The effect of transient voltage protective devices on stresses in rower transformers

SHORT time transients such as lightning waves and switching surges cause very high o ver-voltages in transformers due to high amplitudes of these voltages allowed by transmission line insulation and the non-uniform distribution of such voltages throughout the winding and internal resonance. The internal stresses can be reduced by limiting the amplitude of the impulse waves (gaps and lightning arresters), by changing their shape (wave modifiers), by making voltage distribution uniform throughout the winding irrespective of the shape of the wave (electrostatic shielding of the windings) or by a combination of these means. Coil, turn, and major insulation (except at line end) transient voltages are reduced far more by making the voltage distribution uniform throughout the winding then by reducing the amplitude of the applied wave by any means available at present.