WO2021069878A1

WO2021069878A1 - Partial discharge monitoring device, system and method for a substation asset provided with a voltage presence indication system (vpis)

Info

Publication number: WO2021069878A1
Application number: PCT/GB2020/052461
Authority: WO
Inventors: Peter Sandell CODD; Richard Ash; Gareth Anthony DEVINE; William Edward PLATTS; Atli THRASTARSON; Thomas James WILKINSON
Original assignee: Ea Technology Limited
Priority date: 2019-10-08
Filing date: 2020-10-06
Publication date: 2021-04-15
Also published as: GB201914550D0; GB2588133A

Abstract

The present invention relates to a partial discharge detection device for a substation asset provided with a voltage presence indication system (VPIS), comprising: connection means configured to connect to a VPIS port mounted on the substation asset; an amplifier configured to amplify signals presented across the terminal of the VPIS port, the amplifier having an input stage being controllable to prevent clipping of the amplified output; and monitoring means configured to monitor the amplified output, and outputting at least one output signal based on detected partial discharge activity.

Description

PARTIAL DISCHARGE MONITORING DEVICE, SYSTEM AND METHOD FOR A SUBSTATION ASSET PROVIDED WITH A VOLTAGE PRESENCE INDICATION SYSTEM (VPIS)

TECHNICAL FIELD OF THE INVENTION

This invention relates to a partial discharge monitoring device, system and method for substation assets and power distribution automation provided with a voltage presence indication system (VPIS). In particular, the present invention relates to a VPIS module that can be coupled between a VPIS port provided on the substation asset and an asset monitoring and partial discharge alarm system which can receive the coupled VPIS signal and monitor any partial discharge activity on the substation asset.

BACKGROUND For many years, it has been known to inspect or monitor substation assets for partial discharge (PD) activity to provide an early warning of the deterioration of assets. Such non- intrusive condition monitoring of PD activity has now been adopted as standard practice for substation assets around the world. Partial discharge is a well-understood mechanism which begins within voids, cracks or inclusions within solid insulation, or in bubbles with liquid insulation. Partial discharge is a localised dielectric breakdown of a small portion of a solid or liquid electrical insulation system under high voltage stress but which does not completely bridge the space between the conductors. Once begun, partial discharge causes progressive deterioration or degradation of insulation material, and ultimately leads to dielectric breakdown and hence asset failure.

One of the well-established and convenient methods of PD detection is to measure transient earth voltages (TEV) induced in the surrounding metalwork of the substation asset. It is possible to detect TEV via periodic inspections using handheld instruments which do not make any electrical connection to the substation asset. A popular handheld instrument for inspection and early detection of PD activity is the UltraTEV™ Plus² device available from EA Technology Limited. This handheld device includes sensors which can detect transient earth voltages (TEV) and acoustic ultrasonic signals which enable an operator to distinguish between true PD activity, noise and other interference in a straightforward and quick measurement.

Whilst handheld instruments are useful for regular inspection of PD activity, there are also semi-portable and fixed solutions available in the marketplace that can be retrofitted to switchgear and cables and which can be continuously monitored to provide an early indication of degradation of assets. Such semi-portable and fixed monitoring equipment generally comprises partial discharge sensors, data collection and communication modules which are retrofitted either inside and/or outside the switchgear asset under test. Online monitoring of PD events using such monitoring equipment allows asset owners to more accurately anticipate potential issues, as well as forecasting when an asset may need replacing. Such semi-portable and fixed monitoring systems are also available from EA Technology Limited, and which include the UltraTEV™ Monitor and the Astute HV Monitoring^® service.

These handheld, semi-portable and fixed monitoring solutions all allow for additional sensor technologies to be provided over-and-above the detection of transient earth voltages, and these can include high frequency current transformers (HFCTs) for detecting PD signals on cables, airborne ultrasonic sensors for detecting ultrasonic emissions and various environmental sensors can all provide further information about the condition of substation assets. The skilled person will appreciate however that an increasing quantity of modern switchgear is produced having a double-skin construction, which poses difficulties for the detection of both TEV and ultrasonic sensors.

The skilled person will also understand that voltage presence indication systems (VPIS) have become an increasingly common feature on modern switchgear. VPIS ports are fitted to provide a means of indicating the presence of high voltage and provide a connection for cable phase sequencing. VPIS generally comprise a capacitive connection to the HV conductor (busbar) which is outputted at a test port (and which may include overvoltage protection, and a neon lamp or LED-based display). The capacitance to the busbar is of a very low value (typically tens of pF), and is just enough to allow sufficient line frequency current through to provide an indication or light an LED or neon. Although not envisaged for this purpose, the capacitance also couples any voltage impulses from the HV conductor to the test port. These include the impulses created by PD and so can provide a convenient means of detecting them.

Whilst the VPIS port does appear to be a promising means for monitoring partial discharge activity in modem substation assets there are disadvantages in that the direct capacitive connection to the busbar does suffer from large signal losses and due to the variation in VPIS system designs, in particular, the capacitance value and line voltage, the signal presented at the terminal of the VPIS port for a given discharge can vary from system-to- system.

Whilst the need for both handheld inspection instruments, and semi-portable and fixed monitoring systems which can locate, measure and record PD activity in all types of modern substation assets continues to grow, there is a corresponding need for a VPIS module which can provide an automatic ranging function, thereby passing the maximum VPIS signal output in each instance and providing a phase resolved view of all PD events from the VPIS bushing capacitor coupled to each phase. Such an external or integrated VPIS module being capable of coupling and amplifying low-level, high-impedance signals to the asset monitoring and partial discharge alarm system.

It is an object of the present invention to provide a partial discharge monitoring device for substation assets provided with a voltage presence indication system and its method of use which alleviates or reduces the drawbacks associated with the variation in VPIS pulse responses. It is a further object of the present invention to provide a VPIS module whose switchable impedance is matched to that of the VPIS bushing capacitor to provide the maximum high-frequency pulse signal generated by any partial discharge activity to improve PD detection, sensitivity and pulse resolution. It is a further object of the present invention to provide a PD detection system comprising a plurality of semi-portable or fixed PD detection devices which are coupled to such VPIS modules and being able to receive and amplify the matched VPIS input to allow for a more precise real-time, or near real-time, PD monitoring from multiple sensors and locations on modern switchgear. It is a further object of the present invention to provide a VPIS module that includes overvoltage protection to prevent damage from a potentially dangerous overvoltage condition.

SUMMARY OF THE INVENTION

The present invention is described herein and in the claims.

According to a first aspect of the present invention there is provided a partial discharge detection device for a substation asset provided with a voltage presence indication system (VPIS), comprising: connection means configured to connect to a VPIS port mounted on the substation asset; an amplifier configured to amplify signals presented across the terminal of the VPIS port, the amplifier having an input stage being controllable to prevent clipping of the amplified output; and monitoring means configured to monitor the amplified output, and outputting at least one output signal based on detected partial discharge activity.

An advantage of the present invention is that it can be used to reliably detect partial discharge activity on all types of modem switchgear by impedance matching the signal generated by any partial discharge activity to the amplifier and minimising the signal due to line frequency.

Preferably, the substation asset comprises MV or HV electrical switchgear.

In use, the signals presented across the terminal of the VPIS port may be coupled from a VPIS bushing capacitor positioned adjacent to each phase. Preferably, the connection means comprise flying leads.

Further preferably, the signals presented across the terminal of the VPIS port are inputted to a filter and a clamping arrangement before being passed to the input stage of the amplifier.

In use, the filter may be a high pass filter.

Preferably, the high pass filter comprises an in-series protective capacitor and a termination resistance being placed in parallel across the input line from the connection means.

Further preferably, the termination resistance comprises a termination resistor array comprising a plurality of switchable resistors.

Preferably, a microcontroller configured is to control the switching of the switchable resistors disposed in the termination resistor array using an ADC and a comparison circuit which determines any clipping of the signal before amplification.

Further preferably, the voltage output from the clamping arrangement is inputted into the ADC and the microcontroller determines the levels at which an auto-range function switches the switchable resistors to a lower or higher resistance.

In use, a peak voltage detection circuit may determine the voltage level on the microcontroller.

Preferably, the peak voltage detection circuit is implemented as a half wave rectifier to ensure that the peak is averaged over at least several cycles.

Further preferably, a phase detection circuit which takes the output of the voltage detection circuit as a reference voltage.

In use, the amplifier may be a differential operational amplifier. Preferably, the monitoring means is implemented as a handheld device or as a semi-portable or fixed monitoring node.

In use, any number of such VPIS partial discharge detection devices and HFCT cable partial discharge detection nodes may be connected together to form partial discharge alarm and monitoring system.

Preferably, the detected partial discharge activity gathered by the VPIS partial discharge detection devices and/or the HFCT cable partial discharge detection nodes can be transferred to a corporate network and/or Supervisory Control and Data Acquisition (SCADA) computer system and/or remote cloud-based system for further processing using a wired local area network (LAN) and/or wirelessly using Wi-Fi and/or via mobile telecommunications signals and networks or the like.

According to a second aspect of the present invention there is provided a system for processing data from one or more partial discharge detection devices for monitoring substation assets provided with a voltage presence indication system (VPIS) sensors, the system determines the severity and/or location of partial discharge activity within substation assets.

According to a third aspect of the present invention there is provided a method of detecting partial discharge activity in a substation asset provided with a voltage presence indication system (VPIS), the method comprising the steps of: connecting an amplifier circuit to the VPIS port mounted on the substation asset; amplifying signals presented across the terminal of the VPIS port, the amplifying step being controllable to prevent clipping of the amplified output; and monitoring the amplified output, and outputting at least one output signal based on detected partial discharge activity. It is believed that a partial discharge monitoring device, system and method for substation assets and power distribution automation provided with a voltage presence indication system in accordance with the present invention at least addresses the problems outlined above.

It will be obvious to those skilled in the art that variations of the present invention are possible and it is intended that the present invention may be used other than as specifically described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of example only, and with reference to the accompanying drawings, in which:

Figure 1 shows a side sectional view of a gas-insulated high voltage switchgear (GIS) cabinet comprising a VPIS port on its front panel being connected to a VPIS module in accordance with the present invention; and

Figure 2 is a high-level block diagram of a partial discharge detection device which is connected to the output of the VPIS module which conditions and amplifies signals presented at the terminal of the VPIS port in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention has adopted the approach of utilising a partial discharge monitoring device for substation assets and power distribution automation provided with a voltage presence indication system and its method of use which alleviates or reduces the drawbacks associated with the variation in VPIS pulse responses. Advantageously, the present invention provides a VPIS module whose switchable impedance is matched to that of the VPIS bushing capacitor to provide the maximum high-frequency pulse signal generated by any partial discharge activity to improve PD detection, sensitivity and pulse resolution. Further advantageously, the present invention also provides a PD detection system comprising a plurality of semi-portable or fixed PD detection devices which are coupled to such VPIS modules and being able to receive and amplify the matched VPIS input to allow for a more precise real-time, or near real-time, PD monitoring from multiple sensors and locations on modern switchgear. Further advantageously, the present invention also provides a VPIS module that includes overvoltage protection to prevent damage from a potentially dangerous overvoltage condition.

Referring now to the drawings, a VPIS module 10 according to the present invention is depicted with gas-insulated high voltage switchgear (GIS) 12. Although particular embodiments of the invention refer to utilising the VPIS module 10 with GIS switchgear 12, this is in no way intended to be limiting as the present invention can be utilised with any number of different types of substation assets 12 and power distribution automation provided with a voltage presence indication system.

As shown in Figure 1, the VPIS accessory or module 10 is provided as a small, low-profile enclosure which can be magnetically mounted to the switchgear 12 for ease of installation. In Figure 1, the VPIS module 10 is magnetically mounted to the front panel 16 of switchgear 12 for illustration purposes only, and placed adjacent to the VPIS port 14. The output of the VPIS port 14 is taken by 4mm flying leads 52 to the input of the VPIS module 10. The VPIS port 14 provides a direct capacitive connection to the HV conductors (busbars) enclosed within the switchgear 12, via a dedicated VPIS bushing capacitor (not shown). The VPIS port 14 on GIS switchgear assets 12 provides a direct capacitive connection to the GIS busbar which does not suffer from the large signal losses normally experienced at the cable/switchgear earth termination.

The main function of the VPIS port 14 on switchgear 12 is to provide a means of indicating the presence of high voltage (usually via a neon lamp or LED), and provide a connection for cable phase sequencing, for example. Although not envisaged for the purpose of detecting PD activity, the capacitance also couples any voltage impulses from the HV conductor to the test port 14. These include the impulses created by PD and the present invention therefore describes a precise and convenient means of detecting such PD activity utilising a signal conditioning VPIS module 10 which outputs a signal to a detection device or node 28 that can optionally communicate to other nodes 28', 28” etc. to form a modular, scalable semi- portable or fixed monitoring system 30. The data gathered by can by such semi-portable or fixed monitoring system 30 can further be transferred to a corporate network and/or Supervisory Control and Data Acquisition (SCADA) computer system and/or remote cloud- based system for further processing and/or reporting.

Figure 2 shows a high-level block diagram of a partial discharge detection device or node 28 which is connected to the output of the VPIS module 10 which conditions and amplifies signals presented at the terminal of the VPIS port 14 in accordance with the present invention. The PD detection device or node 28 can be provided as a handheld device (such as, for example, the UltraTEV™ Plus² device available from EA Technology Limited) or as a semi-portable or fixed monitoring node 28 (such as, for example, the UltraTEV™ Monitor or the Astute HV Monitoring^® service available from EA Technology Limited). The skilled person will appreciate that any number of such PD detection devices or nodes 28, 28', 28” etc. can be connected together to form an easily deployable monitoring and partial discharge alarm system 30.

In essence, each PD detection device or node 28, 28', 28” etc. is implemented as a microcontroller that receives a number of inputs, including the conditioned and amplified signals from the VPIS module 10, and they can display and output data directly to an inspector (in the case that the PD detection device 28 is implemented as a handheld instrument), or passed to an asset monitoring and partial discharge alarm system 30. Each PD detection device or node 28, 28', 28” etc. can be considered a self-contained system with a processor, memory and peripherals. In a preferred embodiment, all collected data from each PD detection device or node 28, 28', 28” etc. can be made available via a wired local area network (LAN), or wirelessly using Wi-Fi, or via mobile telecommunications signals and networks. The skilled person will appreciate that other communication interfaces and protocols are possible, and which are within the scope of the present invention.

As shown in Figure 2, the output from the VPIS port 14 is taken by flying leads 52 to the input of the VPIS module 10 and shown schematically towards the left hand side of Figure 2. The signals are conditioned and amplified, as described below, and the output of the VPIS module 10 is outputted to the PD detection device or node 28, as shown schematically towards the right hand side of Figure 2.

The PD signal amplitude at the VPIS port 14 is small and is needed to be conditioned and amplified by the VPIS module 10 for processing by the PD detection device or node 28. The method of signal processing to be described below, which embodies the present invention, involves an impedance-matching automatic ranging function which passes the maximum VPIS signal output in each instance from the VPIS bushing capacitor coupled to each phase. Such a VPIS module 10 is needed to connect to VPIS port 14 as a high input impedance is needed. Taking low-level, high-impedance signals over a potentially long cable would otherwise very likely pick-up noise.

The impedance obtained from the high-frequency pulse signal generated by partial discharge and the amplifier 42 must match, which determines detection sensitivity and pulse resolution. It is important that the VPIS output is terminated correctly to prevent any clipping of the signal. With the present invention, this clipping prevention is automatic and based on an array of optocouplers which switch in/out different termination resistors.

The VPIS module 10 conditions and amplifies the phase signal before sending it through a wire to the PD detection device or node 28. The VPIS module 10 terminates the signal in one of a plurality of resistors, selected by an auto-ranging function, allowing maximum signal output in each instance and providing a phase resolved view of all events.

As shown in Figure 2, the coupled signals at the VPIS port 14 from the VPIS bushing capacitors in response to partial discharge activity are inputted to an auto-ranging termination 32 provided on the VPIS module 10. The skilled person will understand that Figure 2 is a schematic diagram and, in order to aid clarification, many circuit elements are not shown.

The pulse termination stage 32 consists of several elements. To ensure the safety of the VPIS module 10 if it were, for example, erroneously plugged in to something other than the VPIS port 14, an in-series protective capacitor 34 is provided. To sufficiently limit the current, the maximum capacitance is around 5nF. The value of the protective capacitor 34 is selected to be as high as possible, otherwise it has more effect on the frequency response of the high pass filter. The high pass filter referred to being one that is formed by the termination resistance and the in-series capacitor 34 on the VPIS module 10, as described below.

The frequency response of the high pass filter is of course influenced by the termination resistance that is placed across the signals presented from the terminal of the VPIS port 14. The skilled person will understand that due to the variation in VPIS system designs, in particular, the capacitance value and line voltage, the signal for a given discharge can vary considerably from system-to-system and it is imperative that the VPIS output is terminated correctly to prevent any clipping of the signal. With the present invention, this is achieved by having a termination resistor array 36 comprising a plurality of switchable resistors.

The chosen way of switching the resistors of the array 36 is by switching on the VPIS side using an optocoupler which comprises a phototransistor optically-connected to an infrared- emitting diode. A single optocoupler is each placed in series with each of the resistors in the switchable array 36. This enables the protection capacitor 34 to protect fully, without affecting the bandwidth of the differential amplifier 42.

The VPIS module 10 also includes clamping protection components 40 to ensure the differential operational amplifier 42 is not damaged due to voltage spikes or being plugged into the wrong voltages. These clamps 40 are capable of sinking the necessary current that the protective capacitor 34 restricts the input to, without adding a large capacitance on the line. The VPIS module 10 uses an operational amplifier 42 with a differential configuration. The output of the operational amplifier 42 is passed to the PD detection device or node 28 to extract the envelope of the high frequency pulse.

The microcontroller 44 controls the selection of the termination resistor array 36 using an ADC and 50Hz comparison circuit 46. The comparison circuit 46 determines the clipping of the signal. The voltage levels from the clamp 40 are be fed directly into the ADC allowing the firmware of the microcontroller 44 to determine how to interpret these signals and determine the levels at which the auto-range function 48 switches to a smaller/higher resistance value 36. In a preferred embodiment, a peak voltage detection method will be used to determine the voltage level on the microcontroller 44. The output from the comparator 46 and peak detector are inputted to the microcontroller 44 which detects the pulse event, measures the pulse amplitude and records the data for later access by the PD detection device or node 28 and/or semi-portable or fixed monitoring system 30.

The peak detection circuit can be implemented on both the output of the buffer stage and the output of the output stage. It comprises a half wave rectifier with a capacitive filter on the output of the diode that correlates to an RC constant of about 5 cycles. Each cycle is 20ms (50Hz), and if a capacitor of lpF is selected, a 100k W resistor is required. This will ensure that the peak is averaged over at least a few cycles, and gives a good indication of how much the signal is being driven by the termination resistance 32.

A phase detection circuit can also be implemented. This uses the output of the peak detection as a reference voltage, then divide it by two, and then compare it with the input voltage wave. This will generate a square wave that could be used to detect the phase, by detecting the peaks of the positive cycle of the sine wave.

The microprocessor 44 controls the process and communicates the result back to device 28 for display, for example. The microprocessor 44, amongst other things, also sets auto ranging levels, as described below. The skilled person will appreciate that the microcontroller 44 also includes a UART 50, and commands and requests can be implemented on the communications interface to (amongst other things) either request the VPIS module 10 to use specific termination resistors 36 which will force the VPIS module 10 to turn-on specific resistors 36 as defined in the command parameters. Alternatively it is possible to request it to auto-range. This will put the VPIS module 10 into auto-range mode, where it will find the best termination resistors 36 to turn on. It will configure itself into the optimum configuration and then stop changing. Automatic gain selection must be prompted, i.e. for repeat measurements, the same gain settings should be used unless the user prompts a change.

Due to the variation in VPIS system designs, in particular the capacitance value and line voltage the signal presented at the terminal of the VPIS module 10 for a given discharge can vary system to system. The VPIS module 10 offers an auto-ranging feature, allowing maximum signal output in each instance and providing a phase resolved view of all events.

As therefore described, utilising a high sampling rate, the PD detection device or node 28 continuously monitors all three phases of the switchgear 12 simultaneously. The VPIS module 10 is provided with a capacitive connection, via the VPIS port 14, to the main busbar giving it access to the high frequency current pulses induced by discharge activity.

The cut-off frequency of the bushing capacitor and connected signal cabling 52 limit the detection area of the VPIS sensor to the switchgear 12 and cable terminations 22, allowing clear identification of discharge sites for both phase-to-phase and phase-to-earth activity.

Analysis of VPIS activity is based on event count, phase relationship and variation from a base reading rather than absolute amplitude readings.

Therefore, the partial discharge monitoring device, system and method according to the present invention reliably detects and localises PD activity in all substation assets provided with a voltage presence indication system. When used in this specification and claims, the terms “comprises” and “comprising” and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in the terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, separately, or in any combination of such features, can be utilised for realising the invention in diverse forms thereof.

The invention is not intended to be limited to the details of the embodiments described herein, which are described by way of example only. It will be understood that features described in relation to any particular embodiment can be featured in combination with other embodiments.

It is contemplated by the inventor that various substitutions, alterations, and modifications may be made to the invention without departing from the spirit and scope of the invention as defined by the claims. Examples of these include the following:

Figure 1 shows that a VPIS module 10 is connected to the VPIS port 14 on GIS switchgear 12. It is envisaged that to provide a comprehensive monitoring of modern GIS 12 systems, the VPIS module 10 incorporates connectivity for all three VPIS channels, providing three phase detection of PD sources within switchgear 12. Complementing this direct coupling method, the VPIS module 10 can also comprise contact temperature and environmental sensors, thereby delivering a complete package for GIS switchgear 12 monitoring.

As no single PD sensor can provide a comprehensive coverage of both switchgear assets and cables, the skilled person will appreciate that each installation can be composed of multiple sensor technologies. In this regard, Figures 1 and 2 show that the VPIS module 10 coupled between the VPIS port 14 provided on the substation asset 12 and the PD detection device or node 28 as described herein, can also be supplemented by the inclusion of HFCT sensors 20 disposed on the same switchgear asset 12. Non-intrusive condition monitoring of the switchgear asset 12 and the cables 22 and cable accessories enclosed therein is therefore further enhanced by the use of an additional cable PD node 18 connected to a plurality of HFCTs 20 disposed on the cable terminations 22 from the circuit breaker 24. The cable PD node 18 (which in Figure 1 is magnetically mounted to the rear panel 26 of switchgear 12 for illustration purposes only) monitors for PD activity on cables 22 and cable accessories, and therefore provides a complete, fully-integrated modular alarm system 30 which is entirely flexible and scalable.

Claims

1. A partial discharge detection device for a substation asset provided with a voltage presence indication system (VPIS), comprising: connection means configured to connect to a VPIS port mounted on the substation asset; an amplifier configured to amplify signals presented across the terminal of the VPIS port, the amplifier having an input stage being controllable to prevent clipping of the amplified output; and monitoring means configured to monitor the amplified output, and outputting at least one output signal based on detected partial discharge activity.

2. The partial discharge detection device as claimed in claim 1, wherein the substation asset comprises MV or HV electrical switchgear.

3. The partial discharge detection device as claimed in claims 1 or 2, wherein the signals presented across the terminal of the VPIS port are coupled from a VPIS bushing capacitor positioned adjacent to each phase.

4. The partial discharge detection device as claimed in claim 1, wherein the connection means comprise flying leads.

5. The partial discharge detection device as claimed in any of the preceding claims, wherein the signals presented across the terminal of the VPIS port are inputted to a filter and a clamping arrangement before being passed to the input stage of the amplifier.

6. The partial discharge detection device as claimed in claim 5, wherein the filter is a high pass filter.

7. The partial discharge detection device as claimed in claim 6, wherein the high pass filter comprises an in-series protective capacitor and a termination resistance being placed in parallel across the input line from the connection means.

8. The partial discharge detection device as claimed in claim 7, wherein the termination resistance comprises a termination resistor array comprising a plurality of switchable resistors.

9. The partial discharge detection device as claimed in claim 8, further comprising a microcontroller configured to control the switching of the switchable resistors disposed in the termination resistor array using an ADC and a comparison circuit which determines any clipping of the signal before amplification.

10. The partial discharge detection device as claimed in claim 9, wherein the voltage output from the clamping arrangement is inputted into the ADC and the microcontroller determines the levels at which an auto-range function switches the switchable resistors to a lower or higher resistance.

11. The partial discharge detection device as claimed in claim 10, wherein a peak voltage detection circuit determines the voltage level on the microcontroller.

12. The partial discharge detection device as claimed in claim 11, wherein the peak voltage detection circuit is implemented as a half wave rectifier to ensure that the peak is averaged over at least several cycles.

13. The partial discharge detection device as claimed in claims 11, further comprising a phase detection circuit which takes the output of the voltage detection circuit as a reference voltage.

14. The partial discharge detection device as claimed in claim 1, wherein the amplifier is a differential operational amplifier.

15. The partial discharge detection device as claimed in any of the preceding claims, wherein the monitoring means is implemented as a handheld device or as a semi-portable or fixed monitoring node.

16. The partial discharge detection device as claimed in claim 15, wherein any number of such VPIS partial discharge detection devices and HFCT cable partial discharge detection nodes can be connected together to form partial discharge alarm and monitoring system.

17. The partial discharge detection device as claimed in claim 16, wherein the detected partial discharge activity gathered by the VPIS partial discharge detection devices and/or the HFCT cable partial discharge detection nodes can be transferred to a corporate network and/or Supervisory Control and Data Acquisition (SCADA) computer system and/or remote cloud-based system for further processing using a wired local area network (LAN) and/or wirelessly using Wi-Fi and/or via mobile telecommunications signals and networks or the like.

18. A system for processing data from one or more partial discharge detection devices for monitoring substation assets provided with a voltage presence indication system (VPIS) sensors, the system determines the severity and/or location of partial discharge activity within substation assets.

19. A method of detecting partial discharge activity in a substation asset provided with a voltage presence indication system (VPIS), the method comprising the steps of: connecting an amplifier circuit to the VPIS port mounted on the substation asset; amplifying signals presented across the terminal of the VPIS port, the amplifying step being controllable to prevent clipping of the amplified output; and monitoring the amplified output, and outputting at least one output signal based on detected partial discharge activity.