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                         

Download:

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.

An example of calculating the technical losses of T&D lines

Introduction to Losses

There are two types of losses in transmission and distribution line.

1. Technical Losses and
2. Commercial Losses.

It’s necessary to calculate technical and commercial losses. Normally technical losses and commercial losses are calculated separately.

Transmission (technical) losses are directly effected on electrical tariff, but commercial losses are not implemented to all consumers.

Technical losses of the distribution line mostly depend upon electrical load, type and size of conductor, length of line etc.
Let’s try to calculate technical losses of one of following 11 KV distribution line

Vector Group of Transformer

Introduction:

Three phase transformer consists of three sets of primary windings, one for each phase, and three sets of secondary windings wound on the same iron core. Separate single-phase transformers can be used and externally interconnected to yield the same results as a 3-phase unit.
The primary windings are connected in one of several ways. The two most common configurations are the delta, in which the polarity end of one winding is connected to the non-polarity end of the next, and the star, in which all three non-polarities (or polarity) ends are connected together. The secondary windings are connected similarly. This means that a 3-phase transformer can have its primary and secondary windings connected the same (delta-delta or star-star), or differently (delta-star or star-delta).
It’s important to remember that the secondary voltage waveforms are in phase with the primary waveforms when the primary and secondary windings are connected the same way. This condition is called “no phase shift.” But when the primary and secondary windings are connected differently, the secondary voltage waveforms will differ from the corresponding primary voltage waveforms by 30 electrical degrees. This is called a 30 degree phase shift. When two transformers are connected in parallel, their phase shifts must be identical; if not, a short circuit will occur when the transformers are energized.”

 Basic Idea of Winding:

Calculate Voltage Regulation of Distribution Line

Introduction:

• Voltage regulation or Load Reguation is to maintain a fixed voltage under different load.Voltage regulation is limiting factor to decide the size of either conductor or type of insulation.
  
• In circuit current need to be lower than this in order to keep the voltage drop within permissible values. The high voltage circuit should be carried as far as possible so that the secondary circuit have small voltage drop.

Voltage Regulation for 11KV, 22KV, 33KV Overhead Line (As per REC):

• % Voltage Regulation= (1.06xPxLxPF) / (LDFxRCxDF)

Total Losses in Power Distribution and Transmission Lines-Part 2

(2) Non-Technical (Commercial Losses):

• Non-technical losses are at 16.6%, and related to meter reading, defective meter and error in meter reading, billing of customer energy consumption, lack of administration, financial constraints, and estimating unmetered supply of energy as well as energy thefts.

 Main Reasons for Non-Technical Losses:

(1)  Power Theft :

• Theft of power is energy delivered to customers that is not measured by the energy meter for the customer. Customer tempers the meter by mechanical jerks, placement of powerful magnets or disturbing the disc rotation with foreign matters, stopping the meters by remote control.

(2)  Metering Inaccuracies:

• Losses due to metering inaccuracies are defined as the difference between the amount of energy actually delivered through the meters and the amount registered by the meters.
• All energy meters have some level of error which requires that standards be established. Measurement Canada, formerly Industry Canada, is responsible for regulating energy meter accuracy.
• Statutory requirements5 are for meters to be within an accuracy range of +2.5% and – 3.5%. Old technology meters normally started life with negligible errors, but as their mechanisms aged they slowed down resulting
• in under-recording. Modern electronic meters do not under-record with age in this way.
• Consequently, with the introduction of electronic meters, there should have been a progressive reduction in meter errors. Increasing the rate of replacement of mechanical meters should accelerate this process

(3)  Un metered Losses for very small Load:

Total Losses in Power Distribution & Transmission Lines-Part 1

Introduction:

• Power generated in power stations pass through large & complex networks like transformers, overhead lines, cables & other equipments and reaches at the end users. It is fact that the Unit of electric energy generated by Power Station does not match with the units distributed to the consumers. Some percentage of the units is lost in the Distribution network. This difference in the generated & distributed units is known as Transmission and Distribution loss.
• Transmission and Distribution loss are the amounts that are not paid for by users.
• T&D Losses= (Energy Input to feeder(Kwh)-Billed Energy to Consumer(Kwh)) / Energy Input kwh x100
• Distribution Sector considered as the weakest link in the entire power sector. Transmission Losses is approximate 17% while Distribution Losses is approximate 50%.
• There are two types of Transmission and Distribution Losses

1. Technical Losses
2. Non Technical Losses (Commercial Losses)