Megger Tests

The insulation resistance meter test method for determining the condition of electrical insulation has been widely used for many years as a general nondestructive test method.

A serious limitation of this test is that its operating voltage of 500 to 1,000 volts will not always detect insulation punctures, whereas the higher voltages used by the high-voltage, DC testers will detect these punctures.

The insulation resistance meter test will show following parameters:

(a) Relative amount of moisture in the insulation,
(b) Leakage current over dirty or moist surfaces of the insulation, and
(c) Winding deterioration or faults by means of insulation resistance versus time curves.

Description of Test

How To Use A Digital Multimeter

A digital multimeter is used to make various electrical measurements, such as AC and DC voltage, AC and DC current, and resistance. It is called a multimeter because it combines the functions of a voltmeter, ammeter, and ohmmeter.
Multimeters may also have other functions, such as diode and continuity tests.

What is HIPOT Testing (Dielectric Strength Test)?

Hipot Test is short name of high potential (high voltage) Test and it is also known as Dielectric Withstand Test. A hipot test checks for “good isolation.”
Hipot test makes surety of no current will flow from one point to another point.
Hipot test is the opposite of a continuity test.
Continuity Test checks surety of current flows easily from one point to another point while Hipot Test checks surety of current would not flow from one point to another point (and turn up the voltage really high just to make sure no current will flow).

Importance of HIPOT Testing

The hipot test is a nondestructive test that determines the adequacy of electrical insulation for the normally occurring over voltage transient. This is a high-voltage test that is applied to all devices for a specific time in order to ensure that the insulation is not marginal.

Basic-Stand-Alone-Application-of-Reclosers

Overcurrent protection

Reclosers are self-contained fault interrupting and reclosing devices, specifically designed for overcurrent protection in secondary distribution systems.
Reclosers are situated in selected locations within the overhead distribution network. With the correct protection setting and MV fuse selection coordination, concerning the whole supply loop from the supplying primary distribution substation feeder to the fuse-protected distribution transformer, it is possible to achieve a discriminative fault isolation function.

Traditionally, the recloser units do not have any remote communication facilities. To enhance the system monitoring and restoration facilities, the reclosers can be equipped with remote communicating protection and control units.

ABB – Electrical Installation Handbook PART I

Scope and objectives                         

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Right here

The scope of this electrical installation handbook is to provide the designer and user of electrical plants with a quick reference, immediate-use working tool.
This is not intended to be a theoretical document, nor a technical catalogue, but, in addition to the latter, aims to be of help in the correct definition of equipment, in numerous practical installation situations.
The dimensioning of an electrical plant requires knowledge of different factors relating to, for example, installation utilities, the electrical conductors and other components; this knowledge leads the design engineer to consult numerous documents and technical catalogues.

This electrical installation handbook, however, aims to supply, in a single document, tables for the quick definition of the main parameters of the components of an electrical plant and for the selection of the protection devices for a wide range of installations.

Some application examples are included to aid comprehension of the selection tables.

Protection and control devices

Good Voltage Regulation and Justified Power Factor Correction

Power factor correction and voltage regulation are closely related. In many cases, the desired voltage regulation is costly to obtain. Larger or paralleled conductors to reduce voltage drop under load are, in many cases, the proper solution.
However, power factor correction may also be justified for four reasons:

1. To improve voltage
2. To lower the cost of electric energy, when the electric utility rates vary with the power factor at the metering point
3. To reduce the energy losses in conductors
4. To utilize the full capacity of transformers, switches, overcurrent devices, buses, and conductors for active power only, thereby lowering the capital investment and annual costs

Location of Current Transformers in HV Substation

Power flow

Current transformers are used for protection, instrumentation, metering and control. It is only the first function that has any bearing on the location of the current transformer.

Ideally the current transformers should be on the power source side of the circuit breaker that is tripped by the protection so that the circuit breaker is included in the protective zone.