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Dips and Variations Test
Electrical and electronic equipment may be affected by voltage dips, short
interruptions or voltage variations of power supply.
Voltage dips and short interruptions are caused by faults in the network, in
installations or by a sudden large change of load. In certain cases, two or more
consecutive dips or interruptions may occur. Voltage variations are caused by the
continuously varying loads connected to the network.
These phenomena are random in nature and can be characterized in terms of the deviation
from the rated voltage and duration. Voltage dips and short interruptions are not always
abrupt, because of the reaction time of rotating machines and protection elements
connected to the power supply network. If large mains networks are disconnected (local
within a plant or wide area within a region) the voltage will only decrease gradually due
to the many rotating machines, which are connected to the mains networks. For a short
period, the rotating machines will operate as generators sending power into the network.
Some equipment is more sensitive to gradual variations in voltage than to abrupt change.
Most data-processing equipment has built-in power-fail detectors in order to protect and
save the data in internal memory so that after the mains voltage has been restored, the
equipment will start up in the correct way. Some power-fail detectors will not react
sufficiently fast on a gradual decrease of the mains voltage. Therefore, the d.c. voltage
to the power-fail detector is activated and data will be lost or distorted. When the mains
voltage is restored, the data-processing equipment will not be able to restart correctly
before it has been re-programmed.
Consequently, different types of tests are specified to simulate the effects of abrupt
change voltage, and, optionally, for the reasons explained above, a type test is specified
also for gradual voltage change. This test is to be used only for particular and justified
cases.
The EUT is tested for test levels of 30%, 60% and >95% below the rated voltage for
the equipment. The duration of the dips/interruptions are 10ms, 100ms and 5000ms
respectively. Five dips are performed for each test level at a rate of one dip per minute.
The changes in supply voltage occur at zero crossing of the voltage.
The voltages in these tests use the rated voltage for the equipment (UT) as
a basis for voltage test level specification.
Where the equipment has a rated voltage range the following shall apply:
 | If the voltage range does not exceed 20% of the lower voltage specified for the rated
voltage range, a single voltage from that range is specified as a basis for the test level
specification (UT). |
| In all other cases, the test procedure shall be applied for both the lower and upper
voltages declared in the voltage range. |
Voltage dips and short interruptions
The change between UT and the changed voltage is abrupt. The step can start
and stop at any phase angles on the mains voltage. The following test voltage levels (in %
UT) are used: 0%, 40% and 70%, corresponding to dips and interruptions of 100%,
60% and 30%.
The preferred test levels and durations are given below. A test level of 0% corresponds
to a total supply voltage interruption. In practice, a test voltage level from 0% to 20%
of the rated voltage may be considered as a total interruption.
Shorter durations in the table, in particular the half-cycle, should be tested to be
sure that the equipment under test (EUT) works in its intended performance.
Preferred test levels and durations for voltage dips and short interruptions
Test level
% UT |
Voltage dip and short
interruptions % UT |
Duration
(in period) |
0 |
100 |
0.5 *
1
5
10
25
50
x |
40 |
60 |
70 |
30 |
*
For 0.5 period, the test shall be made in positive and negative polarity, i.e. starting at
0° and 180° , respectively. |
| Notes: 1 One or more of the above test
levels and durations may be chosen.
2 If the EUT is tested for voltage dips of 100%, it is generally unnecessary to test
for other levels for the same durations. However, for some cases (safeguard systems or
electromechanical devices) it is not true. The product specification or product committee
shall give an indication of the applicability of this note.
3 "x" is an open duration. This duration can be given in the product
specification. Utilities in Europe have measured dips and short interruptions of duration
between ½ a period and 3000 periods, but durations less than 50 periods are most common.
4 Any duration may apply to any test level. |
Voltage variations (optional)
This test considers a defined transition between rated voltage UT and the
changed voltage.
Note – The voltage change takes place over a short period, and may occur
due to change of load or stored energy in local power networks.
The preferred duration of the voltage changes and the time for which the reduced
voltages are to be maintained are given in the table below. The rate of change of voltage
should be constant; however, the voltage may be stepped. The steps should be positioned at
zero crossing, and shall be not larger than 10% of UT. Steps under 1% of UT
are considered as constant rate of change of voltage.
Timing of short-term supply voltage variations
Voltage test level |
Time for decreasing voltage |
Time at reduced voltage |
Time for increasing voltage |
40% UT |
2 s ±
20% |
1 s ±
20% |
2 s ±
20% |
0% UT |
2 s ±
20% |
1 s ±
20% |
2 s ±
20% |
| |
X |
X |
X |
| Note – X represents an open set of
durations and can be given in the product specification. |
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