Numerical differential protection : principles and by Gerhard Ziegler

By Gerhard Ziegler

Differential safeguard is a quick and selective approach to safety opposed to short-circuits. it truly is utilized in lots of variations for electric machines, trans?formers, busbars, and electrical lines.
in the beginning this publication covers the speculation and basics of analog and numerical differential defense. present transformers are handled intimately together with temporary behaviour, effect on safeguard functionality, and sensible dimensioning. a longer bankruptcy is devoted to sign transmission for line defense, particularly, glossy electronic conversation and GPS timing.
The emphasis is then put on the several variations of differential safeguard and their sensible software illustrated by way of concrete examples. this is often accomplished through strategies for commissioning, checking out and upkeep. eventually the layout and administration of recent differential security is defined by way of the newest Siemens SIPROTEC relay series.
As a textbook and traditional paintings in a single, this ebook covers all issues, that have to be paid consciousness to for making plans, designing, configuring and utilising differential defense structures. The booklet is aimed toward scholars and engineers who desire to familiarise themselves with the topic of differential safety, in addition to the skilled person coming into the world of numerical differential security. in addition, it serves as a reference consultant for fixing program problems.
For the recent variation all contents were revised, prolonged and up to date to the most recent cutting-edge of protecting relaying.

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1· In (smallest setting value). Task: What must the resolution (how many bits) of the A/D converter be? Solution: 5% accuracy requires a resolution of 100/5 = 20 steps. 1· In. 1)·20 = 10,000 steps based on the RMS value. The maximum instantaneous value is then 2· 2 ·50 = 141 A, which corresponds with 2· 2 ·10,000 = 28,284 steps. The next higher power of 2 is 215 = 32,768. A 16 bit (15 bit plus sign bit) A/D converter must therefore be applied. g. the transformer vector group adaptation by transformer differential protection) can simply be implemented.

3 Differential protection with bridge rectifier circuit and moving coil relay 53 4 Measuring Technique direction and activates a contact. The moving coil relay is a polarised DC current relay and only operates when the current flows in the tripping direction through the core of the moving coil relay. 3). The inertia of the mechanical system results in a smoothening and filtering of the current, which however for small fault currents also results in an increase of the response time. The fastest tripping times of 30–40 ms were therefore only achieved for fault currents that are greater than 5 times the nominal current.

2 Differential protection with induction relay which the fixed coil induces current. The moving conductor is either a disk or a cylinder. The differential protection generates opposing alternating flux with the restraint and operating (differential) current via the corresponding excitation coils. The operating current acts as an accelerating torque on the disk and is opposed by the torque produced by the restraint current. The Ferraris disk is restrained towards its initial position with a restraining spring.

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