Rapid Voltage Changes Defintion and Minimum Requirements

Transcription

1 Rapid Voltage Changes Defintion and Minimum Requirements Karstein Brekke Norwegian Water Resources and Energy Directorate, Norway

2 Content Introduction Existing standards Results from a research project Norwegian Regulation on RVC Conclusion

3 Rapid Voltage Changes Normally categorising rapid voltage changes not exceeding ± 10% of the nominal or declared voltage level But how rapid is a rapid voltage change? Voltage [V] Voltage [V] Voltage [V] V dt dv 207 V Time [s] 253 V Umax = Usteady-state 207 V Time [s] Usteady-state Umax Time [s]

4 RVC Definition in standards EN rapid voltage change single rapid variation of the r.m.s. value of a voltage between two consecutive levels which are sustained for definite but unspecified durations (for more information see EN ) IEC Rapid voltage changes NOTE Clause A.4 provides some information on the significant parameters necessary to characterize a rapid voltage change.

5 RVC Definition in standards U(t) IEC Defines: ΔU(t) ΔU max ΔU steady-state U(t) U steady-state U max 10 ms t1 t2 t3 t

6 RVC in the public distribution network One of the most common reasons for customer complaints on power quality in Norway is caused by rapid voltage changes (RVC) The customers simply get annoyed by the light intensity changing often Most common in rural areas with low short circuit power

7 Motivation For setting requirements for RVC Limiting annoying visible changes in the light due to single RVCs. For generating a new research project Setting requirements require that a unique definition of RVC exists in order to ensure reliable measurements.

8 RVC Required details in definition In order to ensure reliable measurements of rapid voltage changes, the following elements must be defined: 1. The steadiness of the steady state conditions; 2. The minimum duration of a steady state condition (between two voltage change characteristics); 3. The minimum rate of change (dv/dt) to consider; 4. The steady state voltage change; 5. The maximum voltage change during a voltage change characteristic; 6. Which voltage level to relate the change to (i.e. the voltage before the change or the nominal voltage); 7. The maximum duration of a rapid voltage change.

9 RVC Required details in definition In order to ensure reliable measurements of rapid voltage changes, the following elements must be defined: 1. The steadiness of the steady state conditions; 2. The What minimum elements duration are of a steady defined state in condition standards? (between two voltage change characteristics); 3. The minimum rate of change (dv/dt) to consider; 4. The steady state voltage change; 5. The maximum voltage change during a voltage change characteristic; 6. Which voltage level to relate the change to (i.e. the voltage before the change or the nominal voltage); 7. The maximum duration of a rapid voltage change.

10 RVC Required details in definition In order to ensure reliable measurements of rapid voltage changes, the following elements must be defined: 1. The steadiness of the steady state conditions; 2. The What minimum elements duration are of a steady defined state in condition standards? (between two voltage change characteristics); 3. The IEC minimum : rate of change (1),(dv/dt) 2, 4, to 5 consider; og The steady state voltage change; 5. The IEC maximum : voltage change nonduring a voltage change characteristic; 6. Which voltage level to relate the change to (i.e. EN the 50160: voltage before diffuse the change or the nominal voltage); 7. The maximum duration of a rapid voltage change. In the Norwegian Quality of Supply Regulation: (1), 2, 3, 4, 5 og 6

11 RVC Research Project

12 The RVC tests in Norway The total test carried out with 96 test persons Two main groups of age Young people (16 to 26 years old) Elderly people (65 to 80 years old) Two types of tests What is visible? What is acceptable?

13 The RVC tests in Norway Tests with 60 W incandescent lamps only No, or almost no daylight in the test rooms Mainly RVC from 0,5 % to 5 % Both motor start-up RVC, ramp RVC and rectangular RVC

14 Rectangular Visibility depends on voltage change Ramp Visibility depends on voltage change and duration of the change Motor start Visibility depends on the initial peak voltage change, the duration of voltage recovery to the new voltage level and the voltage change from the previous to the new voltage level

15 Minimum duration of a steady state condition Perception of two separate RVCs RVC [%] Time between RVC [s] 0, ,5 1 2 Perceived as 2 RVCs 0,39 0,84 0,91 0,42 0,82 0,97

16 The minimum rate of change (dv/dt) Visibility of ramp RVCs Magnitude of RVC 4,0 % 4,0 % 4,0 % 4,0 % 4,0 % 5,0 % 5,0 % 5,0 % 5,0 % 5,0 % dv/dt change pr sec. 0,2 V/s 0,5 V/s 1 V/s 2 V/s 5 V/s 0,2 V/s 0,5 V/s 1 V/s 2 V/s 5 V/s Average visibility 0,05 0,18 0,56 0,81 0,95 0,05 0,22 0,61 0,95 1,00

17 Steadiness of the steady state condition From the previous two slides: dv/dt equal to or less than 0.5 % of the nominal or declared voltage level per sec. 0.5 % of 230V per sec equals 1.15 V/s In a steady state condition for at least 1 sec. Practical measurement requires also a limit for max/min variations in a steady state conditions

18 Maximum duration for RVCs Will indirectly be given by: The def for the steadiness of the steady state voltage The minimum duration of a steady state condition The minimum rate of change (dv/dt)

19 Visibility of rectangular RVCs Magnitude of RVC 0,5 % 1,0 % 2,0 % 3,0 % 4,0 % 5,0 % 6,0 % 7,0 % Average visibility 0,04 0,21 0,67 0,84 0,95 1,00 1,00 1,00 Standard deviation 0,18 0,22 0,21 0,11 0,11 0,00 0,00 0,00

20 Visibility of motor starts Initial voltage drop, ΔU max 2,0 % 2,0 % 3,0 % 3,0 % 4,0 % 4,0 % 5,0 % 5,0 % 6,0 % 6,0 % Speed up time in seconds 0,5 s 1,5 s 0,5 s 1,5 s 0,5 s 1,5 s 0,5 s 1,5 s 0,5 s 1,5 s Average visibility 0,21 0,32 0,35 0,54 0,52 0,71 0,68 0,86 0,79 0,98

21 Norwegian regulation on RVC A RMS voltage change within ± 10% of agreed voltage level, which occur more rapid than 0.5 % of the agreed voltage level per second. Rapid voltage changes are expressed as the steady state and the maximum voltage changes given respectively by: ΔU steadystate % U steadystate = 100% U agreed ΔU max % U max = U agreed 100% where ΔU steadystate is the steady state voltage change due to a voltage change characteristic, ΔU max is the maximum voltage difference during a voltage change characteristic, and U agreed is the agreed voltage level (i.e. the nominal or the declared).

22 ΔU steadystate % U steadystate = 100% U agreed Prague, 8-11 June 2009 Norwegian regulation on RVC Network companies shall ensure that rapid voltage changes do not exceed the following limits in points of connection with the respective nominal voltage value, UN [kv], for the respective frequency: RVCs ΔU steadystate 3 % ΔU max 5 % Maximum frequency pr 24 hours period 0,23 kv U N 35 kv kv< U N Rapid voltage changes due to earth faults or short circuits in the network, inrush current from transformers, back feeding after faults and necessary operation couplings to uphold a satisfactory quality of supply as a whole, are not embraced by the limits in the first paragraph.

23 Conclusion A precise and unambiguous definition is necessary for any voltage disturbance in order to achieve reliable measurements There exist yet no unique definition for RVCs in international standards, though the term exist A Norwegian research project contains results useful for making a more unique definition for RVCs for the visibility of RVCs as basis for limits The Norwegian quality regulation contains minimum requirements for RVCs and a more detailed definition in order to better ensure reliable measurements