Voltage Transformers
Voltage transformers carry full system voltage but no significant current. They have a fine wire of many turns on the primary winding (very high resistance and inductance) connected between the phase conductor and earth, and…
Industry Leading Electrical Courses
Switching Programs & Switching Operations
High voltage switching is a high-risk task, and as such the use of switching programs is critical. A switching program is a written list of sequential logical operations to permit isolation and re-energisation of electrical…
Earthing Switches
Earthing switches are usually installed in combination with an isolator and the two should be interlocked electrically or mechanically to ensure that the isolator is open before the earthing switch is closed, and conversely that…
Current Transformers
Current transformers normally have a single conductor as a primary winding connected in the run of the line conductors. The voltage which appears across the primary terminals is very small and therefore the voltage at…
Switching Programs Terminology & Abbreviations
Before starting to write a switching program, it is important to understand and use standard terminology. The table below includes some common fields found on templates. Program Field Meaning Program number This is obtained…
Ring Main Units
Ring main units (RMU) are widely used in industry and for distribution systems. RMUs operate independently, which means that it is possible to earth an incoming supply cable while it is still energised from the…
Power & Distribution Transformers
The standard power transformer is “on-load tap changing” (OLTC) to ensure that the secondary distribution voltage is within limits although the primary voltage may change. Tap changer range is usually from 15% above normal to…
Circuit breakers
The following basic types are available, typically rated at 350 or 500 MVA at 11 or 22 kV respectively: bulk oil minimum oil air break vacuum SF6 Circuit breakers are designed to deliberately create an…
Power System Switches
The main four different switches used in a power system are: Circuit breakers are designed for controlled closing and controlled or automatic opening of load and fault current. Their duties are to close onto a…