|Key: G – Voltage Source EUT – Equipment Under Test M – Measuring Equipment S – Supply Source including reference impedance and voltage generator output impedance RA = 0.24Ω jXA = 0.15Ω @ 50Hz RN = 0.16Ω jXN = 0.10Ω @ 50Hz Note: The reference impedance within the source (S) block includes both the output impedance of the AC Source (G) and the reference impedance network (RA, jXA, RN, jXN)|
|Figure 1. (IEC61000-3-3:2013,2013)|
In real world compliant flicker testing, Zref is a physical impedance network consisting of a resistive element and an inductive element that is placed in between the AC Power Source and the equipment under test. N4L can provide the entire test system including Programmable AC Power source, Impedance Network and Flicker (+Harmonics +Power) Analyzer. We will discuss the different elements of the test system below;
1. Programmable AC Power Source – Section 6.3 of IEC61000-3-3:2013 describes the requirements for the AC Power Source for compliant Flicker Testing, this can be summarized in the table below.
|IEC61000-3-3:2013 Test Supply Voltage (AC Power Source) Requirements|
|Requirement||N4L N4Axx Programmable AC Power Source Performance|
|Open Circuit Voltage shall be the rated voltage of the equipment||0-300Vrms Single Phase, 520Vrms Three Phase|
|Test Voltage Maintained within ±2% of the nominal value||±0.1%|
|Frequency Stability ±0.25Hz||±0.01Hz|
|THD < 3%||Better than 0.3%|
2. Zref – Reference Source Impedance – Section 6.4 of IEC61000-3-3:2013 describes the requirements for Zref
IEC61000-3-3:2013 refers to IEC/TR 60725 which specifies the in-phase and quadrature component of the reference impedance Zref. It is important to note that Zref includes the impedance of the reference network and the output impedance of the AC source, the output impedance of the N4A series AC Power Sources is very low and can be considered negligible for this application.
3. Flicker Analyzer – Section 4.2.2 of IEC61000-3-3:2013 refers the reader to IEC61000-4-15:2010 which lays out the specification and signal processing requirements for compliant flicker measurements. All N4L PPA5511 and N4L PPA5531 Harmonics and Flicker Analyzers offer full compliance to IEC61000-4-15. Furthermore, N4L are able to offer IEC61000 Harmonics and Flicker calibration to ISO17025 from our in house UKAS Laboratory.
|Figure 2. (IEC 61000-3-3:2013,2013)|
If we analyze various working points on the Pst = 1 curve it is possible to determine the relative voltage change (d value) and the number of voltage changes per minute at that perturbation level.
For a 230V system a relative voltage change of 1% resulting in a Pst of 1 would require 25 voltage changes per minute. Figure 3 below is annotated at the 1% voltage change point and we can follow the graph across to the intersecting value on the y-axis at approximately 25 voltage changes per minute.
|Figure 3. (IEC 61000-3-3:2013,2013)|
We can state that for a voltage change of 1% at a frequency of 25 changes per minute, we would achieve a Pst equal to 1.
If we cross refer to table D1, found in Annex D of IEC61000-3-3 we discover that the findings above correlate to the test protocol table.
|Table 2. (IEC 61000-3-3:2013,2013)|
|Voltage Fluctuation and Flicker Limits|
|Pst||Less than or equal to 1.0|
|Plt||Less than or equal to 0.65|
|Tmax||Accumulated time of d(t) with a deviation exceeding 3.3% during a single voltage change at the equipment under test terminals must not exceed 500ms|
|dc||The maximum relative steady state voltage change must not exceed 3.3%|
|dmax||Maximum relative voltage change (between two half periods) shall not exceed: 4% without additional conditions 6% for equipment that is; – switched manually – switched automatically more than twice a day and is also fitted with a delayed restart not less than a few tens of seconds. Alternatively a manual restart after a power supply interruption. 7% for equipment that is; – attended whilst in use – switched on automatically or intended to be switched on automatically no more than twice per day. Must also be fitted with a delayed restart of not less than a few tens of seconds (or manual restart) after a power supply interruption.|
Pst and Plt limits need not be applied to voltage changes caused by manual switching.
Nor do the limits need to be applied to voltage changes associated with emergency switching or emergency conditions, this is sensible as such occurrences will be very rare.
|Flickermeter Accuracy Requirements|
|Parameter||Limit||N4L PPA55x1 Performance|
|Current||±(1% + 10mA)||0.01% Reading + 0.038% Range|
|Total Measurement Uncertainty, including tolerance of Impedance Network and Impedance of AC Power Source||±8%||<1%|
|Reference Impedance 50Hz (60Hz)|
The standard recommends that the observation period should cover the part of the operation cycle that includes the most “unfavorable sequence of voltage changes”.
Assessing Pst requires the cycle of operation to be repeated continuously unless otherwise specified in Annex A of IEC61000-3-3. The minimum time it takes to restart the equipment, for equipment that automatically stops shall be included in the observation period if the cycle of operation is shorter than the observation period.
The assessment of Plt does not require the cycle of operation to be repeated unless otherwise stated in Annex A, when the cycle of operation is less than 2hrs and the equipment is not used continuously.
Cycle of operation: 35 minutes
Four consecutive Pst values are measured during an initial period of 40 minutes.
Remaining eight Pst values in the 2Hr test period are deemed to be zero.
The standard provides guidance on general test conditions for devices not mentioned in Annex A, advising that the equipment should be set up to produce the most unfavorable conditions with respect to voltage fluctuations at the input terminals of the equipment when connected to the power source and reference network.
The equipment should only use settings and programmable modes that are mentioned by the manufacturer in the instruction manual or that are otherwise likely to be used.
The underlying message of the standard is one that the equipment must be working in a similar manner to that which it would be in normal day to day use when in the field. The standard concentrates on simulation of the equipment when connected to a real power grid, therefore it makes sense to ensure that the equipment being tested is being used in a realistic manner.
Guidance for Motors
When a motor is first started, the back emf created by a rotating rotor across the static motor windings is zero, therefore when the rotor mechanical frequency is zero the supply current will be maximum. It is sensible to conclude that a locked rotor test (in which the rotors mechanical frequency is zero) could be used to determine the maximum inrush current. A secondary effect of maximum inrush current is a large dmax measurement, in fact the maximum dmax will occur during a locked rotor test and this approach is acceptable for dmax assessment.
Separately Controlled Circuits
For equipment consisting of separately controlled circuits, each system should be considered as an entirely separate item of equipment. This is providing that each sub circuit is not designed to be switched at exactly the same moment.
If several sub circuits are designed to be switched simultaneously then each group of circuits should be considered a separate item of equipment.
A system contains 14 sub circuits
Circuits 1,3,5 and 7 all switch simultaneously (System A)
Circuits 2, 4, 6 and 8 ~ 14 all switch simultaneously (System B)
Therefore, two “Items of equipment” are separately tested for the 14 sub circuits.
If a control system regulates only part of a load, the fluctuations in the supply voltage produced by each variable part should be separately considered.
Annex A provides mores specific product type related information regarding test conditions, a brief overview of the recommended test conditions are tabulated below;
|IEC61000-3-3 Annex A|
|Product Type||Type Test Conditions|
|Cookers||No requirement to test Plt for domestic cookers Pst performed at steady state, unless specified Hotplates – Tested using standard saucepans with water quantity specified in table A.1 of IEC61000-3-3:2013 Boiling – Perform 5 tests at boiling point and take the mean to calculate final result Frying – Fill pan to 1.5 times quantity in table A.1, set temperature to 180 deg C, confirm temperature with thermocouple Power Settings – Test all discrete power stages up to a maximum of 10. If non discrete stages are available separate range into 10 discrete steps. Baking Ovens – Test empty with door closed Place thermocouple in center of oven Set temperature to 220 deg C (conventional ovens), 200 deg C (hot air ovens) Grills – Test with doors closed, unless otherwise stated If settings are available – set to lowest, middle and highest settings and record worst result. Baking Oven/Grill Combinations – Test with door closed Place thermocouple in the center of the oven Set temperature to 250 deg C (or closest available temperature to this value) Microwave Ovens – Use a 1000g glass bowl of water as a load Test at low, medium and third power stage (less than or equal to 90% maximum power) Worst result recorded|
|Lighting||Use lamp rated at power rating of equipment Plt and Pst evaluation only required for equipment likely to produce flicker, such as disco equipment No limits apply to individual lamps, such as fluorescent tubes Incandescent Lamps (≤1000W), Discharge Lamps (≤600W), LED Lamps (≤200W) are deemed to pass dmax without the requirement for testing. Luminaries with higher ratings that do not comply to the limits specified in IEC61000-3-3 shall be subject to conditional connection in accordance with IEC61000-3-11|
|Washing Machines||Complete laundry program, normal wash cycle, 60deg C cotton without pre wash program if available Rated load of double hemmed press washed cotton cloths (70x70cm, 140g/m2 ~ 175g/m2) Water temperature 65degC (heater element), 15degC (other) Heating elements not controlled by programmer – preheat to 65degC Heating elements with no programmer – preheat to 90degC or lower if steady state is reached Ignore simultaneous switching of motor and heater for assessment of dc, dmax and Tmax Evaluate Pst and Plt|
|Tumble Dryers||Fill with textiles, 50% dry load double hemmed press washed cotton cloths (70x70cm, 140g/m2 ~ 175g/m2) Soak with 25degC water, adding 60% of original mass Where possible, perform test at maximum and minimum heat settings Evaluate Pst and Plt|
|Refrigerators||Operate continuously with the door closed Adjust thermostat to the mid value Empty the cabinet, no heat required Do not evaluate Pst and Plt|
|Copying Machines, Laser Printers and Similar||Test for Pst at the maximum rate of copying Copy medium is white blank paper, 80g/m2 if not otherwise stated Evaluate Plt in standby mode|
|Vacuum Cleaners||Do not evaluate Pst and Plt|
|Food Mixers||Do not evaluate Pst and Plt|
|Portable Tools||Do not evaluate Plt For portable tools without heating elements fitted do not evaluate Pst Switch on for 10 minutes|
|Hairdryers||For hand held dryers Plt shall not be evaluated Evaluate Plt by switching on for 10 minutes If power ranges are available, test complete range up to a maximum of 20 stages (for discrete steps)|
|Television, Audio, Computer, DVD and similar equipment||Refer to Annex A, if no special test conditions are appropriate, only compliance to dmax is required.|
The table is not exhaustive and reference to Annex A in IEC61000-3-3 is recommended, further test conditions recommendations are made for other equipment such as water heaters, audio-frequency amplifiers, air conditioners, heat pumps, commercial refrigeration equipment and arc welding equipment.
Annex B describes test conditions for measuring dmax, also known as voltage changes at the terminals of the equipment under test caused by manual switching.
When an item of equipment is manually switched on or off, current inrush to the EUT causes voltage changes over the supply network. A statistical method is used in order to achieve a repeatable measurement of dmax.
The procedure includes 24 separate measurements, described below;
|Half Period RMS as specified in IEC61000-3-3 (Uhp)|
dhp(t) = Uhp(t) / UnSteady State Voltage Change dc,i Value of the difference between two consecutive steady state voltage changes, normally expressed as a percentage of the nominal voltage Un.
dc,i = [dend,i-1 – dstart,i]/Undc Measurement Example:
|Steady State Voltage Change Example|
dc,i = [dend,i-1 – dstart,i]/Un
dc,i = [230-227.7]/230 = 0.01 = 1%
This is an example of a steady state voltage calculation, you will notice that the next steady state occurs after 1 second at the 227.7Vrms half period value.
Maximum Voltage Change dmax,i
This is the maximum recorded voltage difference between a steady state condition and a following half period Vrms ( dhp(t)) during the test period.
dmax,i = max [dend,i-1 – dhp(t)]
Polarity is indicated, the direction of polarity is dependent upon the direction of the voltage change in comparison to the dend,i-1 value.
The dmax value is a result of a reduction in voltage then the value of dmax is positive.
The dmax value is a result of an increase in voltage then the value of dmax is negative.
Maximum steady state Voltage change during observation period dc
dc is the highest absolute value of all dc,i values recorded during a test.
dc = max i [|dc,i|]
Maximum absolute Voltage change during test period dmax
Highest absolute value of all dmax,i values during the test period.
dmax = max i [|dmax,i|]
Voltage deviation d(t)
d(t) is the deviation of the current half period Vrms(dhp(t)) to the previous dend,i-1 inside a voltage change characteristic. Polarity is optional for this parameter and a voltage drop is considered positive.
d(t) = dend,i-1 – dhp(t)
Steady State Voltage Change and Voltage Change Characteristics
A steady state condition is defined as when the half period r.m.s. voltage Uhp remains within a tolerance band of ±0.2% for a minimum of 100 half cycles of the fundamental frequency (50Hz), this clearly equates to a steady state for 2 seconds.
At the beginning of a flicker test, the initial reference voltage is defined to be the average r.m.s. voltage acquired during the preceding second to the commencement of the test period. This is the starting reference value for dc and dhp(t) calculations and well as for the calculation of dmax and d(t) measurements.
If a steady state condition cannot be established during the test, dc shall be reported as zero.
As the test progresses, an average Uhp,avg is calculated from the last 100 (50Hz) Uhp values. The Uhp,avg value is used to determine whether or not the steady state condition continues, it is also used as the reference for dc, dmax and Tmax in the event voltage changes occur.
What this essentially means is that a 100 sample average, Uhp,avg of the half period r.m.s. voltage is continually taken, this average value is then compared to the last half period r.m.s. voltage Uhp. If the last half period r.m.s. voltage is within 0.2% of the Uhp,avg value then the steady state condition continues.
A new steady state condition dc,i is determined after a voltage change has occurred by calculating an initial value – dstart,i = dhp(t=tstart) is used. A tolerance value of 0.2% is set and a steady state condition is detected if 100 half period r.m.s. values are within the 0.2% band.
The reason Uhp,avg is used is to prevent slowly changing line voltages triggering a dc or dmax indication.
The last value of Uhp that lies within the 0.2% tolerance is denoted as dend,i. The new half period r.m.s. value following this final value within the 0.2% limit is denoted as dhp. This value is used as the starting value for determining the value of the next steady state condition, known as dc,i+1.
Once a new Uhp,avg is present (after 100 half cycles), a new steady state condition is measurement is taken. If any value falls outside the tolerance band for the 100 half periods, then this new value is used as the starting point for the steady state condition, until a period of 100 consecutive half cycles fall within the tolerance band of 0.2%.
|Table C.1 – Test Specification for dc – dmax – td(t)|
|PPA5511 Verification : td(t) = 500ms|
|Table C.2 – Test Specification for dc – dmax – td(t)|
|PPA5511 Verification : td(t) = 600ms|