High voltage systems require specialist testing devices in order to carry out maintenance. Conventional test equipment is generally made for use on lower voltage systems, so is unsuitable for safe usage on HV installations.
Live high voltage lines in particular must be tested using correctly earthed and insulating equipment that ensures that the user won't receive extremely powerful electrical shocks. Live line testers come in various different forms ranging from smaller devices up to long poles designed for hooking onto HV systems without the need to use insulating ladders and other equipment.
These devices work by using an insulated pole attached to an indicator that alerts the user to the presence of voltage on a system. As the device is insulated and earthed the flow of electricity will not pass down the tester and into the person holding it, instead returning safely down to earth. Live line testers are also compatible with specific adapters known as bent end adaptors. These are used for direct connection to switchgear or similar applications and come in different angles for use on different types of equipment.
It is of the utmost importance that insulated live line testers are regularly checked for efficiency via the use of a high voltage proving unit. These devices should be used both before and after testing to ensure that the live line tester is working correctly and its generated result values are not outside the norm. Proving units such as those on the site are ideal for this purpose.
Phase comparators are also used commonly on high voltage systems, allowing the user to compare phase by the use of dual-pole devices that are made for attachment to the HV system under test. Like live line testers these can generally be hooked onto overhead lines, switchgear and other applications and provide indication of phase either via visual indicators or by the use of analogue meters attached to the rod.