High Voltage Insulator Testing Based on Electric Field Method CHARLES JEAN
Personnel Safety Through Assessment of Electric Field Distribution Along Energized Insulators By Charles Jean P. Eng. Personnel Safety Through Assessment of Electric Field Distribution Along Energized Insulators
Introduction The condition of insulators on transmission and distribution power grid is of prime importance for the successful operation of a power network. Particularly since a damaged, electrically deficient insulator can lead to costly systems outages, serious injury, or loss of life. Personnel Safety Through Assessment of Electric Field Distribution Along Energized Insulators 2
Scope In this presentation, some of the dangers and a solution will be described and applied to improve the safety of personnel working in close proximity of live high voltage insulators. Personnel Safety Through Assessment of Electric Field Distribution Along Energized Insulators 3
High Voltage Insulators Types Porcelain Glass Composite or Polymer (Non Ceramic Insulator) Personnel Safety Through Assessment of Electric Field Distribution Along Energized Insulators 4
Some Testing Techniques Visual Inspection Infrared /UV Detection Electric Field Measurement HV DC Tests Buzz Sticking Composite Porcelain Universal Personnel Safety Through Assessment of Electric Field Distribution Along Energized Insulators 5
Diagnostic Test Chart Some Testing Type of Insulators Techniques Porcelain Glass Composite X (1) Visual Inspection X X Infrared/UV detection X HV DC Tests X Buzz Sticking X Electric Field measurement (3) X (2) X X (1) A punctured glass insulator can be identified visually (2) Used for surface contamination evaluation (3) Electric Field measurement will be the technique described in this presentation Personnel Safety Through Assessment of Electric Field Distribution Along Energized Insulators 6
Comments on some Testing Techniques • BUZZ STICKING: Used on Porcelain insulator strings only. Shorting out an insulator using a buzz stick can be cause a line-to-ground power arc if the insulator string contains multiple failed insulators and only one or several insulators are holding off the entire voltage. • Can be potentially dangerous • Requires operator judgement • Difficulty of counting to ensure that each insulator is checked on a long string • HV DC TEST : Very heavy device. Used on Porcelain insulators only. This involves injecting a 10 kV DC voltage across each insulator which can cause a line-to-ground power arc if the insulator string contains multiple failed insulators. Personnel Safety Through Assessment of Electric Field Distribution Along Energized Insulators 7
Comments on some Testing Techniques ( con’t ) • UV DETECTION: Does not detect internal cracks on composite or porcelain insulators nor puncturing through porcelain. There may not be sufficient external cracks to produce detectable signatures. Very expensive. • INFRARED DETECTION : Used on composite insulators only. Very expensive. Small defects will be undetectable and consequently, will not produce an early fault indication. The defect has to be major to produce a detectable temperature rise. Ambient temperature, sun and wind may mask the temperature rise. Sensitivity is low for this application. Requires operator judgement. • VISUAL INSPECTION: Only detects obvious external visible damage facing the observer for composite and porcelain insulators. Useful for detecting failed glass insulators because they shatter. Personnel Safety Through Assessment of Electric Field Distribution Along Energized Insulators 8
Our Development Objectives • Safe to operate • Lightweight (less than 2 kg) • Ease and speed of operation • Reliable and early detection of faults • Instant reporting: number of bad discs • GO/NO-GO indication: safe or not safe • Visual and audible alarm • Contamination assessment • Database compliant to allow degradation over time assessment • Can be used on live line up to 1M Volts Personnel Safety Through Assessment of Electric Field Distribution Along Energized Insulators 9
Electric Field Measurement Technique Electric field testing technique involves the use of devices to measure and plot the Electric Field along the length of the insulator (Composite or Porcelain) or string (Porcelain). • This technique can be used on many types of insulators including: – Porcelain, Composite, Post, Bushings, Lightning arrestors, etc. 3 different sizes of lightweight sleds with mounted sensors are required to accommodate all these types of insulators. • This technique can be used to detect many types of defects including: – Leaking insulators, punctured insulators, severe surface contamination, carbon tracking, captive moisture, etc. • This technique uses a microprocessor based automatic measuring, processing, data gathering and reporting device which is attached to lightweight sled at the end of a non-conductive stick that slides along the insulator or insulator string. Personnel Safety Through Assessment of Electric Field Distribution Along Energized Insulators 10
Electric Field Distribution The disc #8 is leaking (Low resistance), consequently, the voltage across its Cap and Pin is lower This simulation confirms that the Electric Field surrounding the disc #8 is lower Source: Background of the method Personnel Safety Through Assessment of Electric Field Distribution Along Energized Insulators 11
Insulator Scanning Hot stick The Electric Field sensor & processing device is mounted on a high impact ABS sled which is moved along the insulator by means of a hot stick. Personnel Safety Through Assessment of Electric Field Distribution Along Energized Insulators 12
Porcelain & Glass Insulator Cap Metal Pin Glass Porcelain Electric Field measurement location Punctured Glass disc can be visually detected Personnel Safety Through Assessment of Electric Field Distribution Along Energized Insulators 13
Electric Field Measurement The Electric Field measured by the sensor is proportional to the voltage between the Socket Cap and the Ball Pin Note that there is no electrical contact between the sensor and the metal parts of the disc for added security A reading is taken as the sled passes each disc Electric Field sensor Personnel Safety Through Assessment of Electric Field Distribution Along Energized Insulators 14
Faulty Porcelain Insulator String Note: Electric Field is lower under the HV corona ring Disc #15 is punctured Ground end High voltage end Personnel Safety Through Assessment of Electric Field Distribution Along Energized Insulators 15
Faulty Porcelain Insulator String Disc #7, 9, 15, 16, 23 and 29 are punctured Danger: This Porcelain string presents a dangerous situation for close proximity workers The minimum number of good insulators in a string shall be specified by the relevant power company before attempting close proximity working Ground end High voltage end Personnel Safety Through Assessment of Electric Field Distribution Along Energized Insulators 16
Composite Insulator Ground end High Voltage end Optional Corona Ring There is no metal part along the path. Any conduction along that path will be Corona Ring detected by the Electric Field Sensor Personnel Safety Through Assessment of Electric Field Distribution Along Energized Insulators 17
Floating Defect Graph showing the effect of 3 types of simulated defect placed near the center of the insulator Personnel Safety Through Assessment of Electric Field Distribution Along Energized Insulators 18
High Voltage Connected Defect High Voltage Connected Defects are the most common type of defects on Composite Insulators Danger: This Composite Insulator represents a very dangerous situation for close proximity workers Note: Two curves per scan are displayed, one curve (red) Graph showing the Electric Field distribution of two 735 kV for the Forward scan towards HV end and one curve (blue) Composite Insulators. The colored curves show a dangerous for the Backward scan towards the Ground end insulator, the curve in black shows a healthy insulator Personnel Safety Through Assessment of Electric Field Distribution Along Energized Insulators 19
Instant Reporting & GO/NO-GO • The sensor has a built-in microprocessor that uses programs and algorithms to automatically interpret the result of an insulator scan and instantly report a DANGEROUS status to the operator using visual and audible alarms (Validated by extensive tests on live lines under all types of insulator failure conditions) • The condition of each insulator is stored for 100’s of towers and strings. It can be downloaded to a PC for investigation and future reference for maintenance purposes Personnel Safety Through Assessment of Electric Field Distribution Along Energized Insulators 20
Conclusion • The Electric Field Measurement Technique is safe and has a long record of reliable results • Based on science and extensive experience, Instant Reporting and GO/NO-GO features, it is now possible to ensure better safety for workers • This Personal Safety innovation is now part of the insulator testing & maintenance process Personnel Safety Through Assessment of Electric Field Distribution Along Energized Insulators 21
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