ONLINE INSULATION TESTING
Partial Discharge
Partial Discharge is "A localized electrical discharge that only partially bridges the insulation between conductors and which can or cannot occur adjacent to a conductor" ---- quoted from IEC60270.
When the Voltage stress exceeds the breakdown strength of that portion of the insulating material, a Partial Discharge begins and continues to deteriorate that insulation.
When Partial discharges occur, various physical and chemical changes may happen, which produce emissions that we can detect, localize, and characterize to provide the information needed to prevent insulation failures of Medium and High Voltage electrical equipment.
PD occurs in Solid, Liquid or Gaseous insulating mediums. PD can also occur in the form of Corona, Surface Tracking, or floating electrodes (metal to metal discharge) causing degradation of the insulation. Once PD begins it will always get worse. 80% of electrical fires are caused by insulation breakdown or failure and PD is the very first indication that insulation is breaking down. NFPA 70B states that insulation breakdown is the number one cause of electrical failures.
5 types of Partial Discharge(Partial Discharge Mechanisms)
- Corona - discharge to air
- Floating Electrode - metal to metal
- Particle discharge - conductive particles contaminate insulation medium
- Voids - gaps in solid insulation or gas bubbles in oil
- Surface discharge - tracking over outside of insulators/bushings
Partial Discharge Emissions(Bi-products of PD Activity)
- Light - sometimes visible
- Heat - infrared
- Gasses - nitrous oxide, ozone other gasses with odor
- Acoustic - audible and inaudible ultrasonic
- Electromagnetic - transmitted UHF or induced TEV and HFCT
- Chemical - Verdigris -nitrous oxide +moisture=nitric acid
PD Testing Methods
Acoustic Emissions(AE)
- Airborne - ultrasonic microphone 40kHz center frequency
- Contact Probe - broad range 20kHz -300Khz (PD in oil or SF6 gas)
Electromagnetic
- UHF Ultra-High Frequency 300MHz-1.5GHz
- TEV Transient Earth Voltage 3MHz-100MHz
- HFCT High Frequency Current Transformer 500kHz-50MHz
PDStar and PDetector
PDStar is the ideal tool for condition-based maintenance programs. Online partial discharge testing is a method of inspecting the insulation of electric power systems while equipment remains energized and in service. PDetector incorporates all 5 types of online PD sensor technology. Information from multiple sensors gives PDetector the versatility to detect all types of PD in all types of substation apparatus. Furthermore, the exact type of PD activity can be determined using PRPS: void, corona, surface, particle, or floating electrode.
Applications:
- Power Cables
- Transformers
- GIS
- Switchgear
- Substation Apparatus
Sensor Technology: Detection Bandwidth
Electromagnetic (EM)- TEV - Transient Earth Voltage (built-in to the main handheld unit) 3MHz - 100MHz
- UHF - Ultra High Frequency - 300MHz - 1.5GHz
- HFCT - High Frequency Current Transformer 500kHz - 50MHz
Acoustic Sensors (AE)
- Acoustic Contact - 20kHz- 300kHz
- Airborne Ultrasonic - 40kHz
Infrared Image Sensor(Infrared)
Phase Resolved Partial Discharge (PRPD) - PD activity produces both electromagnetic and acoustic emissions. PRPD mode will automatically relate the occurrence of the incoming signals to the power frequency 60Hz (or 50Hz). This gives the user the ability to instantly determine if PD is present.UHF Ultra High Frequency
300MHz - 1.5GHzTransmitted Electromagnetic Waves (EMI) are emitted when PD occurs. The UHF sensor is a special antenna with a response range from 300MHz to 1.5GHz. Virtually all types of partial discharge have an emission in this range. The UHF sensor is the most versatile PD sensor. For convenience and safety, it interfaces wirelessly with the main handheld PDetector unit.
TEV Transient Earth Voltage
3MHz to 100MHzInduced TEV signals serve as a good indicator of PD activity in metal-clad switchgear. These RF signals can be induced on surrounding metal work and adjacent switchgear panels. The TEV sensor is built-in to the main handheld unit. It also serves as an important safety tool for personnel approaching apparatus whose condition is unknown.
HFCT High Frequency Current Transformer
500kHz - 50MHzHFCT sensor is a split core CT with High freuency response. It does not respond to 60Hz power. PD activity induces a HF current pulses onto surronding grounds. For safety and conveneince , the HFCT sensor is connected wirelessly to the main handheld analyzer
Acoustic Contact
20kHz -300kHzPD inside of oil-filled equipment or SF6 equipment will have an acoustic emission at a high frequency near 90kHz in SF6 and near 160kHz in oil. These emissions do not travel through air. The contact probe is used by placing the sensor onto the transformer or GIS tank. A vacuum gel is used to bridge the airgap and ensure the signal is received by the probe. Acoustic contact measurements are very sensitive. Very small PD signals can be detected and characterized. Also because they travel at the speed of sound, the origin of the signals can be triangulated using multiple sensors simultaneously.
PDMonitorC Power Cable Online Partial Discharge Monitoring System
PDMonitorG GIS Online Partial Discharge Monitoring System
PDMonitorS Switchgear Online Partial Discharge Monitoring System
PDiagnostic
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
Hardware
Sensors
UHF Ultra High Frequency
300MHz - 1.5GHzTransmitted Electromagnetic Waves (EMI) are emitted when PD occurs. The UHF sensor is a special antenna with a response range from 300MHz to 1.5GHz. Virtually all types of partial discharge have an emission in this range. The UHF sensor is the most versatile PD sensor. For convenience and safety, it interfaces wirelessly with the main handheld PDetector unit.
HFCT High Frequency Current Transformer
500kHz - 50MHzHFCT sensor is a split core CT with High freuency response. It does not respond to 60Hz power. PD activity induces a HF current pulses onto surronding grounds. For safety and conveneince , the HFCT sensor is connected wirelessly to the main handheld analyzer
Acoustic Contact
20kHz -300kHzPD inside of oil-filled equipment or SF6 equipment will have an acoustic emission at a high frequency near 90kHz in SF6 and near 160kHz in oil. These emissions do not travel through air. The contact probe is used by placing the sensor onto the transformer or GIS tank. A vacuum gel is used to bridge the airgap and ensure the signal is received by the probe. Acoustic contact measurements are very sensitive. Very small PD signals can be detected and characterized. Also because they travel at the speed of sound, the origin of the signals can be triangulated using multiple sensors simultaneously.
PMDTiSmart
The Smart Sensors are a revolutionary design which builds a wireless smart sensor network to autonomously sample asset condition data periodically from all kinds of power equipment. The test data is collected by the sensor and uploaded to the PMDTCloud for data diagnostics wirelessly
The PMDTiSmart Smart Sensor Series is one of PMDT’s latest cutting-edge online testing technologies. It builds a wireless smart sensor network which autonomously samples data periodically from all kinds of medium and high voltage power equipment wirelessly. The test data is collected by the sensor easily, and uploaded to the PMDTCloud by the Data Collecting Units. The PMDTCloud analyzes the data collected through our Proprietary Cloud Diagnostic technology. The condition of the power asset is evaluated and appropriate maintenance suggestions are provided when an issue is found to exist. This revolutionary design provides a new, leading-edge, efficient, and intelligent way of online testing, which will greatly help in simplifying the traditional way of doing online PD testing. It also provides solutions for NFPA’s 70E 2015 more restricted approach boundaries for live assets.
Applications:
- MV Switchgear
- Transformers
- GIS
- Power Cables
- And Other Equipment
Feature:
- Safe, reliable, and non-intrusive online testing with wireless installation method, does not need any modification of the original structure of the power equipment.
- Reliable data transmission with encrypted wireless communication technology.
- Autonomously samples signals from power equipment periodically. The measuring cycle of each sensor is selectable from 6 to 10000 minutes. The recommended measuring cycle is 24-hour interval. Test data could be saved locally or saved on the cloud if this option is purchased separately.
- The data collection units obtain data from the smart sensors wirelessly and upload the data to the PMDTCloud via 3G/4G/ethernet for data storage and analysis.
- The PMDTCloud analyzes the data by utilizing the Deep Learning Technology to produce a more accurate diagnostic of the data.
- Eliminates opening MV switchgear equipment for OLPD testing of cables.
- Low power consumption technology allows the battery life to last for up to an estimated 5 to 8 years of operation.
- Employs a waterproof design which is suitable for outdoor applications.
- Cost-effective compared to permanent online monitoring systems.