Dangerous contact currents induced by electrical field in 400 kV substations

Work performed in a substation

Every kind of task in a substation will give exposure to different levels of electric and magnetic field as well as contact currents. The major part of exposure levels and time will occur for those people that work with maintenance of breakers. This work requires special skill and most of their time, they are working with breakers.

Inspection and small work

Inspections are carried out in the substation at regular basis to check the function of every control unit and check gas pressure of the breakers in order to gain high reliability.

The control boxes of the disconnectors are checked as well. The works involve a lot of touching of control units of circuit breakers and disconnectors as well as other grounded metallic objects exposed to high electrical fields.

Figure 1 shows the control unit of a breaker in Stenkullen. When reaching to touch the handle, the person is discharged through repeatedly occurring sparks.

Maintenance, mounting and service at breakers

Breaker maintenance is the most exposed kind of work from the electric field point of view. It often involves work of long duration. The breakers are sometimes in operation during work with high voltages a few meters above ones head.

Work with disconnectors

When service and maintenance at high voltage disconnecting switches are performed, the power is disconnected and the device well grounded. For security reason, a ground wire is always attached to the incoming phase wire during work.

The electrical field is low since the sources are from surrounding wires and busbars. Often, a sky lift is used; elevating the worker closer to the higher overhead lines, but the distance to line voltage is still large.