PMDT Field Testing Services


Online Partial Discharge Testing is used to verify proper working condition of electrical insulation components in high voltage equipment.  The testing methods are non-invasive and performed on live equipment without the need for an outage. Our well-trained expert technicians use PMDT PDetector , PD Diagnostics,  and PD Expert Instruments.  Each electrical device is inspected using UHF, HFCT, Ultrasonic, Acoustic, and TEV measurements. PMDT methods utilize state-of-the-art electromagnetic sensors and analysis techniques which are more sensitive than conventional methods.  80% of power equipment failures are caused by issues that can be detected with PMDT online partial discharge test methods.   



Non-Invasive approach does not risk the device under test.


No outage required. Test is performed on live equipment during normal service.


Verify the health and proper working condition of high voltage insulation components. 


Identify incipient faults.


Identify insulation deficiencies which cause pre-mature degradation.  


Reduce or defer unnecessary maintenance.


Prioritize urgent maintenance.  



Bushings and Insulators 


Breakers, SF6, Vacuum Bottles 


Cables, Splices and Terminations


CT's, PT's, Lightning Arrestors






Metal-Clad Switchgear









PD Test  & Inspect
Cable Condition Assesment

Level 1 - Terminations and Splices - Power cable terminations and splices are a common failure point for shielded power cables. Cable terminations and splices can be checked in a Level 1 PD test which uses the handheld PDetector.  Possible defects in cable terminations can be either internal or external.  External is cause by surface contaminants or environmental damage. Surface PD will cause airborne ultrasonic emissions that can be detected with the ultrasonic dish sensor.  Also if there is a defect on the insulation surface there will be electromagnetic emissions in the UHF range.  If the defect is internal, deep inside the termination, then there will not be an ultrasonic signal, but there will still be a UHF signal which can be measured by the PDetector with the UHF sensor.

These UHF waves can travel through the insulation and out into the air around the termination. UHF sensor can detect these emissions from several meters away from the terminations.   

Level 2 - Mid-Cable defects - If defects or voids are present within the shielded portion of the cable, these can be diagnosed and located using the specialized PDiagnosticC. It utilizes 3 HFCT for testing the entire length of the cable and also uses UHF sensors for inspecting the terminations and splices. Most cables will have a lot of induced noise on them because they are like long antennas. The PMDT PDC4 Cable Diagnostic Instrument is designed to handle these situations with its ability to separate PD signals from noise signals. Then it can also identify a single PD pulse and provide the accurate location of the incipient fault.

Partial Discharge Testing is the key component of in-service power testing. Over 80% of disruptive failures are caused by insulation failures.  PD signals are the leading indicator of incipient faults and imminent failures of electrical equipment.


PMDT will provide an Online Partial Discharge Test Report for each device under test. Each device will be tested using UHF, HFCT, TEV, ultrasonic and AE sensors where applicable. The measurement values and phase-resolved charts are recorded and associated with the device under test. 



RFID tagging of each electrical asset can speed up the process of documenting the test and organizing and trending the results. The RFID system can also benefit the utility in other ways such as by documenting the nameplates and locations of many pieces of electrical apparatus.  

Transformer DGA 
Indication of PD

If a DGA report from a transformer or other oil filled apparatus is indicating PD, what do you do next?  In many cases, it may be wise to use an acoustic PD location technique to pinpoint the issue. Our advanced PDiagnosticT is sure to find the exact source of the PD fault inside. Acoustic techniques are very sensitive and can typically locate a signal origin with one square inch. Find out if the PD is in between windings, at the lead connections, in oil, or elsewhere. Location of PD activity prior to de-energization can save valuable time. Without prior knowledge of the PD location, techs could spend hours searching for a fault and never even find it. PMDT's acoustic location technique is a proven solution for locating incipient PD faults in oil and SF6 insulation.

Combined Testing :
PD   IR   DGA   1st trip

PMDT offers IR/UV DGA and 1st Trip Testing and Consulting in addition to PD testing. This concept incorporates all of the in-service test data that is available. This gives strong support to the Condition Based Maintenance Program. 

IR Thermography - Abnormal heating of conductors is driven by the load current going through the conductors. IR testing is good for conductor testing, but not ideal to detect insulation problems that are driven by voltage. Simply put: IR is for conductors. PD is for insulators.

UV / Corona Inspections – If PD on the surface of an insulator, then there will be an emission of light in the ultraviolet range. UV camera inspections are good for locating cracked insulators or dirty insulators with conductive contaminants, or degraded insulator surfaces. There are 2 main limitations of UV camera testing.  1. The defect must be out on the surface of the insulation. Internal PD cannot be detected by UV camera.  2. The location of the PD must be visible to the camera. There are many insulators which are inside of cabinets or enclosures that are not accessible for the UV camera inspection.   PD sensors can also perform the same job as a UV camera by using the ultrasonic dish and the UHF sensor to find the exact same problems that you could find with a corona camera.  

DGA - Dissolved Gas Analysis - is used to test for issues inside of oil-filled power transformers. DGA is a reliable indication of PD, corona, arcing or discharges occurring inside the oil. DGA cannot provide the precise location of the defect. Level II PD Diagnostics can locate the precise origin of the combustible gasses by detecting and locating the signal with 3D acoustic methods.  DGA will not detect any issue outside of the oil. In fact, it’s more likely to have a problem on a bushing or on a cable connected to a transformer than inside of the actual transformer tank. PD can find all types of insulation problems internal or external.

1st Trip Breaker Test – Identify mis-operating breakers which need maintenance. Simply by measuring the trip time when the breaker is operated, the breakers with lubrication or mechanical problems can be quickly identified.  This information can be collected with a portable test set or the proactive relays can be configured to capture and report this information.  


"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.