Magnetic and electric fields influence
The electromagnetic fields occurring in substations due to the high currents and high voltages produce different effects on people and objects nearby. High levels of permanent magnetic or electric fields have impacts on the health of people exposed to them. These effects depend on the field strength and duration of exposure. There are specific legislations specifying the maximum values that should not be exceeded.
Permanent magnetic fields can also cause effects of magnetic induction and overheating in metal parts near to their source. In addition, transient magnetic fields produced by high currents at rated frequency (short circuit) or higher frequencies like in the switching of capacitive circuits, can induce high voltages in the control circuits and other closed circuits in substations.
The more frequent objectives of such studies are:
Objective #1
To verify if the values of electromagnetic fields in a substation are lower than the reference levels established in references like ICNIRP “Guidelines for Limiting Exposure to Time-varying Electric and Magnetic Fields (1 Hz to 100 kHz)”. There you may find limits for human exposure to electric and magnetic fields in generation, transmission and distribution of electricity.
ICNIRP means International Commission on Non‐Ionizing Radiation Protection.
Figure 1 – Magnetic field inside a low voltage switchgear (Three phase currents 3200 A and with aluminum enclosure + non-magnetic supports)
Objective #2
To see if local gradients of voltage / electric field are higher than the values which could produce a dielectric discharge or corona in an energized circuit
Objective #3
To see if the magnetic field acting in a metal plate or part is sufficient to produce overheating by magnetic induction.
This report intends to help the users of the software SwitchgearDesign to do validations of their simulations.
The software permit to simulate:
- Temperature rise tests
- Short time current and crest tests (electro dynamical forces)
- Internal arc tests.
- Mapping of electric and magnetic fields. This ability enable the user to estimate the results of dielectric tests (impulse and applied AC voltage) as well as to solve EMC (Electromagnetic Compatibility) problems.
Table 1 – Tolerances between test results and simulation results
| Type of test | Parameter to compare | Typical values of acceptable tolerance |
| Temperature rise test | Temperature rise in solid and fluid parts | 1% to 5% |
| Internal arc test | Overpressure in the enclosure above the atmospheric pressure (crest and duration) | 5% to 10% |
| Short-time withstand current and peak withstand current tests | Electrodynamic forces and mechanical stresses | 5% to 15% |
| Magnetic and electrical field mapping | Module and XYZ components of the field at any point | 5% |
Such validations are to prove, transparently, that the simulation results are within an acceptable tolerance from the values of the actual results obtained in the laboratory tests. Table 1 present values of acceptable tolerances considered here. These values as well as a “technical standard” for the use of simulatio are in Annex F.
An IEC technical standard is missing on this theme and so, this is the best reference in the moment.
| Title: | Solving health and EMC problems due to magnetic and electric fields in substations and neighborhood – Cognitor |
| Format: | |
| Size: | 2.0 MB |
| Pages: | 37 |
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Further Study – A Guide to Substation Earthing Design and Understanding Dangerous Voltages
A Guide to Substation Earthing Design and Understanding Dangerous Voltages
