Distance relays are characterised by having two input quantities proportional to the voltage and current at a particular point in the power system, referred to as the relaying point. Ideal static distance relays have characteristics independent of actual magnitudes of voltage and current but dependent only on their ratio and phase angle between them. The versatile family of distance relays [...]
In this article we will discuss about the classification and design of relays used in an electric circuit. Classification of Relays: The protective relay may be defined as an electrical device interposed between the main circuit and the circuit breaker in such a manner that any abnormality in the circuit acts on the relay, which in turn, if the abnormality [...]
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 [...]
There are two methods of arc extinction in circuit breakers. They are: 1. High Resistance Method 2. Low Resistance or Current Zero Interruption. 1. High Resistance Method: In this case the arc is controlled in such a way that its effective resistance increases with the time so that the current is reduced to such a value that the heat produced [...]
The circuit breakers may be subjected to widely varying stresses under different operating conditions. The current may vary from a few amperes due to no-load magnetizing current of a transformer to the heaviest short-circuit currents amounting to a hundred kilo-amperes. The circuit impedance may also change within the first 10–4 to 10–3 second because open lines or cables connected to [...]
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: [...]