What Happen If Cables Placed In Magnetic Metal Conduit

What Happens If Cables Placed In Magnetic Metal Conduits 

Do we know what happens if cables are in a magnetic metal conduit? Yes, at least we know that in any circumstances, the individual phase of an AC (alternating current) circuit is in a separate magnetic metal conduit. 

MYSTERIOUS CORONA EFFECTS IN TRANSMISSION LINES

Fig-Corona Effect in Transmission Line Visible at Night

What Are Corona's effects on electrical energy transmission lines?

If you look along the high voltage power transmission line in a clear sky at night, you will observe the dreamiest violet glow phenomenon embedded with hissing noise along the transmission line conductors. This indefinable phenomenon causes nothing but a production of ozone gas surrounding overhead electrical energy transmission lines known as the Corona or Corona effect.

Cable Pulling & Jointing Tools and Equipment

Cable pulling, Jointing, and Termination equipment play very important roles to ensure quality work to operate a safe and long-life operation. Cable pulling tools make for easy and safe cable laying, less cable sheath or screen damage/scarce, applying pulling tension correctly, and spacing cable in trench or duct properly. Cable Joint and Termination tools are very much special for cable jointing and cable sealing end termination.

How Use Cable Pulling Tools & Prepare Cable Trench?

Before laying cable, cable trench or cable duct must prepare as per site requirement. Cable ducts or trench measurements will not same for all, depending on the voltage rating, cable size, laying location, and other vicinity factors cable ducts or trenches' depth and width vary.

ARMOUR EARTHING ASSEMBLING FOR SINGLE CORE CABLE

Armour Earthing Assembly for Wire Armour Single Core Cable

33kV Cable Earthing System

Cable armour earthing is important for medium voltage (MV), high voltage (HV) and extra high voltage (EHV) system. 

Our discussion on this article is limited only single core plastic or paper cable wired armour earthing procedure for medium voltage (MV) system or 7.2 kV to 36 kV ranges.

The crystal clear step-by-step assembly figure shown the complete procedure of earthing system for wired armour cable.

If you follow the shown 9 step carefully, we hope you will be able to assemble the cable armour earthing successfully.

9 Step to Earth Cable Armour  

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1. First of all remove the over-sheath according to the dimension given the appropriate manufacturer Installation Instruction, Remove the armour according to dimension as per shown in the drawing. Clean the end of the over-sheath for a length of 250 mm.
2. Then slide the outer sleeve over the cable, and disassemble the clamping rings. Slide one clamping ring lug-downwards over the cable as shown in the figure 2.
3. Following the figure no-3 spread the armour wires as shown in the drawing and screw the other clamping ring loosely to the lugged clamping ring.
4. Install the termination in accordance with the Installation Instruction of termination manufacturer. Pass the end of the earth lead down through the clamping rings and connect it to one lug of the clamping ring. Tighten the clamping rings, refer to figure no-4.
5. With a small overlap and slight tension wrap two layers of sealant tape round the overs-heath for a length of 50 mm, just below the armour wire ends. Wrap two layers of sealant tape round the earth conductor so that it will be just below the armour wire ends. Attach the earth conductor to the other lug of the clamping ring as figure-5.
6. As shown in figure-6, bend the armour wires back and bind the ends to the over-sheath with a wire binder or plastic tape. noted that all sharp wire ends must be covered with plastic tape.
7. With a slight tension and small overlap wrap two layers of sealant tape over the lower end of the termination for a length of 50 mm.
8. Position the top end of the outer sleeve level with the top of the sealant tape. Shrink it into place starting at the center. Shrink the lower end first and work towards the upper end.
9. Yes, you have done; installation of earthing assembly for armour is completed.

This is the basic instruction for cable armour earthing, to do it physically you must follow the manufacturer installation instruction and necessary safety code. If it is helpful, then share with others to help them. 

Relays: LEXIS OF RELAY

What Is Relay? How Do Relay Work?

 Relay a device that opens or closes a contact when energized. Relays are most commonly used in power systems, where their function is to detect defective lines or apparatus or other abnormal or dangerous occurrences and to initiate appropriate control action. 

When the voltage or current in a relay exceeds the specified “pickup” value, the relay contact changes its position and causes an action in the circuit breaker. A decision is made based on the information from the measuring instruments and relayed to the trip coil of the breaker, hence the name “relay.” Other relays are used as switches to turn on or off equipment.

 

How Vibration Damper Works in Transmission Line?

How Does a Small Size Damper Reduce Vibration in Transmission Lines?

Vibration dampers are usually used in high voltage and extra-high voltage electrical energy overhead transmission lines to handle aeolian and galloping or dancing vibrations in the transmission lines' conductors. The dampers are designed in such a way that they attenuate the line vibrations by reaching the same frequency as the cable that has wind-induced vibrations.

The overhead Transmission Line mainly experiences two types of vibrations in a vertical plane which can be categorized into two groups.

• Aeolian Vibration;
• Galloping or Dancing vibration.

PARTIAL DISCHARGE TESTING OF POWER CABLE

Partial Discharge (PD) in Electrical Power Cable:

Why PD?

No matter way where you are an engineer or a technician for electrical power cable, you need a piece of pretty good knowledge about Partial Discharge or shortly PD to understand your cable life or the possibility of unwanted cable faults. You may gather knowledge about PD by watching video clips on YouTube or reading a blog or article about PD.

Introduction of Partial Discharge (PD):  

Partial discharge (PD) is one of the most important factors for a power cable system. The partial discharge measurement methods of assessing the quality of the insulation of power cable systems, especially for extruded insulation materials.

Where Partial Discharge Occur:

We can think of partial discharge for cable systems from two major points of view:

01. Partial Discharge within the whole cable

02. Partial Discharge in an individual              location

Partial Discharge Measurement:

 

Normally major factory test carried out on the insulation of the whole drum of extruded cable is the partial discharge test. This is usually done at power frequency, but can also be carried out at very low frequency and at some voltage significantly higher than normal working voltage to ground. PD test is a very sensitive method to find out very minor failures such as little void or skip of insulation layer during manufacturing time.

But this factory test is not sufficient for the end users of the cable systems, during cable shipping, cable installation, cable jointing, and termination; cable insulation may damage or crack. Minor damage or crack is not possible to find out during commissioning or energizing time. After a little longer time this defect increased slowly and finally cracked. By statistics from the cable systems, most of the cable faults occur in cable jointing and termination point.

For Better Results:

So it is better to observe the magnitude and phase of the partial discharge signals and how they vary with increasing and then decreasing test voltage, results will disclose information on the type and position of the defects and their probable effect on cable life.

Finally in conclusion we can say, if the cable system can be tested in the field to show that its partial discharge level is comparable with that obtained in the factory tests on the cable and accessories, it is the most convincing evidence that the cable system is in excellent condition.

History of Electricity in Bangladesh

Bangladesh: Developing every day every moment

History of First Electricity Uses in Dhaka even Bangladesh:

Bangladesh borne in 1971, but electricity utilization started in this region as a part of India before creation Bangladesh. First electricity switched on 7 December 1901 in Ahsan Monjeel, the residence of the Nawab of Dhaka. Latter on Dhanmondi powerhouse was set up and the journey of commercial distribution started in 1930.

Brief History of Electricity In Bangladesh:

Up to the partition of the country and independence of India and Pakistan in 1947, electricity generation and distribution was authorized by some private companies in this region. Electricity facility was limited within 17 provincial district urban area and of course only for nighttime. Total power generation capacity was then only 21 MW for East Pakistan; the most privileged Dhaka city used two 1500kW generators to supply electricity.

To improve the power supply situation, the government of Pakistan created Electricity Directorate in 1948 and issued an ordinance in 1959 to form WAPDA (Water And Power Development Authority) to take over all electrical systems from the private sector to the Government sector. As a result, this organization got more autonomy and basic infrastructure developed during this time. From 1960 to 1970 power generation increased from 88MW to 475MW, Dhaka-Chittagong 132kV transmission line network, shiddirgonj, Khulna, Chittagong power plant and Kaptai dam started.

After independence of Bangladesh in 1972, the government realized to boost up the power sector and create BPDB (Bangladesh Power Development Board). The achievement the highlight of BPDB considering time period from 1972 to 1995 is: power generation capacity 2818 MW; high voltage transmission line network 132 kV 2469 km & 230 kV 419 km; highest voltage 230kV capacity transmission line of the country East-west (Tongi-Ishurdi) interconnector is switched on in December 1982. BPDB created an electricity facility in most of the district city area, but the government had to make sense that for developing the whole country electricity need in a rural area, especially for irrigation. 

So, the government created REB (Rural Electrification Board) in October 1977 who works for electrification in a rural area all over the country through PBS (Palli Bidyut Samity) except major district towns.

To segregate electric supply within Dhaka city from the jurisdiction of BPDB, DESA (Dhaka Electric Supply Authority) was created in 1992, but in latter DESA abolished and formed two company DESCO (Dhaka Electric Supply Company) and DPDC (Dhaka Power Distribution Company). 

Not only for Dhaka but also to improve consumer services and reduce losses for all over the country government rearranged and created different companies and organizations in the power sector many times. The major company and organization under the Ministry of Power, Energy and Mineral Resource in Bangladesh is as below:

List of Electricity Utility Organizations in Bangladesh:

BERC (Bangladesh Power Regulatory Commission)

BPDB (Bangladesh Power Development Board)

APSCL ( Ashuganj Power Station Company Limited)

EGCB (Electricity Generation Company of Bangladesh)

NWPGCL (North-West Power Generation Company Limited)

IPP (Independent Power Producer)

RPCL (Rural Power Company Limited)

PGCB (Power Grid Company of Bangladesh)

DPDC (Dhaka Power Distribution Company Ltd)

DESCO (Dhaka Power Supply Company Ltd)

WZPDCL (West Zone Power Distribution Company Ltd)

SZPDCL (South Zone Power Distribution Company Ltd)

BREB (Rural Electrification Board)

PBS ( Palli Bidyut Samity)

STEP AND TOUCH POTENTIAL: REDUCE ELECTRICAL HAZARD AND IMPROVE SAFETY AWARENESS

Fig- Step and Touch Potential 

Understanding of Step and Touch Potential in Power Transmission System to Reduce Electrical Hazard and Improve Line Crew Safety.

The purpose of this article to focus on some less familiar but the most important safety induction  like- step potential or step voltage, touch potential or touch voltage. We also try to give you some pint-size attention on basics of reducing touch potential and why power grid substation yard needs washed clean gravels or stone rather than others.

 We are here using some less familiar literature; means, we everybody knows the importance of electrical safety. But todays discussing topics like step potential or touch potential is little professional and not well known to all, even not to all electrical engineer. Especially who deals with power transmission and distribution substation they are very well familiar with these terms step and touch potential.

What Is Step Potential or Step Voltage

Step potential simply is the potential or voltage difference between a footsteps of a person onto the electrical grounding yard. 


When fault occur near a metallic structure or steel tower then large amount fault current flows from tower to the earth ground. 
Consequently ground potential raises at the tower earthing point and voltage gradient develops depending on the soil resistivity near surrounding the tower earth point.  

This voltage gradient is causes to develop voltage difference between two points like step between two feet of a person is known as step potential.

The Occupational Safety and Health Administration (OSHA) defines step potential as- the voltage between the feet of a person standing near an energized grounded object.

Why Step Potential Is Dangerous

Each electrical potential try to find some easy or less resistive path and when some voltage feel in between two feet of a person; if resistance through person’s body is less than the resistance of ground in between two feet of a person; then obliviously current will flow through the legs via human body and the person will be experience an electrical shock. 


Because human body acts here as a shunt with the ground resistance, and larger current flow through less resistive shunt. Here shocking current may not passes through the vital organ of the person, only passes through lower limbs of the body; but level of injury depends on developed voltage and duration of current flow.


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What Is Touch Potential or Touch Voltage

Touch potential or touch voltage is equal to the difference in voltage between the energized object and a grounded point some distance away. 


Other way we can say, touch potential is the voltage between any two points on a person’s body like – hand to hand, shoulder to back, elbow to hip, hand to foot and so on touching the energized and ground point.

Touch Voltage

Say, if an energized conductor falls on a metal fence, and a person touches that fence then current may passes from the energized fence through the person to the ground.

The touch potential or touch voltage can be approximately the full voltage across the touched grounded and energized point.

Why Touch Potential or Voltage is Dangerous for Electrical Shock

Each electrical potential try to find some easy or less resistive path and when it passes through a human body then it causes an electrical shock-injury and the degree of injury depends on the amount of current and duration of current flowing through it. 


In the above 1^st figure shown in the cartoon at right-side, touching the grounded tower is experiencing electrical shock because the ground connection between the tower and the soil is high resistance that energized the tower itself. 
Touch potential or the voltage developed between the energized object (tower) and the feet of a person in contact with the object (soil).

Here current passes through the vital organ of the human body that may causes serious shock-injury.

How Reduce Step and Touch Potential Hazard: Improve Transmission Network Safety Awareness

Step and Touch potential actually a kind of hidden potential hazard that makes more dangerous than other typical electrical hazards. Touch voltage hazard may happen even away from electric tower like substation fence etc.

There are many way to reduce step potential and touch potential hazards, some of them are as follows:

§  Reducing ground resistance;

§  Ground conductor placing properly;

§  Using gravels or stone on surface area;

§  Using a good quality Person’s safety shoe, etc.

Reducing ground resistance

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Reducing ground resistance is the best way to reduce the step potential and touch potential hazard, for example- if the fault current for a high-voltage line is 10 kA and the resistance to ground of the grounding system is 10-ohms, then ground potential will be 100 kV. If ground resistance reduced to 5 ohms then ground potential will become 50 kV which almost 50 percent, means fault current may increase 50 percent for same ground potential.A typical soil resistivity is as bellow:
Expected particulars permissible values of resistance is as bellow:

Type of Soil                                     Resistivity in (Ohm-m)

Moist Humus                                                     30

Farmland & Clay                                               100

Sandy Clay                                                       150

Moist Sandy                                                      300

Moist Gravel                                                      500

Dry Sandy or Gravel                                        1,000

Rocky Ground                                                30,000

Location                                                       Resistivity in (Ohms)

 Power Stations                                                  0.5

 EHT Substations                                                1.0

33 KV Stations                                                    2.0

D/T centers                                                         5.0

Tower foot resistance                                          10.0

Ground conductor placing properly

Placing ground conductor is important to reduce step and touch potential hazard, generally to minimize touch potential a minimum 2/0 AWG bare copper conductor in direct buried as earth conductor, 3 feet or 1 meter from the perimeter of the object and 18 inches below grade is uses. 


But a soil with a dry and high resistivity conductor will be less effective than soil with wet and low resistivity. Soil study is very important before placing ground conductor.

Using gravels or stone on surface area

Adding more resistive surface layer in tower or substation is easy way to mitigate step and touch potential. 


So washed clean gravels or stone layer is the perfect solution to increase the uniform resistive surface and isolate from gradient soil layer. 

This gravels layer isolate the person from current flowing earth and reduce the step and touch potential hazards, also control growing weed and oil splitting sleepy surface.

Using a good quality safety shoe

A simple and easy way to mitigate step and touch potential hazards just wearing personal electrical hazard safety shoes. Safety shoes ensure some mega ohms of resistance, but notable that a wet and dirty shoes losses the resistance and current may bypass.

Finally we can say personal awareness is the key important to understand the step and touch potential hazard, and practicing safety rules every day in workplace can help to develop a professional line crew. Keep safe your coworker, share this article with them.

AGGREGATES CIVIL WORKS FOR UNDERGROUND CABLE INSTALLATION

Aggregated Civil Works and Construction Materials Management in Cable Installation Site

The underground cable installation project is not a contemporary high-tech major aggregates civil work, but some special complaint and engineering practice  should followed to keep the power cable safe and liveliness for long lifetime.

This article is introduced on the aggregated civil work for high voltage electrical power transmission underground cable installation project. The scope of civil works for such project as highlighted as below:

• Cable trench cutting, bedding, backfilling;

• Cable protection RCC slab;

• Pipe trench, bridge trench, road and canal crossing etc;

• Piling for bridge trench and terminal equipment structure;

• Cable joint and cable earthing or grounding RCC Bay construction;

• Concrete structure and foundation for outdoor steel structure, etc.

To ensure quality and follow engineering layout the aggregates for all concrete should be take approval of the Engineer. Un-reinforced mass cement may use first class broken brick, aggregate. Reinforced concrete should use only stone aggregate.

They must be hard, strong, durable, clean and free from adherent coatings and should be protected from contact with any deleterious mater whatsoever.

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Delivery and Storage System

Sufficient quantities of each grade of aggregate should be kept on the site to ensure continuity of work. 


Aggregate of different sizes should be stored in different stacks and the arrangements for storage should be subject to the approval of the Engineer.

Aggregates for Reinforced Concrete

For reinforced concrete work the fine aggregate should consist of clean well graded Sunarganj, Jaladia or Savar sand.

The coarse aggregate for reinforced concrete should consist of well graded Sylhet shingles.

The fine and coarse aggregate should be kept well separated during storage on site and during mixing, measured separately and mixed in the proportions specified or permitted. 
The individual and combined grading should be to the satisfaction of the Engineer.

 Aggregates for Mass Concrete

All brick aggregate should be tested periodically and as often as the Engineer should decide to be necessary, to ascertain the proportions of the sand contents. In such testing the following conditions should be observed:

o  All material passing a 5mm square mesh should be defined as sand and the residue on such a sieve as coarse aggregate.

o The sand and coarse aggregate are to be separated by sifting a dry sample and the proportion of each ascertained.

o  The proportions by volume in a shaken measure are to be approximately one part sand and two parts coarse aggregate.

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Aggregate for cement Mortar

The aggregate for cement mortar should consist of natural sand as specified in British standard BS 1200; sands for mortar for plain and reinforced brickwork. Mortar for brickwork should generally consist of 1 part cement to 0.5 parts to 4 or 4.5 parts of sand as per BS 5628.

Water for Concrete

The size of aggregate effects on workability and strength of concrete and also influences the water demand for getting a certain work-strength and fine aggregate content required for achieving a unified mix.

Water for concrete, cement mortar and grout should be free from salt, oil, alkali, organic matter or other deleterious substances and the Engineer’s approval must be obtained prior to its use. Any tests required by the Engineer on the suitability of the water should be carried out in accordance with BS 3148.