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.

GA…D switch disconnectorGE…DT4 switch disconnector

GA…D switch disconnectorGE…DT4 switch disconnector

GA…D switch disconnectorGE…DT4 switch disconnector

GA…D switch disconnectorGE…DT4 switch disconnector

1° PV string combiner box

Main control panel

2° PV string combiner box

3° PV string combiner box Photovoltaic modules

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

LOVATO Electric product offering for AC side system

Photovoltaic modules

Photovoltaic modules

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 theGA...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,

GA…A - C switch disconnectorGE… switch disconnector Energy meter

Power analyzer

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.

GE0160DT4GE0160 DT4P

GE0250DT4GE0315DT4

GE0630DT4GE0800DT4

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.

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

GAX6001GAX6000

GA125D + GAX42125DGA080D + GAX42080DGA040D + GAX2040D

GE1250DT4

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 forLOVATO Electric GA…D switch disconnectors

Maximum operational current in DC21-B

Voltage Ue Poles in series GA040D GA080D GA125D

VDC n° A A A48 3 40 80 125110 3 35 70 120220 3 32 40 95500 3 12 15 20

400 4 35 40 64440 4 32 40 64500 4 32 40 56600 4 20 30 40700 4 15 18 20750 4 15 18 20800 4 15 18 20

600 6 35 45 50700 6 30 35 40750 6 25 35 40800 6 25 35 401000 6 10 20 25

700 8 40 60 80750 8 35 50 60800 8 35 50 601000 8 25 32 40

Summary table of maximum operational current in DC21-B utilisation category for LOVATO Electric GE..DT4 switch disconnectors

Maximum operational current in DC21-B

Voltage Poles in series

GE0160 DT4

GE0160 DT4P

GE0250 DT4

GE0315DT4

GE0630DT4

GE0800DT4

GE1250DT4

VDC n° A A A A A A A48 4 160 160 250 315 630 800 1250110 4 160 160 250 315 630 800 1250220 4 160 160 250 315 630 800 1250400 4 150 150 250 315 630 800 1250500 4 150 150 250 315 630 700 1250600 4 150 150 250 315 500 700 1250750 4 80 80 250 290 400 650 1050800 4 70 70 250 280 350 630 1000850 4 45 45 240 270 320 580 940900 4 40 40 220 260 300 550 8701000 4 30 30 200 250 270 500 850