Partial Discharge Diagnostics

Defects in medium and high voltage systems not only require costly repairs, but also can lead to failures of entire network sections with corresponding consequences. Therefore, it is in the interest of all network operators to recognize signs of impending defects as early as possible and to be able to take appropriate countermeasures on time.

With the PD Scan, Megger offers a lightweight, robust and portable PD scanner that can quickly inspect various type of equipment for partial discharge signals.

Component failure in a substation has serious repercussions. It has the potential to cause injury, damage and unplanned outages, which result in significant disruption and cost. Predictive condition assessment aims to identify faults developing in electrical equipment so that they can be addressed before failure.

The UHF PD Detector is the ideal tool for quick, non-invasive surveys in MV and HV substations and should be part of the toolkit for all maintenance and service teams. Due to its high measurement bandwidth, the UHF method provides accurate local online partial discharge (PD) measurements on HV components such as cable end-terminations, surge arrestors, voltage transformers and isolators.

Dual measurement channels allow two phases or two types of UHF sensors to be compared, which further increases the scope of use of the UHF Detector. MV switchgear surveys can also be carried out using the radio frequencies in combination with the wide selection of TEV and HFCT sensors. The phase resolved PD pattern (PRPD) display helps to identify type of defect and, importantly, differentiate the noise from the PD signal. Noise can affect PD readings, leading to a false interpretation of the results and unnecessary component replacement. The noise handling capability of the Megger UFH PDD ensures a true reading of PD, eliminating false positives, so only failing component are identified for replacement.

The handheld unit can either be operated using a keypad or using the large 6” colour touch-screen. It has a battery life of over 10 hours. Its mix of features and performance make the UHF detector the most cost effective unit of its kind.

Network operators can now get faster and significantly more reliable information about the quality and the condition of their cables. This is made possible thanks to the brand-new 50 Hz Slope Technology. For the first time, it has become possible to immediately locate faults in underground cables during the actual PD measurement.

With the 50 Hz Slope Technology for the first time, a withstand test with VLF cosine-rectangular voltage (VLF CR) and PD diagnosis with damped alternating voltage (DAC) is combined in one unit. This allows an efficient and integrated solution for precise inventory of the network infrastructure. The important fact here is that the PD measurement data, gained with the VLF CR or with the DAC test voltage, can be compared directly with the 50 / 60 Hz network voltage. This facilitates reliable decision making.

Developed with the individual needs of our customers in mind, the Megger Cable Test Van Systems deliver superior ergonomics, optimum speed, user friendliness, and reliability. Incorporated into this unique test van concept are the requirements and field experiences of the users. The result is a test system that sets new benchmarks in cable fault location.

Whether you are working on-site, in the countryside or an urban environment, having the right equipment available when conducting fault location operations is vital. When the correct tools can be accessed easily, fault-location time speeds up dramatically, and faults can be dealt with more efficiently. Megger’s range of cable test vans offer solutions to the challenges of fault location in the real world, no matter the environment. Our test van systems have been developed in collaboration with end users to ensure that they live up to the standards of daily fieldwork. Our vans are designed to be adaptable to the end users needs so that the most appropriate tests may be carried out for the cable in question, regardless of whether it is low, medium or high voltage.

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Power Diagnostix provides a complete line of modular preamplifiers for various testing applications. The most significant difference among the preamplifiers is the frequency range in which they detect partial discharge signals. Other features that distinguish one preamplifier from another are: options for transparency and on/off switching, unipolar vs. bipolar charge detection, and the possibiltiy of galvanic isolation in the test setup.

All of the Power Diagnostix external signal conditioning modules and preamplifiers are remote supplied and remote controlled through a simple coaxial signal cable (RG58). This technique allows placement of these units close to the sensor or signal source. Furthermore, as these modules act as impedance converter and line driver, the weak signal source, such as voltage divider or coupling impedance, is not loaded by the cable capacitance or impedance.

This technique also provides enhanced over-voltage protection. All preamplifiers of the RPA series can drive a 50 W cable up to 50 m long.

The RPA1 is the standard preamplifier for measurements in the low frequency range according to standards such as the IEC 60270. The RPA1D, RPA1E, RPA1F, and RPA1G are variations on the RPA1.

The RPA1D and RPA1G are suited to connect directly to ultra-sonic acoustic sensors. To simplify connection, they provide the selectable power supply for the sensor (15 VDC or 28 VDC).

The RPA1L and RPA1H are intended primarily for measurements on medium- and high-voltage power cables using the ICMcompact.

The RPA2 is primarily for measuring the PD signal spectra found with rotating machines, while the RPA2B is used with capacitive sensors to monitor cables and cable accessories at a higher sensitivity.

The RPA3 module is well-suited for measuring PD signal spectra, detected by sensors and antennas installed with gas insulated switchgear (GIS).

The RPA4 is a preamplifier set with fiber optic transmission, offering outstanding isolation properties.

The frequency converter unit FCU2 is an ultra-wide band preaquisition unit, covering 100 to 1800 MHz. It has a logarithmic output and is mainly used for GIS applications.

The UHF1 and UHF2 offer an amplification of 27 dB in the range from 200 MHz to 1 GHz resp. 300 MHz to 2 GHz, and are suitable for boosting weak signals from GIS sensors.

When a quadrupole and a coupling capacitor are used together as the coupling device, high voltage is applied both to a test object and to the coupling capacitor in parallel with the test object. A quadrupole (sometimes called a measuring impedance) can then be placed in series with either the coupling capacitor or in series with the test object. Some quadrupoles also output a low-voltage copy of the applied high-voltage wave for synchronizing the PD detector. The three basic models of available Power Diagnostix quadrupoles are briefly described here.

CIL Quadrupoles

The CIL quadrupoles consist of an inductor in parallel with a damping resistor. The inductor and resistor are calculated to form, together with a high-voltage coupling capacitor, a second order high pass filter. Therefore, matching the range of the CIL with the size of the coupling capacitor with which it will be used is important.

CIT Quadrupoles

The CIT coupling units are transformer type units, where a preamplifier’s input resistance functions as the required damping resistor. CIT units offer a higher sensitivity than the CIL coupling units. Furthermore, CIT units are available for bridged configurations to connect to two similar test objects as well.

CIL/V and CIT/V Quadrupoles

The CIL/V and CIT/V quadrupoles are similar to the CIL and CIT quadrupoles but also contain a capacitor acting as a voltage divider together with the high voltage coupling capacitor. This provides a low-voltage copy of the applied high-voltage wave that can be used through a HST to synchronize the PD detector and monitor the quality of the applied high-voltage wave.

Optionally, the quadrupoles with built-in divider capacitor for voltage measurement can be supplied with a rotary switch to select the divider capacitor. Especially, when connected to the measurement tap of transformer bushings, the selectable capacitors expand the applicable voltage range.

Analyzing the discharge activity requires the permanent installation of coupling devices. Preferably, such coupling devices are capacitive couplers terminated by a power separation filter.

Power Diagnostix standard coupling capacitors are mounted on sturdy cast aluminum enclosures and can be used for on-line and off-line measurements on rotating machines as well as for a variety of smaller test setups. A wider range of coupling capacitors and capacitor assemblies complete with quadrupoles and preamplifiers is available on request. The table to the right lists some standard models of coupling capacitors provided by Power Diagnostix, along with their built-in circuits, if present.

ATEX Couplers

For areas exposed to explosion hazards Power Diagnostix offers the CC15A /Ex, a special coupling capacitor for Ex environments to prevent igniting of explosive atmospheres. The coupler can be used in hazardous areas in zone 2 for fixed mounted coupling of high frequency partial discharge signals with low energy.

The AS75I and AS150I are active sensors with very high sensitivity for measurements on GIS, transformer tanks, or cable joints. They come with a built-in 40 dB preamplifier and can be connected to the RPA1D, RPA1F, RPA1G, or directly to the AIAcompact, ICMsystem, ICMcompact, or ICMmonitor.

The sensor fixture SFX1 is suited to secure the acoustis sensors on a GIS. The magnetic sensor fixture SFX2 and the sucking fixture SFX3 are for temporarily mounting of the acoustic sensors on a transformer tank.

UHF transformer sensors can be used to detect internal PD on power transformers in a frequency range between 300 MHz and 1 GHz. The UHF frequency range can be chosen under difficult on-site conditions, such as high impact of the measurements due to corona discharges or other disturbances within the typical HF range (100 kHz to 10 MHz).

UHF sensors are suitable for retrofitting as well as for pre-installation. The sensitivity can be proven by injecting an impulse generator signal  in the UHF range into the system. UHF PD signals can be used for PD pattern analysis as well as for triggering acoustic measurement systems, like the FOS4, for instance. Power Diagnostix provides the TFS1 for valve flanges and the TVS2 for oil valves. Both sensors can be modified and designed in accordance of special customer specifications.

External window sensors are used to conveniently equip older GIS with UHF monitoring. Power Diagnostix offers such window sensors of different sizes to fit the inspection windows of older GIS. Here, the obtained results with sensitivity are comparable to embedded sensors, if the window has a diameter of 80 mm or higher. In case well matched, such external window sensors offer a sensitivity of few pC.

External Flange Sensor EFS1

The external flange sensor EFS1 is a wide-band UHF antenna for PD detection on GIS and GIL. Since it is wrapped round the unshielded flange connection, the flange dimensions are required on order. With the N-connector it can be directly jointed with a UHF preamplifier like the UHF1 and UHF2 or the preacquisition unit FCU2. Power Diagnostix offers two different models, for permanent and for temporary installation.

Besides the embedded coaxial sensor of cable accessories, external sensors can be applied to joints and terminations. Especially on cross-bonding joints differential foil sensors serve to capture partial discharge signals in elevated frequencies. Such foil sensors can be permanently installed for monitoring or temporary applied for survey type measurements.

The main task of the partial discharge monitoring system type ICMmonitor CA is to detect internal partial discharge in power cables caused by cracks in joints and terminations or degradation in the insulation system at an early stage. PD signals are picked up by a current transformer and preprocessed by an FCU3. A monitoring control rack (PDMCR) with ICMmonitor CA software installed receives the measured data from the monitoring units and processes it.

Due to the dielectric properties of cable materials and their attenuation, partial discharge activity in power cables is typically measured in a frequency band of several tenth of MHz. The frequency converter unit (FCU3) is a signal conditioning unit with a demodulating logarithmic transfer function. It picks up the HF signal from a current transformer (CT). The output of the FCU3 is the envelope of the HF signal down-converted into the frequency range of the instrument (< 1 MHz). The FCU3 is mainly used with monitoring applications and for gating purposes. This unit is remote powered by a DC phantom voltage provided by the ICMmonitor CA. A malfunction of the FCU3 will be detected automatically by the monitoring unit and will be indicated in the main panel of the software. An external synchronization signal is usually derived from a VT, which is installed in short distance to the PD measuring device. If such a short distance installation is not possible, due to space restrictions e. g., Power Diagnostix offers a special synchronization unit FSYNC1, which allows transmission of synchronization signals over long distances via fiber optic cables. The number of current transformers to be monitored depends on the type of cable and the individual specification of the customer. The signal of each CT is converted into lower frequencies by an FCU3. Up to six signal cables from current transformers are brought together into one ICMmonitor CA instrument.

All monitoring instruments are interconnected via a fiber optic LAN ring, providing n+1 communication redundancy. A monitoring control rack (PDMCR) receives the measured data and processes it. With this system architecture a nearly infinite number of current transformers can be continuously monitored and observed.

A special software reads the measured data of all stand-alone ICMmonitor CAs, each scanning up to six signal sources.

The ICMmonitor Portable is part of the Power Diagnostix ICM series of digital partial discharge detectors. It is a compact, stand-alone instrument for evaluating the condition of medium and high voltage insulation. A built-in four-, or eightchannel multiplexer offers scanning of three-phase systems or multiple sensors. It is used principally for permanent, continuous on-line monitoring of rotating machines, cable systems, power transformers, and gas-insulated switch gear (GIS).

The multifunctional ICMmonitor Portable, with its embedded display, convenient trending, and settable alarms, is an ideal solution for continuous on-line monitoring of rotating machines and other electric devices in industrial and utility applications.

The GISmonitor Portable is a portable unit for partial discharge measurements on gas-insulated switchgear (GIS) caused by hopping particles, floating potentials, cracks in insulators or spacers, or other degradation in the insulation system. The instrument offers parallel real time PD acquisition on up to 40 channels. To eliminate disturbance signals from the measurement, the instrument can be connected to a disturbance antenna that provides a gating signal.

The GISmonitor Portable offers parallel real-time acquisition on gas-insulated switchgear (GIS) on up to 40 channels.

The GISmonitor builds on 20 years experience in online PD monitoring on rotating machines, transformers, cables, and especially GIS systems. It combines proven technology of the ICMmonitor with new processor technology and embedded hardware capabilities. The hardware core of the system has been optimized for parallel, real time PD acquisition on multiple channels. Any UHF signal can be detected and digitized within micro seconds.

A separation of PD events from external disturbances or internal switching pulses is calculated in real time and therefore an effective PD and alarm detection is given. Each 8-channel acquisition plug-in board operates fully stand alone, but can be combined with a virtually unlimited number of units, to monitor all PD sensors in one GIS PD monitoring system in parallel. A partial discharge monitoring acquisition rack (PDMAR) carries up to 15 plug-in boards – each with eight channels – providing up to 120 channels. An industrial type PC installed in a partial discharge monitoring control rack (PDMCR) reads all data of the instruments via the high speed fiber optic LAN ring, providing communication redundancy. Storage redundancy is provided due to a RAID controller and data mirroring on multiple drives.

Each cabinet comes with an uninterruptible power supply, a network switch and temperature controlled cooling. Cabinets for indoor applications feature a protection class of IP54, while cabinets for outdoor applications reach a protection class of IP65. All cables from external are feed through the bottom into the rack.

The ICMflex high voltage instrument family offers inherent operator safety and greatly simplifies distribution class cable testing and other field tasks involving partial discharge detection, loss factor (tanδ) measurements, and PD fault location. It has been designed to simplify the application and to combine different measurement tasks with one instrument. With the unique concept of the ICMflex instruments, the entire acquisition hardware is placed on high voltage potential right at the position where the signals are. Thus, no signal cables are needed, as the instrument is fully self-contained and battery operated. In case that the instruments are used for measurements in an environment with high frequency (HF) disturbance, they can be equipped with a gating input for effective noise reduction. Every ICMflex instrument is fully remote controlled via Bluetooth or fiber optic communication. Using wireless Bluetooth or fiber optic technology the ICMflex tanδ and partial discharge analyzer family increases operator’s safety and greatly simplifies off-line testing and analysis of distribution class cables and rotating machine stator windings.

The AIAcompact is a portable unit for in-service acoustic and electric (UHF) partial discharge measurements on gas-insulated switchgear (GIS), transformers, and cable accessories. The instrument is fitted with a battery pack for independent operation up to 3 hours and adapts to a variety of piezo-electric acoustic sensors and is supplied with a versatile sensor fixture. Additionally, the AIAcompact allows partial discharge measurements on external UHF sensors.

Offering easy-to-use acoustic partial discharge analysis of gas-insulated switchgear (GIS) and other high voltage equipment plus the optional analysis on embedded or external UHF sensors makes the AIAcompact the ideal solution for convenient in-service substation condition assessment.

The ICMcompact is part of the ICM series of digital partial discharge detectors. The ICMcompact is a compact, stand-alone instrument for evaluating the condition of medium and high voltage insulation. It is often used in quality assurance and quality control tests in manufacturing.

The easy portability, simple operation, and flexibility of the ICMcompact make it a good choice for routine PD testing in a variety of utility and industrial applications.

The multi-channel version of the ICMsystem is specifically designed to meet the requirements of partial discharge acceptance tests on large power transformers.

The instrument builds on the acquisition core of the standard ICMsystem. However, by introducing an individual amplifier plug-in board for each channel, true parallel acquisition of the discharge magnitude of up to ten channels is achieved. The instrument can be equipped with optional features like RIV or acoustic PD measurement. In acceptance test mode, the software shows up to ten meter displays, each indicating PD level, voltage, and frequency of the specific channel.

TDM 45 series is a revolutionary breakthrough in testing and diagnosis of MV cables. The patented concept addresses the utilities increasing need for flexibility in use of test and measuring equipment based on the type of application.

The modular concept alloows the engineer to individually setup the unit based on the type of job that needs to be executed, e.g. for tanDelta diagnostics, PD diagnostics or VLF withstand testing. The TDM 45 series is available in eight varients; upgrades are possible without sending the unit back to the factory.