12
Electrical
news
Coming to
grips with the
safe use of
HV gloves
The Victorian High Voltage Customers
Committee advised Energy Safe Victoria that
there were safety concerns about the use
of high voltage rubber gloves with leather
outer-gloves, which are commonly used for
mechanical protection during HV switching.
The issue was risk of electric shock or
flashover related to the distance between the cuffs
of the HV inner rubber glove and the cuff of the
leather protector glove.
Optec, a specialist HV training company,
arranged testing to be carried out at the Silcar
offices in Moe. Testing was designed to investigate
whether there is a risk of electric shock when the
HV gloves are used. To understand the results
there is a requirement to understand the
test performed.
The gloves were tested in water with leather
outer-gloves fitted. It was found that with leather
outer-gloves fitted, depending on the distance
between the cuff of the leather glove and the cuff
of the rubber glove, a flash over or leakage could
occur if the over-glove reduces the clearance
between the two cuffs more than the water does.
The test results showed that the glove can fail
due to two possibilities:
1/ he glove insulation between the two water
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bodies breaks down. This tests the integrity
of the glove’s operational surface.
2/ he surface area above the water line leaks
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current between the electrodes or flashes over.
As the leather over-gloves absorb water it
should not greatly change the result of the first test
as it will conduct just as the water would. However,
the second test checking the flashover would be
affected by the leather over-gloves and, depending
on the distance between the cuff of the leather glove
and cuff of the rubber glove, a flash over or leakage
will occur if the over-glove reduces the clearance
between the two cuffs more than the water does.
After further research, the only standard that
specified a distance that should be maintained
between the cuff of the leather outer-glove and
the cuff of the rubber glove is ASTM F496, an
American standard.
ESV thanks Alan Harlow, National Operation
Manager at OPTEC, for the information.
Suitable: Sufficient distance shown between
leather outer-glove and rubber glove underneath.
Not suitable: There’s insufficient distance between
the cuffs of both gloves.
Maximum use
voltage AC/DC
Glove class
Minimum distance between protectors
and rubber gloves
1000/1500
0
½ inch
13mm
7500/11,250
1
1 inch
25mm
17,000/25,500
2
2 inch
51mm
26,500/39,750
3
3 inch
76mm
36,00/54,000
4
4 inch
102mm
Advertorial
Increased safety for PV systems with
integrated DC isolators
DC isolators in PV systems are imperative to
ensure work being carried out on a PV system/
inverter is safe as they protect installers and PV
system owners from dangerous high voltages.
External isolators are generally a safe option,
however there have been cases in the past when
external isolators have created additional hazards
due to wrong sizing or incorrect installation.
It is essential that the DC isolators are
appropriately sized, compliant and installed
correctly. These potential points of failure are
eliminated when using integrated isolators.
It must also be ensured that integrated
isolators are safe. In 2012, the revision of
AS/NZS 5033 was updated to make it possible for
isolators to be integrated by inverter manufacturers
given that they met certain requirements.
Summed up, the requirements for integrated
isolators as per AS/NZS 5033:2012 are as follows:
»» DC switch is of utilisation category DC 21B
(see chapter 4.3.5.1)
»» DC switch disconnector is certified to
IEC 60947 (see chapter 4.3.5.2)
»» DC switch disconnector is not polarity
sensitive (see chapter 4.3.5.2)
»» DC switch disconnector is able to interrupt
full load and the maximum fault currents
from the PV array attached to the inverter
(see chapter 4.3.5.2)
»» DC switch disconnector interrupts all live
conductors simultaneously (see chapter 4.3.5.2)
»» DC switch disconnector isolates the
inverter from all poles of the array such that
maintenance of the inverter is possible without
risk of electrical hazards (see chapter 4.4.1.2)
»» The DC switch disconnector is interlocked
so that the inverter can only be removed or
connected when the switch is in the open
position (see chapter 4.4.1.2).
New inverters such as the Fronius Galvo
and Fronius Symo (launched in 2013 and 2014
respectively) have been specifically designed
with integrated DC isolators that comply with
AS/NZS 5033:2012.
The integrated DC isolators featured in the
Fronius Galvo and Fronius Symo are tested to
AS 4777:2005 Part 2 and 3 together with the
inverter, sized by the manufacturer and equipped
with a mechanical interlock (to ensure isolation
prior to installation or service).
T