Introduction - Siemens SIMEAS R-PMU Manual

Introduction

Shortly after digital protection devices had been introduced, many experts predicted the soon to
come end of digital fault recorders. However, things turned out rather different since the further
development of the fault recorders provided completely new functions. The application of these
functions facilitates a more transparent management of communications and distribution
systems, as well as of power plants.
Modern digital fault recorders or "universal recording devices" are mainly installed for the
following reasons today:
Although the term "digital fault recorder" is still alive for historical reasons, it would be more
appropriate to talk about "modern recording devices" because the new functions not only
include the recording of faults but also of system and power plant conditions which are critical
but do not necessarily cause a malfunction. Application engineers can use the recording of
critical conditions such as power oscillations, frequency variations, ferromagnetic resonance
effects etc., in order to implement countermeasures well in time.
The triggered recording function Transient Phasor Recorder (TPR) can be used for the most
exact recording of oscillations in active and reactive power, frequency, rms values of the
currents and voltages. An analysis of the records makes it possible, for example, to assess
the quality of the power plant control system.
The continuous recorders such as Continuous Phasor Recorder (CPR) and various
continuous mean value recorders can be used for a comprehensive analysis of long-term
problems in voltage and frequency stability, power oscillations etc.
With the application of the Phasor Measurement Unit function in power plants, as well as in
high-voltage and extra high-voltage switching stations, the current load situation of the
system can be determined and bottlenecks can be detected.
In digital protection devices, the Transient Analog Recorder (TAR) function is almost
exclusively triggered by internal, integrated protective functions. However, there are system
conditions that do not cause a pickup of the protection devices but pose a danger in the long
run. An example is the ferromagnetic resonance effect that is caused by the stray
capacitance of a substation and the inductances of the voltage transformers and may lead to
the explosion of the voltage transformers. Another example is the Ferranti effect occurring in
long lines. There may be significant voltage increases at the end of a line without load.
The scanning frequency of modern protection devices is 600 Hz to 1.2 kHz, in few cases
higher. It is not rare that cables are laid unfavorably in the substation and thus cause stray
capacitances of the cables, or the inductance of the voltage transformers leads to high-
frequency fault signals in the voltage path in the event of a short-circuit. These can cause
delayed reactions in the protection devices, sometimes even non-selective tripping. A similar
effect can also be caused by capacitor voltage dividers. Fault recorders with a scanning
frequency between 5 kHz and 10 kHz are used in order to exactly understand such problems
and to develop appropriate countermeasures.
Digital Fault Recorder, SIMEAS R-PMU, Manual
E50417-H1076-C360-A5, Release 10.2012
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