From Protection of Electricity Distribution Networks, 2nd Edition

Previous chapters have detailed the make up and operating characteristics of various types of protection relays. This chapter considers the combination of relays required to protect various items of power system equipment, plus a brief reference to the diagrams that are part of substation design work. A general knowledge of these diagrams is important in understanding the background to relay applications.

12.1 Protection Schemes

It is difficult to define precisely the protection schemes that should be adopted for an electricity distribution system, given the large number of valid alternatives for each situation, but some schemes will be presented as a guide for protecting the various elements that make up a power system. However, any protection scheme should strike a balance between the technical and economic aspects so that, for example, sophisticated protection devices are not used for small machines or for less important power system elements.

12.1.1 Generator Protection

Generator protection should take into account the importance of the generator and its technical characteristics such as power, voltage and earthing arrangement, plus any economic considerations. A complex protection scheme can ensure that the generator is protected against whatever faults may occur. However, it is unlikely that such a cost could be justified for every generating station, especially those with small units. It is, therefore, necessary to define a protection scheme that is adequate for the size of the machine.

Two generator protection schemes are given below, based on suggestions by manufacturing companies.

Small Generators

For small generators, typically up to...

Products & Services
Protective Relays and Monitoring Relays
Protective relays and monitoring relays detect or monitor for abnormal power system conditions.
Venturi Vacuum Generators
Venturi vacuum generators use the flow of motive fluid such as air, steam, or liquid to evacuate air.
Signal Generators
Signal generators and waveform generators are used to test and align all types of transmitters and receivers, to measure frequency and to generate a signal, waveform or noise source. Signal generators can use AC energy, audio frequency (AF) and radio frequency (RF) to function.
Generator Heads and Alternators

Generator heads and alternators convert mechanical energy into electrical power through electromagnetic induction.

Power Supplies
Power supplies are electrical devices that deliver electric power to one or several loads. They generate the output power by converting an input signal into an output signal.

Topics of Interest

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INTRODUCTION Figure 25.1 illustrates the overall protection scheme in a generating station. The auxiliary equipment inside the plant requires 5 to 10 percent of the power generated. The remainder...