soft starter

Difference between DOL, Star Delta, VFD and Soft starter

DOL-Direct on line Starter: here the starting current will be 6 times of full load current. A bimetallic thermal overload relay provides protection against the over load. There will be no reduction of starting torque during starting. Star Delta Starter: In order to limit the starting current of motors this method is followed. Initially motor…

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How to calculate cable size for LT Motors

What is the difference between LT and HT Motors? Well, as the word LT (Low Tension i.e. Low Voltage) and HT (High Tension i.e. High Voltage) or low torque and high torque respectively describe the whole story itself. its also depends on the availability of supply voltage, i.e. in USA and EU, LT Motors ranges…

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types of insulator

Causes of failure of insulator

The causes of the failure of insulator are :-   Cracking of insulator: The main cause of cracking is due the stress produced in the porcelain due to unequal expansion and construction produced in cement, steel and porcelain caused by seasonal heat cold, dryness, and dampness or by heating of the insulator. To avoid such…

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maintenance of transformer

Maintenance of Transformer

A power transformer is most costly and essential equipment of an electrical transformer. So for getting high performance and long functional life of the transformer, it is desired to perform various maintenance activities. Not only that, a power transformer also requires various maintenance actions including measurement and testing of different parameters of the transformer. There…

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vector group test of transformer

Vector Group Test of Power Transformer

Vector Group Test of Transformer The vector group of transformer is an essential property for successful parallel operation of transformers. Hence every electrical power transformer must undergo through vector group test of transformer at factory site for ensuring the customer specified vector group of transformer. The phase sequence or the order in which the phases…

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transformer routine testing

Type Test and Routine Test of Transformer

For confirming the specifications and performances of an electrical power transformer it has to go through numbers of testing procedures. Some tests are done at manufacturer premises before delivering the transformer. Mainly two types of transformer testing are done at manufacturer premises- type test of transformer and routine test of transformer. In addition to that…

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neutral ground resistor

Neutral-Grounding-Resistor System

Neutral-Grounding-Resistor System Neutral-Grounding Resistors (NGRs) are used to ground power systems by inserting a resistor between the system neutral and ground. This lowers the prospective ground-fault current to a predetermined value. A properly designed resistance-grounded system provides benefits over both ungrounded and solidly grounded systems. Because the system is grounded, transient over voltages do not…

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restricted earth fault

Restricted Earth Fault Protection of Transformer | REF Protection

REF Protection: An external fault in the star side will result in current flowing in the line current transformer of the affected phase and at the same time a balancing current flows in the neutral current transformer, hence the resultant current in the relay is therefore zero. So this REF relay will not be actuated…

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air core transformer

Air Core Transformer

If an alternating current is supplied to a coil, an alternating magnetic field is produced surrounding it. If another coil is brought inside this magnetic field, an alternating emf is induced across the second coil also as per Faraday’s law of electromagnetic induction. This induced emf in the second coil can be utilized to feed…

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power transformer

Maintenance of power transformer

Power Transformer Transformer is the heart of any power system. Hence preventive maintenance is always cost effective and time saving. Any failure to the transformer can extremely affect the whole functioning of the organization. Important components in power transformer to consider for preventive maintenance: The best way of protecting a transformer is to have good…

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