MULTI-FUNCTIONAL DISTURBANCES RECORDERS

Disturbances recording units have existed for many years in many shapes, names and functionalities. The required capabilities are continuously increasing as the grid complexity evolves and new technologies are introduced. This creates analysis challenges for the engineers.

There are many factors to be considered before selecting the right recording device, from the events to be monitored to the recording time, resolution, parameters and sensors accuracy.

This article discussed the various recording applications, the required feature for each application (events type, recording time, etc.) and the available options in today’s market. The advantage of the G5 as a modular platform to comply with any need is also discussed.

TYPES OF DISTURBANCE RECORDING UNITS

 

Disturbance recorders are split into 4 main groups:

  1. Transient recorder – This group include recorders that have the capability to record instantaneous values (waveforms) of current and voltage at relative high sampling rate (tens of sample per cycle). Some are also have the option to record computed quantities such RMS, Powers and even harmonics. These recorders designed to analyze system protection operations and circuit breaker performance.
  2. Change of state recorder – This group includes recorders that records the trends of binary inputs (digital signals). These recorders designed to analyze control operation and protection systems.
  3. Long term recorder – This group includes recorders that have the capability to measure frequency, phases and RMS values of power computed quantities such as Voltage and current RMS, Powers – active, reactive. Calculation are in a relative high sampling rate of 10Hz – 50Hz. These recorders designed to analyze complex power system events.
  4. Continuous recorder – This group includes PMUs (Phasor Measurement Unit) and PQAs (Power Quality Analyzers). These recorders consider to be the most complicated and accurate recorders. Both PMU and PQA required to comply with strict standards that define calculation methods and accuracy levels.
Figure 1: Types of disturbances recording units

TYPES OF EVENTS

Power engineers are typically interested in 4 types of events deviated by the event duration and required resolution as follow:

  1. Transients’ events – These are a very short duration spikes in voltage or current. These events are generally no longer than 1/2 cycle and are typically caused by: Lightning strikes, power outages and tripped circuit breakers.
  2. Short term events – These are short duration events that might cause damages to electronic/industrial equipment, outages and other power quality issues. voltage Dips, swells and frequency rate of change are common events in this group. These events are typically 1/2 cycle to 1 minute in length but may be longer if multiple protection operations are required to clear the fault. These events are usually analyzed to determine correct protection operation, fault location or verification of system model parameters.
  3. Long term events – Power swing, frequency variation and abnormal voltage problem are example of long term events that may affect system stability. These events are relatively harder to define. Therefore, required some investigation prior actual recording.
  4. Steady state condition – There are steady state disturbances where system operation is not threatened, but power quality is affected.  This may include harmonics or sub-harmonics produced by the load and/or the interaction between power system’s components.  Depending upon the type of phenomena being analyzed, higher sample rates may be required to capture the events and data of interest. Record length parameters may be defined.
 

TYPES OF RECORDING MECHANISM

Depends on the event being analyzed – sample rate, recorded parameter and recording period need to be defined. There are three primary types of recording mechanism:

  • High-speed recording
  • Low-speed recording
  • Steady state recording
 

HIGH-SPEED RECORDING

High-speed recording is used to record the currents and voltage waveforms at relatively high sampling rate to display system faults and transients. The recording is triggered when the magnitude of an analog quantity exceeds a pre-define threshold. Pre and post recording margins are also required to be configured.

Before choosing the appropriate device to record waveform data, it is important to understand what the instrument recording capabilities are, as significant differences exist between meters in terms of triggering method, type of triggers, sampling rate and recording length. Care must be taken on the supplied analysis software features, as some software are simple viewer and some include comprehensive analysis tools such as FFT and other parameters calculations.

LOW-SPEED RECORDING

Low-speed recording is used to record short term events such as dips, swells and power swings at resolution of 1/2 cycle to few cycles. The captured data are analog quantities such as RMS, phasor or powers. Recording is triggered when the analog quantity exceed a pre-define threshold. Pre and post recording margins are also required. Typical recording length is in the range of 1-3 minutes. Same as in the high-speed recording, significant differences exist between meters in terms of triggering method, type of triggers, sampling rate, recording length and software features. Power quality analyzer will most likely be the most advance meter in the category.

Figure 3 shows the 1/2 cycle RMS voltage values, the line impedance and phasor diagram during a ground fault.

 
 

STEADY STATE RECORDING

Steady state recordings captures a low resolution statistical quantities such min, max and average values and are mainly used for a compliances criteria such EN51160 or IEEE 519. Phasor Measurement Units are considered steady-state recording devices, which collect the system state information over a wide area. Depending upon the type of phenomena being analyzed, higher sample rates may be required to capture the events and data of interest.

 

CONTINUOUS WAVEFORM RECORDING

In order to sufficiently monitor unforeseen events, the following challenges need to be addressed by the engineers:

  • Which parameter need to be recorded?
  • In which resolution data should be captured?
  • Does waveform data is required?
  • What is the memory capacity disturbance recorder have?
  • What type of events need to be triggered?
  • What should be the thresholds to trigger the recording?
  • What should be the pre and post recording margins?

Current and voltage waveforms are the raw data of any power parameter. Therefore, the above challenges will not rise in the first place if continuous waveform recording was available.

The PQZIP, power quality compression algorithm, enables disturbances recorders to record the waveform signal of multiple analog channels, onboard, continuously, without the need to set triggers or thresholds, for more than a year.

When coupled with Elspec PQSCADA Sapphire, a multi-vendors support power management software, ~5,000 power parameters at any given resolution are calculated for displaying and reporting purposes from the acquired waveform signals.

Since 2004, thousands of recorders with continuous waveform recording have been worldwide installed. In 2018 Elspec presented its 5th generation, multi-functional disturbance recorder, that incorporate functions of Digital Fault Recorder, Phasor Measurement Unit and Power Quality Analyzer.