What is a Multifunctional Disturbance Fault Recording Device?

A multifunctional disturbance recorder or fault recording device uses 6 different recording methods to produce data that gives an unprecedented level of penetration and visibility into complex behaviour of electrical networks. Based on a typical multifunctional disturbance recorder device, table 1 and figure 1 below summarizes the long-term potential return on investment. This document sets out in detail the benefits and cost savings gained when a multi functional device is used to its full potential.

Table 1 – Payback Period Summary

Figure 1 – Payback Period

What are the benefits of a multifunctional disturbance recorder?

The multifunctional disturbance recorder fault recorder along with the multifunctional disturbance recorder software enables users to make strategic, data-driven decisions on various aspects of their networks resulting in increased network reliability, improved power quality and reduced system loses. In addition to its traditional use in post disturbance analysis the multi functional multifunctional disturbance recorder can help highlight areas of concern in anticipation of blackouts or network losses. This gives operators the ability to rectify problems before they cause significant financial damages.

What are the recording functions of a multifunctional disturbance recorder?

The multifunctional disturbance recorder has 6 main recording functions in one box. Each recording function focuses on detecting different problems related to the power grid. These problems if identified and rectified in a timely manner will improve the overall stability of the power grid and ultimately save on many ongoing costs incurred during trouble shooting, maintenance, repairs and replacements. The recording features include: –

• Fast Disturbance Recording
• Slow (dynamic) Disturbance Recording
• Power Quality monitoring
• Travelling wave fault location
• Sequence of event recording
• Phasor measurement streaming

Multifunctional disturbance recorders can speed up the fault-finding process to help save on costs

Using either “fast disturbance recording” or “traveling wave fault location” an multifunctional disturbance recorder can help speed up the fault-finding process and get critical networks back on line quicker following a disturbance. The fault-finding process is mapped out in the following diagram. Each stage of the process incurs a cost as shown in figure 2 below.

Figure 2 – Costs to Fault Finding Process

Traditional fault location relies on impedance methods with accuracies of 1-15% the length of the line. Traveling wave fault location give accuracies to within a tower span no matter what the line length ensuring more fault causes are identified faster.

Table 2 below estimates how much cost is incurred due to errors on the distance to fault and specifically looking at the need for extra hours on the line looking for the root cause. The analysis assumes the multifunctional disturbance recorder is monitoring two circuits.

Table 2 – Cost of sending out ground line patrol team

Table 3 below shows another cost comparison between impedance fault location and traveling wave fault location. This time it estimates the cost of eliminating preventable faults using both methods. It is important to accurately locate intermittent faults that can be successfully re-closed as partial damage may exist at the fault site that could result in further line trips. Such trips cause voltage dips and the partial damage may transition to serious damage and result in a permanent line outage.

If distances to fault are inaccurate then areas with rough terrain will require aerial assistance to locate the fault. Table 4 below shows a cost comparison between an multifunctional disturbance recorder and traditional fault location methods found in protection relays if a helicopter is dispatched.

Table 4 – Cost of aerial patrol on the fault-finding process

Multifunctional disturbance recorders can identify previously undetected breaker issues saving on costs

Using “fast disturbance recording” and “Sequence of event” recording and an multifunctional disturbance recorder software feature called “record analysis” an multifunctional disturbance recorder can detect a number of circuit breaker issues such as stuck or slow breaker operation that cause long fault clearances.. Many of these types of problems go unnoticed and can result in the breaker failing on a subsequent fault resulting in a wider area of the network tripping than just the faulted asset. Table 5 below estimates the costs associated with these types of issues.

Table 5 – Cost of preventable failed circuit breaker

Identify protection mal operation with multifunctional disturbance recorders

Analyses of DFR records can identify relay mal operation that can warn of a possible non- operation for the subsequent fault and the risk of wider area tripping. Table 6 below outlines the costs saved by pinpointing mal operations.

 Fault recording software can save time when analyzing a large number of DFR Records

There could be as many as 200-300 DFR records triggered across a network during storm conditions. Manually analyzing these can take one week even though many show correct operation of relays and breakers. The Record Analysis feature in multifunctional disturbance recorder software can automatically detect ‘non-compliant’ records and point to where a problem exists. The time to analyse the DFR records captured during the storm can be reduced to 4 hours by identifying and flagging the non-compliant cases. Table 7 below gives estimates on the cost saving by using automated record analysis.

Table 7 – Costs on using automated analysis

How Power Quality issues can help save on costs

There are many different aspects to power quality including transient issues such as dips/swells/interruptions and longer trending issues such as flicker, unbalance, harmonics etc. The multifunctional disturbance recorder can detect all of these types of problems and therefore alert a utility to the fact that they may be happening on their system and allow them time to rectify the problems before they cause additional costs. The following section takes each type of power quality issue and describes in detail the type of issue recorded, the typical causes and the financial costs if not found and rectified.

Voltage sag (or dip)

Causes: Faults on the transmission or distribution network (most of the times on parallel feeders). Faults in consumer’s installation. Connection of heavy loads and start-up of large motors.

Description: A decrease of the normal voltage level between 10% and 90% of the nominal rms voltage at the power frequency, for durations of 0,5 cycle to 1 minute.

Financial costs: Malfunction of information technology equipment, namely microprocessor- based control systems (PCs, PLCs, ASDs, etc) that may lead to a process stoppage and fines. Tripping of contactors and electromechanical relays resulting in loss of load and financial revenue. Disconnection and loss of efficiency in electric rotating machines resulting in unhappy customers and potential fines.

Very short interruptions

Description: Total interruption of electrical supply for duration from few milliseconds to one or two seconds.

Causes: Mainly due to the opening and automatic reclosure of protection devices to decommission a faulty section of the network. The main fault causes are insulation failure, lightning and insulator flashover.

Financial costs: Tripping of protection devices, loss of information and malfunction of data processing equipment resulting in loss of load and financial revenue. Stoppage of sensitive equipment, such as ASDs, PCs, PLCs, if they’re not prepared to deal with this situation and potential fines.

Long interruptions

Description: Total interruption of electrical supply for duration greater than 1 to 2 seconds

Causes: Equipment failure in the power system network, storms and objects (trees, cars, etc.), striking lines or poles, fire, human error, bad coordination or failure of protection devices.

Financial costs: Stoppage of all equipment resulting in loss of load and therefore revenue or financial fines.

Voltage spike

Description: Very fast variation of the voltage value for durations from a several microseconds to few milliseconds. These variations may reach thousands of volts, even in low voltage.

Causes: Lightning, switching of lines or power factor correction capacitors, disconnection of heavy loads.

Financial costs: Destruction of components (particularly electronic components) and of insulation materials, data processing errors or data loss, electromagnetic interference resulting in potential fines.

Voltage swell

Description: Momentary inc

rease of the voltage, at the power frequency, outside the normal tolerances, with duration of more than one cycle and typically less than a few seconds.

Causes: Start/stop of heavy loads, badly dimensioned power sources, badly regulated transformers (mainly during off-peak hours).

Financial costs: Data loss, flickering of lighting and screens, stoppage or damage of sensitive equipment, if the voltage values are too high resulting in potential fines.

Harmonic distortion

Description: Voltage or current waveforms assume non-sinusoidal shape. The waveform corresponds to the sum of different sine-waves with different magnitude and phase, having frequencies that are multiples of power-system frequency.

Causes: Classic sources: electric machines working above the knee of the magnetization curve (magnetic saturation), arc furnaces, welding machines, rectifiers, and DC brush motors.

Modern sources: all non-linear loads, such as power electronics equipment including ASDs, switched mode power supplies, data processing equipment, high efficiency lighting.

Financial costs: Increased probability in occurrence of resonance, neutral overload in 3- phase systems, overheating of all cables and equipment, loss of efficiency in electric machines, electromagnetic interference with communication systems, errors in measures when using average reading meters, nuisance tripping of thermal protections. All of which can reduce the life time of high priced assets and therefore long term financial pain.

Voltage fluctuation

Description: Oscillation of voltage value, amplitude modulated by a signal with frequency of 0 to 30 Hz.

Causes: Arc furnaces, frequent start/stop of electric motors (for instance elevators), oscillating loads.

Financial costs: Most consequences are common to undervoltages. The most perceptible consequence is the flickering of lighting and screens, giving the impression of unsteadiness of visual perception resulting in regulatory fines.

Noise

Description: Superimposing of high frequency signals on the waveform of the power-system frequency.

Causes: Electromagnetic interferences provoked by Hertzian waves such as microwaves, television diffusion, and radiation due to welding machines, arc furnaces, and electronic equipment. Improper grounding may also be a cause.

Financial costs: Disturbances on sensitive electronic equipment, usually not destructive. May cause data loss and data processing errors resulting in fines.

Voltage Unbalance

Description: A voltage variation in a three-phase system in which the three voltage magnitudes or the phase-angle differences between them are not equal.

Causes: Large single-phase loads (induction furnaces, traction loads), incorrect distribution of all single-phase loads by the three phases of the system (this may be also due to a fault).

Financial costs: Unbalanced systems imply the existence of a negative sequence that is harmful to all three- phase loads. The most affected loads are three-phase induction machines and therefore down time and financial fines.

The cost of poor power quality

Poor power quality is estimated to cost the European economy up to €150 billion annually, according to the Leonardo Power Quality Initiative, and the U.S. sees losses ranging from $119 billion to $188 billion, according to research by the Electric Power Research Institute (EPRI).

From a network operator point of view, poor power quality impacts the components that make up the grid such as cables, transformers, capacitor banks etc. These components might suffer excessive heating, overloading, reduced energy efficiency, undesired tripping and early aging. It is also clear the network operators experience additional losses in the networks because of harmonic currents, mostly originated by various customers’ devices. In addition, the costs of unwanted tripping of protective devices or control equipment in the network can be significant as those can lead to unplanned supply interruption. The cost of reduced equipment’s lifetime due to early aging is also very high, especially for expensive network devices. A transformer is expected to have a lifetime of at least 30-40 years. It is possible that it has to be replaced in 10 years earlier due to its early aging caused by increased harmonic pollutions in the network. Most of the time, the effects of harmonics are hidden and not immediately visible.

Light flicker is another PQ problem that has drawn high attention even though it has lesser financial impacts than harmonics and voltage dip problems. It can cause bad reputation of the network operator as a service provider in the electricity business. Also, when a customer complaints to the network operator about flicker problem, then an inspection engineer has to be sent to the site to supervise the problem to take necessary action. All this causes extra cost for the network operator.

Multifunctional disturbance recorders improve overall power grid stability

To quicken the fault-finding process and to mitigate the effect of poor power quality a utility must choose to monitor their network in a way that enables users to make strategic, data- driven decisions on various aspects of their networks. In doing so, the network operator will have the ability to correct issues and ultimately save on costs. Some of the areas where savings can be realized include:

• Reduction in line & equipment currents and losses and hence lower energy
• Release of blocked capacity and consequent avoided cost of capital investment
• Improvement in power factor and avoided penalty for low power factor or incentive for high power
• Reduction in maximum demand and reduction in demand
• Tax benefits such as accelerated depreciation benefits for installation of power conditioning/ energy saving
• Improvement in voltage profile and consequent efficient operation of power
• Reduction in harmonic distortion and consequent reduction in copper loss, core loss and stray
• Prevention of malfunction of equipment and avoided loss of
• Elimination of unplanned outages and reduction in loss of production and
• Reduction/elimination of failure of equipment due to reduced electrical and thermal stress.
• Enhanced life / reliability of equipment due to lower operating temperature due to lower losses