NUMERICAL PROTECTIONS.

By

Y. k. Pandharipande.

Numerical Protections Advantages.

Choice Of Alternative CT Ratings / Aux. Voltages and Characteristics in Single Execution.

Enhanced Protection Functions and Related Features. Data Acquisition Capabilities Adaptive Protections. Communication. Continuous Self Monitoring.

1. Choice Of Alternative CT / Aux. Voltage Ratings and Characteristics.

Choice Of Alternative CT Secondary ratings (1A / 5A). Choice of Wide Range of Auxiliary Voltages (Typically 80 –

300 Volts AC/DC to cover standard Aux. voltages of 110 / 220 V DC or 240 V AC)

Choice of Several Characteristics and Scheme Options, For example,

1. Choice of Various IEC / ANSI Characteristics in case of IDMT Relays (NI, VI, EI, LI etc.)

2. Choice of Multi Carrier Scheme Options in case of Distance Relays (e.g. PUR, POR, Blocking, Weak Infeed, Zone Extension etc.)

2. Enhanced Protection Functions and Related Features.

Start up Supervision, Too Many Start, Loss of Load, Prolonged Starting Time Protection in case of Motors.

Integral 100% Stator Earth Fault, Dead Machine Charging Protections in case of Generators.

User Selectable Out of Step Trip / Blocking Options for Distance Protection.

Amplitude / Phase Correction and Zero Sequence Compensation through Soft ware in case of Biased Differential Protection.

User Programmable Trip Logic and Out put Relay Configuration for internal protection functions.

Logic Inputs for Integrating external protection functions.

Integral Event Logging and Disturbance Recording Options.

3 Data Acquisition Capabilities.

Service Data, Historic Data and Trip Data provided by the relay on interrogation.

Service Data provides alternative Instrumentation functions and helps cross-checking Analogue Meters.

Historic Data helps refining the settings for optimum protection.

Trip Data helps analysing tripping. Event logs / Disturbance Records also help

analysing tripping occurrences

4. Adaptive Protections.

Multi Setting Groups in case of Motor, Generator and Line Protections.

Group 1 (Coarser Settings) during Start up and Group 2 (Sensitive Settings) on normal running in case of Motor Protection.

Group 1(Coarser Settings) during Start-up / Pre-synchronising and Group 2 (Sensitive / Time Co-ordinated settings) on Normal Running for Generator.

Multi-Setting Groups can be used for Distance Relays when a single relay is selectively applied for Number of Line feeders e.g. when the line breaker is bypassed and substituted by the TBC, a common relay on TBC is used, particularly when Line CTs are located within bypass zone.

Voltage Controlled / Voltage Restraint Options in case of Backup O/C protection of Generators are also examples of Adaptive Protections.

5 Communication.

Protection Functions can be integrated with SCADA / DCS.

Enables Common Access to number of Relays.

Enables Data Transfer to Remote Terminals. Thus, Relay can be accessed / monitored from a Remote Terminal.

6 Continuous Self Monitoring

Enhances Availability of Protection (no silent failures)

Internal failures are alarmed enabling quick corrective action.

Periodic Testing can be less frequent.