Electricity in factories – How is it distributed

Electricity is distributed from the Generating Station to the equipment or machinery or lights of a factory through the following 18 vital components, in order. The brief purposes of these components are also explained in the below section.

1. Generating Station – Generates electricity. Mainly Generating stations are situated outside the factory or Industry premises but in Some of the factories have their own generating station for electricity use.
2. External Grid – Transmits power from the generating stations to the distribution substation through Aluminium Core Steel-Reinforced(ACSR) cables. (In case the Generating station is outside of the factory premises)
3. Grid Isolator – Helps to isolate the grid, to work in the internal distribution system for PM or other breakdown work.
4. Transformer protection system from Grid part (L.A, A.C.B, Section Isolator, V.C.B, Relay Circuits) – Protection of Transformer from the fault from the generating side.
5. Distribution Transformer – Steps down high voltage to low voltage for factory uses. We can say the Distribution Transformer is the Heart of the Electric Distribution System of a Factory’s Whole Electricity Distribution system. So the Protection system is installed on both sides of the Transformer to protect it from any type of voltage spikes or surges.
6. Transformer protection system from distributor part ( L.A, V.C.B, C.T., P.T., Relay Circuits) – Protection circuit of Transformer from the fault from the Distribution End.
7. Distributors – Distribute the electricity throughout the factory.
8. Feeders – Feeders (basically interconnecting conductors) are the connecting lines between the distributors to switchgear systems which supply the current in the distribution system.
9. LT panels – Switchgear for distribution.
10. A.C.Bs for protection of the whole system.
11. Bus bars, Bus couplers – Interlocking facilities between ACB and switchgear.
12. Capacitor Bank – For power factor correction.
13. Metering Devices – For metering the Voltage and Current (Voltmeter, Ammeter etc.)
14. Service Mains– Service mains are actually the terminal points of the distribution system.
15. Sub-LT panels – same as LT panels but a shorter version.
16. SDB – Sub-distribution boards to distribute powers to PDBs and LDBs.
17. PDB – Power distribution boards and also protection for electrical equipment.
18. LDB – Lighting distribution board for load switch and internal consumption.
19. Equipment or machinery or lights of a factory

Now we can categorize the above components of electricity distributed in a factory as below…

1. Generating Part (Consists of Generators, Turbines etc.)
2. Transformer and Voltage Regulation Part (The main component is Transformer)
3. Isolation Part (Mainly Isolators, Bus bars, Bus-couplers etc.)
4. Protection Part (Security system consists of ACB, VCB, Relays, MCBs etc.)
5. Distribution Part (Consists of Feeders, Distributors etc.)
6. Metering and Power Factor correction Part (Mainly Voltmeter, Ammeter, Capacitor Bank etc.)

Hope you got an idea of how is electricity distributed in a factory. Now let’s dive into more detail.

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Overview of the Electric Power Distribution System in a Factory

Electric Power Distribution in a Factory mainly operates on higher voltage ranges than the normal operating ranges in households. High voltages like 11KV, 33KV, 66KV, or 132KV from the generating stations are supplied through the main Grid to the respective industries or factories.

In each factory or Industry, substations are built to maintain the internal electric power distribution system. In the Internal substations, Transformers are the main component that is used to step down these high voltages to a low voltage range. Now, these low voltages are distributed through internal feeders to the various workstations of a factory.

The step-down voltage at the end of each service terminal varies between 240V-480V (for small-medium factories) work as the operating voltages of the motors, machinery, heavy instruments etc.

What exactly is Electric Power Distribution?

The component of the power system is known as the distribution system which is responsible for distributing electricity for local use. A distribution system is typically the electrical network that runs from the substation supplied by the transmission system to the consumer’s meters. In the illustration, A typical distribution system is shown in the figure

Components of Electric Power Distribution

Feeders – A feeder is a conductor which connects the distribution sub-station to the area where power is to be distributed. Because no tapings are taken from a feeder, the current remains constant along its length. An induction regulator is used to maintain constant voltage in the feeder circuit. The current carrying capacity of a feeder is the most important element in its design.

Distribution Sub-Station – A distribution sub-station transmits power from a transmission system to an area’s distribution system.

Distribution Transformers – The distribution transformer is a step-down transformer in which primary and secondary are delta and star connected respectively. It is also termed a service transformer. In India, the output voltage of a distribution transformer is 440 V in a three-phase system and 230 V in a single-phase system.

Distributor – A distributor is a conductor from which tapings are taken for supply to the output. Mainly in the Industrial language, the 400V distribution lines are called Distributors. Due to the taping at various places in a distributor, the current is not the same throughout its length. The primary design consideration of a distributor is the voltage drop across its length because the statutory limit of voltage variations is ± 6 % of the rated voltage at the terminals.

Service Mains – Service Mains is a small cable that connects the distributor to the terminal meter.

Classification of Electric Power Distribution System in a Factory

• Nature of the Current

• Type of construction

1. Over-head system (Mostly used system in distribution, Over-head lines are the medium of electricity distribution)

2. Underground system (Mostly used where the over-head system is prohibited, Under-ground Lines are the medium of electricity distribution)

• Scheme of connection

1. Radial system (Distribution system operates from One End, In this system, separate feeders radiate from a single substation and feed the distributors at one end only)

2. Ring main system (Distribution is fed via Two End, In this system, the primaries of distribution transformers form a loop. The loop circuit starts from the substation bus bars, makes a loop through the area to be served, and returns to the substation)

3. Inter-connected system (Distribution can be fed from various interconnected systems, In this system, The feeder ring is energized by two or more than two generating stations or sub-stations)

Nowadays, the A.C. distribution system is universally adopted for the distribution of electricity as it is simpler and more economical than the D.C. method. All the households, as well as factories, are connected through the A.C. Distribution system. So now let’s focus on the A.C. Distribution systems and their advantages.

Types of AC Distribution System

Primary Distribution System The primary distribution system is the part of the AC distribution system which operates at voltages slightly higher than general utilization. The voltage used for primary distribution is determined by the quantity of power to be delivered and the distance of the substation to be supplied. Common primary distribution voltages include 11 kV, 6.6 kV, and 3.3 kV. Due to cost considerations, the major distribution is handled by a three-phase, three-wire system.

Secondary Distribution System The secondary distribution system includes the voltage range at which the consumer utilizes the electrical energy. In India, the secondary distribution employs 440V (3-phase) & 230V (1-phase), 3-phase 4-wire system.

Why Distribution system is Needed in the Factories/Industries

An Electrical distribution system is necessary for every factory and industry. The distribution system distributes the electrical power through the internal factory feeders to the service terminal for the operation of multiple types of machinery.

Requirements of a stable Distribution System

Proper Voltage – The voltage variations at the output terminals should be as low as possible. The statutory limit of voltage variations is ± 6 % (India) of the rated voltage at terminals.

Availability of Power on Demand – Electric power must be available to the consumers in any amount that they may require from time to time.

Reliability – The modern industry is almost dependent on electric power for its operation. This calls for reliable service as much as possible.

Structure of Electric Power Distribution in a Factory

A schematic of the power distribution of a factory can be seen in the figure below. The majority of factories using this model approach are large and medium-sized ones. Depending on the size of the distribution region, where the number of units or sections to be supplied is a key factor, sub-LT panels may not be present always and electricity may instead be directly provided from LT panels to SDBs.

In the above figure, the elements in this power distribution model included – 

• LT panel
• Sub-LT panel
• SDB (sub-distribution board)
• PDB (power distribution board)
• LDB (lighting distribution board)

The LT panels receive a supply of various transformers, acting as the main switching system for the entire power distribution system and carrying the total load demand. In a subsequent section of this post, we will provide a quick overview of the components inside LT panels. In order to meet the demand, sub-LT panels for a certain section’s worth of loads are linked to the output feeders of the LT panel.

The sub-LT panels’ incomer is used at SDB, which are located for powering loads made up of a variety of machines, such as hoists and electrical furnaces (that are connected to various PDBs).

PDBs function as a true load-to-source power connection where individual pieces of equipment are linked directly to the supply. Additionally, a portion of the power from PDB is sent to LDBs, which in turn supply power to lighting fixtures such as street lights, workplace lights, plug boards, etc.

Major Components and their Purposes of Electric Power Distribution in a Factory

Low Tension (LT) Panel
The LT Panel is a power distribution board that receives electricity from the generator or transformer and distributes it to various electronic devices and distribution boards.

Air Circuit Breaker (ACB)
An air circuit breaker is a circuit breaker used to safeguard low voltage circuits by activating and cutting off the high currents. It is employed as a factory and building master, as well as the main circuit breaker, and it is possible to connect various equipment depending on the purpose.

Bus Bar and Connections
High conductivity copper is used to making bus bars (in some cases, aluminium bus bars are used to reduce the cost). The LT panel is made up of a system of primary horizontal bus bars and supplemental vertical bus bars in bus bar alleyways, with front access to connect cables.
Bus bars receive power from transformer terminals and distribute it to different panel elements such as ACBs, capacitor bank switchgear, and other associated loads. The bus bars can be run on either the top or bottom of the panel or on both sides, although the top side bus bars often take the transformer supply, while the bottom side bus bars take the supply from the DG (Diesel Generator) set.

Bus Coupler
It connects one bus bar to another bus bar of a different source (but with the same rating) without causing any arcs or interruptions in the supply system. When other circuit breakers on the same panel are being serviced, this bus coupler diverts the power source to the other. It is also a switchgear configuration with ACB with interlocking functionality.

Capacitor Bank
Bus bars, MCCBs, tuned reactors, capacitor units, contactors, metering equipment, and cables are all part of this distinguished panel. It’s also known as the automated power factor correction panel (APFC). The capacitor banks are linked across the supply to increase the system’s power factor.

Metering and indication
Voltmeters, ammeters, and power factor metres in the LT panel show numerous parameters and are protected by MCBs. Indicating LEDs are provided for each phase on all LT panels to indicate a live or fault state. On the metering panel, start and stop push buttons are also provided to offer input commands such as turn on supply and emergency stop.

Sub-LT Panels
These panels are identical to LT panels, but their rating is somewhat lower than LT panels’, and they are also located in a specific sector of an industry (such as the assembly or dispatching section) rather than near the transformer as LT panels are. These panels serve as mains for various SDBs since they receive electricity from LT panels and transfer it to the SDBs.

Sub-Distribution Boards
These are offered by many manufacturers (such as Havells, ABB India) in both regular and unique designs. SDBs are made up of bus bars (copper or aluminium) that accept electricity from sub-LT panels or main LT panels and transfer it to different heavy-rated pieces of machinery (such as furnaces, chillers, water pumps, ovens, and so on) and PDBs (power distribution boards).

Power Distribution Boards (PDBs)
These are meant to transfer electricity to various machinery and equipment; we may see such power distribution arrangements in large buildings. Short circuit and overload protection features are integrated into PDBs. These are outfitted with several protection relays that can trip the various Circuit breakers (of large capacity) in the event of various sorts of faults.

Lighting Distribution Boards (LDBs)
These are the last switchboards (in electrical wiring and installation) and are found at minor electrical load switching places such as lighting, air conditioners, small motor switching, distribution boards for plugging portable equipment such as blowers, and so on. These LDBs may also be found in our homes and businesses, where they are used in low switching activities.

From the above discussion, we get a brief idea of the Functions, Components, Working principles, Effectiveness, Types and Advantages of Electric Power Distribution in a Factory.

Hopefully, you have got a clear idea about Power distribution and its components.