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Why do we need to conduct PD
measurements
• PD a major cause of early failure for HV insulation.
Partial Discharge
• PD is a symptom of degradation.
• Once present – it dominates as it’s own “inherent” stress degradation mechanism
• Its an early waning signal and precursor to complete insulation failure and breakdown
• PD diagnostics can be used to trend changes in the level and severity of insulation degradation
• Early detection of PD is critical in the prevention of in catastrophic failures
What Does PD Depend On?
• Electrical field stress
• Environment conditions - Temp and humidity
• Load or current
• Mechanical vibration
Important to have early stage of detection for PD
PD diagnostics: Used to trend changes in level and severity of the degradation of equipment installation
Partial Discharge
• Causes of PD in insulation system: – Voids in epoxy resins, polymers, paper
– Bubbles in liquids/oils
– Metal deposits, irregularities such as protrusions, contaminants
– Electrodes and insulation surfaces and interfaces
• Can arise through: – Poor design and manufacture
– Damage of equipment e.g. Transport damage
– Poor installation processes – poor workmanship
– General “ageing” or deterioration of materials
Why is Testing and Monitoring for PD Important?
Why is Testing and Monitoring for PD Important?
Why is Testing and Monitoring for PD Important?
Why Is testing and monitoring for PD Important?
9
Doble’s 4-Phased PD Products
Phase 1
Survey Instrument (PDS
100 and DFA) 100)
Phase 4
Permanent Monitoring
(Guard-Family)
Phase 2
PD-Smart
Testing
Phase 3
LDA6
Acoustic Locator
(Transformers Only)
PD Alignment with Doble Services
Four phases: Services wrapped into Phase 2-4
• Phase 1: Surveying
• Phase 2: Testing on- or off-line
• Phase 3: Investigative methods
• Phase 4: Permanent monitoring
• Phase 5: Doble Service Agreement (DSA)
• Includes electrical and UHF capabilities combined into one unit that will test PD on:
– Transformers
– Rotating machines (RM)
– MV/HV cables
– GIS
– And MORE!
PD-Smart Combine System
PD-Guard Monitoring System
• Key features:
– Advanced signal processing
– Interference suppressions
– Analysis software
• Continuously monitors your critical assets
• Most important: Automatic alarm system based on changes in activity rates rather than maximum values; this avoids false alarms due to one-time “outliers”
An important part of a thorough condition-
based maintenance program
Activity Rate Changes
• Monitoring changes in activity rates rather than maximum values avoids false alarms.
14
PD Key Markets
Testing
Rotating Machines
(Motors & Generators)
PD of Rotating Machines
Rotating Machines Testing/Monitoring
Periodic testing
with PD-Smart
Permanent
monitoring with
PD-Guard
+
Sensor + Connection
Box
System Components
• Permanent PD testing with PD-Smart on machines
• Permanent PD monitoring on machines
System Components N
eutr
al
Bus Work Motor or
Generator
A
B
C
PD Evaluation Server
Analysis Software Calibrator
PD-Guard
Coupling Capacitors &
Installation Kits
Fiber
Optic
LAN
+
Inductive Sensor
Pulse Disturbance Gate
System Components
• PD-Guard
• 3-4 PDDC-24 or PDDC-17
• Calibrator
• Doble PD Support
IEC60270: Frequency is important!
• Doble Lemke uses 2nF coupler, whilst other suppliers using 80pF, 200pF coupler
• A coupler with a capacitance of 80F,200pF “sees” only the first part of the winding. Deeper Discharges / Slot Discharges will maybe not detected
• Coupler with 80pF, 200pF are not conform to the international standard as the measuring frequency is much higher as specified in the standard
PD Pulse vs. Location in RM
• Many generators have high frequency (HF) couplers installed with a strong high pass behavior, hampering PD measurement.
• HF couplers exhibit good performance for measuring PD close to it that is at the line end of the winding.
• They are worse than low frequency (LF) couplers for detecting PD in the middle and neutral end of the winding.
BC-Matching Unit (HF-Expander)
• PD-Measurement according to the standard of IEC60270 with a HF coupler
High Frequency
Coupler
+
BC-Matching
Unit
+
PD-Smart
PD Key Markets
Transformer Testing
Reasons for Testing and Monitoring
to Avoid…
UHF PD-Smart Testing
Pulse
Generator
LDC-7/UHF
Interfaces:
ActiveX Control
DCOM-Interface
M MODBUS
Ethernet Hub
Computer(s)
for Remote
Control &
Analysis
PD
Monitoring
Server
Software
LAN / WAN / Internet
PD-Guard/UHF
UHF Drain Valve
Sensors
UHF Plate Sensors
(Mounted in Hatch)
Fiber optic
LAN
Doble TransformerGuard
UHF PD-Guard Monitoring
PD Measurement on Transformers
Valve Connector Tank
Sensor Application
Measuring Impedance
• PD Measuring Impedance for Bushing Tap Installation
Doble Acoustic PD Locator: LDA-6 For Transformers Only
• Multi-channel acoustic transient recorder • 4 or 8 acoustical channel
• External triggering channel
– Intuitive PD location software
– Piezo-electric acoustic sensors & magnetic clamps
Comments Acoustics
• Acoustics are a valid technique for locating PD but it’s the wrong approach for detecting PD due to low sensitivity of the AE method and the fact that PD imbedded in the winding will not produce acoustic pressure waves detectable on the tank wall. So no Acoustic Signal does not mean no PD and detection via HF-CT on the star point end will only work for strong PD
Comments Acoustics (Cont’d)
• Some companies have convinced many Clients in our Region that Acoustic Measurements is detection of PD which is fundamentally wrong
• We obtain greater location accuracy using UHF triggering.
• Biggest Market for Location is probably service work
Acoustic PD Locator: LDA-6
Sensor 1
Sensor 4
Sensor 3
Sensor 2
1
Online Monitoring
PD Key Markets
Cable Testing
(on Site)
Terminations & Joints
1. Incorrect installation / poor workmanship
2. Manufacturing issues – poor QA
The Problems
Termination Aging Joint Weak Spot
• There is a wide range of possible problems in cable installations
• Apart from physical damage external defects in joints and terminations is the dominant cause of failure
• In addition some type and vintage of cables developed water treeing for various reasons but often related to outer sheath /jacket damage
• All of these problems may result in reduced life expectancy and premature failure of the cable
+
UHF Sensors + HFCT +
Connection box
PD-Smart:
For Periodic
Online testing
PD-Guard
For Online
monitoring
Cable Termination: PD-Smart/Guard
PD-Smart Cable Termination
HFCT
Cable Termination: PD-Smart/Guard
PD Key Markets
Switchgear Testing
(MV & GIS)
MV Switchgear Monitoring
• In MV switchgear often high humidity leading to surface tracking, material defects and incorrect assembly are responsible for PD activity
Schematic diagram of the PD-UHF-Monitoring-Setup at GIS by using UHF-Spacer-Sensor or internal sensor
PD sensor: spacer type frequency range: 100 MHz – 1200 MHz
Internal UHF sensor integrated in GIS
PD Smart -UHF
LDS6-UHF
Gas Insulated Switchgear (GIS) On-line
Doble’s PD Product Offerings
Phase 1
Survey Instrument (PDS
100 and DFA) 100)
Phase 4
Permanent Monitoring
(Guard-Family)
Phase 2
PD-Smart
Testing
Phase 3
LDA6
Acoustic Locator
(Transformers Only)
Questions?
Contact:
Greg Topjian
Solutions Manager
617-393-3129
