To understand the drawings and comprehend the different connections it is important to know the meanings of basic electrical symbols in the drawing , this helps in quick understanding the drawings and also helps in troubleshooting the circuit if required.
1.Symbols of Electric Equipment in Electrical drawing
First step of understanding the drawing of any equipment or panel is understanding different symbols used for different equipment like C.T, C.B, C.V.T, L.A, terminal block, Buzzer etc and next is understanding what ferrule (tag) written on several wires mean. In the diagram shown below most of the symbols of different equipment have been mentioned. Single line or three line diagram can also be drawn using these symbols. Let us try to understand electrical drawings in three steps:
Electric drawing symbols:
2.Understanding different ferrules
Several wires run from control room of a substation to different equipment placed in the switchyard of a substation to operate and monitor these equipment from remote i.e from the control room. These wires are laid usually through underground cable trenches .These wires are also tagged for identification as well as rectification of fault if any , faulty cable or wire can be traced easily with name tags on it. Tags are also called ferrule and they appear on wires as K1,C11,D33,U11,E31 etc .The first Alphabet K,C,D,U,E etc of these tags have specific meaning and one can know for what specific purpose they are being used. Ferrules look like this:
PC-Indiamart
3.Ferrule numbering standards
Ferrule “A” used for: CT circuit -Main Protection
Ferrule “B” used for : CT circuit -Busbar Protection
Ferrule “C” used for : CT circuit -Backup Protection
Ferrule “D” used for : CT circuit-Metering circuit
Ferrule “E” used for : PT circuit-Protection/Metering circuit
Ferrule “G” used for: PT circuit-Synchronizing
Ferrule “H” used for: Auxiliary AC circuit
Ferrule “J” used for: Auxiliary DC circuit
Ferrule “K” used for: Control circuit (DC)
Ferrule “L” used for: Alarm and Indication circuit
Ferrule “P” used for: DC circuit-Busbar Protection
Ferrule “S” used for: Event logger/SCADA/BCU circuits
Ferrule “U” used for: Spare Contacts
Now that we have understanding of different symbols and ferrules ,let us try to understand the electrical drawing below which is of circuit breaker closing circuit ( HV side of the transformer) from remote i.e from control panel :
Drawing of a panel can be in many sheets which are serially numbered from 1 and onwards, kindly observe in the above drawing that “SHT” has been indicated at many places, SHT is short for Sheet and the number which follows after this indicates the page/sheet number of the drawing where the detailed drawing of that particular relay, switch etc has been provided.
In the drawing above , K301 and K302 is DC +Ve and DC -Ve Supply respectively and if we want to know more about these terminals and from where they are getting DC power and its connection, we will have to refer to Sheet no-07.
A Circuit Breaker in a substation is usually located in the switchyard and 195,295, 86 relays,TNC switches etc as shown in the above drawing are housed in a control and relay panel which is located in Control room. 52CB-Hv shown in the above drawing in dotted rectangular shape is HV side circuit breaker. RPT written on top of above drawing means Relay Panel terminals.
From the diagram it is clear that +Ve DC supply for remote closing is taken from Circuit breaker itself ,it first enters the relay panel in the terminal block(T.B) shown as HV53TB4.03 , name of T.B is HV53TB4 and the wire connects in no.03 position of this T.B. A terminal block looks like this and it is numbered serially from 1 to its max capacity:
From the mentioned T.B ,ferrule K310 is the wire which carries +Ve DC supply ahead , after this it enters into protective relays -195,295 & 86 relay and then further to Trip and Close (TNC) switch of the Panel. Only when the relay contacts of 86 HV ,86 LV &195 is closed , +Ve DC supply will reach TNC switch terminal for closing the breaker.
When any relay is in operated condition, the relay contacts will open and it will not allow DC voltage to pass through it and close the C.B. Therefore for closing the C.B all relays should be reset. As soon as the +Ve DC voltage is available on ferrule K314 , it will be available on one end of TNC switch, and when this switch is moved to close position ,+Ve DC voltage reaches the closing coil in the Circuit breaker which turns on the breaker. It is to be noted that trip and closing coil of breaker is given -Ve supply at all times and +Ve supply is extended through relays and TNC switch.
By understanding the above drawing we can easily understand all kinds of drawings of control panels. Please feel free to contact us in case any clarification is required.
Read our other posts:
Electrical drawing of Tripping circuit
Basics of Electric Metering circuit
FAQs:
- What is an electrical drawing?
Its a drawing which is often referred to as an electrical schematic or diagram, is a visual representation of an electrical system or circuit. It uses symbols and lines to depict the components, connections, and electrical flow within a system. - Why are these drawings important?
These drawings are essential for designing, constructing, and maintaining electrical systems. They provide a clear and standardized way to understand and communicate the details of an electrical installation. - What are the common types of electrical drawings?
Common types of these drawings include single-line diagrams, wiring diagrams, circuit diagrams, and panel schedules. Each serves a specific purpose in electrical system documentation. - What is a single-line diagram (SLD)?
A single-line diagram is a simplified representation of an electrical system. It shows the major components and their interconnections using single lines and standardized symbols. - What is the difference between a wiring diagram and a circuit diagram?
Wiring diagrams focus on the physical layout of wires and connections, while circuit diagrams show the electrical components and their connections. Wiring diagrams are more detailed and specific to the physical installation. - How are electrical symbols used in drawings?
Electrical symbols are standardized icons that represent components like switches, resistors, capacitors, and more. They are used in drawings to denote the presence of these components and their functions. - What is a panel schedule?
A panel schedule is a detailed list of all the circuits and loads connected to an electrical distribution panel. It includes information about circuit breakers, wire sizes, and the loads each circuit serves. - Are there international standards for electrical drawings?
Yes, various international standards and codes, such as the IEC, ANSI, and NEC, provide guidelines for creating consistent and standardized electrical drawings. - Who uses electrical drawings?
Electrical drawings are used by electricians, engineers, architects, contractors, and anyone involved in the design, installation, or maintenance of electrical systems. - How can I learn to read electrical drawings?
Learning to read the drawings requires familiarity with electrical symbols and a basic understanding of electrical circuits. You can take courses, study textbooks, or seek guidance from experienced professionals. - Can these drawings be created using software?
Yes, there are various computer-aided design (CAD) software programs designed for creating electrical drawings. These tools make it easier to create, edit, and store electronic versions of drawings. - What information is typically included in this drawing?
Electrical drawings usually include information about circuit connections, component locations, wire sizes, voltage ratings, and any specific notes or details relevant to the installation. - How can errors in the drawings be avoided?
Errors can be reduced by double-checking symbols and connections, adhering to standards, and having drawings reviewed by experienced professionals before implementation. - Are there specific requirements for labeling in these drawings?
Yes, labels and identification of components, wires, and equipment are important in electrical drawings. They should be clear, consistent, and follow established conventions. - Can electrical drawings be updated as systems change? Yes, these drawings should be updated whenever there are modifications or additions to an electrical system. Keeping drawings current is crucial for safety and maintenance.
Click here for more information.
