2nd October 2019

siemens

15

What is power frequency voltage test?

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Insulation levels in electrical equipment are characterized by the withstand voltages used during the design tests. There are two basic classifications of insulation strength: Basic Insulation Level (BIL) or lightning-impulse withstand voltage, and power-frequency withstand voltage (often called “hipot” voltage).

What is flashover voltage?

flashover voltage. [′flash‚ō·v?r ‚vōl·tij] (electronics) The voltage at which an electric discharge occurs between two electrodes that are separated by an insulator; the value depends on whether the insulator surface is dry or wet. Also known as sparkover voltage.

What is the Megger test?

As you know good insulation has high resistance and poor insulation relatively low resistance. The Megger insulation tester is a small, portable instrument that gives you a direct reading of insulation resistance in ohms or megohms. For good insulation, the resistance usually reads in the megohm range.

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Why high voltage test is done?

A hipot test (also called Dielectric Withstanding Voltage (DWV) test) verifies that the insulation of a product or component is sufficient to protect the operator from electrical shock. In a typical hipot test, high voltage is applied between a product's current-carrying conductors and its metallic shielding.

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What is the impulse withstand voltage?

What is Rated impulse-withstand voltage (Uimp) for Circuit-breakers. This characteristic expresses, in kV peak, the value of voltage which the equipment is capable of withstanding. without failure, under test conditions. Generally, for industrial circuit-breakers, Uimp = 8 kV and for domestic types, Uimp = 6 kV.

3

What is IR test?

Insulation resistance measurement is based on Ohm's Law. By injecting a known DC voltage lower than the voltage for dielectric testing and then measuring the current flowing, it is very simple to determine the value of the resistance.

4

What do you mean by impulse voltage?

An impulse generator is an electrical apparatus which produces very short high-voltage or high-current surges. Such devices can be classified into two types: impulse voltage generators and impulse current generators. Also, steep-front impulse voltages are sometimes used in nuclear physics experiments.

5

What is the frequency of electricity?

The utility frequency, (power) line frequency (American English) or mains frequency (British English) is the nominal frequency of the oscillations of alternating current (AC) in an electric power grid transmitted from a power station to the end-user.

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What is dielectric test in transformer?

A single phase power frequency voltage of shape approximately sinusoidal is applied for 60 seconds to the terminals of the winding under test. The test shall be performed on all the windings one by one. The test is successful if no breakdown in the dielectric of the insulation occurs during test.

7

What is HV infection?

No cause for HV is found in between one third and one half of patients. HV can be caused by a specific drug or by infection. Infections which may be associated with HV include: hepatitis B or C virus, chronic infection with bacteria or HIV.

8

What is lightning impulse test of a transformer?

The purpose of the impulse voltage test is to secure that the transformer insulation withstand the lightning overvoltage which may occur in service. The impulse generator design is based on the Marx circuit. The basic circuit diagram is shown on Figure above.

9

What is lightning impulse test?

Impulse Testing A world-wide novelty in respect of High-Voltage testing of power transformers on site is a high-performance mobile impulse generator. Lightning and Switching The lightning and switching impulse test on a power transformer is a routine test for transformers with rated voltages greater than 300 kV.

10

What is a switching impulse?

The switching impulse test is applied to confirm the withstand of the transformer's insulation against excessive voltages occuring during switching. During switching impulse voltage test, the insulation between windings and between winding and earth and withstand between different terminals is checked.

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What is lightning impulse?

The purpose of the impulse test is to determine the ability of the transformer insulation to withstand the transient voltages due to lightning. • It is well known that power system components are subjected to severe over voltage due to internal switching or external lightning surges.

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What is meant by chopped wave?

Chopped voltage wave is generated e.g. when a protective spark gap at the input connection of a transformer starts to operate with a relatively low time delay (4-10 microseconds). Steepness of the wave at the moment of chopping is significantly higher than the steepness at the front.

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What is basic insulation level?

Insulation levels in electrical equipment are characterized by the withstand voltages used during the design tests. There are two basic classifications of insulation strength: basic insulation level (BIL) or lightning-impulse withstand voltage, and power-frequency withstand voltage (often called “hipot” voltage).

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What do you mean by insulation coordination?

In a few more words, Insulation Coordination is a series of steps used to select the dielectric strength of equipment in relation to the operating voltages and transient overvoltages which can appear on the system for which the equipment is intended.

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What is meant by impulse ratio?

Impulses Ratio. This is normally used for Flashover or puncture of insulation. It is the ratio of the impulse peak voltage to the value of the 60 Hz voltage that causes flashover or puncture. Or, it is the ratio of breakdown voltage at surge frequency to breakdown voltage at normal system frequency (60 Hz).

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What is basic insulation level BIL?

Hence, the insulation of such equipment must be designed to withstand a certain minimum voltage before the lightning impulse over voltage gets discharged through surge protecting devices. This minimum voltage rating is defined as BIL or basic insulation level of electrical equipment.

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What is bil of a transformer?

Impulse tests are dielectric tests that consist of the application of a high frequency steep wave front voltage between windings, and between windings and ground. The BIL of a transformer is a method of expressing the voltage surge that a transformer will tolerate without breakdown.

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