Chapter 1: Overview of The Power Distribution System

In this chapter, we will give an overview of the Power Distribution System starting from the Medium Voltage transmission line through the transformers into the Low Voltage (LV) Switchboard. Inside the site linking the Switchboard into the Sub Distribution Board, right down to the loads such as the pieces of machinery, lighting, HVAC, and Control Panels. Along the way, we will also cover various types of Electrical Panels such as the Load Center and the Motor Control Center.

We will explain the functions and purposes of each component of the system. Let’s go!

Electricity enters the site from a Transformer through the ‘Service Entrance’ to the main electrical panel called the Main Switchboard. From the Main switchboard, the power gets distributed around the site in a tree network running from the main switchboard to other Distribution Boards. Each distribution board is responsible for an area of the site.

The site may need a specific power to supply to the motors. The electrical panel that is dedicated to these motors is called the Motor Control Center.

We have two very detail videos that clearly explain this concept

Here is an outline of the Power Distribution Panels starting from the Main Switchboard to the smallest Distribution boards. We explain their purposes and functions in details as well as the equipment that you will find inside the panel. They are as follow:

• Main Switchboard/Switchgear/Main Distribution Board
• Sub Switchboard/Distribution Board
• Panel Board/Load Center
• Motor Control Center

Click on the link to view their specific details or read the more general information below

The Main Switchboard is the first electrical panel that connects the electricity and power to the site. The primary role of the panel is to distribute power to different areas of the site. We will discuss the 4 main purposes of the Main Switchboard, the pieces of equipment that are used to meet these purposes.

Distribution Boards are responsible for a particular area of the site. They perform similar objectives as the Switchboard. As the Distribution Board are closer to the load consideration on protection and uninterruptible power supply option for the load in the area has to be taken.

Panel Board is designed to split the 3 phase supply into single phases circuit for use with single phases devices such as lighting, computers as well as the machinery Control Panels.

Motor Control Center is like a Distribution Board but is designed for the purpose of controlling a large set of motors. For smaller motors in the manufacturing lines or the motors in the pieces of machinery, there may be some components of the Motor Control Center inside the Distribution Board or a smaller local Motor Control Center Panel that is attached directly to a Distribution board.

This system is designed to assist in the situation when there is a problem with the site’s primary source of electrical supply. The most sophisticated system can automatically detect any issue with the primary supply, startup a secondary supply such as a generator and connects it to the site to this secondary source. When used in combination with the UPS (Uninterrupted Power Supply) can guarantee an uninterrupted supply to the site’s essential loads.

Monitoring the usage and pattern of usage of electrical power and uses the information to adjust the user’s behavior or special equipment to increase the efficiency and reducing waste.

The panel consist of two main components; the capacitors, and the controllers. The controller monitors the Power Factor value and connects the capacitors to the circuit to correct the Power Factor.

Invertors inside the UPS and VSD (Variable Speed Drives) are the main sources of harmonic noises. Harmonic Filters are used to filter out the harmonic noise in the system.

This was a quick run through of the Power Distribution Systems, an overview of the Electrical Panels in the system, their purposes and the key components inside. We will go through in details each of the electrical panels starting from the Main Switchboard in the next chapter.