Protective apparatus for turbo-generators

The paper deals briefly with the causes of breakdowns in turbo-alternators, particularly in the stator winding, and discusses means for limiting damage in case breakdowns do occur. Some of the systems of alternator protection which are at present in use are dealt with briefly and their advantages and disadvantages pointed out, particularly as regards protection for faults between turns of the same phase winding. A new system of protection is proposed which has the advantage of protection against faults between turns. The system has been tried out in the factory, but the author recommends that it be tested under actual operating conditions. An investigation has been made of the phenomena occurring when the field circuit is opened, and it is shown that it is permissible to open the main field circuit without any discharge resistance. Different methods at present in use of opening the main or exciter field are discussed, and it is shown that they unnecessarily prolong the discharge of the field and the destructive effect of the fault currents. It is therefore recommended that a simple circuit breaker without discharge resistance and operated directly by the fault-current relays be provided in the main field circuit.