Page 450 - Industrial Power Engineering and Applications Handbook

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(iii) Additional test requirements for outdoor HT Measurement of temperature of enclosure,
assemblies insulation and current-carrying parts
The following are a few additional test requirements for The thermocouples or RTDs should be located such as
an outdoor HT assembly, recommended by IEC 60694 to measure the hottest spot, even if this means drilling a
for rated voltages up to 100 kV.
hole in the current-carrying parts.
Wet test While an indoor type switchgear asscmbly
requires only a dry power frequency voltage with- Procedure
stand test, the outdoor type switchgear assembly also I The test may be conducted on a completed assembly
needs a wet test under wet conditions to check the of a switchgear or a controlgear or a part of it,
external insulation. For the test procedure refer to IEC whichever may be regarded as a complete section.
60060- 1. The purpose is to achieve a near-service condition.
Artificial pollution test The purpose of this test is to To do this in a multi-section switchgear or controlgear
provide information on the behaviour of the external assembly it is advisable to test at least three vertical
insulation while operating in pollutcd conditions. The sections joined together and measuring the temperature
test may be performed only if thought necessary, rise on the middle section. This is to restrict the extra
depending upon the degree of contamination at the heat dissipation, through the sides, except natural heat
place of installation. For the test procedure refer to transfer, and also to simulate the influence of heat
IEC 60060- I. transfer to this section through other sections.
Test results Any disruptive discharge or electrical 2 The test must be conducted at the rated* current, at a
breakdown during the application of high voltage should frequency with a tolerance of +2% and -5% of the
be considered as a dielectric failure. rated frequency and the voltage in a sinusoidal
waveform, as much as practicable. See also Section
14.3.4 Impulse voltage withstand test (for system 11.3.2. The test is carried out until the temperature
voltages 2.4 kV and above) reaches almost a stable state, i.e. when the variation
does not exceed 1°C per hour. To shorten the test
The impulse voltage is applied as shown in Tables 14.1 duration, the current may be enhanced during the initial
and 14.2 for series I1 or Table 13.2 for series I voltage period to reach a fast, stable state.
systems, with a full wave standard lightning impulse 3 Since it may not be practical to create the actual
1.2/50 p (Section 17.6.1) a front time equal to or less operating conditions at the place of testing, normal
than 1.2 ,LE, and the crest value equal to or more than the practice is to simulate these conditions on the following
rated full wave impulse withstand voltage. According to basis.
ANSI C-37/20C, three positive and three negative The heat generated by a current-carrying component
impulses must be applied without causing damage or or conductor is its watt loss and is expressed by I’R,
flashover. Should a flashover occur in only one or any where I is the current and R the resistance of the
group of three consecutive tests, three more tests are circuit under consideration. The watt loss of each
allowed to be conducted. If the equipment passes the current-carrying component installed in the test
second group of three consecutive tests, it should be assembly is estimated and added to arrive at the
considered as acceptable. The flashover which occurred approximate watt loss during the actual operation.
earlier may be considered as random and irrelevant. Based on this loss is calculated of the total heaters
required. These heaters are then suitably located in
14.3.5 Verification of temperature rise limits (or the test assembly to represent all the incoming and
rated continuous current capacity) outgoing feeders, their power cables and any other
current-carrying component.
The test must be carried out indoors, reasonably free
from draughts. Thermocouples should be used to measure Sources generating heat
the temperature, and the ambient temperature can be 1 Power circuits
measured by thermocouples or thermometers. Interrupting devices - switches, breakers, MCCBs,

Measurement of ambient temperafure
The ambient temperature should be measured during
the last quarter of the test by at least three thermometers
or thermocouples placed equally around the switchgear
assembly, at almost the centre level and at about 1 metre
from the body of the enclosure. The ambient temperature
to be considered must be the average of these readings
and should be within 10-40°C. To ensure that the
ambient temperature is unaffected by magnetic field,
alcohol thermometers must be used and not mercury
thermometers.