All the relays employed for protection against short circuits operate by virtue of the current and/or voltage supplied to them by CTs or PTs. Failures in the system are indicated by the individual or relative changes in the currents or voltages supplied to the protective relaying equipment. For every type and location failure, there is some distinctive difference in these [...]
Electromagnetic induction relays are the most widely used relays for protective relaying purposes involving only ac quantities. These relays operate on the simple principle of split-phase induction motor. Actuating force is developed on a moving element, that may be a disc or other form of rotor of non-magnetic current-conducting material (such as aluminium), by the interaction of electromagnetic fluxes with [...]
The application of a particular relay is governed by its characteristics and other factors such as accuracy, operating time, reliability, burden, method of setting adjustment etc. The function of a protective relay is to sense any abnormal condition in the system and send a signal to the breaker which in turn isolates the faulty section of the feeder from the [...]
Amplitude comparator compares the amplitudes of two (or more) input quantities. The phase angle between the quantities under comparison (inputs) is not recognized or noticed by the amplitude comparator. If the two input signals are S1 and S2 (say S1 the operating and S2 restraining), the amplitude comparator gives positive output only if – S2/S1 < K. The function is [...]
In this article we will discus about:- 1. Introduction to Re-Striking Voltage Transient 2. Expression for Re-Striking Voltage Transient 3. Classification 4. Characteristics 5. Factors Affecting. Introduction to Re-Striking Voltage Transient: Electrically a power system is an oscillatory network so that it is logical to expect that the interruption of fault current will give rise to a transient whose frequency [...]
Generator faults can be considered under the following heads: 1. Stator Winding Faults 2. Field Winding or Rotor Circuit Faults 3. Abnormal Operating Conditions. 1. Stator Winding Faults: Such faults occur mainly due to the insulation failure of the stator coils. The main types of stator winding faults are: (i) Phase-to-earth faults (ii) Phase-to-phase faults and (iii) Inter-turn faults involving [...]
In this article we will discuss about:- 1. Stator Protection of Generators 2. Overload or Overcurrent Protection of Generators 3. Over-Voltage Protection 4. Over-Speed Protection 5. Protection against Motoring 6. Negative Sequence Protection 7. Protection against Vibration 8. Bearing Overheating Protection 9. External Fault Backup Protection 10. Direct Connected Protection. Stator Protection of Generators: The earth fault current is usually [...]
The following points highlight the top seven systems employed for stator protection of generators. The systems are: 1. Differential Protection for Generators 2. Modified Differential Protection for Generators 3. Biased Circulating Current Protection (Percentage Differential Relay Protection) 4. Self-Balance Protection System 5. Balanced Earth-Fault Protection 6. Stator Inter-Turn Protection 7. Stator Overheating Protection. System # 1. Differential Protection for Generators: [...]
In this article we will discuss about:- 1. Protection of Low-Voltage (Below 1,000 V) 3-Phase Induction Motors 2. Protection of Large Sized Motors 3. Protection for Exclusively Synchronous Motors. Protection of Low-Voltage (Below 1,000 V) 3-Phase Induction Motors: These are the most widely used industrial motors. Circuit diagram for a magnetic contactor starter for a low-voltage 3-phase induction motor is [...]
The different protection schemes for rotor protection of generators are described as follows: 1. Rotor Earth Fault Protection 2. Loss of Excitation (or Field Failure) Protection 3. Protection against Rotor Over-Heating Because of Over-Excitation 4. Rotor Temperature Alarm 5. Automatic Field Suppression and Use of Neutral Circuit Breaker. Scheme # 1. Rotor Earth Fault Protection: Field circuits are operated unearthed [...]