Title
LOVATO Electric switch disconnectors for photovoltaic applications
Abstract
The latest offer of LOVATO Electric to meet recent requirements of the photovoltaic industry: switch disconnectors to use
on the DC side of installations due to the presence of direct-current energy, the disconnection of which requires high
performance products to ensure the necessary isolation.
Article
In recent years, the photovoltaic business has grown rapidly and its expansion, under the drive to find sources of
renewable and eco-friendly energy, is relentless.
LOVATO Electric thereby decided to extend its product offering to photovoltaics in view of this growth and its awareness
of market trends, by introducing specific solutions to issues related to DC control.
In particular, the disconnection and isolation of direct current is a key factor for safety especially during service and
maintenance work. Semiconductor cells which compose solar panels converts solar radiation into electricity so when
exposed to sunlight, they generate a potential difference and hence a direct current. This can reach very high levels of
voltage output when multiple panels are connected in series to form strings or when multiple strings are connected to
create photovoltaic array installations.
Up to now, IEC standards have not provided indications regarding the DC voltage values of photovoltaic systems;
consequently, the voltages in these systems can greatly vary depending on the configuration of the panels installed and
connected together.
For low power systems such as residential facilities, it is common to find voltage values that can reach 600VDC
maximum.
For medium power systems, the voltage level is normally between 800 and 1000VDC in IEC countries, while voltage
limits in North America are up to 600VDC only in compliance with NEC standards.
As mentioned above, it is clear installation drawbacks can arise upstream and downstream of the inverter, used to
convert DC voltage of the PV installation in to AC for direct use to supply island or stand-alone systems or common
electric machines or feeding power into electricity grid. These can greatly vary one from the other and result to be
particularly critical, especially upstream where there often are high DC voltage values.
On the direct-current side, it is therefore necessary to use dedicated switch disconnectors, capable of interrupting
currents and ensure the required isolation for instance when the system needs to be in safety conditions during
maintenance..
The disconnection and isolation of direct current is actually more difficult than for alternating current. While the latter is
the natural zero crossing of current through every half-wave during which there is arc extinction while the circuit is
opening, this step does not take place with direct current and thus involves far more difficult arc extinction.
In principle, the factors contributing to make it difficult to break and isolate the current are arc temperature, arc
conductivity, load inductance and voltage upstream of the switch disconnector.
In order to shorten the time for current isolation, it is necessary that the switch disconnector breaking is done with as
much clearance distance possible between its contacts so the path for electric arc is longer.
To avoid inefficiency, maintenance on each string must be carried out without having to completely stop the
production of energy, so it is useful that each string be isolated separately from the others using a DC switch
disconnector mounted on the string combiner box.
In addition, each string should be protected by a DC fuse to ensure short circuit protection if the total number of strings
is equal to or greater than three.
If combiner boxes are installed more than 30 metres away from the AC/DC inverter, it is also recommended to use
appropriate DC surge protection devices.
LOVATO Electric product offering for DC side of photovoltaic systems
Photovoltaic modules
1° PV string combiner box
GA…D switch disconnector
GE…DT4 switch disconnector
Photovoltaic modules
2° PV string combiner box
Main control panel
GA…D switch disconnector
GE…DT4 switch disconnector
GA…D switch disconnector
GE…DT4 switch disconnector
Photovoltaic modules
3° PV string combiner box
GA…D switch disconnector
GE…DT4 switch disconnector
LOVATO Electric product offering for AC side system
Power analyzer
GA…A - C switch disconnector
GE… switch disconnector
Energy meter
LOVATO Electric introduced on the market special switch-disconnectors for the DC side which serve to isolate the PV
array so the maintenance of the inverter can be done in complete safety.
The new GA ... D switch disconnectors include direct operating and door coupling facility to meet installation
requirements according to the number of strings connected in parallel.
Owing to their significant technical features along with size flexibility and modularity, the new switch disconnectors are
capable of disconnecting current values up to 40A at 1000VDC and the configuration can be customised on the basis of
the system power rating.
They can be used both as switch disconnector for protecting a combiner box, where various strings are connected to in
parallel, and as main switch disconnector for isolating the DC side of the photovoltaic system.
Technical characteristics
GA...D switch disconnectors are available in two frame sizes: the first with maximum operational current (Ie) up to 25A
and the second up to 32A and 40A and rated operational voltage (Ue) up to 1000VDC in DC21-B category in an 8-pole
configuration.
The modular 45mm design and the DIN rail or screw fixing make the GA ... D type suitable for use in modular type
control panel and insulated enclosures. The switch disconnector is sold in three-pole configuration with direct operating
control. Door coupling can be obtained by purchasing the shaft extension and door-mount handle. Four-pole switch
disconnectors can be easily made by using the side snap-on fourth pole.
The modular structure of GA...D types permits to couple two switch disconnectors of the same rating together with the
mechanical interlock mechanism mounted on the front and obtain six or eight-pole configuration. Two auxiliary
1NO+1NC contact blocks can be fitted to provide for signalling and used in conjunction with the AC/DC inverter.
Compact size and four, six and eight-pole configurations connected in series, make the
GA...D switch disconnectors suitable to switch, disconnect and isolate interrupting currents up to 40A at 1000VDC and
can consequently be used as protection switch disconnector in the combiner boxes (upstream of the main protection
switchboard installed before AC/DC inverter).
The modularity of these devices permits to customise the configuration based on the system power and always
provides the most appropriate solution,
Lovato Electric GE...DT4 switch disconnectors are available in four frame sizes and six electrical ratings with maximum
current (Ie), respectively of 30, 200, 250, 270, 500 and 850A at an operational voltage (Ue) up to 1000VDC in DC21-B
category. The switch disconnector is provided in 4-pole single-structure configuration. Based on the user’s needs, a
direct operating control is obtained by purchasing a direct-control handle or a door-coupling version by purchasing a
shaft extension and a relative door-mount handle. These types can be fitted with an auxiliary 1NO +1NC changeover
contact to use with the AC/DC inverter.
The larger frame size and the capability to break higher currents up to 1000VDC up to 850A make these switch
disconnectors particularly suitable for use in the main switchboard on the DC side.
The utilisation categories used for switch disconnectors are defined by IEC/EN 60947-3 standards. Lovato Electric
declares operational characteristics per DC21-B duty for the switch disconnectors used in photovoltaic applications since
the PV inverters are considered non-inductive loads. Possible overload conditions in PV applications are modest and the
ON / OFF operations of the switch disconnector are not frequent.
Range
The range of GA ... D switch disconnectors includes three types (GA040D, GA080D, GA125D), the fourth pole add-on
(GAX42040D, GAX42080D, GAX42125D) and accessories for 6 / 8 pole configuration (GAX6000 for the small type
GA040D and GAX6001 for the other two types GA080D and GA125D).
The GE…DT4 range includes seven four-pole switch disconnectors:
GE0160DT4, GE0160DT4P, GE0250DT4, GE0315DT4, GE0630DT4, GE0800DT4, GE1250DT4.
GA040D + GAX2040D
GA080D + GAX42080D
GAX6000
GE0160DT4
GE0160 DT4P
GA125D + GAX42125D
GAX6001
GE0250DT4
GE0315DT4
GE1250DT4
GE0630DT4
GE0800DT4
Series pole connection
To break and disconnect high current and voltage values, generated on the DC side of photovoltaic installations owing to
the serial connection of many modules or strings, LOVATO Electric offers a solution with three, four, six and eight-pole
configuration of switch disconnectors. By connecting the poles in series and dividing the current load to disconnect
among the power poles, the disconnection is a simple operation.
Examples of various applications
Summary table of maximum operational current in DC21-B utilisation category for
LOVATO Electric GA…D switch disconnectors
Maximum operational current in DC21-B
Poles in
Voltage Ue
GA040D GA080D GA125D
series
VDC
n°
A
A
A
48
3
40
80
125
110
3
35
70
120
220
3
32
40
95
500
3
12
15
20
400
440
500
600
700
750
800
4
4
4
4
4
4
4
35
32
32
20
15
15
15
40
40
40
30
18
18
18
64
64
56
40
20
20
20
600
700
750
800
1000
6
6
6
6
6
35
30
25
25
10
45
35
35
35
20
50
40
40
40
25
700
750
800
1000
8
8
8
8
40
35
35
25
60
50
50
32
80
60
60
40
Summary table of maximum operational current in DC21-B utilisation category for
LOVATO Electric GE..DT4 switch disconnectors
Voltage
VDC
48
110
220
400
500
600
750
800
850
900
1000
Poles in
series
n°
4
4
4
4
4
4
4
4
4
4
4
Maximum operational current in DC21-B
GE0160
GE0160
GE0250
GE0315
GE0630
DT4
DT4P
DT4
DT4
DT4
A
A
A
A
A
160
160
250
315
630
160
160
250
315
630
160
160
250
315
630
150
150
250
315
630
150
150
250
315
630
150
150
250
315
500
80
80
250
290
400
70
70
250
280
350
45
45
240
270
320
40
40
220
260
300
30
30
200
250
270
GE0800
DT4
A
800
800
800
800
700
700
650
630
580
550
500
GE1250
DT4
A
1250
1250
1250
1250
1250
1250
1050
1000
940
870
850