1. Ph¹m vi 9 Tµi liÖu tham chiÕu chuÈn

Testing and measurement techniques

1. Scope

The standard applies to electrical and electronic equipment having a rated input current not exceeding 16 A per phase.

It does not apply to electrical and electronic equipment for connection to DC networks or 400 Hz AC networks. Tests for these networks will be covered by other technical standards.

The object of this standard is to establish a common reference for evaluating the immunity of electrical and electronic equipment when subjected to voltage dips. short interruptions, and voltage variations.

2. Normative references

1. 
   IEV 50(161):1990 "International Electrotechnical Vocabulary (IEV) - Chapter 161: Electromagnetic compatibility";
   
2. 
   IEC 68-1:1988 "Environmental testing - Part 1: General and guidance";
   
3. 
   IEC 1000-2-1:1990 "Electromagnetic compatibility (EMC) - Part 2: Environment - Section 1: Description of the environment - Electromagnetic environment for low-frequency conducted disturbances and signalling in public power supply systems";
   
4. 
   IEC 1000-2-2:1990 "Electromagnetic compatibility (EMC) - Part 2: Environment - Section 2: Compatibility levels for low-frequency conducted disturbances and signalling in public power supply systems";
   
5. 
   IEC 1000-4-1:1992 "Electromagnetic compatibility (EMC) - Part 4: Testing and measurement techniques - Section 2: Overview of immunity tests - Basic EMC publication".
   

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 the 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 DC voltage to the integrated circuits will decrease to a level below the minimum operating voltage before 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 in this standard 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, under the responsibility of product specification or product committees.

It is the responsibility of the product committees to establish which phenomena among the ones considered in this standard are relevant and to decide on the applicability of the test.

4. Definitions

For the purpose of this standard, the following definitions apply.

Standard giving general and fundamental conditions or rules for the achievement of EMC, which are related or applicable to all products and systems, and serve as reference documents for product committees.

The ability of a device, equipment or system to perform without degradation in the presence of an electromagnetic disturbance (IEV 161-01-20).

A sudden reduction of the voltage at a point in the electrical system, followed by voltage recovery after a short period of time, from half a cycle to a few seconds (IEV 161-08-10, modified).

The disappearance of the supply voltage for a period of time typically not exceeding 1 min. Short interruptions can be considered as voltage dips with 100% amplitude (See also 8.1, IEC 1000-2-1).

A gradual change of the supply voltage to a higher or lower value than the rated voltage. The duration of the change can be short or long with regard to the period.

The termination of the ability of an equipment to carry out intended functions or the execution of unintended functions by the equipment.

5. Test levels

The voltages in this standard use the rated voltage for the equipment (U_T) 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 may be specified as a basis for test level specification (U_T);

- In all other cases, the test procedure shall be applied for both the lower and upper voltages declared in the voltage range:

- Guidance for the selection of test levels and durations is given in annex B.

The change between U_T 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 % U_T) are used: 0%, 40% and 70% corresponding to dips and interruptions of 100%, 60% and 30%.

The preferred test levels and durations are given in table 1, and an example is shown in figure 1. The levels and durations shall be given in the product specification. 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.

This test considers a defined transition between rated voltage U_T and the changed voltage.

The preferred duration of the voltage changes and the time for which the reduced voltages are to be maintained are given in table 2. The rate of change of voltage should be constant; however, the voltage may be stepped. The steps should be positioned at zero crossings, and shall be not larger than 10% of U_T. Steps under 1% of U_T are considered as constant rate of change of voltage.

6. Test instrumentation

The following features are common to the generator for voltage dips, short interruptions and voltage variations, except as indicated.

Examples of generators are given in annex C.

The generator shall have provision to prevent the emission of heavy disturbances which, if injected in the power supply network, may influence the test results.

Specifications

The output impedance of the test voltage generator must be low even during the transition.

In order to compare the test results obtained from different test generators, the generator characteristics shall be verified according to the following:

- The 100%, 70% and 40% r.m.s. output voltages of the generator shall conform to those percentages of the selected operating voltage: 230 V, 120 V, etc.;

- The r.m.s. values of all three voltages shall be measured at no toad, and shall be maintained within a specified percentage of their nominal values;

- Load regulation shall be verified at each of the three outputs, and shall not exceed 5% for 16 A loading at 100%, and specified percentages for 23 A loading at 70% and for 40 A loading at 40%;

- Tests at 70% and 40% need not exceed 5 s in duration.

If it is necessary to verify the peak inrush drive current capability, the generator shall be switched from 0% to 100% of full output, when driving a load consisting of an uncharged capacitor whose value is 1700 F in series with a suitable rectifier. The test shall be carried out at phase angles of both 90⁰ and 270⁰. The circuit required to measure gener­ator inrush current drive capability is given in A.1.

When it is believed that a generator with less than the specified standard generator peak inrush current may be used because the EUT may draw less than the specified standard generator peak inrush current (e.g., 500 A for 220 V  240 V mains), this shall first be confirmed by measuring the EUT peak inrush current. When power is applied from the test generator, measured EUT peak inrush current shall be less than 70% of the peak current drive capability of the generator, as already verified according to annex A. The actual EUT inrush current shall be measured both from a cold start and after a 5s turn-off, using the procedure of annex B.

Generator switching characteristics shall be measured with a 100  load of suitable power dissipation rating.

Rise and fall time, as well as overshoot and undershoot, shall be verified for switching at both 90⁰ and 270⁰, from 0% to 100%, 100% to 70%, 100% to 40%, and 100% to 0%.

Phase angle accuracy shall be verified for switching from 0% to 100% and 100% to 0%, at nine phase angles from 0 to 360⁰ in 45⁰ increments. It shall also be verified for switchi­ng from 100% to 70% and 70% to 100%, as well as from 100% to 40% and 40% to 100%, at 90⁰ and 180⁰.

The voltage generators shall be recalibrated at defined time periods in accordance with a recognized quality assurance system.

The frequency of the test voltage must be within  2% of rated frequency.

7. Test set-up

The test shall be performed with the EUT connected to the test generator with the shortest power supply cable as specified by the EUT manufacturer. It no cable length is specified, it shall be the shortest possible length suitable to the application of the EUT.

The test set-up for the two types of phenomena described in this standard are:

- Voltage dips and short interruptions:

- Voltage variations with gradual transition between the rated voltage and the changed voltage.

Figure C.1(a) shows a schematic for the generation of voltage dips, short interruptions and voltage variations with gradual transition between rated and changed voltage using a generator with internal switching, and figure C.l(b) using a generator and a power amplifier.

Figure C.2 shows a schematic only for the generation of voltage variations with gradual transition between rated and changed voltage using variable transformers.

Both tests may be implemented with these set-ups.

Tests on the three-phase EUT are accomplished by using three sets of equipment mutu­ally synchronized.

Examples of test set-ups are given in annex C.

8. Test procedures

Before starting the test of a given equipment, a test plan shall be prepared.

It is recommended that the test plan shall comprise the following items:

- The type designation of the EUT;

- Information on possible connections (plugs, terminals, etc.) and correspon-ding cables, and peripherals;

- Input power port of equipment to be tested;

- Representative operational modes of the EUT for the test:

- Performance criteria used and defined in the technical specifications;

- Operational mode(s) of equipment:

- Description of the test set-up.

If the actual operating signal sources are not available to the EUT they may be simulated.

For each test any degradation of performance shall be recorded. The monitoring equip­ment should be capable of displaying the status of the operational mode of the EUT during and after the tests. After each group at tests a full functional check shall be performed.

The tests shall be carried out in standard climatic conditions in accordance with IEC 68-1:

- Temperature: 15 ⁰C  35 ⁰C;

- Relative humidity: 25%  75%;

- Barometric pressure: 86 kPa  106 kPa (860 mbar  1060 mbar).

Note: Any other value may be given in the product specifications.

8.1.2. Electromagnetic conditions

The electromagnetic conditions of the laboratory shall be such as to guarantee the correct operation of the EUT in order not to influence the test results.

During the tests the main voltage for testing is monitored within accuracy at 2%. The zero crossing control of the generators must have an accuracy of 10⁰.

The EUT shall be tested for each selected combination of test level and duration with a sequence of three dips/interruptions with intervals of 10 s minimum (between each test event). Each representative mode of operation shall be tested.

Abrupt changes in supply voltage shall occur at zero crossings of the voltage, and at additional angles considered critical by product committees or individual product spec­ifications preferably selected from 45⁰, 90⁰, 135⁰, 180⁰, 225⁰, 270⁰ and 315⁰ on each phase.

For three-phase systems, phase-by-phase test is preferred. In certain cases e.g. three-phase meters and three-phase power-supply equipment, all the three phases must be simultaneously tested. In the case of simultaneous application at dips or interruptions on all the three phases, the zero crossing condition at the voltage, as given in 6.1, will be fulfilled only on one phase.

The EUT is tested to each of the specified voltage variations, three times at 10 s interval or the most representative modes of operations.

9. Test results and test report

This clause gives a guide for the evaluation of the test results and for the test report related to this standard.

The variety and diversity of equipment and systems to be tested make the task of establishing the effects of voltage dips, short interruptions and voltage variations on equipment and systems difficult.

The test results shall be classified on the basis of the operating conditions and functional specifications of the equipment under test, as in the following, unless different speci­fications are given by product committees or product specifications.

a) Normal performance within the specification limits.

b) Temporary degradation or loss of function or performance which is self-recoverable.

c) Temporary degradation or loss of function or performance which requires operator intervention or system reset.

d) Degradation or loss of function which is not recoverable due to damage of equip­ment (components) or software, or loss of data.

EUT shall not become dangerous or unsafe as a result at the application of the test defined in this standard.

In case of acceptance tests, the test programme and the interpretation of the results shall be described in the specific product standard.

As a general rule, the test result is positive if the equipment shows its immunity, for all the period of application of the test, and at the end of the tests the EUT fulfils the functional requirements established in the technical specification.

The technical specification may define effects on the EUT, that may be considered not relevant and therefore acceptable.

For these conditions it shall be verified that the equipment is able to recover its operative capabilities by itself at the end of application of the test levels and durations; therefore, the time interval during which the equipment has lost its full functional capabilities shall be recorded. These verifications are binding for the definitive evaluation of the test result.

The test report shall include the test conditions and the test results.

100% U_T

40% U_T

0% U_T

t (s)

(Normative)