Topic 2: Short Duration Voltage Variation

Group 3: Islam, Hisyam, Amad Aslam

Group 1: Faiq, Fatin & Aiman

Mitigation Technique

Voltage Swell:Increase in voltage magnitude (110% to 180% of nominal voltage) for a duration of 0.5 cycle to 1 min

Group 2: Ibrahim, Nazim, Dayana

Effect of V.sags

Standard of V.sags

Other characteristic of v.sag

Estimating v.sag performance

Source of V.Sags

1: Power system faults
a) Lightning, TNB grid system will operate to
clear any fault due to lightning.TNB's protection system operates instantly isolating and causing voltage sag. lightning
b) Wind/Ice
c) Insulator contamination
d) Animal contacts
e) Accidents (Crane encroachment /Fires objects etc) crane
POWER SYSTEM FAULTS

2: Energization of transformer

3: Starting of Induction motors

4: Sudden load changes

Voltage Sag indices 1

Indices are used to indicate the quality and reliability of the service provided by Utility companies and compare power quality in different network,They should be kept at a minimum, easy to access and be representative of the disturbance they characterize.

Voltage Sag indices 2

Utility system level

Individual customer level

Serve as a specific metric of compatibility between customer processes and the electrical environment

Serve as a general quality metric to be used by the power provider for proactive planning and maintenance

Voltage sag indices 3

Magnitude-Duration Characterization of RMS Voltage Variations Screenshot 2020-04-06 at 10.41.10 PM

Voltage sag indices 4

Voltage sag indices 4

1. Single-event index: A parameter indicating the severity of a voltage or current event, or otherwise describing the event.

  1. Single-site index: A parameter indicating the voltage or current quality or a certain aspect of voltage or current quality at a specific site.
  1. System index: A parameter indicating the voltage or current quality for a whole or part of a power system

Voltage sag indices 5

SARFI related index and curve
SARFI index

Voltage sag indices 6

SARFI-90: below 90% of voltage reference

✓ SARFI-80: below 80% of voltage reference

SARFI-110: above 110% of voltage reference

Short-Duration Index: it only 1⁄2 cycle and 60 seconds

Voltage Sag indices 7

SARFI-CBEMA : Count or rate of voltage sags and interruptions with retained voltage and duration

SARFI-ITIC: : Count or rate of voltage sags and interruptions with retained voltage and duration

SARFI-SEMI: : Count or rate of voltage sags and interruptions with retained voltage and duration

Voltage Sag indices 8 Screenshot 2020-04-06 at 11.04.31 PM

Group 4: Zamira, Muhammad Khalid, Basir Safi

Voltage Sag: Parameter- Voltage sag duration and Ma
gnitude

Interruption

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An interruption occurs when the supply voltage or load current decreases to less than 0.1 pu for a period of time not exceeding 1 min. The result of ; Power system faults, equipment failures and control malfunctions

Measured by their duration since the voltage magnitude is always less than 10% of nominal

The duration of an interruption due to a fault on the utility system is determined by the operating time of utility protective devices.

Instantaneous reclosing generally will limit the interruption caused by a non-permanent fault to less than 30 cycles

Delayed reclosing of the protective device may cause a momentary or temporary interruption.

The duration of an interruption due to equipment malfunctions or loose connections can be irregular

Some interruptions may be preceded by a voltage sag when these interruptions are due to faults on the source system

The voltage sag occurs between the time a fault initiates and the protective device operates.

topic 2

Three phase rms voltages for a instantaneous interruption due to a fault and subsequent re closer operation

topic 22

Sudden connection of heavy load will cause the voltage at recieving to drop.

Induction motors draw excessive current 4 to 5 times the rate current causing voltage dip during starting or sometimes can cause interruption by operation of protective devices if excessive curretn drawn lasts longer.

Temporary interruption plots. ( Courtesy of Dranetx BMI/Electrotek.)

Inrsuh transformer current during energization is also very high causing voltage drop

topic 222

topic 2222

Voltage waveform

Short Supply Intteruption

The common methods of reducing the impact of costly interruptions include on-site and off site alternative sources of electrical supply

End user may install on-site sources, such as battery-operated uninterruptible power supplies (UPS) or motor-generator sets

Utility may provide an off-site source that includes two feeders with a high-speed switch that switches to the alternate feeder when one feeder fails

Voltage Dip Duration

magnitude of voltage sag and its calculation methodology(monitoring and theoretical calculations)

PARAMETERS

The typical power system including generators,loads and coupling impedance is a single,integrated and dynamic system
any change of voltage,current ,impedance,else,at one point immediately brings about a change in every other point in the system

Voltage dip duration is mainly determined
by
operating time of protection devices such as
Fuses, circuit-breakers and relays
which designed to have an inverse time characteristic
in a manner lower short circuit current would have longer fault clearance time

Solution Classes

Method

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magnitude-duration plot common tool used to show the quality of supply at a certain location or the average quality of supply of number of locations

Between the grid and process

Grid

Very expensive

Not always possible

  • Faster times may be achieved for short circuits on transmission lines (60-150 ms)
  • Slower times for fault clearing on distribution circuits (for MV about 05 to 2 s and for LV , depending on the fuse characteristic)
  • Slower times for fault clearing in remote distribution fault where the asg magnitude is shallow and high
    - Electric motors draw a large inrush current during starting leading exending the duration for the voltage dip (longer time)

In the manufacturing process

Cheapest

No suitable equipment readily available

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Install protective measures between sensitive process and the grid

Reduction of the Fault Clearance Time

Modification of the Supply System Configuration

Reduction of The Number of Faults

Voltage Stabilizers

Improvement in Equipment Immunity

Magnitude of the voltage sag can be determined using rms voltage monitors or calculation methods for calculation knowledge of network impedance ,fault impedance (if any) and fault location are required

voltage signal recorded (monitor)

Theoretical

for computer based analysis by matrix calculations (meshes systems)also theoretical

for the case of zero-impedance short circuit the system represented by a single-phase equivalent circuit

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rms can be calculated using the following equation referring to sampled time-domain voltages

Transmission Network

Distribution Network

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or using analayser containing algorithm
One also half cycle rms voltage for the voltage sag shown

Screenshot_42

Install line arresters

Regular insulator washing

Adjust tower footing resistance

for power system voltage magnitude can be calculated by using voltage divider model

Regular tree trimming

Install animal guards

Install arresters

Significantly limit duration of voltage dip

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the result plot should illustrates sag magnitude in pu and distance to the fualt in Km

during fault based on Thevenin's superposition therm and node impedance matrix

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Use current-limiting fuses

capable of clearing fault in a very short time

Increase number of substations and busbars

Install current-limiting reactors

Install generators close to sensitive loads

Supply sensitive customers' busbars from several substations

Energy Storage System

No-energy Storage Capabilty

To supply critical load during disturbance

Particularly sensitive equipment only

Example

UPS

SMES

Flywheel

Only to reduce effect of voltage dips

Cheaper cost

Example

Constant voltage transformer,CVT

Static fast transfer switching,SFTS

Static generators

Procedures

Importance of Voltage Sag Immunity

Acquire equipment sensitivity information

Determine the potential effect

Acquire system operation information

Reliable operation of sophisticated system

Able to ride through typical voltage sags

Selecting appropriate sag immunity spec when purchasing equipments

  • Voltage dips at points O1,O2 or O3 for short circuit at the point SC
  • The nearer the short-circuit location to the considered point, the lower is the residual voltage. on the other hand, systems nearer to supply source can experience lesser voltage reduction during disturbance

A short circuit on the transmission system is likely to result in a voltage dip that is observed over a very wide area, even at a distance of some hundreds of kilometers. A short circuit in a distribution circuit has a much smaller field of influence. The severity of the disturbance will be moderated considerably by neighboring circuits.

The depth of avoltage dip depends on the kind of short circuit and connection of winding of the transformer(s) between the short corcuit's location and the condidered point of the system

in practice. loads that are sensitive to voltage dips (power converters,adjustable speed drives,motors, control equipments ,else)often connected line to line in industrial installations so they subjected line to line voltage dips

The phasing of the short circuit or other disturbance, the cause of a dip, the connection methods of the primary and secondary transformer windings are significant factors of the negative impact of the disturbance. For instance, considering a step-down transformer connected as Dyn or Dy, a single line-to-neutral fault on the primary side (initially a voltage dip of 0 V residual voltage on one phase) results in voltage dips on the secondary side in two phases, each 58 %

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sags in short duration variation

Instantaneous

Momentary

Temporary

Typical duration : 0.5-30 cycles

Typical voltage magnitude : 0.1-0.9 pu

Typical duration : 30 cycles-3 s

Typical duration : 3 s-1 min

Typical voltage magnitude : 01- 0.9 pu

Typical voltage magnitude : 0.1-0.9 pu

The change of phase angle called phase angle jump it causes the shift in zero crossing of the instantaneous voltage

V.sag indices

Area of vulnerability

Equipment sensitivity to voltage sag

Transmission system voltage sag performance evaluation

Utility distribution system sag performance evaluation

Area of vulnerability can define the equipment voltage sag immunity or minimum voltage sag ride through capability.

Sources

Area of vulnerability is determined by the total circuit miles of exposure to fault

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Sudden loss of heavy load

Voltage rise on healthy phase during unbalanced fault

Motor contactors having a minimum voltage sag ride-through capability of 0.5 pu would have tripped out when a fault causing a voltage sag with duration of more than 1 cycle occurs within the area of vulnerability. Faults outside this area will not cause the voltage to drop below 0.5 which end user voltage drop below 0.5pu.

Effects

1.Equipment sensitive to only the magnitude of voltage sag

2.Equipment sensitive to both the magnitude and duration of a voltage sag

3.Equipment sensitive to characteristics other than magnitude and duration

Types

Momentory: It has a magnitude of (1.1 to 1.8 pu) for (30 cycle to 3 sec) duration

Temporary: It has a magnitude of (1.1 to 1.8 pu) for (3 sec to 1 min) duration

Instantaneous: It has a magnitude of (1.1 to 1.8 pu) for (0.5 to 30 cycle) duration

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Unwanted tripping of equipment

Fault on parallel feeders

Fault on same feeder

For each equipment it is important to determine how long it operates after interruption by performing a simple test.

The same test can be operated for different voltage magnitude ( eg, 90%, 80%,.....,10% of V rated )

Equipment will stop within one second ( Desktop computers ) and other longer (eg, lap-tops for hours).

Connecting point >>> voltage tolerance curve

Electrical equipment work best under rated V, and it will stop operating if V= 0 for a certain period.

Equipment have different voltage - tolerance curve

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Electronic component damage

Voltage Sag indices 9 Screenshot 2020-04-08 at 9.38.09 AM

Limits

Voltage Sag indices 10 Screenshot 2020-04-08 at 9.40.36 AM

Voltage Sag indices 11 Screenshot 2020-04-08 at 9.41.39 AM

Voltage Sag indices 13

The immunity of equipment to voltage swells is given
by the upper limit of the ITIC Curve

Assessment

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The trigger level should be set a 110% of the nominal voltage (230 V for phase‐to‐neutral
LV).

Mitigation

Mitigation of the sources of the voltage swell

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Interruption V< 0.1pu

Sags 0.1<V<0.9 pu

Voltage Sag indices 12 Screenshot 2020-04-08 at 9.48.19 AM

Swells 1.1<V<1.8pu

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Fault conditions

The energization of large loads which require high starting current

Intermittent loose connections in power wiring

8 disturbances have been recorded during 61 days of measurement (at the assumed threshold value X), then after calculation to a standardized one-month period (30 days) SARFI for a given location will be SARFI90 = (8/61) x 30 = 3.93. Screenshot 2020-04-08 at 9.52.10 AM

limits

Voltage Sag indices 14

Voltage Sag indices 15

Voltage Sag indices 16

Description of the Phenomena

SARFIx: average number of specified rms variation measurement event that occurred over the assessment period per customer served, where the specified disturbances are those with the magnitude less than x for sags and more than x for swells.
• 𝑆𝐴𝑅𝐹𝐼𝑥=σ𝑁𝑖 𝑁𝑇

Short duration voltage variations are caused by

The System Average RMS (Variation) Frequency Index or SARFIx in short is the number of sags per year a customer on the average would have experienced, with remaining voltage is less than x percent of the declared voltage.

Screenshot 2020-04-08 at 9.59.20 AM Screenshot 2020-04-08 at 9.58.28 AM

Voltage Sag indices 17 Screenshot 2020-04-08 at 10.01.25 AM

Voltage Sag indices 18

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Indices are needed for standardization of terminology.

• Indices should be compatibility-based.

• Indices should allow for general planning or specific evaluation.

application of surge suppression on load equipment

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CBEMA Curve

STANDARD 1

Standards for voltage sags or dips use reliability indices to set voltage sag limits (IEEE uses the term sag or momentary interruption, but IEC uses the term dip or short time interruption to refer to the same phenomenon)

SEMI-F47-0706 Curve

Voltage sags are typically the most important power quality variation affecting industrial and commercial customers

STANDARD 2

Apart from the IEC 61000-2-8 which is a guide on voltage sags and short interruptions on public electric power supply systems, the other standards on voltage sags deal only with the equipment sensitivity on voltage sags

Standards on equipment immunity began as an industry standard which is the CBEMA and ITIC

Following this the IEC develops a standard on
equipment compatibility the IEC 6100-4-11

Another industry which is the Semiconductor
Equipment and Material Industry SEMI, develop their standards particularly the SEMI F 47 in the early 2000

STANDARD 3

Computer Business Equipment Manufacturers Association (CBEMA) used to describe the tolerance between the voltage and duration that computers or other electrical control devices can operate without failure

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IEC 61000-4-11 standard and SEMI F47 Standard

STANDARD 4

Information Technology Industry Council (introduced a curve based on the CBEMA)- digitized version of the CBEMA curve-provides guidelines related to voltage tolerance limits within which information technology could function properly

ITIC Curve

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STANDARD 5

SEMI-F47-0706 Curve- CBEMA curve does not define voltage sag immunity for semiconductor manufacturing tools effectively- Thus, SEMI introduces standard that overcome this weakness-It is for the "Specification for Semicon. Processing Equipment Voltage Sag Immunity" in order to meet semicon. industry needs.

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STANDARD 6

IEC 61000-4-11 and IEC 61000-4-34-introduced by IEC-for the testing and the measuring techniques for voltage sags, short interruptions and voltage variation immunity tests- The 2 key variable parameters are sag depth and duration

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STANDARD 7

The standards accommodated the differences by having three different classes of testing

CLASS 1

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CLASS 2

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CLASS 3

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CLASS X

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series dynamic voltage restorer, DVR

shunt static VAR compensator, SVC

series-shunt unified power quality conditioner

Install on both supplier or customer side and connected between distributed supply source and sensitive loads

Overheating and equipment damage

Screen Shot 2020-04-12 at 12.08.05 PM

Voltage-tolerance curve was introduced by Thomas Key for reliability of power supply to military installation, become well-known when computer business equipment manufacturers association (CBEMA) used them.

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CBEMA curve was replaced by the ITIC curve, as recommended by the information technology industry council

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applies to protected supplies and compatibility levels lower than public network levels.

applies to point of common coupling (PCC for consumer system) and PCC in the industrial environment in general.

applies to PCC in the industrial environments. It has higher compatibility levels than those of class 2 for some disturbance phenomena.

user defined - incase of SEMI F47-0706, the test points are defined in the SEMI F47 Standard.

observations - We see that the rms voltage does not immediately drop to a lower value but takes one cycle for the transition.- We also see that the rms value during the sag isnot completely constant and that the voltage does not immediately recover after the fault.

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the sag magnitude increases for increasing distance to the fault and for increasing fault level. We also see that faults at tens of kilometers distance may still cause a severe sag.

The sag magnitude can be influences also by the cross section of the line or cable ** also fault levels

can culculate the voltage sag at any node due to a fault at any other node

In Non-Radial Systems
theoretical

Local Generators.(with and without)

Screenshot_47

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mitigates voltage sags - The generator increases the fault level at the distribution bus, which mitigates voltage sags due to faults on the distribution feeders. This especially holds for a weak system.

For a strong system, the fault level cannot be increased much without the risk of exceeding the maximum-allowable short-circuit current of the switchgear.

An overview of the fault-clearing time of various protective devices:-
• current-limiting fuses: less than one cycle
expulsion fuses: 10-1000 ms
• distance relay with fast breaker: 50-100 ms
• distance relay in zone 1: 100-200 ms
• distance relay in zone 2: 200-500 ms
• differential relay: 100-300 ms
• overcurrent relay: 200-2000 ms

caused by : faults, motor starting or utility protective equipment