The art and science of protective relaying

The art and science of protective relaying

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1. The philosophy of protective relaying

What is protective relaying?

The function of protective relaying

Fundamental principles of protective relaying

- primary relaying

- back-up relaying

- protection against other abnormal conditions

Functional characteristics of protective relaying

- sensitivity, selectivity, and speed

- reliability

How do protective relays operate?

2. Fundamental relay-operating principles and characteristics

General considerations

- operating principles

- definitions of operation

- operation indicators

- seal-in and holding coils, and seal-in relays

- adjustment of pickup or reset

- time delay and its definitions

Single-quantity relays of the electromagnetic-attraction type

- operating principle

- ratio of reset to pickup

- tendency toward vibration

Directional relays of the electromagnetic attraction type

- operating principle

- efficiency

- ratio of continuous thermal capacity to pickup

Induction-type relays–general operating principles

- the production of actuating force

- types of actuating structure

Single-quantity induction relays

- torque control

- effect of frequency

- effect of d-c offset

- ratio of reset to pickup

Directional induction relays

- torque relations in terms of actuating quantities

- the significance of the term “directional”

- the polarizing quantity of a directional relay

- the operating characteristic of a directional relay

- the “constant-product” characteristic

- effect of d-c offset and other transients

The universal relay-torque equation

3. Current, voltage, directional, current (or voltage)-balance, and differential relays

General protective-relay features

Overcurrent, undercurrent, overvoltage, and undervoltage relays

D-C directional relays

A-C directional relays

Current (or voltage) - balance relays

Differential relays

4. Distance relays

The impedance-type distance relay

The modified impedance-type distance relay

The reactance-type distance relay

The mho-type distance relay

General considerations applicable to all distance relays

5. Wire-pilot relays

Why current-differential relaying is not used

Purpose of a pilot

Tripping and blocking pilots

D-C wire-pilot relaying

Additional fundamental considerations

A-C wire-pilot relaying

6. Carrier-current-pilot and microwave-pilot relays

The carrier-current pilot

The microwave pilot

Phase-comparison relaying

Directional-comparison relaying

Looking ahead

7. Current transformers

Types of current transformers

Calculation of ct accuracy

Polarity and connections

8. Voltage transformers

Accuracy of potential transformers

Capacitance potential devices

The use of low-tension voltage

Polarity and connections

9. Methods for analyzing generalizing, and visualizing relay response

The R-X diagram

Short circuits

Power swings and loss of synchronism

Response of polyphase directional relays to positive- and negative-phase-sequence volt-amperes

Response of single-phase directional relays to short circuits

Phase-sequence filters

10 A-C generator and motor protection

Generator protection

11. Transformer protection

Power transformers and power autotransformers

Step voltage regulators

Grounding transformers

Electric arc-furnace transformers

Power-rectifier transformers

12 bus protection

Protection by back-up relays

The fault bus1

Directional-comparison relaying

Current-differential relaying with overcurrent relays

Partial-differential relaying

Current-differential relaying with percentage-differential relays

Voltage-differential relaying with “linear couplers”

Current-differential relaying with overvoltage relays

Combined power-transformer and bus protection

The value of bus sectionalizing

Back-up protection for bus faults

Grounding the secondaries of differentially connected ct’s

Once-a-shift testing of differential-relaying equipment

13. Line protection with overcurrent relays

How to set inverse-time-overcurrent relays for coordination

Arc and ground resistance

Effect of loop circuits on overcurrent relay adjustments

Effect of system on choice of inverseness of relay characteristic

The use of instantaneous overcurrent relays

An incidental advantage of instantaneous overcurrent relaying

Overreach of instantaneous overcurrent relays

The directional feature

Use of two versus three relays for phase-fault protection

Single-phase versus polyphase directional-overcurrent relays

How to prevent single-phase directional overcurrent-relay misoperation during ground faults

Adjustment of ground versus phase relays

Effect of limiting the magnitude of ground-fault current

Transient ct errors

Detection of ground faults in ungrounded systems

Effect of ground-fault neutralizers on line relaying

The effect of open phases not accompanied by a short circuit

The effect of open phases accompanied by short circuits

Polarizing the directional units of ground relays

Negative-phase-sequence directional units for ground-fault relaying

Current-balance and power-balance relaying

Automatic reclosing

Restoration of service to distribution feeders after prolonged outages

Coordinating with fuses

A-C and capacitor tripping

14. Line protection with distance relays

The choice between impedance, reactance, or mho

The adjustment of distance relays

The effect of arcs on distance-relay operation

The effect of intermediate current sources on distance-relay operation

Overreach because of offset current waves

Overreach of ground distance relays for phase faults

Use of low-tension voltage

Use of low-tension current

Effect of power-transformer magnetizing-current inrush on distance-relay operation

The connections of ground distance relays

Operation when PT fuses blow

Purposeful tripping on loss of synchronism

Blocking tripping on loss of synchronism

Automatic reclosing

Effect of presence of expulsion protective gaps

Effect of a series capacitor

Cost-reduction schemes for distance relaying

Electronic distance relays

15. Line protection with pilot relays

Wire-pilot relaying

Obtaining adequate sensitivity

The protection of multiterminal lines

Current-transformer requirements

Back-up protection

Carrier-current-pilot relaying

Phase comparison

Directional comparison

Combined phase and directional comparison

All-electronic directional-comparison equipment

High-speed reclosing


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