In this article we article we will discuss about the metallic and non-metallic types of coating metals. Cost is a very important factor while choosing an engineering material. In majority of applications of metals, the importance of the corrosion factor does not warrant the use of expensive corrosion-resistant alloys. Thus, when an easily corrodible alloy like steel is used, some [...]
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 [...]
For power transformers, the protection is to be provided usually against dangerous overloads and excessive temperature rise. Dangerous overloads may be due to external faults or the internal ones. External faults, however, are cleared by the relay system outside the transformer within the shortest possible time in order to avoid any danger to the transformer due to these faults. Hence [...]
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: [...]
There are several protective schemes for transmission lines and may be grouped into two groups viz., non-unit type and unit type. The non-unit type of protection includes time-graded overcurrent protection, current-graded overcurrent protection, and distance protection, while the unit type protection includes pilot-wire differential protection, carrier-current protection based on phase comparison method etc. Separate protection systems are necessary for ground [...]
The most commonly used schemes for bus-zone protection are: 1. Backup Protection for Bus-Bars 2. Frame Leakage or Fault-Bus Protection 3. Differential Overcurrent Protection. All the protection schemes must also be provided with a check system to ensure that the protection responds only to earth faults occurring within the bus zone and not to extraneous earth faults. 1. Backup Protection [...]
Unless special precautions are taken, heating the steel results usually in certain amounts of oxidation or scaling and may also result in decarburisation. Both are usually undesirable. To prevent oxidation and decarburisation of steels, various methods from the simplest, but not completely reliable, to complex and expensive but almost full proof, are used depending on the criticality of the part, [...]
Thyrite arrester is most common and is mostly used for the protection against high dangerous voltages. It operates on the fact that thyrite, a dense inorganic compound of ceramic nature, has high resistance decreasing rapidly from high value to low value for currents of low value to those of high value. The current increases 9.6 times on doubling the voltage. [...]