Chapter 2: Main Switchboard and Switchgear
The Main Switchboard may also be known as the Switchgear Panel and Main Distribution board in other countries than in Singapore. It is essentially 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 according to the area’s load and nature of the load’s requirements.
In this section, we will discuss the 4 main purposes of the Main Switchboard, the pieces of equipment that are used to meet these purposes and provide links to the related information.
4 Purposes of the Switchboard
Main Switchboard is the single point where electricity enters the building. The switchboard panel is built with functions to perform the following 4 main functions.
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1. Power Distribution
The first function of the Switchboard is to connect the electricity from the Power Grid to the site via a big switch called Switchgear. The electricity is usually stepped down to 3-phase 400V, 50Hz. This is one of the main differences between the commercial and industrial buildings where 3-phase power is supplied instead of a single-phase 230V, 50Hz. The connection and the disconnection of the electricity to the site can be done via a Circuit Breaker or a Switch Disconnector.
The second function of the power distribution of the switchboard is to distribute power to each area of the site. i.e. to the Sub Switchboard which is also known as the Distribution Board.
The main Low Voltage Switch that is used to disconnect the electricity. Electricity can arc (jump) from the switches’ contact at high current. These switches are designed to safely disconnect the circuit according to the IEC 60947-3:2008 standard.
A circuit breaker can also be used to disconnect the site electrical supply. They perform the added Protection Function discussed below as well. This is not always an advantage and we will discuss this in the Electrical Protection section.
Cables & Cabling Systems
Busbar and Busbar Supports
2. Electrical Protection
Abnormal incoming supply of electricity, if left unprotected, will damage equipment, may cause significate damage, fire hazard, and is a danger to the people on site. Issues that may arise are as follow:
- Short Circuit
- Over Voltage
- Under Voltage
- Phase lost
- Phase Sequence
- Earth Leakage
- Surge Protection
Short Circuit and Overload Protection
Devices that protect against these two electrical faults are as follow:
Circuit Breakers are designed for the protection of Short Circuit and Overload. A breaker will ‘tripped’ when a Short Circuit or an Overload occurs. A tripped breaker can be reset to re-connect the circuit. However, they have a limited lifetime for the Short-Circuit fault. More information about a circuit breaker…
Fuses are also designed for the protection of Short Circuit and Overload. A Fuse will melt and ‘break’ when a Short Circuit or an Overload occurs thus disconnecting the circuit. A fuse can work much faster than a Circuit Breaker giving a greater protection but may only be used once and has to be replaced if a fault occurs.
Over Voltage/Under Voltage/Phase lost/Phase Sequence/Earth Leakage
Individual Protection relays that protect against these faults are as follow:
Separate Protection relays are used to protect against Over Voltage, Under Voltage, Phase Lost, Phase Sequence, Earth Leakage or Surge Protection
3. Monitoring of Electricity Status and Quality
Power meter displays electrical parameters such as the Voltage, the Current, the Active Power, the Reactive Power, and Harmonics. It is used to measure the quality of the power as well as measure an record the amount of power being used for the purpose of Energy Saving. They can be separated into two major group of Analog Power Meter and Digital Power Meter shown here.
Power Meter - Energy Meter
Power Meter has become more and more popular as the price has decreased over the years.
4. Backup Power to Prevent interruption of power for the key area
Backup power comes in many form and many levels. From a manually starting a generator and switching over the power supply to a fully automated system that has an Uninterrupted Power Supply (UPS) supporting the essential circuit while a Generator Controller automatically start up the generator and when the power is ready an Automatic Transfer Switch switches over the supply to re-charge the UPS battery. The reverse happens when the primary supply is back to normal.
UPS Uninterrupted Power Supplies
UPS is essentially a big battery and inverters that switch Alternating Current (AC) to Direct Current (DC) for energy storage and DC to AC to supply to load.
Diesel Generator is made up of a diesel engine and an electric generator. It is used to provide temporary power in case the primary power failure. The generator controller can detect that the primary power has failed and starts up the generator.
ATS Automatic Transfer Switches
An ATS is an automatic switch that detects that the secondary source of power is ready and switches the power source over. It does the same when the primary power return to normal.
MTS Manual Transfer Switches
A manual transfer switch is simply an ATS without the motorize switching unit. It has to be activated manually.
This video here gives a very good summary of the switchboard from 3.11 mins onwards