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Home / Download Center / Electrical Engineering Books and Technical Guides / Power substation guides / 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.

Dangerous currents induced by electrical field in 400 kV substations
Serviceman serves a 400 kV breaker in Kilanda with isolative SF6-gas. He is standing on a working platform with the insulating porcelain starting a few centimetres above his head. Even though wet and snowy weather conditions, he here experiences a contact current of 160 µA through his hand when touching the grounded pole.

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.

When inspections of the 400 kV switchyard in Stenkullen are performed, the checklist includes a visit to a big three-phase transformer used for reactive and inductive power distribution, see Figure 1. This implies exposure for high magnetic fields, sometimes over 100 µT due to high currents in big reactance coils.

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.

Serviceman is just about to open the door to the control unit of a breaker
Figure 1 – Serviceman is just about to open the door to the control unit of a breaker. He feels pain right before contact is established due to spark discharges. The stationary contact current through his hand was measured to around 120 µA.

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.

A working platform is often used to get within reach. It is a dangerous situation since it is easy to fall down from the platform if one may lean towards the pole and inevitable getting a number of spark discharges.

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.

Title:Human contact currents induced by electrical field in Swedish 400 kV substations – Master of Science Thesis by Jonas Cedergren, Department of Signals and Systems, CHALMERS UNIVERSITY OF TECHNOLOGY, Göteborg, Sweden
Size:4.50 MB
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Dangerous currents induced by electrical field in 400 kV substations
Dangerous currents induced by electrical field in 400 kV substations

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  1. Kameshwar Rao.N
    Dec 30, 2020

    we are Manufacturing of Drive Boxes for Disconnectors 110,220,400 and 750 KV we need latest Technology development of Drive Boxes .

    May 03, 2019

    This is very relevant information with respect to 400KV switchyard.

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