ULD-40. Ultrasonic Leakage Detection, Accoustic emission & Corona detection

Transcription

1 ULD-40 Ultrasonic Leakage Detection, Accoustic emission & Corona detection

2 Common events leading to Metalclad and Breaker Failures Moisture Dust Rodents Animals Poor conductivity do to high resistance contacts Voids in insulation causing partial discharges

3 Moisture Problems Moisture can come from multiple sources. Condensation Humidity Failed seals and gaskets Problems associated with free breathing or non-insulated metalclads.

4 How can Ultrasonic Testing Help? None invasive. Can detect surface tracking. Can detect loose components. Can detect electrical floating shields or other components. Can detect non-electrical problems such as leaks. Can detect partial discharges in various components.

5 Ultrasonic Testing The ULD-40 Ultrasonic detector is designed to operate in the 38,000 to 48,000 Hz range. Can detect corona discharges. Can detect some charged fields that start to discharge via contaminated surfaces or arcing between two objects. Can detect pressure vessel leaks.

6 Example of maintenance with Ultrasonic Detection Case Study 1 Free breather metalclad. Tie breaker had history of noises. (Although none at time of survey) Tie breaker runs normally closed paralleling transformers. Westinghouse type 150DH-P500 AMCB style breakers at 13.2kV. Ultrasonic readings of +15dB were detected

7 Minor damage to composite pieces of the phase barriers with broken pieces in the breaker.

8 Main Contacts - Found arc carbon tracking developing arc chute

9 Pitting and rough surfaces

10 Molten metal slag splattered on actuating arms

11 Remediation of problems Arc chutes were cleaned. Contacts were burnished to remove pitting and slag. Breaker was vacuumed and surfaces wiped down. (Found oily residue on puffer tubes and some support structures). Breaker was returned to service and resurveyed. Ultrasonic readings are now within normal parameters.

12 Ultrasonic detection Case Study 2 Another free breather metalclad that had previous failures. McGraw Edison type WSA AMCB style breakers. had high Ultrasonic readings. (40,000Hz range). Breaker was +18dB located in lower left side of front of breaker while in service.

13 When breaker was removed nothing obvious could be noticed at first until a visual inspection down the back between the arc chutes and the barrier board on the side that had the high readings.

14 A metal object was laying on the bottom barrier board along with particles of some material.

15 What was this piece of metal and where did it come from? The side barrier board was taken off to inspect further.

16 The keeper ring had broken and the holder fell off.

17 What it should look like - Notice keeper clip on this side of breaker

18 How did an Ultrasonic detector pick this up? Metal objects isolated from ground and not part of conductor. In an energized field. Gave off corona which was detectable.

19 MAJOR SAVINGS This condition would have resulted in an catastrophic failure eventually. Metal piece holds main nut that keeps linkage rod holding all three poles together. Nut was already loose and backing off.

20 Case Study 3 London Hydro Performance Review and a New Perspective for Inservice 27.6 kv Three-Phase Air Insulated Sectionalizing Enclosures using Ultrasonic leakage detection

21 London Hydro research pointed towards a possible mechanism of failure that was ultimately confirmed by expert opinions: the corona phenomenon. Its effect in switchgear was studied and validated through field visual evidence and measurements. A representative illustration is included below to attest the authenticity of the facts.

22 London Hydro Unit manufactured in 1980; Failed in 2005 and 2006; Affected SAIDI with overall; Measured 40 db (approx. 2,500 pc) Cables reterminated in one bay after the unit was replaced; Corona measured was reduced to 10% of the original value at similar humidity levels Water is still present in the base after a month, although it was drained during the replacement.

23 What is Corona? Part 1 Corona is an electrical phenomenon caused by a chemical reaction in the air. Also known as PARTIAL DISCHARGE, corona is the ionization of the nitrogen in the air caused by an intense electrical field.

24 What is Corona? Part 2 partial discharge refers to the fact that the electric current produced travels only part of the distance between phases or phase-toground. The fast negative ions and slower positive ions bombard the fibrous insulation, eventually destroying it or producing conductive tracking on the surface of the insulation.

25 What is Corona Part 3 Tracking effectively shortens the distance between phases or phase-to-ground. If the enclosed equipment is not well ventilated, ions reduce the dielectric strength of the air and the shorter insulation distance will eventually cause high energy phase-to-phase or phase-to-ground arcing!

26 The ULD-40 has the ability to detect and measure corona at any time during the day. Symptoms of corona presence in mediumvoltage solid insulation and cable terminations can sometimes seen by fading of color, white powder, dark tracks on insulation near busbar or conductors, noise and smell of ozone. **Visual Inspection is not Enough to detect corona activity London Hydro inspections have proven that High corona levels do not always present visual side effects

27 Histogram showing the Corona db of S.E s and the categories of Clean and Dirty units Note: most of the High level db where found in enclosures that looked clean!!

28 Corona in medium voltage switchgear The accumulation of the nitric acid inside an enclosed space like airinsulated switchgear will create carbon marks across insulating materials. ion bombardment also destroys some solid insulation materials, eventually turning them into dust

29 These Ion bombardments can cause carbon treeing in cables and conductive tracking on cable terminations and on solid insulating pieces, like fiberboards. Also, defects in insulating materials that create an intense electrical field can overtime result in corona that creates punctures, carbon tracks and discoloration of the non-ceramic insulators (NCI).

30 Ionized air (corona) trapped in switchgear enclosures can result in arcing, especially when a door is opened and the sudden ventilation causes conductive ionized air to pass between energized buses. Corona can contribute to the chemical destruction of insulators resulting in internal flashovers.

31 Example of an inspection on a Live Front Switch using the ULD-40

32 Example of an inspection on a Live Front Switch using the ULD-40

33 Thank You Brad MacDonald NDB Technologies St-Jean-Baptiste Quebec, PQ, Canada G2E 5K2 Phone: Fax: