average specialist PD Diagnostic Test kit, a company can issue its fitters/operations staff with a means to pre-screen for PD all cables and switchgear in a substation, all for around 10% of the normal hardware outlay, 50% of the salary of a skilled PD technician, and 3% of the testing time of a comprehensive PD survey.

Rolled into that, the inescapable heath and safety assurance that the quick (few minutes) substation survey offers upon entering a substation means this is truly a win-win outcome for all parties. It could be convincingly argued that this innovation is one of the biggest revolutions yet in partial discharge surveying of power systems assets.

The PDSurveyor™ incorporates three individual partial discharge sensors and corresponding measurement circuits which are designed to pick up different types of PD activity in different types of HV plant, as follows:

CT - Cable PD Circuit - Cable PD is measured using the external, split-core, High Frequency Current Transformer (HFCT 100/50) sensor which is clipped around the earth strap of the cable to be tested. Cable PD pulses are generally in the frequency range of between 200kHz - 4MHz and are typically monopolar in shape. The unit measures the charge content of the Cable PD pulses in picoCoulombs (pC's) by using an integrator circuit to measure the area underneath the monopolar pulse.

TEV Circuit - Transient Earth Voltage (TEV) PD signals are generated by internal partial discharges in 'local' HV equipment including switchgear, cable terminations, motors and transformers. TEV signals are in a higher frequency range of between 4MHz - 100MHz and are normally oscillatory in shape (as opposed to monopolar for cable PDs). The unit has a built-in TEV sensor which is placed against the equipment under test to measure these signals. The resultant PD signals are measured in dB (decibels), as is the convention for on-line switchgear testing.

AA - Airborne Acoustic Circuit - Acoustic/Ultrasonic PD signals are generated by partial discharges into air and are detected using the unit's built-in 40kHz airborne acoustic (ultrasonic) sensor ('line-of-sound' to the pd site is required). The PDSurveyor™ sensor is very useful when testing Air Insulated Switchgear and has been designed with high sensitivity to pick-up small discharges into air which are inaudible to the human ear. The resultant PD signals are measured in dB (decibels) as is the convention for measuring acoustic signals.

The outputs of each of the above measurement circuits are displayed on the PDSurveyor's display screen which consists of 3x rows of 7 x colour-coded LEDs, 1 row for each sensor. The PD levels vs Plant Condition/Action to be taken for each LED are shown below. These range as follows:

Note: It should be noted that the PD levels and actions recommended are Guideline Levels Only and are based on IPEC's experience of testing HV plant. It is recommended that any moderate or high level PD 'screening' measurements (Yellow, Orange or Red Levels) obtained using the PDSurveyor™ are further qualified using high-specification diagnostic PD test and/or monitoring technology (such as the OSM-Longshot© PD Test Unit from IPEC HV Ltd).

Example 1: 11kV Cable & Switchgear Test

The CT LEDs (top line) show an 'Orange 1' Cable PD Level which equates to 3300pC.

The TEV LEDs show a 'Yellow 2' PD Level which equates to 28dB.

The Action here would be to investigate this further by PD testing with the OSM-Longshot© Diagnostic PD Tester - refer to IPEC for details)

Example 2: 11kV Solid Insulated Switchgear

The TEV LEDs (middle line) show a 'Red 2' TEV PD Level which equates to 48dB+.

The action here was to use the high level OSM-Longshot© PD Diagnostic Test Unit to test and locate the site of the PD activity. This was found to be coming from a nearby Hydro Generator.