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…
Industry Leading Electrical Courses
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…
Arc Flash/Arc Blast Risk Assessment
The likelihood of an arc flash/arc blast event is dependent upon the type of activity being undertaken at the time. It is generally accepted that the greatest likelihood occurs when there is direct interaction by…
Understanding Safe Approach Distance/SAD
The safe approach distance (SAD) is based on an “exclusion zone” principle. This principle defines an area around an exposed conductor into which no part of the person, mobile plant or object (other than approved…
Electrical Safety
The main considerations of safe working procedures on electrical equipment are to ensure safety of workers and safety of the general public. In addition to this, the continuity of supply, and the welfare of plant…
High Voltage Equipment Rating
Most high voltage distribution equipment has four basic ratings – service voltage; basic insulation level; rated current carrying capacity; and fault capacity. Service voltage The IEC sets standards for manufacturers to produce cables and switchgear…
Fault Current
Power systems are effectively earthed by the neutral points being connected directly to earth. The only resistance being the inherent resistance of the connections and the earth itself. A system fault comprises either one or…