Mastering Medium Voltage Schematics Episode 01

Learn from Professionals, Electrical Power Engineering

Dear All,

What you’ll learn

  • Medium Voltage Switchgear Schematics.
  • Single Line Diagram.
  • Components of switchgear.
  • Basics of schematics.
  • Symbols.
  • Protection Philosophy.

Course Content

  • Introduction –> 1 lecture • 14min.
  • SLD Part 2 –> 1 lecture • 15min.
  • Components of MV SWGR –> 1 lecture • 5min.
  • Rack Out and Rack In Position –> 1 lecture • 3min.
  • Circuit Breaker Mechanism –> 1 lecture • 6min.
  • Auxiliary Relays –> 1 lecture • 13min.
  • CB aux contacts –> 1 lecture • 3min.
  • Limit Switch –> 1 lecture • 5min.
  • Circuit Breaker Compartment drawing –> 1 lecture • 7min.
  • Symbols –> 1 lecture • 7min.
  • Single Line Diagram of Out Going Feeder –> 1 lecture • 4min.

Mastering Medium Voltage Schematics Episode 01


Dear All,

The capability of reading different types of drawings is an essential skill to perform almost all of the engineering tasks. The engineering drawings form the building blocks of industry method to convey detailed information to implement, gather, troubleshoot, maintain, and run a system. Basically, the very first step to learning how to read such drawings is to become acquainted with standard procedures and basic symbols that are utilized in these drawings.

1. Single-Line Diagram

A complete single-line diagram along with the physical installment layout should be sufficient to properly plan and assess power systems. Broadly, there are two types of the single-line diagram: the system single-line diagram and the equipment single-line diagram.

The former is a general system layout that does not usually provide much detailed information, while the latter is more descriptive in terms of system capacity, control, protection, etc. The equipment single-line diagram could be for transformers, motors, busbars, feeders, or any subsystem of interest.

The single-line diagram should contain at least the following:

  1. Power sources in conjunction with voltage level and available short circuit current
  2. Conductor specifications, including size, ampacities, types, and total number
  3. Transformers’ ratings, capacities, impedances, voltages, vector groups, and grounding arrangement
  4. Protective elements quantity and type identification (i.e. fuse, breaker, and relay)
  5. Instrument transformers (CT & PT) ratios
  6. Capacitors and surge arrestors locations and types
  7. Loads (learn about load flow calculation and network planning)
  8. Any other distribution equipment
  9. Relay type and setting on utility source for both phase and ground faults

Details of connections and geographical locations are not important for the single-line diagram, as it needs to remain as simple as possible. After being familiar with the universally accepted single-line diagram symbols and what are the possible structure of it, one can proceed to read and understand the electric system at hand.

A single-line diagram often starts from the top of the page working its way to the bottom. It starts with utility supply or any given incomer and keeps flowing down till the load centers. Of course, one needs to pay attention to all given component details as mentioned above along the road.

It is helpful to segregate a given drawing into sections for easier analysis. For example, the main substation that has incomers delivering the bulk power from the supplier, the primary and secondary distribution, and a local generation (if any) compose one single-line diagram.

The single-line diagram might have different voltage levels that are linked by transformers, so it is important to shift focus on the transformers to see the different voltage levels in detail. For example, parallel transformers should match in impedance, voltage, vector group, and turns ratio that can be checked easily in the diagram.

The protective components and the instrument transformers provide insight into the protection functions implemented in the system. These protection functions are numbered in accordance with ANSI/IEEE C37.2 that list specific numbering system for all protection functions in literature.


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