Their theory, design, and practical operation
By Victor H. Todd
McGraw-Hill book company, Inc. , 1922
In preparing a work of this nature, it will be realized that the subject is so broad and varied in its scope as to preclude an author's intimate personal knowledge of each and every system described. Attempt has been made to cover the subject the first principles of Protective Relays to the protection of high tension net-works, the object being to make the work of value not only to the operator and tester who has a fair knowledge of electricity and is seeking more information, but also to the designer of the system who may find many points not previously
taken into consideration in his calculations.
Consequently, many reliable sources of information were freely consulted and in several instances, passages were quoted verbatim a booklet entitled "Performance of Instrument
Transformers" and "Protective Relays" which in turn was reprinted an article by Mr. L. N. Crichton in The Electric Journal. Full credit is hereby given to the Westinghouse Electric & Manufacturing Company for such excerpts; also to the American Institute of Electrical Engineers for several paragraphs quoted its June, 1919, Proceedings.
Some of this material has been published in the form of articles by the author in Power, Power Plant Engineering, Electrical Record and Southern Engineer, and thanks are hereby given to their editors for permission to use the text and electro-types for illustrations.
The author also wishes to extend his thanks and appreciation to Mr. F. A. Annett, Associate Editor of Power, for personal interest and assistance in the preparation of the work; to Mr. L. N. Crichton, Relay Engineer of the Westinghouse Electric & Manufacturing Company, and writer of several articles which much valuable information was obtained, who kindly read this manuscript, and offered many helpful suggestions and constructive criticisms; and to officials of the Westinghouse Electric & Manufacturing Company, the General Electric Company and the Condit Electric Company, for valuable assistance in procuring photographs for illustrations.
What are Protective Relays
Early Systems—Fire Risks—Insulated Fuses—Objections—Automatic Switches—Definition—Reasons for Relays—Requirements— Savings—Principles of Operation—Nomenclature.
Circuit Breakers and Releases
Classes—Principles of Operation—Adjustment—Shunt-trip Attachment—Underload Release—Undervoltage Release—Overvoltage Release—Why Releases are not Always Sufficient.
Trip Circuits and Time Delays
Object of Trip—Trip Circuit Sources—Shunt Trip—Auxiliary Contacts—Circuit Opening or Series Trip—Objections—Transfer Relays—Time Delays—Classifications—Inverse-time Limit—Definite Time—Inverse-definite Time—How Time Delays are Obtained.
Plunger-type Protective Relays
Various Forms—Adjustments—More Forms—Definite-time Relay — Bellows-type—Objections—Simple System — Typical A.C. Plunger-type—Illustration of Setting—Relays Required— More Bellows Types—Oil Dashpot Types—Limitations—Definite-time—Tripping Sources.
D.C. Power-directional Relays
Necessity of this Type—D'Arsonval Type—Used as Excess-current Relay—Polarized Type—Moving Iron Type—Busbar Types.
Applications of D.C. Power-directional Relays
Limitations to Use—Storage Battery Protection—Other Methods —Standby Batteries—Failure of Prime Movers—Loss of Field Protection—Parallel Feeders on D.C.—Ring System on D.C.—Wider Applications—Undercurrent Protection—Overvoltage Protection—Undervoltage Protection.
Induction-type Current Relays
Development—Typical Relay—Settings—Torque Compensator—Time Delays—Continuity of Trip Indicator—Induction vs. Solenoid-plunger Relays—Relay Contacts—Load on Transformer—Relay Specifications.
A.C. Power-directional Relays
Early development—Most Common Use—Overload and Reverse-current Relays—Objections and Failings—Latest Developments—The Contactor Switch—The Torque Compensator—Stray Field Effect—Other Types—Differential Power-directional Relay
Characteristics op A.C. Disturbances
Important Points—Effects of Overload—Nature of Short-circuits on Transmission Lines—Calculation of the Short-circuit Current—nator and Transformer Constants—Effect of Low Voltage—Effect of Unbalanced Short-circuits—Characteristics of Relays.
Instrument Transformers and Groupings
Current and Voltage Transformers—Inherent Errors—Ratio Eiror—Magnetization of Core—Effect of Secondary Load—Other Sources of Error—Single-phase Groupings—Two-phase Groupings—Necessity for Three Transformers on Three-phase—Advantages of the Z-connection—Opening of Secondary—Voltage Transformers—Various Errors—Polyphase Groupings—Load on Transformers—Use of Both Current and Potential Transformers—
Connections to Watt Relay—Star-delta Connection—Determining Phase Rotation.
Protection op Motors, Transformers, Generators and Lines
Protection of Motors—Settings—Two-phase Protection—Three-phase Protection—Protection of Synchronous
Motors—Protection of Rotary Converters—Transformer Protection—Protection in Banks—Power-directional Relay Protection—Other Differential Methods—Polyphase Transformer Protections—Protecting Three-phase Star-delta Banks—Protection of Generators—Protection by Power-directional Relays—Protection of Single Lines—Protection
Protection of Parallel Feeders
Objects—Various Methods—Inverse-time-limit Discrimination—Balanced Protection System—Differential Balance Relay Protection—Split-conductor System—The Pilot Wire System—Protection by Power-directional Relays—Cross-connected Power-directional Relays—Differential Power-directional or Double-contact Relays—Disadvantages of Cross-connected Systems.
Protection op Radial Ring and Network Systems
Simple Radial System—Selecting the Proper Relay—Limit of Divisions—The Ring System—Time Settings—Parallel Feeders on Ring—Rings with More than One Source—Protection of Networks—The Under voltage and Excess-current System.
Over and Undervoltage—Undercurrent—Overload Telegraph—Reversed Phases—Service-restoring Relays—Interesting Oscillograms—Bell-ringing Relays—D.C. Temperature Relays—A.C. Temperature Relays—Relay Switches—Transfer Relays—High-tension Relays—Timing Relays with a Cycle Counter—Principle of Cycle Counter—Timing a Circuit-closing Relay—Timing a Circuit-opening Relay—Timing the Breaker or Oil Switch—
Testing Direct-current Relays
Ground-testing—Testing Relay Switches—Various Loads and Testing Sources—Testing Millivolt-type Relays—Testing Plunger-type Relays—Testing Time-limit Relays—Curves and Tables—Conclusions.
Testing nating-current Relays
Reasons for Testing—Relays Requiring Current Only—Sources—Rheostats—Phantom Loads—Standards—Current Transformers —Trip Circuits—Timing the Relay—An Actual Test—The Cycle Counter—Making the Adjustment—Additional Precautions—Testing Voltage Relays—Power-directional Relays—Reverse-phase Relays—Temperature Relays—Conclusion.
Locating Faults in Feeders and Wiring
Most Common Faults—Apparatus Required—Testing for Opens, Shorts or Grounds—Accurately Locating the Short-circuit—Localizing a Ground—Calculating the Location—Two-ammeter Method—The Fault Localizer—L and N Power Bridge—Burning out the Fault.
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