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Test circuit details

A.1. Test generator peak inrush current drive capability

The circuit for measuring generator peak inrush current drive capability is shown in figure Al. Use of the bridge rectifier makes it unnecessary to change rectifier polarity for tests at 270⁰ versus 90⁰. The rectifier half-cycle mains current rating should be at least twice the generator's inrush current drive capability to provide a suitable operating safety factor.

The 1700 F electrolytic capacitor shall have a tolerance of  20%. It shall have a voltage rating preferably 15%  20% in excess of the nominal peak voltage of the mains e.g. 400 V for 220 V  240 V mains. It shall also be able to accommodate peak inrush current up to at least twice the generator’s inrush current drive capability, to provide an adequate operating safety factor. The capacitor shall have the lowest possible equivalent series resistance (ESR) at both 100 Hz and 20 kHz, not exceeding 0.1  at either frequency.

Since the test shall be performed with the 1700 F capacitor discharged, a resistor shall be connected in parallel with it and several RC time constants must be allowed between tests. With a 10000  resistor, the RC time constant is 17s, so that a wait of 1.5 min to 2 min should be used between inrush drive capability tests. Resistors as low as 100  may be used when shorter wait times are desired.

The current probe shall be able to accommodate the full generator peak inrush current drive for one-quarter cycle without saturation.

Tests shall be run by switching the generator output from 0% to 100% at mains phasings of both 90⁰ and 270⁰, to ensure sufficient peak inrush current drive capability for both polarities.

A.2. EUT peak inrush current requirement

When a generator peak inrush current drive capability meets the specified requirement (e.g., at least 500 A for a 220 V  240 V mains), it is not necessary to measure the EUT peak inrush current requirement.

However, a generator with less than this inrush current may be used for the test, if the inrush requirement of the EUT is less than the inrush drive capability of the generator. The circuit of figure A.2 shows an example of how to measure the peak inrush current of an EUT to determine if it is less than the inrush drive capability of a low-inrush drive capa­bility generator.

The circuit uses the same current transformer as the circuit of figure A.1. Four peak inrush current tests are performed:

a) Power off for at least 5 min; measure peak inrush current when it is turned back on at 90⁰;

b) Repeat (a), at 270⁰;

c) Power on preferably for at least one minute; off for 5 s; then measure peak inrush current when it is turned back on again at 90⁰;

d) Repeat (c), at 270⁰.

In order to be able to use a low-inrush drive current capability generator to test a particular EUT, that EUT’s measured inrush current shall be less than 70% of the measured inrush current drive capability of the generator.

G is the voltage interrupt generator, switched on at 90⁰ and 270⁰;

T is the current probe, with monitoring output to oscilloscope;

B is the rectifier bridge;

R is the bleeder resistor, not over 10000  or less than 100 ;

C is the 1700 F  20% electrolytic capacitor.

Figure A.1: Circuit for determining the inrush current drive
capability of the short interruptions generator

Annex B

(Informative)

Guide for the selection of test levels

The test parameters, duration and depth, should be selected by considering the data given below.

Consideration of the consequences of failure (including modes of potential failure and the action necessary to restore operation) should be borne in mind in selecting these parameters.

The following data is an extract from a UNIPEDE study [1].

This study was conducted with the purpose of providing customers and manufacturers with adequate information an the relative rate of occurrence, duration/depth of voltage dips and short interruptions, according to the definition of voltage dips issued from IEC 1000-2-2.

The study was confined to disturbances caused by faults or switching operations in the public supply systems.

Table B.1

Depth %	Duration
	10 ms to < 100 ms	100 ms to <500 ms	500 ms to < 1s	1 s to < 3s
10 to < 30	61	66	12	6
30 to < 60	8	36	4	1
60 to < 100	2	17	3	2
100	0	12	24	5
	Number of disturbances/annum

Reference document

[1] International Union of Producers and Distributors of Electrical Energy (UNIPEDE), 1991, No 50.02.

Annex C

(Informative)

Test instrumentation

Examples of generators and test set-ups.

Figures C.1a and C.1b show two possible test configurations for mains supply simulation. To show the behaviour of the EUT under certain conditions, interruptions and voltage variations are simulated by means of two transformers with variable output voltages.

Opening both switches simultaneously interrupts the power supply. The duration of the interruption can be preset. Voltage drops and rises are simulated by alternately closing switch 1 and switch 2. These two switches are never closed at the same time. It shall be possible to open and close the switches independently of the phase angle. Modern semiconductors such as power MOSFET and IGBT fulfil this requirement, whereas the thyristors and triacs used in the past can only open during zero crossing, and therefore do not simulate the real situation correctly.

The output voltage of the variable transformers can either be adjusted manually or auto­matically by means of a motor.

Wave-form generators and power amplifiers can be used instead of variable transformers and switches (see figure C.1(b)).

This configuration also allows testing of the EUT in the context of frequency variations and harmonics.

The first configuration (see figure C.1(a) can be simplified for partial tests. e.g. only one variable transformer is required for voltage variations (see figure C.2).

Figure C.1(a): Schematic of test instrumentation for voltage dips and short interruptions using variable transformers and switches




Figure C.1(b): Schematic of test instrumentation for voltage dips, short interruptions and variations using power amplifier

Figure C.2: Schematic of simplified test instrumentation for voltage variations

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