One-line Diagram -- How to Read Them

We unremarkably draw the electric distribution arrangement by a graphic representation called a single line diagram (SLD). A single line tin can show all or part of a arrangement. It is very versatile and comprehensive because it can depict a very complicated three-phase system.

We utilise universally accustomed electric symbols to represent the different electrical components and their human relationship within a circuit or system. To interpret one-lines you lot first need to be familiar with the electric symbols. This chart shows the almost oftentimes used symbols.

Symbol	Identification	Explanation
	Transformer	Represents a diversity of transformers from liquid filled to dry types. Additional information is unremarkably printed next to symbol indicating winding connections, principal /secondary voltages and KVA or MVA ratings.
	Non-drawout circuit breaker	Represents a stock-still mounted depression voltage circuit breaker.
	Disconnect switch	Represents a switch in low or medium/loftier voltage applications (open position shown)
	Fuse	Represents low voltage and power fuses.
	Electric current transformer	Represents electric current transformers mounted in assembled equipment. A ratio of 4000A to 5A shown.
	Potential or voltage transformer	Represents potential transformers usuallymounted in assembled equipment. A ratio of 480V to 120V shown.
	Footing (earth)	Represents a grounding (earthing) signal
	Battery	Represents a battery in an equipment parcel
	Motor	Represents a motor and is likewise shown with an "G" inside the circumvolve. Additional motor information is commonly printed next to symbol, such every bit horsepower, RPMand voltage.
	Normally open (NO) contact	Can represent a single contact or single pole switch in the open position for motor control
	Normally closed (NC) contact	Can represent a single contact or single pole switch in the closedposition for motor command
	Overload relay	Protects a motor should an overload condition develop.
	Capacitor	Represents a diversity of capacitors.
	Emergency generator	The symbol is frequently shown in conjuction with a transfer switch.
	Fused disconnect switch	The symbol is a combination of a fuse and disconnect switch with the switch in the open position.
	Low voltage motor control	The symbol is a combination of a normally open contact (switch), overload relay, motor and disconnect device.
	Meter eye	A series of circle symbols representing meters usually mounted in a common enclosure.
	Load center or panelboard	One excursion billow representing a principal device and other circuit breakers representing feeder circuits usually in a mutual enclosure.
	Transfer switch	• Circuit breaker type transfer switch •Not-excursion billow type transfer switch

Lets go through a industrial single line diagram. When interpreting a single line diagram, you should always start at the top where the highest voltage is and work your way down to the lowest voltage. This helps to proceed the voltages and their paths straight.

To explain this easier, we accept divided the single line into three sections.

The diagram below was created using free online diagram maker located at www.draw.io The draw.io online is a free-to-license web application for everyone. It is free for any usage, there is no premium pay-for functionality, watermarking, etc. You own the content you produce and may use it for whatever purpose. You can store your draw.io projects in .xml format on your desktop, in Dropbox or Google Drive. Whichever storage option you lot select, when you start draw.io, you will always be presented with a screen asking whether you want to create a new file or open up a new one.

Although draw.io provides an all-encompassing set of default libraries, there may be times when y'all would like to use symbols that are not provided. Provided yous are able to locate and use the relevant symbols, yous tin can incorporate them into a custom library, which can then be used in the same way as any of the existing default libraries. Check describe.io user manual and online tutorials for basic and advanced options.

Surface area A

Starting at the summit, yous will notice that a transformer is feeding ability to the whole organization. The transformer steps the voltage downward from 35kV to 15kV, every bit indicated by the numbers next to the transformer symbol. One time the voltage has been stepped down, a removable circuit billow (a1) is encountered. Do you recognize the removable circuit breaker symbol? Yous can assume this circuit breaker tin handle 15kV, since it is attached to the 15kV side of the transformer, and nix different is indicated on the one-line.

Following the drawout circuit breaker (a1) from the transformer, information technology is fastened to a heavier, horizontal line. This horizontal line represents an electrical bus, which is a means used to become electricity to other areas or circuits.

Area B

You will notice that two more removable circuit breakers (b1 and b2) are attached to the bus and feed other circuits, which are at 15kV, since there has been no indication of voltage change in the arrangement. Fastened to the removable circuit breaker (b1), a stride-downwards transformer is used to accept the voltage in that surface area of the arrangement from 15kV downward to 5kV.

On the 5kV side of this transformer, a disconnect switch is shown. The disconnect is used to connect or isolate the equipment below it from the transformer. The equipment below the disconnect is at 5kV, since nothing indicates the opposite. Do yous recognize the equipment fastened to the lower side of the disconnect switch every bit being 2 medium-voltage motor starters? A number of starters could be continued depending upon the particular arrangement requirements.

Now locate the second removable circuit breaker (b2). This circuit breaker is attached to a fused disconnect switch and it is connected to a pace-downwardly transformer. Find that all the equipment below the transformer is at present considered low voltage equipment, because the voltage has been stepped downwards to a level of 600 volts or lower.

The final piece of electrical equipment in the center portion of the diagram is some other excursion breaker (b3). This fourth dimension, still, the excursion breaker is a fixed depression voltage circuit breaker, every bit indicated past the symbol. Moving to the bottom surface area of the ane-line, find that the circuit billow (b3) in the center is continued to the coach in the bottom portion.

Area C

To the bottom left and connected to the autobus is some other fixed circuit billow. Await carefully at the side by side grouping of symbols. Do you lot recognize the automatic transfer switch symbol?

As well, notice that a circle symbol which represents an emergency generator is attached to the automated transfer switch. This surface area of the one-line tells the states that it is important for the equipment connected beneath the automatic transfer switch to keep running, even if ability from the motorcoach is lost. You can tell from the i-line that the automatic transfer switch would connect the emergency generator into the circuit to keep equipment running, if ability from the motorcoach were lost.

A low-voltage motor command circuit is attached to the automatic transfer switch through a low-voltage omnibus. Brand sure you recognize these symbols. Although we do non know the exact function of the low voltage motor command in this circuit, it is obvious that it is of import to go on the equipment up and running. A written specification would normally provide the details of the application.

On the right side of the third expanse there is another stock-still circuit breaker connected to the omnibus. It is fastened to a meter centre, as indicated by the symbol formed past iii circles. This indicates that the electric company is using these meters to keep track of power consumed by the equipment beneath the meter center.

Below the meter center is a load-centre or console-board that is feeding a number of smaller circuits. This could represent a load middle in a edifice that feeds power to the lights, air conditioning, heat and whatsoever other electrical equipment connected to the building.

This over-simplified analysis of a i-line diagram gives y'all an idea of the kind of story such diagrams tell about electrical system connections and equipment. Just proceed in mind that although some ane-line diagrams may appear overwhelming by virtue of their size and the wide variety of equipment represented, they can all be analyzed using the same step-by-stride method.

Reference // Fundamentals of Electrical Distribution by EATON

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Source: https://arcadvisor.com/faq/interpret-single-line-diagram

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