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Tuesday, January 17, 2017

ELECTRICAL DISTRIBUTION BOARD DB WIRING

3 Phase Electrical Distribution Board DB Wiring Procedure
To understand and wiring an electrical distribution board, first of all you have to clear understanding about DB or Distribution Board wiring definition and systems as per international and local standard. Here you will find some basic idea about Distribution Board and its types.

Electrical Distribution Board wiring system

What Distribution Board (DB) Is?

A safe electrical system designed for a house or premises that included isolation switches, protective devices, connecting of multiple cable circuits including their associated neutral and earth conductors. Distribution Boards are normally following three (3) types-

 Main Distribution Board (MDB):

The Distribution Board which in generally receive incoming source of Low Voltage (LV) from transformer secondary of customer or the distribution company’s service outlets. MDB is the first receiving point (bus bar) from Transformer or Distribution Company.

The MDB may also be known as the ‘Consumer Unit’ where the main isolation device and Protective Devices are integrated.

Sub Distribution Board (SDB):

The Distribution Board which is supplied from the Main Distribution Board in a building and which is used to distribute wiring and circuits within a selected area, e.g.  floor in a multi-storey building.

Final Distribution Board (FDB):

The Distribution Board which supplies to Final Circuits. From FDB power goes to switching board from where switch uses for power on/off particular devices.

Wiring Accessories for 3 Phase Distribution Board:
The Distribution Board or Fuse Boards usually contains following three things to control and distribute electric supply safely:


v DP or Double Pole MCB  as main switch or main isolator;
v RCD (also DP) Residual Current Devices for safety;
v SP or Single Pole MCB as Circuit Breakers and Fuses.


Double Pole (DP) MCB (The main switch or Isolator):

This the main operating switch to control electric supply in the premises, to turn off and on the electric supply immediately due to any emergency like electric shock, fire or  while working on main board. Multiple mains switch may use if one have more supply units.

RCD- DP, Residual Current Devices:

Residual Current Device, (RCD) or Residual Current Circuit Breaker (RCCB) is an electrical wiring device or switch that disconnects or trip a circuit whenever it detects that the electric current is not balanced between the energized conductor and the return neutral conductor. Then instantly go safe mode disconnecting the electric circuit.

Circuit Breakers (CB)

Circuit breaker is a device which switches on at normal condition and off automatically electricity at any abnormal condition. Alternately we can say these are automatic protection devices in DB that switch off a circuit if they detect a fault. Circuit Breaker may be SP-Single Pole, DP-Double Pole and TP-Triple Pole.


In the wiring diagram shown that 3 phase Read-Yellow-Blue receiving from a MCCB, these 3 phases are feeding 3 individual DP-MCB isolator switches, all SP-MCB receiving through a common RCCB-DP and feeding to final distribution board. Please check the above 3-ph to 1-ph wiring diagram where 3 phase electrical distribution board wiring procedure with accessories are shown details.



Wednesday, November 30, 2016

Dielectric Loss Calculation for XLPE Insulated Single Core Copper Cable

 

Dielectric loss calculation means the calculation of electromagnetic energy loss as inherent dissipation of dielectric material. Dielectric loss is represents as tan δ widely known as loss angle or loss tangent.
Dielectric Loss Calculation
Above formula shows the calculated dielectric loss for mentioned cable is 0.38 watt per meter. Where the parameters used to calculate this value are shown.
Rated voltage 132 kV, so, phase to earth voltage is 76.2 kV or 76,200 volt (132/sq. root 3);
Insulation thickness 18 mm (outer diameter – inner diameter)/2 or (74.5-38.5)/2;
Value of loss angle tan δ depends on type of material.
Loss Angle

What Is XLPE?

XLPEXLPE is the shorten of Crossed Link Polyethylene,  Cross-Linked Polyethylene (XLPE) is modified three-dimensional molecular Polyethylene structure  that is manufactured from polyethylene plastic to improve some specific properties like- heat deformation, smokeless during fire, abrasion, continuous work at 90 deg. and highest 250 deg. centigrade temperature and so on.  
Basic molecular difference between LDPE, HDPE and XLPE are shown in the figure. In modern cable engineering technology, the XLPE provide may advantage to use as insulation.

Why Happen Dielectric Loss in XLPE?

If you look carefully at the XLPE molecular structure in the figure, you will find some open ended brunches. The main brunches are strongly bonded to each other and formed a three dimensional strong structure, but one end opened brunch comparatively weak bonded. When this material is placed in a high electromagnetic field, these weak brunches vibrate continuously and loss energy which is known as Dielectric Loss.

What Is Dielectric Loss?

PolarizationA definition for Dielectric Loss is very difficult to find an easy and understandable to all. Most of the definitions are for specialized, not recognizable for a non-technical or general person. That is why we are here today with this article to make easier the Dielectric Loss definition.
First of all let us see some definitions of Dielectric Loss what today are using:

1> Dielectric Loss is define as the inherent dissipation of electromagnetic energy as heat in dielectric materials which is represents as Loss-angle or Loss-tangent tan δ.

2> Dielectric Loss is an energy loss in a dielectric materials as heat dissipation due to cycle of current alternate in a period of time. In alternating current system dielectric materials charged in first by one direction and then discharge and re-charged by opposite direction of current flow, this repetition system causes of unproductive heat generation which define as Dielectric Loss.

Definition of Loss Tangent

 

What Is Dielectric Materials?

Dielectric material is such a kind of insulator material that can be polarized when applied an electric field to it. So, dielectric material having a polarization property. That means when dielectric material placed in an electric field it’s electric charge get aliened and attempt to flow but not flows. Dielectric materials are mainly use in capacitor for their dielectric property.

Dielectric material is a poor electrical conductive material used as an insulator for electrical system. Porcelain, Plastics, Glass, Mica, and the oxides of various metals are used as Insulator. In electrical cable PVC, HDPE, MDPE, LDPE, LLDPE, XLPE, EPR etc. are used as insulation.

What is the Dielectric Strength?

Simply we can explain the dielectric strength of an insulating material that the material can withstand in their insulating property in which maximum electric field. Other way, how much strength can take a dielectric material without any breakdown.

Dielectric strength not same for all materials, to understand the comparison of dielectric strength in various materials find the table.

What is Difference Between Insulator and Dielectric?

The material used as insulator for their electrical insulating or obstructing property; on the other hand dielectric used for electric charge holding or storing property. A common example of insulator is outer jacket of electrical cable and dielectric is the insulating material in capacitor.
Comparison of Dielectric Strength

Material
Dielectric strength (kV/inch)
20
Air
20 to 75
Porcelain
40 to 200
Paraffin Wax
200 to 300
Transformer Oil
400
Bakelite
300 to 550
Rubber
450 to 700
Shellac
900
Paper
1250
Teflon
1500
Glass
2000 to 3000
Mica
5000



Friday, November 25, 2016

CONDUIT AND ACCESSORIES USING AS PER WIRING REGULATIONS

Cable Trunking 

Conduit and Accessories Installation Factors


Conduit, accessories and trunking installation should comply with the latest issued Regulations for the Electrical Equipment of Buildings by the Institution of Electrical Engineers, unless otherwise approved by the Engineer. In addition installation should also comply with all local electricity regulations.

All metallic conduit and conduit fittings should be galvanized, heavy gauge steel, screwed, solid drawn or weld type complying with IEC 423 and IEC 614.

Conduit Types and Specifications

Following conduit and raceways specification should be utilize if where it is required or as per instruction of authorized engineer:

·        Power Conduit- HDPE/ASTM F2160;
·        Electrical Conduit- EB, PE & rigid PVC/UL 651A/UL 651B;
·        Telecommunication Conduit- HDPE/ASTM F2160;
·        Premise Raceways- UL 2024 Optical Fiber Cable Raceway.

PE Conduit uses in power transmission and communication like substation to transformer, secondary transformer to end-user cable, telephone, CATV and data transmission etc. PE conduit uses mainly for its significant physical advantages over other materials like-
·        Resist brightness with age or cold weather;
·        Low temperature impact resistance;
·        Permanent flexibility;
·        Ambient temperature range -30oC to 180oC

PE Conduit Feature
01. Multiple colour and stripes are available;
02. Pre-installed or cable in conduits are available;
03.Corrugated flexible inner ducts are available;
04.Self-supporting or built-in suspension strands are available.

What Is Difference between Conduit and Pipe   

In general it is very similar between plastic pipe and conduit; but in use completely different between them. So, it must be consider what it is and where it is going to use for.

o   Conduit do not have long term internal pressure what have in pipe;
o   Due to long term stress pipes need hydrostatic design basis where is not require in conduit;
o   Internal clearance for pipe is required on flow of volume where in conduit it’s depends on cable possession, group of cable, diameter of cable, cable pulling system, length of cable etc;
o   Conduit installation path in vertical, horizontal, curvature is very much important on cable nature;
o   In short pulling length up to 55% and for long pulling length below 40% should be fill-up the conduit volume, but in pipe no need to keep any empty space.

Conduit Installation Factors

Mechanical Stress is an issue to select the placement the conduit. If exceed the maximum allowable pulling tension and bending radii, conduit may damage.

Pulling Tension should consider during conduit installation. Tail loading, length of conduit, bending radii should control to keep the safe pulling tension.

Bending Radii often face on conduit pulling route, pulling tension and mechanical stress increase in bending curve. It’s important to select bending radii to avoid conduit damage in curved area.

Conduit Trenching may various types, but open trench and continuous trench methods are very traditional. Also trench digging, placing conduit and backfilling is important in conduit trenching.

Conduit Jointing can be variety of thermal and mechanical methods, but for each proper engineering design and system should follow.

Cable Installation in conduit is an important job which can be accomplished in a few ways, such as-

§  Cable pulling in conduit using rope or pull line;
§  Cable pulling in conduit using specialized high volume jet of air;
§  Cable-in-Conduit or pre-installed cable in conduit by manufacturer.

Conditions for Conduit and Trunking Wiring  

No conduit smaller than 19mm outside diameter should be used.

Standard circular boxes or machined face heavy-duty steel adaptable boxes with machined heavy type lids should be used throughout. For outdoor mounting all boxes should be galvanized, weatherproof and fitted with external fixing lugs.

Conduit terminations should be fitted with brass bushes.
The use of running threads, solid elbows and solid tees will not be permitted.

Conduit ends should be carefully reamed to remove burrs. Draw-in boxes should be provided at intervals not exceeding 10m in straight-through runs.

Conduit runs should be in either the vertical or horizontal direction unless otherwise approved and should be arranged to minimize accumulation of moisture. Provision for drainage should be made at the lowest points of each run.

Conduits should be supported on heavy galvanized spacer saddles so as to stand off at least 6 mm from the fixing surface.

Provision should be made for the support of internal conductors in instances where the length of the vertical run exceeds 5m.

All conduits run in any circuit are to be completed before any cables are pulled in.

Flexible metallic conduit should be used where relative movement is required between the conduit and connected apparatus, and a separate copper connection provided to maintain earth continuity.

Ensure the better service life of conduit and cable installed into conduit should follow the international and local standard and wiring regulations. The maximum number of cables in any conduit should be in accordance with the latest issue of the IEE Regulations for the Electrical Equipment of Buildings.