protection and control guide _ eep

7/29/2019 Protection and Control Guide _ EEP

1/4

Protection and Control Guide

System with two transformer incomers - Phase-to-earth faults

Equipment behaviour during short-circuits

There are 2 types of system equipment, the type that intervenes and the type that does not intervene at th

time of a fault.
http://electrical-engineering-portal.com/download-center/books-and-guides/electrical-engineering/protection-control-guide


2/4

Passive equipment

This category comprises all equipment which, due to its function, must have the capacity to transport bot

normal current and short-circuit current without damage.

This equipment includes cables, lines, busbars, disconnecting switches, switches, transformers, series

reactances and capacitors, instrument transformers.

For this equipment, the capacity to withstand a short-circuit without damage is defined in terms of:

Electrodynamic withstand (expressed in peak kA), characterizing mechanical resistance to

electrodynamic stress.

Thermal withstand (expressed in rms kA for 1 to 5 seconds) characterizing maximum admitted

overheating.

Active equipment

This category comprises the equipment designed to clear short circuit currents: circuit breakers and fuses.

This property is expressed by the breaking capacity and if required, by the making capacity upon

occurrence of a fault.

Breaking capacity

This basic characteristic of a switching device is the maximum current (in rms kA) it is capable of breakin

in the specific conditions defined by the standards, it generally refers to the rms value of the AC

component of the short circuit current; sometimes, for certain switchgear, the rms value of the sum of the

2 components is specified: AC and DC; it is then unbalanced current.

The breaking capacity requires other data such as:

1. Voltage,

2. R/X ratio of broken circuit,

3. System natural frequency,

4. Number of breaks at maximum current, for example the cycle: B M/B M/B (B = breaking; M =

making),

5. Status of the device after test.


3/4

The breaking capacity appears to be a fairly complicated characteristic to define: it therefore comes as no

surprise that the same device can be assigned different breaking capacities depending on the standard by

which it is defined.

Making capacity upon occurrence of a short-circuit

In general, this characteristic is implicitly defined by the breaking capacity: a device should have the

capacity to make upon the occurrence of a short-circuit that it has the capacity to break.

Sometimes making capacity needs to be higher, for example for AC generator circuit breakers.

The making capacity is defined at peak kA since the 1st asymmetric peak is the most restrictive one from

an electrodynamic point of view.

Short-circuit current presumed to be broken

Some devices have the capacity to limit the current they are going to break.

Their breaking capacity is defined as the maximum current presumed to be broken that would develop in

the case of a full short circuit at the upstream terminals of the device.

Title: Protection and Control Guide Merlin Gerin (Schneider Electric)

Format: PDF

Size: 541KB

Pages: 60

Download: Please login first | Get Download Updates | Get Technical articles

Recommended EE articles
http://eepurl.com/lmhNvhttp://eepurl.com/houxMhttp://electrical-engineering-portal.com/wp-login.php?redirect_to=http%3A%2F%2Felectrical-engineering-portal.com%2Fdownload-center%2Fbooks-and-guides%2Felectrical-engineering%2Fprotection-control-guide


4/4

2013 EEP - Electrical Engineering Portal. All Rights Reserved | Privacy PolicyPowered byCsanyiGrou

Subscribe to Monthly Download

Updates

Get EEP's updates without having to keep

checking up on the portal to see if there is

anything new. NewFREE technical articles,

electrical books, guides, software and otherexclusive content you will receive via email.

Pretty simple!

Subscribe here:

Email Address:

Subscribe

Page edited by E.C. (Google).

Become EEP's Contributor and introduce

yourself to 70k+ of our readers all across the

web.

TOP
http://electrical-engineering-portal.com/write-for-us/instructionshttps://plus.google.com/104772136071335658177?rel=authorhttp://www.csanyigroup.com/http://electrical-engineering-portal.com/privacy-policy

protection and control guide _ eep

Documents