Transformer Trip/Fault procedure 1

[hallmg]

Hi,

Where in the UK would i find regulations or procedures to do with what steps to take when an HV transformer has tripped, what tests to do, when to do a reset etc, that kind of thing?

Regards,
hallmg.

 

[prc]

The following IEEE Standards may be helpful:
1) C57.125-2015 -Failure Investigation, documentation, analysis and reporting for Power Transformers
2) C57.152-2013 - Diagnostic Field Testing of Transformers

 

[crshears]

I'm not from the UK, but this is what we do [sorry for any screwy formatting]:

3.1 CONTROLLING AUTHORITY
Immediately following automatic removal from service, the Controlling Authority shall:
(a) Take appropriate remedial operating action using appropriate precautions and guidelines for restoration. Apply subsection 3.1.1 where a transformer, phase shifter, or reactor is involved.
(b) The Controlling Authority shall utilize Station Maintenance staff to perform inspection if they are on site.

3.1.1 TRANSFORMERS/PHASE SHIFTERS/REGULATORS
(a) Place ULTC on manual and log tap position
(b) If appropriate, one attempt at restoration may be made if primary load has been lost.

3.2 MAINTENANCE AUTHORITY - STATION MAINTENANCE AND P&C
(a) If environmental concerns or special operating needs exist, Station Maintenance authorities will perform an inspection and tests at the earliest opportunity.
(b) Where applicable, Protection and Control shall investigate operation of any sequence of event recorders, Digital Fault Recorders and/or relays to provide information about the event.
(c) When there is a requirement to relinquish the series of tests outlined in 3.4 and field staff are not on site, the maintenance authority shall ready the transformer for immediate use in an emergency. This includes the removal of any/all isolation.

3.3 VISUAL INSPECTION AND CHECKS
The visual inspection and checks shall include the following (as applicable):
(a) Condition of explosion vent/Qualitrol relief devices and ejection of oil from same.
(b) Accumulation of gas in gas relay.
(c) Condition of all bushings and oil levels in same.
(d) Oil level in breakers, main and ULTC conservator tanks, etc.
(e) Condition of main tank and any other physical abnormalities.
(f) Possible cause of failure, e.g. animal contact, lightning strike, ruptured piping, etc.
(g) Fault conditions - phase to ground and/or phase to phase.
(h) ULTC tap changer operating pos. and general condition of drive mech. tank, etc.
(i) Damage to associated station equipment, e.g., switches, bus, feeder breakers, current and voltage transformers, surge arresters, etc.
(j) If reactors are installed on transformer or generator neutrals, the electrical/station maintenance authority should be advised (these tend to limit fault current damage).
(k) Record and reset all protections.

3.4 MAINTENANCE TESTING

The following sequence of tests may be performed by Electrical Station Maintenance:

[a] MEGGER
– continuity between phases / winding and core insulation

RATIO/PHASE ANGLE
– on tap positions [ULTC and OLTC] unit was at when removed from service
– on ULTC top, neutral, neutral plus and minus one and bottom tap positions
– if any ratio results are suspect, ratio on ALL ULTC tap positions

[c] FREE GAS
– any accumulations should be collected and analyzed
– if there is sufficient volume, local testing [Drager tubes/combustibles detector] may be carried out

(d) BLED GAS - to ensure gas relay is operating
(e) GAS-IN-OIL - if ratio or megger results are suspect and/or gas accumulation has occurred, a gas-in-oil sample should be taken and sent to research for analysis

All deficiencies, test results, etc., should be discussed with Technical Services Stations prior to return of the unit to service.


3.5 TRANSFORMER DIFFERENTIAL OR GAS PROTECTION OPERATION - DUE TO ANIMAL CONTACT OR OTHER EQUIPMENT FAILURE WITHIN TRANSFORMER ZONE OR PROTECTION MISOPERATION

The Maintenance Authority (Station Maintenance and/or P&C) must confirm that the Transformer Differential protection or Gas protection tripping (i.e. Tap Changer Gas or Transformer Gas) did not misoperate and tripped as a direct result of the failure of other
equipment within the transformer differential zone and not the transformer itself or as a direct result of animal contact.

The Maintenance Authority (Station Maintenance and/or P&C) shall also confirm to the Controlling Authority that the failure of other equipment will not compromise the transformer protections or any other associated protections and that the cause of the fault has been cleared.

No speculation or assumption of animal contact is to be made without finding physical evidence of the animal’s presence during visual inspection.

No attempt shall be made to energize the tripped transformer without the Maintenance Authority’s completed investigation and recommendation.

Blocking of the Transformer Differential or Gas protection shall not be permitted for the purpose of restoration unless the protection has been:

• declared as failed and,
• restoration cannot be delayed until it is repaired and,
• adequate healthy protection remains in-service.
• Gas trip relaying may be blocked for emergency restoration provided that the ‘B’ protection and the equipment’s Gas Accumulation alarms are both functional (as per NMI-0164).

When the cause of Differential or Gas operation is proven to be the result of protection misoperation, equipment failure other than the transformer itself or animal contact, field staff can determine testing requirements when responding to a Transformer Differential or Gas protection operation.

3.5.1 DIFFERENTIAL TRIP DUE TO ANIMAL CONTACT OR OTHER EQUIPMENT FAILURE

To expedite a transformer’s return to service following a Transformer Differential protection operation that was attributed to other equipment failure or animal contact, Dissolved Gas Analysis (DGA) oil sample analysis will be used as the primary screen to determine if any electrical testing is required. In order for DGA oil samples to be used as a primary screen, the following criteria must be met:
a) No gas accumulation
b) Known animal contact and/or equipment failure other than the transformer itself.
c) Associated Protections have not been compromised as a result of equipment failure.
d) No apparent transformer bushing damage

If determined that the Differential trip meets all the criteria above, then the tripped transformer can be energized for Emergency Use Only while DGA is being conducted.


3.5.2 DIFFERENTIAL TRIP DUE TO SUSPECTED PROTECTION MISOPERATION

Following a suspect Transformer Differential Trip (usually from only the ‘A’ or ‘B’ scheme with both in-service) both Station Maintenance and P&C personnel shall be dispatched to further investigate the true legitimacy of the trip by conducting a full interrogation of the protection and inspection of associated equipment in order to expedite the restoration of the tripped transformer without the need to perform DGA oil sampling and required testing.

If the Differential trip is deemed to be the result of protection misoperation for whatever reason including reduced harmonic content during an energization or de-energization switching event, P&C in agreement with Station Maintenance will declare to the Controlling Authority that the transformer is available for a one attempt energization.
If the attempt is still unsuccessful, the Maintenance Authority will provide recommendations prior to any further attempts.

4.0 MAINTENANCE TECHNICAL SERVICES (MTS) TRANSFORMER CONTACTS

In situations where obtaining test results may expedite transformer restoration to prevent or restore load loss, contact Maintenance Technical Services (MTS) Technical Support -Transformers Section (3B2). First call for assistance will be to the staff member responsible for the geographical area where the incident occurred. If no primary response, contact any other person under the Transformers (3B2) section or, as a last resort, the MTS Manager.

Note: MTS Technical Support staff for Transformers are strictly on a voluntary availability basis and not “on-call” during off hours.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[hallmg]

Many thanks for the information, its very much appreciated.