Scheduled Versus Event Driven Testing of Distribution Protection IEDs

Dr. Alexander Apostolov, Benton Vandiver, Will Knapek, OMICRON electronics

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Conventional Fault Clearing System

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Maintenance (Event-driven) Testing Requirements

– In case of events:– Incorrect protection system

operation–Failure to operate–Undesired operation–Testing requirements to:

• determine the reason for the maloperation

• confirm that a required corrective action has been successfully implemented

Waveform Replay

Fault Simulation

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Preventive Maintenance Testing Versus Monitoring–Care and servicing by company

personnel for the purpose of maintaining the components of the fault clearing system in satisfactory operating condition

–Systematic inspection and testing in order to determine problems with the relays or other system components and prevent their failure to operate when necessary.

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Preventive Maintenance Testing Versus Monitoring–Risks such as equipment failure or

human errors that may lead to problems bigger than the eventual benefit from scheduled testing

–Significant number of monitoring functions available in advanced multifunctional protection intelligent electronic devices

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Existing SystemsIt’s time to re-evaluate the fault clearing system to optimize the test process as new technologies are integrated. Areas to consider:

–CT and VT circuit supervision –CB and Trip circuit supervision –Analog inputs supervision –Power Supply supervision–Communication channel

supervision–Relay availability / health

supervision

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Monitoring Functions of the IEDCT and VT Circuit Supervision• Logic for monitoring the individual phases to

determine the circuit integrity (CT Failure logic)• Operational conditions such as blown fuses

(LOP)• Analog Input supervision is also possible where

conditions such as, – abnormal phase imbalance (a ratio

error)– unexpected sequence components

appear (when 3-Ph balanced system conditions are expected)

– stub bus logic, or pole dead logic

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Monitoring Functions of the IEDCB and Trip Circuit Supervision • Traditional trip circuit supervision• Monitor the performance of the CB

for accumulated duty (total interrupted current kA)

• Slow Operation• Pole Disagreement• Flashover Logic• Breaker Failure (BF) Logic.

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Monitoring Functions of the IEDPower Supply Supervision • Station Battery Conditions such as:

– Loss of DC– Reduced Operating Voltage– Relay Power Supply Trouble / Failure– Redundant Supply Failover Scheme

Communication Channel Supervision– Monitoring by guard, check-back, or

watch dog– Failover to backup system or scheme

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Monitoring Functions of the IEDRelay Availability / Health

Supervision • Self Diagnostics as internal health

monitor(A/D, Main & Sub Processors, Memory, Operating System, Firmware, Output Controller, etc.)

• Fail Safe Alarm and remedial action taken

• Time stamped events log with error codes

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Once Commissioned, What’s Next?

• Define what a Scheduled Test consists of– If Settings or Firmware is changed – test with same test

plan used for commissioning (or subset)[No Ad Hoc testing, eliminate variables, H errors]

– Exercise relay output contacts, verify 52b operates– Visual inspection of wiring, insulation, terminals– Event file, Logs, Waveform Capture, Metering– File compare of IED to source settings file– Testing interval determined by Reliability Counsel, critical

asset, events • Under any circumstance, NEVER change a setting

to perform a Scheduled or Routine test – this violates the integrity of the commissioned IED and requires re-commissioning it.

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What Scheduled Tests Are Required?

• They differ by the type and vintage of Protection Relay, (its importance to the system, its economic impact if it fails) and what impact those tests have on the commissioned status of the relay.

• E/M relays should be tested according to Mfg recommendations and schedules

• E/M relays are affected by their environment. Oxidation, moisture, dust, insulation breakdown, mechanical wear, vibration, and tolerance adjustments require routine attention

• Any changes to E/M relays prompt re-commissioning

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What Scheduled Tests Are Required?

• Static relays which are not fully digital can have extended test intervals over E/M relays as the environmental and mechanical weaknesses are removed by design

• Due to switches, potentiometers, and variable resistors, they should be tested according to the Mfg requirements to maintain calibration

• Routine checks are needed to verify availability and health

• Any changes should be treated as re-commissioning

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IEC 61850 Based System

GOOSE

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Conclusions• Maintenance testing plays an

important role in the asset management of IEDs

• Proper use of all monitoring functions allows a significant reduction in the requirements for scheduled testing and covers not only the protection devices themselves, but also other components of the fault clearing system

• IEC 61850 plays an important role and allows reduction of the maintenance tests