"PMDT manufactures the world's most advanced Online Partial Discharge Test Equipment." 

The PDetector is the ideal device for Online Partial Discharge (OLPD) testing of medium and high voltage electrical equipment. Online PD testing is a method of inspecting the insulation of electric power systems while electrical equipment remains energized and in service. The PDetector employs all 5 types of sensor technology for online PD detection: TEV, UHF, HFCT, AE, and Ultrasonic. Information from multiple sensors gives the PDetector the versatility needed to detect all types of PD in all types of substation apparatus. Furthermore, the exact type (mechanism) of PD activity can be determined instantly using on-screen Phase Resolved Partial Discharge (PRPD) & Phase Resolved Pulse Sequence (PRPS).

PMDT 2019 Exhibition Schedule

1.)    MEE (Middle East Electricity), Dubai – March 05-07, 2019. Booth: H1G50
2.)    Powertest, USA – March 11-15, 2019. Booth: 810
3.)    IEEE PES GTD Asia, Thailand – March 21-23, 2019. Booth- F18
4.)    Hannover Messe, Germany – April 01-05, 2019. Hall 12 Stand F51
5.)    IEEE EIC, Canada – June 16-19, 2019. Booth: 1

"The power industry's most advanced Online Partial Discharge test equipment and services."

Online Partial Discharge testing (OLPD) provides valuable information for condition-based asset management. Over 80% of power equipment failures and losses are attributed to insulation failures. Conventional tan delta, infrared, and DGA testing is very effective at discovering a portion of the problems which lead to failures. The remaining unexpected failures are the result of localized insulation defects which are not detected by tan delta measurements, they do not produce significant heat, and they do not produce dissolved gasses unless the defect is in oil. Online Partial Discharge testing is the methodology of detecting and locating these common insulation problems. It can conveniently be performed online while the power system is energized and in service. OLPD can be performed in approximately 10 minutes per asset. OLPD tests cover transformers both internally and externally on the bushings. Additionally, every insulator and insulating material in any power apparatus in the entire substation can quickly be screened for PD. Every switch, lightning arrestor, PT, CT, SF6 breakers, cable terminations and splices can all be tested in a short time. OLPD is the future of power testing and PMDT is the company dedicated to the manufacture of powerful, efficient test and diagnostic instruments, providing expert PD test services, and engineering support.  



In-Service Substation Testing and Inspection Solutions

PD       DGA       IR       UV       SF6       1st Trip

       We are experts in partial discharge testing. We also support and provide services and equipment for all types of online substation testing methods. This includes DGA, Infrared, Partial Discharge, Ultraviolet, SF6 testing, and First trip testing. These inspections do not require de-energization of equipment. These online inspections give utilities a major advantage when implementing condition-based maintenance and also for detecting issues in advance of failure.
•    DGA Dissolved Gas Analysis identifies most issues in transformer oil and other oil-filled equipment. Further analysis is needed to determine the precise location of issues. 
•    IR Infrared Thermography find many defects in conductors which cause abnormal release of thermal energy. 
•    PD Partial Discharge inspections identify insulation defects in solid or fluid dielectrics, surface tracking, corona, arcing, internal PD, voids, and floating electrodes. Partial discharges are very short and confined electrical discharges which give produce electromagnetic signals, induced electrical signals and, acoustic emissions which can be detected non-invasively. PD also causes thermal, physical and chemical changes in the insulating material. PD can also occur on a conductor such as a bus bar, or at the interface between insulation, semi-conductor, and conductors. 
•    UV Corona cameras look into the ultraviolet spectrum to see the light produced by discharges occurring at the exposed surfaces of insulation material. 
•    SF6 Gas Insulation must be tested regularly to ensure the long life of the equipment. Moisture ingress gives rise to a corrosive environment in the gas compartment. 
•    1st Trip: Circuit breaker mechanism issues can be identified by measuring coil currents and operation times.

Online Partial Discharge Detection


Handheld Insrument

Connects to 5 Types of online PD sensors


Phase Resolved Partial Discharge (PRPD)

Instant Analysis, compare signals to local power frequency


Wireless Connectivity to HFCT UHF and Phase Sync


RFID asset tagging and Intelligent Patrol functions - automated data entry


PC Software with data management, trending and export CSV


Training and support package included


Online PD Diagnostics - Tier II


Multi-channel 6 ,12 channels

High sampling rates up to 100MHz


Portable Battery-Powered Unit


Locate and characterize PD insdie oil-filled Transformers, Cables 

Substations, GIS, Switchgear


3D triangulation PD inside of transformers

Acoustic and Electromagnetic Source Localization



PD Monitor  

Online Insulation Condition Monitoring for Substations


Transformers, Cable GIS, Swiitchgear, Overhead - Entire Substations


Modular, Expandable

Mix and Match



Internal UHF

External UHF

Acoustic Contact Probe



Intelligent Monitoring:

  Adjustable Interval and Event-based sampling 





Sensor Technology:

PMDT is the only manufacturer to utilize all 5 types of on-line partial discharge sensor technology. Using mulitple sensor methods ensures that PD activity is always discovered, located, and characterized.  PMDT's handheld PDetector has more capability than the high-end diagnostic equipment of the past. The small handheld, battery powered unit can completely perform the test and analysis without the need for a PC.  PDetector and PDiagnostic insutrments feature high-resoltion phase-resolved analysis of PD signals (PRPD and PRPS) in real time. So you get your test results instantly!


UHF Sensor

UHF  Ultra High Frequency  (300MHz - 1500MHz) (RF/radio/microwave range) - Every time a PD event occurs,  electromagnetic waves are transmitted from the site of the defect. This emission may also be called RFI or EMI.  (Radio Frequency Interference or Electro-Magnetic Interference) The PD emission is a broadband electromagnetic emission which can range from the upper radio frequency range up into the microwave range. The UHF range from 300MHz – 1500MHz is the most ideal bandwidth to probe for PD defects in MV and HV power systems.
All types of partial discharges will produce electromagnetic emissions in the UHF range. In most cases, the UHF emission is detectable with the UHF sensor. The UHF pulses are going to be emitted from the site of the PD defect and will spread in all directions through air and through most materials. However the signal cannot travel through metal. Metal enclosures will shield the UHF emission. The signal can escape through tiny cracks, gaskets, and seals and then spread out into the air. This pulse will occur at or near the positive or negative peak amplitudes of the AC sine wave. Thus the UHF pulses will occur with intervals roughly equal to ½ AC cycle time. (for 60Hz : 1/60 = 16.66ms   16.66/2 = 8.33ms ,  for 50Hz one cycle is 20ms and 20ms/2= 10ms)  To prove that a UHF could be from a PD activity, we can show that there is a 180 degree separation (8.33ms or 10ms) between the UHF pulses. This is the function of (time resolved or “phase resolved” measurements).  These phase-resolved measurements are made in real-time and serve as the basis for quick PD detection in the field.

     In some cases such as inside of a power transformer the UHF emission may be completely shielded by sealed metal enclosures. Fortunately, the UHF signal will also induce a high frequency current pulse onto the grounds of the apparatus. The high frequency current pulse will be detectable with a special High Frequency CT (HFCT). Learn more about HFCT detector is the HFCT section.

​HFCT Sensor

High Frequency Current Transformer     (0.5MHz - 50MHz) When PD occurs, there are small current pulses that are induced onto the ground shield or case ground. These pulses will travel dozens of meters along the ground grid in the form of high frequency current pulses in the range from 500kHz to 50MHz, Usually centered near 10MHz. High Frequency Current Transformers are a reliable method to measure these high frequency PD pulses.  These pulses spread out onto the ground grid like ripples in the water. They are especially useful for quickly testing for internal PD in a large area such as an entire power transformer or an entire cable, or even an entire substation. The HFCT sensor has a split core and so it’s simply clamped around a low resistance grounding lead.  HFCT sensors have a distinct advantage of being able to detect PD signals on cables from long distances up to 1km away (this limit depends on the type of ground shield and the stregnth of the PD pulse).  This means multiple PD signals and noise signals can also be detected from many points on the ground grid where a grounding lead is exposed.  In cable PD testing, the localization of PD via the HFCT sensor is achieved by determining the time difference between the arrival of the initial PD pulse, and the reflected pulse which has bounded off of the opposite end of the cable from where you are testing.  The speed of the pulses on the ground shield is similar to the speed of light. Exact signal speeds are known for various cable types. Knowing the speed, the cable length, and the time difference of arrival between the initial pulse and the reflected pulse enables the calculation of the distance to the PD.  Online Cable PD testing instruments have functions to identify these pulses and perform the distance calculation.PDiagnostc instrumets have the sampling rates required for this function. 

Airborne UltraSonic

Airborne Ultrasonic  Parabolic Dish Concentrator, Internal, and Ultrasonic Extension Wand, 20kHz-80kHz, center frequency 40kHz.  Each time a PD event occurs, an ultrasonic emission is transmitted from the site of the defect. The emissions are typically in the ultrasonic range from 20kHz - 300kHz and may also extend lower into the audible range.  If an insulation defect is close to the surface, then the ultrasonic signal will spread out and become airborne. The airborne ultrasonic signal may be detected by one or more of the 3 types of airborne ultrasonic sensors which are commonly used.

One type is built into the main handheld PD test unit. Also the extension wand can be used to listen in hard-to-reach seams of switchgear cabinets or other enclosures. Another type is the Parabolic dish concentrator which is used to extend the distance range of the ultrasonic microphone. The parabolic dish is ideal for checking bushing and insulators for surface tracking and harmful corona.  When airborne ultrasonic PD signals are detected on exposed insulator surfaces. The parabolic dish enables very quick and precise pinpointing of the PD location. Airborne ultrasonic is best for detecting corona PD and surface tracking PD. Floating electrode PD will also produce a weak airborne ultrasonic signal. But when airborne ultrasonic signals are detected within enclosures, it is not immediately possible to determine the exact location of the PD. Sometimes you cannot see the insulator which has the PD. By using multi-channel PD Diagnostics, 3 or 4 ultrasonic contact sensors can be used to triangulate the signal origin.

Acoustic Contact (AE)

Ultrasonic Contact Probe (20kHz - 300kHz) The ultrasonic contact probe is ideal for detecting and localizing partial discharges in fluid dielectrics such as oil and SF6 gas compartments. This is sometimes called “in-tank” testing. Each time a PD event occurs, an ultrasonic emission is produced at the site of the defect. If the defect is inside of sealed equipment such as a transformer or SF6 compartment, then the signal will (usually) not become airborne.
Fluid and solid dielectrics such as oil, SF6, and resins, will permit ultrasonic PD signals up to around 300kHz. However, air cannot permit ultrasonic signals higher than roughly 80-100kHz. To use the AE/ultrasonic contact probe, we must apply a high-vacuum silicon gel to the contact probe to bridge the air gap between the exterior of the tank and the contact sensor. This gel will conduct the PD signal from the exterior of the tank onto the ceramic head of the AE contact sensor. Precise PD localization can be achieved by using 3 or more ultrasonic contact sensors to triangulate the exact source. This is especially useful when a transformer is producing acetylene and the engineers need to know exactly where the problem is before a maintenance outage to drain oil and go inside. Another important application of ultrasonic localization is in SF6 gas insulated equipment.

TEV Sensor 

Transient Earth Voltage (3MHz -100MHz) Partial discharges in Medium Voltage (MV) power equipment will produce induced radio frequency signals which are sustained and can be detected at the surfaces of MV enclosures such as metal-clad switchgear, man holes, and metal enclosures.  TEV signals spread out quickly on the ground plane. For this reason it is very difficult to locate origin of a TEV signal. PD from overhead can induce a TEV signal on an entire line of switchgear. The TEV sensor is a type of capacitive coupler which is built in to the main PD detection unit. The TEV sensor is reliable for indicating most types of PD in metal-clad switchgear. But it also responds to noise from lighting systems, battery chargers, VFD’s, LED’s, and large motors. Void type PD will typically not generate much TEV range signal. Also PD inside of fluid dielectrics such as transformer oil will not produce a detectable TEV signal.  It’s important to use UHF, HFCT and ultrasonic sensor data in synthesis with TEV in order to see the whole picture and draw an accurate conclusion about the asset’s insulation health. Don’t rely on a TEV sensor for all of your information. The UHF and acoustic sensors are usually needed in order to locate the PD source. 

Wireless Sync 

Perhaps one of the most convenient safety features of the PDetector system is the wireless connectivity of the UHF and HFCT sensors. Additionally, the charger doubles as a wireless transmitter of the local power frequency to the main handheld unit. Simply plug the charger into an outlet which is fed by one phase of the power system under test. PDetector automatically detects and syncs the PRPD with the known local power frequency. This feature enhances the resolution of the PDetector and gives the ability to determine the exact type of PD activity. The charger, of course, is also used to charge the main handheld unit as well as the two wireless transmitters for the HFCT and UHF sensors. A mini USB cable is used for charging as well as to transfer measurement data from instrument to PC.

SoftwareData Management 

PC Software is included. Enables you to build a network tree which includes all of the assets which are periodically tested.  Each test file is stored and trended.


  • PD Recognition Software

  • Trending - Programmable warnings and alarms

  • CSV Data Export to other asset management software


  • RFID - Radio Frequency Identification - Small RFID tags

  • can be used to automatically associate test data with specific assets. Automated Data Entry

  • Intelligent Patrol - Engineers can create a procedure with all test points in a list. The technician fills the list with measurement data as he patrols the substation. 

Engineering Support  and Training

Each PMDT client receives a high level of expert training and support.  PMDT Engineers are always available to review your test samples and to provide guidance to users in the field.

PDetector training session can be hosted online via gotomeeting where all PD theory and testing procedures are taught in complimentary 4-hour session. Users who have attended the session are welcome to submit test results for expert evaluation.  We also provide varying levels of onsite training. In our 5 day baseline training course. We will spend 2 days in the class room and 3 days in the field mastering the skills of PD testing. 


Manufacturing, Training, and Support  San Jose, CA USA

Presentation of PDetector Handheld PD test equipment. Learn how and why the PDdetector is the ultimate tool for online PD testing in substations

Slide show style presentation of Handheld PDetector, Sensor Technology, Phase Resolved Display PRPD. 5 types of PD mechanisms

Detailed overview of partial discharge testing in substations. Includes description of sensors, methods, and concepts involved in on-line PD testing

Field Demo of PDetector using UHF, Acoustic, and HFCT to confirm and characterize dangerous PD activity in a zigzag grounding transformer. 4 minutes

"The Partial Discharge Experts"

© 2015  Power Monitoring and Diagnostic Technology Ltd.

6840 Via del Oro suite 150 San Jose, CA 95119





I'PMDT is an ISO 9001:2015 certified companyy.