The art and science of protective relaying

The art and science of protective relaying

Contents

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 auto transformers
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 over current relays
Partial-differential relaying
Current-differential relaying with percentage-differential relays
Voltage-differential relaying with “linear couplers”
Current-differential relaying with over voltage 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 over current relays
How to set inverse-time-over current relays for coordination
Arc and ground resistance
Effect of loop circuits on over current relay adjustments
Effect of system on choice of inverseness of relay characteristic
The use of instantaneous over current relays
An incidental advantage of instantaneous over current relaying
Overreach of instantaneous over current relays
The directional feature
Use of two versus three relays for phase-fault protection
Single-phase versus poly phase directional-over current relays
How to prevent single-phase directional over current-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 fusesA-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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