Premium Membership ♕

Learn from experienced engineers and study specialized technical articles, guides & courses. Save 50% on courses with the Enterprise Plan.

Home / Technical Articles / Transients – Line Disturbances

Transients - Line DisturbancesLightning strikes and switching transients on power lines will propagate down the line and eventually arrive at a substation. There, the voltage will be clamped by lightning arresters to a level the substation equipment can handle without damage. This voltage will be passed on to the distribution lines in two forms: differential and common modes. The differential-mode voltage is the voltage between the power line conductors themselves, and it does not directly involve voltages to ground. The common-mode voltages are the voltages of the several conductors to ground.

Differential-mode voltages are passed directly through transformers and appear on the secondaries as transformed by the turns ratio. Some attenuation may result from intrawinding capacitances, but interwinding capacitances may actually increase the voltage.

Common-mode voltages are transferred to the secondary through the interwinding capacitances and can be effectively stopped by an electrostatic shield between the windings. Absent the shield, however, they can appear on the secondaries with a magnitude close to that on the primary.

This can be a severe problem on medium-voltage systems where there is the possibility of 10 kV or more being developed on secondaries to ground. The best protection from line-induced transients of all types on secondaries is a set of MOVs.

Line-to-line MOVs on the secondary are best for differential-mode voltages, and line-to-ground MOVs will provide the best protection from common-mode voltages if a shield is not used.

An electrostatic shield (Faraday screen) is a relatively lowcost addition to a transformer, and it is a good practice to specify a shield on transformers with medium-voltage primaries. With a shield, line-to-line MOVs are likely to provide sufficient transient protection.

Dry-type transformers should be equipped with at least distribution-class lightning arresters on medium-voltage circuits.

SOURCE: Power Electronics Design – A Practitioner’s Guide

Premium Membership

Get access to premium HV/MV/LV technical articles, electrical engineering guides, research studies and much more! It helps you to shape up your technical skills in your everyday life as an electrical engineer.
More Information

Edvard Csanyi

Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry facilities. Professional in AutoCAD programming.

Leave a Comment

Tell us what you're thinking. We care about your opinion! Please keep in mind that comments are moderated and rel="nofollow" is in use. So, please do not use a spammy keyword or a domain as your name, or it will be deleted. Let's have a professional and meaningful conversation instead. Thanks for dropping by!

Enter Captcha Here :

Learn How to Design Power Systems

Learn to design LV/MV/HV power systems through professional video courses. Lifetime access. Enjoy learning!

Subscribe to Weekly Newsletter

Subscribe to our Weekly Digest newsletter and receive free updates on new technical articles, video courses and guides (PDF).
EEP Academy Courses - A hand crafted cutting-edge electrical engineering knowledge