Relay Logic Programming Examined

Dinesh Baradi,

Senior Application Engineer

ABB Inc.

Evolution of Relay logic

• Wiring of electrical contacts• Easy to comprehend• Standardized

Numerical Relay logic• Translation• Timer representations may vary

Evolution of Relay logic

• Numerical Relay logic• Vendor dependent standardization• Factors that need consideration

• Scalability of Logic Relays are not longer just ‘relays’ Sophisticated inter-dependent control schemes

• Ease of Documentation Standardized document format – PDF, MS-Excel®, Text etc. Preserves documents for posterity and helpful in testing

• Reusability Standardize on template Digitally replicate logic with minimal re-engineering

Numerical Relay logic• Textual representation

• Simple• Sophisticated Logic is not intuitive• Document explaining logic becomes necessity.• Troubleshooting & testing is a challenge

Symbol Boolean Gates

! NOT

* AND

+ OR

Numerical Relay logic• Graphical

• Ladder Diagram • Continuous Function Chart (CFC)• Signal Mapping

• Ladder Diagram

Ladder Diagram DC Schematics

( )

Numerical Relay logic• Graphical

• Continuous Function Chart

Numerical Relay logic• Graphical

• Signal MappingX – Logical connectionI – Inverted connection

Numerical Relay logic• Graphical

• CFC Digitized logic worksheet – Intuitive, organized & replicable Stored in Portable document format (PDF) just like CAD drawings

of DC Schematics Logic can be easily traced forward and reverse

Testing & troubleshooting made easy• Signal Mapping

Simple Sophisticated logic is not intuitive Can be stored in MS-Excel® based format Testing & troubleshooting is a challenge

Numerical Relay logicExecution Order & Cycle time

Execution order: Sequence of performing a function(s).Cycle time: rate of performing/ executing a function(s).

Why are they important for numerical relays?- Detecting Race conditions prior to validation/ testing- Feedback Loops- Critical functions should be executed at the fastest

rate without any unintentional delays

Numerical Relay logicAnalogy:

Even more significant when branched logic is created

Examples of Execution Order inconsistencies

Example-1:

Examples of Execution Order inconsistencies

Example-2:Delay in execution by one cycle-time

Relay-to-Relay Bit(s) TransferChoice of Protocol:

- Point-to-Point (P2P)- Point-to- Multi-Point (P2MP)

Choice of Topology (with respect to relay)- Point-to-Point (P2P) :

If at least one relay has point-to-point connection- Point-to- Multi-Point (P2MP):If all relays have point-to-multipoint connection

Relay-to-Relay Bit(s) TransferChoice of Topology (with respect to relay)

- Point-to-Point (P2P)

Relay-to-Relay Bit(s) TransferChoice of Topology (with respect to relay)

- Point-to-multipoint (P2MP)

Relay-to-Relay Bit(s) TransferExample 3 – Communicated oriented Scheme

- Automation Transfer Scheme (ATS)- Loss of communication packets should disable the scheme-

made use of communication ‘validity’ signal.- Settings update on a Main relay caused scheme to be disabled- After the update finished scheme was still disabled

- Possible causes:- ATS Logic in the Main relay changed?- Communication address of Main relay changed?- ATS Enabled conditions no-longer prevail?

Relay-to-Relay Bit(s) TransferExample 3 – Communicated oriented SchemeStarted troubleshooting with DC Schematics – ATS Disabled Light wired to TIE Relay output contact.TIE_TRANSFER_BLOCK was latched.

Relay-to-Relay Bit(s) TransferExample 3 – Communicated oriented SchemeTraced SR-1 Input-S1

Relay-to-Relay Bit(s) TransferExample 3 – Communicated oriented SchemeLessons Learnt:Sequence of Operations is critical when designing any

control scheme

Validity of each signal in a message should be considered in logic design.

Testing & Troubleshooting

• Relay testing:Metering – depending on the type of relayFunctional – depending on the type of relayProtection – on all relays

• Control Scheme Tests:Integrated testing Plan – Encompass relays involvedCommunication testing i.e., testing virtual wires –depending on type of relay

Testing & TroubleshootingGeneric Integrated Test Plan:• Suitable for all relay types, create appendices for testing

communication etc.

Testing & TroubleshootingIntegrated tools available:

EM Relays: Flags

Solid State Target lights, pushbutton to trip

Microprocessor/ Numerical Phasor diagrams, Events, Disturbance fault records, online monitoring – Logic etc., communication counters

Relay Logic Programming Examined

Questions?

Relay Logic Programming ExaminedEvolution of Relay logicNumerical Relay logicEvolution of Relay logicNumerical Relay logicNumerical Relay logicNumerical Relay logicNumerical Relay logicNumerical Relay logicNumerical Relay logicNumerical Relay logicExamples of Execution Order inconsistenciesExamples of Execution Order inconsistenciesRelay-to-Relay Bit(s) TransferRelay-to-Relay Bit(s) TransferRelay-to-Relay Bit(s) TransferRelay-to-Relay Bit(s) TransferRelay-to-Relay Bit(s) TransferRelay-to-Relay Bit(s) TransferRelay-to-Relay Bit(s) TransferTesting & TroubleshootingTesting & TroubleshootingTesting & TroubleshootingRelay Logic Programming Examined