Transcript Solar Junction Boxes - GEESYS Technologies

GEESYS Technologies
SWITCHING AND PROTECTION
PHOTOVOLTAICS INSTALLATIONS
Introduction
Range
Applications
Bharathiraja.K
INTRODUCTION
Solar thermal energy
A technology for harnessing the solar energy for thermal energy. Water is heated by solar energy and is
commonly used for domestic solar hot water and heating
Solar photovoltaics energy
Sunlight is directly converted into electricity. The main applications of PV are
•
Grid tied systems Refers to solar electric systems that are capable of generating electricity to the
grid (or utility company). i.e. Solar farms, solar roofs.
• On-grid systems A system connected to the utility grid which utilises the grid for backup electricity
• Off-grid or stand alone systems A system not connected to a utility grid that utilises batteries to
store electricity, it is used in areas that are not connected to the electricity grid.
SOLAR PV. Grid-tied systems. Installation diagram
SOLAR PHOTOVOLTAICS. Grid-tied Systems. Components
Solar panels
A solar panel is composed of solar cells made up of semiconducting material which absorbs sunlight to
produce electricity. Common rates of voltage and current for a single panel are 24Vdc and 8 Amps
Combiner boxes
Since the voltage for a single panel is too low, several panels are connected in series to provide an
output voltage within the inverter’s working rates (500-750Vdc). A group of panels grouped in series is
called array. Depending on the power of the inverter and the number of arrays we will have now to
group several boxes in parallel in order to get higher currents.
A combiner box is composed of: Switch-Disconnector, protection against short circuits and, optionally,
surge arresters
Inverter
A device that converts direct current (DC) produced by solar modules to alternating current (AC) that is
used by most appliances
Metering and AC protection switchboard
Protection and measurement of the electrical energy both used and injected into the grind.
Transformer
A device that transfers the electrical energy before being injected into the grind
SOLAR PHOTOVOLTAICS. Combiner boxes. Components
Short-circuit protection
Protection against short-circuits upstream the fuse-holders
10x38 1000Vdc fuse-holders where arrays are directly
connected
900Vdc ultra-quick gR fuse-links specially indicated for solar
applications.
AC fuse-link breaking risk eliminated.
Switching
Safe disconnection by means of a 900Vdc Switch.Disconnector
Inverter isolation provided in OFF position
Over-voltage protection
Other features
Protection against over-voltages caused by lighting
Class II Surge Arresters
IP65 enclosure
Significant reduction in wiring and connection time
IP20 components
Protection against indirect contacts by means of a methacrylate cover.
SOLAR PHOTOVOLTAICS. Combiner boxes. Components
Monitoring system
Remote monitoring of the principal parameters of a solar plant in
addition to the standard Protection against short-circuits
upstream the fuse-holders
Components
1) DC switch
2) Surge Arrester
3) Fuse protection of the Positive pole
4) Monitoring Kit & Fuse protection of the Negative pole
- (VMU-M): Data logger
- (VMU-P): Environment measurement (cells
temperature,
air temperature, wind speed)
- (VMU-S): String control and fuse protection
Other features
- (VMU-O): Digital inputs and output for alarms or
inputs disabling
IP65 enclosure
Significant reduction in wiring and connection time
IP20 components
Protection against indirect contacts by means of a methacrylate cover
SOLAR PHOTOVOLTAICS. Combiner boxes. Types
Power splitting
Division in areas is recommended in order to keep producing in the rest of the installation and not
having a complete loss of production
Level 1 combiner boxes
Located under the panels structures, combine the arrays
coming from the solar panels. Output can go directly to the
inverter or, depending on the installation, several of these
boxes are re-combined in another combiner box in order to
get higher currents
Level 2 combiner boxes
They are often situated beside the inverter and re-combine
the arrays coming form the other primary boxes.
The pattern is the same as in the primary boxes but adapting
the components to the rated currents. The resulting output
comes up directly into the inverter
SOLAR PHOTOVOLTAICS. Combiner boxes. Selection
Features
•
Minimum number of arrays to be combined: 2 / Maximum: 36
•
Max. Rated Voltage: 900Vdc
• Max. Rated Current: 500Amps (Even higher depending on voltage)
• 10x38 Fuse-links 2…20Amps 900Vdc gR
• NH0 Fuse-links 32…160Amps 900Vdc gR
• Surge arresters. Class II.
• Knockouts and cable glands under request
• IP66 Polyester or IP65 metal enclosures
Selection details
1) Open circuit voltage (Voc)
2) Short-circuit current (Isc)
3) Arrays number
4) Type of protection (Positive&Negative poles, Negative pole)
5) Surge arresters (if included)
SOLAR PHOTOVOLTAICS. Grid connected systems.
Places where a switch-disconnector can be placed in a PV installation
* In the sub-combiner boxes afterwards the solar panel series up
* Just before the inverter (This is required by inspectors)
Why is necessary a Switch-Disconnector in a String-Box?
- Base holder is not a safe disconnection method in normal conditions
- Our switch is able to interrupt short-circuit conditions
- Having a switch in the combiner box the customer can interrupt on the spot in case he detects a
problem. If you only have a switch before the inverter you have to run to the inverter cabinet and
disconnect
-Having a switch in the combiner box which is close to the solar panels, you are confident in case that
you need to carry out maintenance labours that the circuit is open and operator can work safely
- At the time of closing the circuit for the first time it is not a good idea to do it by closing the fuse
holders, it is better to close the fuse holders without load and close the circuit with the switch. In case
of wrong connection of the arrays it is much safer for the operator to provoke it when operating the
switch than the fuse holder with the fingers.
SOLAR PHOTOVOLTAICS. Grid connected systems.
Fuse Selection
Fuses must be properly dimensioned or they won’t work
properly
i.e. For an Isc of 10Amps a fuse is commonly
overdimensionated a 25% percent. That’s 16Amps (not
30Amps as they say). This needs to be checked depending
on the Isc of the panels
In a combiner box, a fuse does not melt due to the Isc of the
own panel array, it melts due to the reverse currents of the
other arrays. Suppose that you have a short-circuit above
the upstream the fuse between a positive/negative of the
same array, you have here a non-voltage point and the other
arrays will tend to supply current to that point. The current
will be added and will try to pass through the fuse which is
going to melt (7x10Amps = 700Amps). This is represented in
the below diagram
SOLAR PHOTOVOLTAICS. Grid connected systems.
Switch-Disconnector versus MCCB’s
When a switch is required in the installation, an MCCB can be used as a switch but it is much more
expensive because it incorporates thermal and magnetic protections and require a maintenance
when short-circuits
A switch is required before the inverter to protect only the positive pole, but there is no point in
protecting the line with a fuse or MCCB thermal/magnetic protection right before the inverter to
protect the positive pole.
When you have a short circuit immediately upstream the MCCB/Switch+Fuse, it won’t be able to
interrupt because it does not detect it.
When you have the a short-circuit immediately downstream the MCCB/Switch+Fuse, it won’t be able
to interrupt because:
-Fuse option: Isc generated < I melting of the fuse
-MCCB option: Isc generated < I minimum release
In any case if we use a fuse/MCCB very adjusted in current the protection could release very often,
causing frequent stops and if the protection is overdimensionated it would never work
Conclusion: An MCCB is not necessary to protect the installations because the string box
fuses will do it. MCCB are expensive and require a maintenance in case of short-circuits.
When the customer wants to protect the positive pole, a combination of fuse+switch is more
effective and less expensive than a MCCB.
SOLAR PV Grid-tied Systems. Switch-Disconnector
Overview
Since a fuse-holders it is not a safe disconnection
method for PV installations, DC load break switches are
required . They are capable of withstand making and
breaking of circuits even in short-circuit conditions.
Also provides isolation to the inverter´s input and
maintenance labours can be done safely.
Each switch has four breaking contacts and bridginglinks must be used to connect in series two of them.
The size of the switch must be selected depending on
the voltage and the short-circuit current that the switch
must withstand. Five sizes are available
Accessories
Handle (Direct or panel handle)
Bridging links
Terminal protection
DIN rail mounting kit (Size 0)
Auxiliary contact
Size 00: 800Vdc 12,5Amps
Size 0: 900Vdc 40Amps
Size 1: 900Vdc 175Amps
Size 2: 900Vdc 200Amps
Size 3: 900Vdc 500Amps
Size 4: 900Vdc 650Amps
A switch must be selected according to the voltage and
current of the following table
SOLAR PHOTOVOLTAICS. Switch-Disconnector. Accessories
Handle (Required)
Direct or external door handle (includes metallic shaft that can be cut to the required depth enclosure)
Door handle satisfies IP65/NEMA-4 rating.
It is made of polyamide which confers a great heat/ultraviolet-resistant.
The replacement of our handle does not imply the replacement of the switch. It is very easy to replace
Bridging-links (Required)
Series up the poles is a requirement to withstand the full current/voltage stated by the switch.
Example: A single pole of a 250A switch withstands 175A/225Vdc, in order to work at 900Vdc we have to
series up the poles and increase the number of breaking of the DC circuit. 4P…900Vdc / 3P…675Vdc
Solar applications in the US involve only breaking positive connections because in installations where the
negative pole is grounded it is not necessary to break both negative and positive poles, it is enough with
breaking the positive one. In Europe these type of installation are not allowed and both positive and
negative poles must be switched. As per the sketches we are showing that we get the same result by
putting in series 2 positive + 2 negative, 3 positive + 1 negative or in your case 4 positive breaking. The
important thing is the total number of breaking that there are (adding positive + negative breaking) At the
stage of designing the string box if you want to enter in the switch from the top and exit from the bottom
you will use the first diagram, if you want in&out from the same side you will use diagram number 2
SOLAR PHOTOVOLTAICS. Switch-Disconnector. Accessories
Europe connection set up
Over-voltage protection (Optional)
Protection against over-voltages caused by lighting
Class II Surge Arresters
Terminal Cover (Optional)
Fiberglass made
Available for all sizes
USA connection set up
Negative pole is directly
grounded before entering the
inverter
SOLAR PV. Grid-tied Systems. Switch-Disconnector
SOLAR PHOTOVOLTAICS. Grid-tied Systems. S-W application
Inverters
A Switch-Disconnector in DC and another in AC is used to break and isolate an inverter from source and
load
UTILITY
AC Disconnect
switch
C
O
M
B
I
N
E
R
B
O
X
DC Disconnect
switch
Inverter
Filter
Transformer
Filter
SOLAR PHOTOVOLTAICS. Off-grid Systems.
Off-grid or stand-alone Systems
It is an energy system that is not connected to the grid. They are intended to cover small supplies in the
same place where is generated and public utility are of difficult access. In order to provide continuous
power, these systems must be connected to storage units that can store excess power produced during
daylight hours for use in at night.
Some examples of application are: Residential, solar street lighting, solar pumps.
A residential off-grid system is composed of:
Solar panels
Regulator
Batteries
Inverters
The rated voltages (12-48Vdc) are not very high,
the products that we have for this application are
Two poles Switch-Disconnectors intended to isolate the regulator for maintenance operations
Fuse-bases with DC fuse-links
An enclosed mounting combination