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…
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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…
Arc Flash/Arc Blast PPE
The incident energy determined at each assessable location will fall within a defined arc flash/arc blast PPE category, as defined in the table below. Incident Energy PPE Category Cal/cm2 >1.2 to 4 1 >4 to…
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…
Arc Flash/Arc Blast & Their Causes
An arc flash/arc blast is a dangerous electrical plasma explosion created by a short circuit through air that causes electric current to flash over from one exposed conductor to another or to ground. An arc…
Consequences of Arc Flash/Arc Blast
Arc faults are potentially fatal to any personnel in the vicinity. The intense heat of the arc flash/arc blast can severely burn human skin and ignite the clothing of anyone within several feet of the…
Arc Flash/Arc Blast Hazard Labels
Arc flash/arc blast hazard labels inform personnel of the arc flash/arc blast hazard and the required PPE at each switchboard or arc flash/arc blast hazard location. The labels should present the following information: electrical hazard…
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…
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