Transformer with Resistance and Leakage Reactance Calculation

Transformer with Resistance and Leakage Reactance

What do you mean by Transformer Resistance and Leakage Reactance?

The Transformer resistance means the resistance of the primary and secondary winding of the transformer. 

Transformer Leakage Reactance means there is some magnetic leaking in both of the primary and secondary windings that should be equal to inductive coils connected in both primary & secondary windings.

Underground Power Cable Bonding Methods

Cross bonding for high voltage underground cable sheath earthing

How Bond Your Cable?

Widely used bonding system for High Voltage or Extra High Voltage power cables are as follows:

1. Both End Bonding Systems
2. Single Point Bonding System
3. Cross Bonding System
4. Both End Bonding systems

The simplest arrangement to eliminate sheath induced voltage is Both End Bonding system. It is very easy and simple to ground both end of cable sheath. Minimum materials are required which lead to economical. 

But circulating current flows through cable sheath and heat produces which increase loss and reduce cable life. Circulating current is proportional to the length of the cable and the magnitude of the load current. This system normally applies to short cable section of tens of meters long.

Single point bonded system

A simple system is single point bonding which arrangement does not allow any path to flow circulating currents or external fault currents. In this system the sheaths of cables are grounded at one end and other end are open or connected with SVL and grounded through earth continuity cable, consequently induced voltage is present at open end. 

The magnitude of sheath induced voltage depends on the length of the cable, longer the cable length higher the induced voltage. Using of this bonding system is limited only for short distance of cable length to keep induced sheath voltage within a safe limit. Generally suitable for less than 500 m cable length.

Advantages of Single Point Bonding:

No circulating current.
No heating in the cable screen.
Economical
Disadvantages of Single Point Bonding:
Induced voltage at the un–earthed end
SVL required if induced sheath voltage during fault is extreme.

Earth Continuity Conductor is required for undesirable fault current.

Cross Bonding system

This arrangement is such that the circuit provides electrically continuous sheath runs from earthed termination to earthed termination. Voltage will be induced between screen and earth, but sectionalized cross bonding system will reduce the sheath circulating currents. 

Screen separation and additional link boxes are require for this system, arrangement carries 3 minor sections in each major section. When number of minor sections is not exactly divisible by 3, then system may consist of mixture of single point bonding with cross bonding. This system is technically complicated and more expensive, but for long route length cross bonding system is suitable because of following advantages- 

-Earth continuity conductor no need.

-Virtually zero circulating current in the screen.

-Standing induced voltage in the sheath is controlled.

-Technically superior than other methods.

-Suitable for long route length.

Power Supplied by V-V Bank Transformer

 

Open-delta or V-V Connection of a Transformer

A V-V connection uses two single-phase transformers to produce a three-phase output. 

Here is one possible connection with $0^o$ phase displacement:

Power Supplied by V-V Bank Transformer

CONFINED SPACE: KEEP WORK SAFETY

How Work in a Confine  Space Safely?

A confined space is one that is both enclosed, and primarily held, and which also has a reasonably foreseeable risk to workers of fire, explosion, loss of consciousness, asphyxiation or drowning even risk of death or serious injury from hazardous substances or dangerous conditions such as lack of oxygen. Some confined spaces are fairly easy to identify, eg enclosures with limited openings:

You must carry out a suitable and sufficient assessment of the risks for all work activities to decide what measures are necessary for safety under the Management of Health and Safety at Work Regulations. Working in confined spaces means identifying the hazards present, assessing the risks, and determining what precautions to take.

You need to check if the work can be done another way to avoid entry or work in confined spaces. Better work planning or a different approach can reduce the need for confined space working.

Sponsored:

If working in a CONFINED space, check:

ØWhether an entry permit required?

ØThe atmosphere is continuously monitored for contaminant gases by trained operators?

ØThere is personnel trained in emergency rescue procedures at all times outside of the confined space?

ØThere is a physical link between the worker in the confined space and the rescue personnel?

Transformer Star-Star Connection Procedure

Source: B.L. Theresa Book

Star-Star Connection of Distribution Transformer

practically reduced to zero whereas EBN and ECN will rise to nearly full primary line voltage. This difficulty of shifting (or floating) neutral can be obviated by connecting the primary neutral (shown dotted in the figure) back to the generator so that primary coil A can take its required power from between its line and the neutral. 

Transformer Delta-Delta Connection

Fig: Delta-Delta or ∆-∆ Connection

Delta-Delta Connection Procedure of Three-Phase Transformer in Power Transmission Network 

This connection is economical for large, low-voltage transformers in which the insulation problem is not so urgent, because it increases the number of turns/phases.