SMA SSM8-21-BS User Manual
Installation Manual
SUNNY STRING-MONITOR SSM8-21-BS / SSM16-21-BS /
SSM8-21-BS-JP / SSM16-21-BS-JP
SSMxx-21-IA-BS-JP-en-20 | 98-116700.03 | Version 2.0 ENGLISH
Legal Provisions SMA Solar Technology AG
Legal Provisions
The information contained in this document is the property of SMA Solar Technology AG. Publishing its content, either
partially or in full, requires the written permission of SMA Solar Technology AG. Any internal company copying of the
document for the purposes of evaluating the product or its correct implementation is allowed and does not require
permission.
SMA Warranty
You can download the current warranty conditions from the Internet at www.SMA-Solar.com.
Trademarks
All trademarks are recognized, even if not explicitly identified as such. A lack of identification does not mean that a
product or symbol is not trademarked.
The BLUETOOTH
marks by SMA Solar Technology AG is under license.
®
Modbus
is a registered trademark of Schneider Electric and is licensed by the Modbus Organization, Inc.
QR Code is a registered trademark of DENSO WAVE INCORPORATED.
®
Phillips
Torx
and Pozidriv® are registered trademarks of Phillips Screw Company.
®
is a registered trademark of Acument Global Technologies, Inc.
®
word mark and logos are registered trademarks owned by Bluetooth SIG, Inc. and any use of these
SMA Solar Technology AG
Sonnenallee 1
34266 Niestetal
Germany
Tel. +49 561 9522-0
Fax +49 561 9522-100
www.SMA.de
E-mail: info@SMA.de
© 2004 bis 2015 SMA Solar Technology AG. Alle Rechte vorbehalten.
2 SSMxx-21-IA-BS-JP-en-20 Installation Manual
SMA Solar Technology AG Inhaltsverzeichnis
Inhaltsverzeichnis
1 Information on this Document. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2 Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1 Intended Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2 Safety Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3 Scope of Delivery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4 Product Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.1 Sunny String-Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.2 String-Current Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.3 DC Load-Break Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.4 String Fuses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.5 Overvoltage Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.6 LEDs on the String-Monitor Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.7 Type Label . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5 Mounting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.1 Wall Mounting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.1.1 Selecting the Mounting Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
5.1.2 Mounting the Sunny String-Monitor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
5.2 Base Mounting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
5.2.1 Selecting the Mounting Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
5.2.2 Mounting the Base. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
5.2.3 Mounting the Sunny String-Monitor on the Base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
6 Electrical Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
6.1 Safety during Electrical Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
6.2 Inserting the Cables into the Switch Cabinet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
6.3 Overview of the Connection Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
6.3.1 SSM8-21-BS/SSM16-21-BS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
6.3.2 SSM8-21-BS-JP/SSM16-21-BS-JP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26
6.4 Connecting the String Cables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
6.5 Connecting the DC Main Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
6.5.1 Cable Requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
6.5.2 Connecting DC Main Cables to the Busbar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
6.5.3 Connecting DC Main Cables to the Terminals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29
6.6 Connecting the Grounding Cable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
6.6.1 Connecting the Grounding Cable in the SSMxx21-BS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
6.6.2 Connecting the Grounding Cable in the SSMxx21-BS-JP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
6.7 Connecting the Data Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
6.7.1 Cable Requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
6.7.2 Connecting the Data Cables in the SSMxx-21-BS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
6.7.3 Connecting the Data Cable in the SSMxx-21-BS-JP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
6.7.4 Connecting the Data Cables in the Sunny Central . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37
7 Commissioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
7.1 Safety during Commissioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
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Inhaltsverzeichnis SMA Solar Technology AG
7.2 Commissioning the Sunny String-Monitor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
7.2.1 Requirements for Commissioning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
7.2.2 Terminating the Data Cable. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
7.2.3 Noting Down the Serial Number of the String-Monitor Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40
7.3 Switching On the Sunny String-Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
8 Disconnecting the Sunny String-Monitor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41
9 Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42
10 Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43
10.1 Maintenance Interval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
10.2 Overview of the Main Components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
10.3 Checking the Mounting Location and the Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
10.4 Checking the Enclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
10.5 Checking the Inside of the Enclosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
10.6 Checking the Base Plate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
10.7 Checking the Covers and Labels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
10.8 Checking the Fuse Holders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
10.9 Checking the Bolted, Clamp and Plug Connections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
10.10 Checking the Surge Arrester for the DC Main Cable. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
10.11 Checking the Surge Arrester for RS485 Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
10.12 Checking the Supply Voltage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
10.13 Checking the Ground Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
10.14 Checking the LEDs of the String-Monitor Unit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
11 Decommissioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50
11.1 Disassembling the Sunny String-Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
11.2 Disposing of the Sunny String-Monitor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
12 Technical Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51
13 Contact. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55
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SMA Solar Technology AG 1 Information on this Document
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1 Information on this Document
Validity
This document is valid for the following device types from the indicated production version:
Device type From production version
SSM8-21-BS B4
SSM16-21-BS B4
SSM8-21-BS-JP A1
SSM16-21-BS-JP A1
Target Group
The activities described in this document must only be performed by qualified persons. Qualified persons must have the
following skills:
• Knowledge of how the device works and is operated
• Training in how to deal with the dangers and risks associated with installing and using electrical devices and
installations
• Training in the installation and commissioning of electrical devices
• Knowledge of all applicable standards and directives
• Knowledge of and compliance with this document and all safety information
Additional Information
Links to additional information can be found at www.SMA-Solar.com:
Document title Document type
Product Details - Features and Mounting Options for SUNNY
STRING-MONITOR SSM8-21-BS /SSM16-21-BS/SSM8-21-BS-JP/SSM16-21-BS-JP
Plant Communication in Large-Scale PV Power Plants Technical Information
SUNNY CENTRAL - Operating Manual Operating Manual
Technical Information
Symbols
Symbol Explanation
Indicates a hazardous situation which, if not avoided, will result in death or serious injury
Indicates a hazardous situation which, if not avoided, can result in death or serious injury
Indicates a hazardous situation which, if not avoided, can result in minor or moderate injury
Indicates a situation which, if not avoided, can result in property damage
☐ Indicates a requirement for meeting a specific goal
☑ Desired result
✖ A problem that might occur
Installation Manual SSMxx-21-IA-BS-JP-en-20 5
Information that is important for a specific topic or goal, but is not safety-relevant
2 Safety SMA Solar Technology AG
Nomenclature
In this document the device types of the Sunny String-Monitor are referred to as "Sunny String-Monitor".
2 Safety
2.1 Intended Use
The Sunny String-Monitor is a PV array junction box to which several strings can be connected in parallel. The
Sunny String-Monitor monitors the input currents of the strings and detects failures, thus helping to minimize power and
yield losses.
Figure1: Principle of a grid-tie PV system
Position Designation
A PV array
B Sunny String-Monitor
CInverter
D MV transformer
E Utility grid
The maximum current values for the Sunny String-Monitors must not be exceeded. The Sunny String-Monitor is suitable
for indoor and outdoor use.
The Sunny String-Monitor can be used in large-scale PV power plants with Sunny Central inverters. For the optimum
operation of the Sunny String-Monitor, observe the mounting location requirements (see Section12 "Technical Data",
page51).
Alterations to the product, e.g. modifications or conversions, are only permitted with the express written permission of
SMA Solar Technology AG. Unauthorized alterations will void guarantee and warranty claims and usually void the
operating license. SMA Solar Technology AG shall not be held liable for any damage caused by such changes.
Any use of the product other than that described in the Intended Use section does not qualify as appropriate.
The enclosed documentation is an integral part of this product. Keep the documentation in a convenient place for future
reference and observe all instructions contained therein.
Only use the Sunny String-Monitor in accordance with the information provided in the enclosed documentation. Any other
use can result in personal injury or property damage.
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2.2 Safety Information
This section contains safety information that must be observed at all times when working on or with the product. To prevent
personal injury and property damage and to ensure long-term operation of the product, read this section carefully and
observe all safety information at all times.
Danger to life from electric shock due to live voltage
High voltages are present in the live components of the Sunny String-Monitor. Touching live components results in death
or serious injury due to electric shock.
• Wear personal protective equipment when working on the Sunny String-Monitor.
• Do not touch live components.
• Before performing any work, always disconnect the Sunny String-Monitor from voltage sources unless supply
voltage is absolutely necessary.
– Switch off the DC load-break switch in the Sunny String-Monitor.
– Remove the DC fuses in the central inverter or main DC distribution box when the power is switched off. Use the
LV/HRC fuse handle.
– Only open the fuse holders in the Sunny String-Monitor when the power is switched off.
• Ensure that the device cannot be reconnected.
• Ensure that no voltage is present.
• Ground and short-circuit the device.
• Cover or isolate any adjacent live components. Protective covers must always be mounted.
Danger to life from electric shock due to live DC cables
DC cables connected to PV modules that are exposed to sunlight are live. Touching live DC cables results in death or
serious injury due to electric shock.
• Prior to connecting the DC cables, ensure that the DC cables are voltage-free.
• Wear suitable personal protective equipment when working on the Sunny String-Monitor.
Danger to life from electric shock due to ground fault
In the event of a ground fault, grounded PV systems can still be live. Touching system components that have not been
properly grounded results in death or serious injuries from electric shock.
• Before working on the PV system, ensure that no ground fault is present.
• Wear suitable personal protective equipment for all work on the product.
Danger to life from electric shock if the Sunny String-Monitor is damaged
If the Sunny String-Monitor is damaged, dangerous situations may arise during operation that result in death or serious
injury from electric shock.
• Only use the Sunny String-Monitor when it is in a technically faultless condition and safe to operate.
• Regularly check the Sunny String-Monitor for visual damage.
• Make sure that all external safety equipment is freely accessible at all times.
• Make sure that all safety equipment is in good working order.
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2 Safety SMA Solar Technology AG
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Danger to life from electric shock if the Sunny String-Monitor is left unlocked
If the Sunny String-Monitor is unlocked, unauthorized persons will have access to components carrying lethal voltages.
Touching live components can result in death or serious injury due to electric shock.
• Always lock the Sunny String-Monitor.
• Remove the keys from the door locks.
• Keep the keys in a safe place.
Risk of fire due to failure to observe torque specifications on live bolted connections
Failure to follow the specified torques reduces the ampacity of live bolted connections so that the contact resistances
increase. This can cause components to overheat and catch fire.
• Ensure that live bolted connections are always tightened with the exact torque specified in this document.
• Use suitable tools when working on the device.
• Avoid repeated tightening of live bolted connections as this may result in inadmissibly high torques.
Danger to life from electric shock if the DC load-break switch is damaged
Switching the DC load-break switch at temperatures below ‒25°C may cause damage to the DC load-break switch.
Correct disconnection function can no longer be guaranteed. High voltages are present in components that are not
properly disconnected. Touching live components can result in death or serious injury due to electric shock.
• Do not switch the DC load-break switch at temperatures below ‒25°C.
Danger to life from electric shock due to damaged fuse holders
Using the fuse holders at temperatures below ‒25°C may cause damage to the fuse holders. Correct disconnection
function can no longer be guaranteed. High voltages are present in components that are not properly disconnected.
Touching live components can result in death or serious injury due to electric shock.
• Do not use the fuse holders at temperatures below ‒25°C.
Risk of burns due to hot components or devices
Some components of the Sunny String-Monitor can get very hot during operation. Touching these components can
cause burns.
• Observe the warnings on the components.
• During operation, do not touch any components or devices marked with such warnings.
• After disconnecting the PV system from voltage sources, wait until all hot components have cooled down sufficiently.
• Wear suitable personal protective equipment for all work on the product.
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Damage to the PV system due to incorrectly rated fuses
If fuses are incorrectly rated, excessive reverse currents can destroy the PV modules.
• Observe the maximum current values for Sunny String-Monitors when rating the fuses.
• Only install string fuses supplied or approved by SMA Solar Technology AG for Sunny String-Monitors.
Damage to the components due to dust or moisture penetration
Dust intrusion or moisture penetration can damage the components of the Sunny String-Monitor or impair their
functionality.
• Do not open the Sunny String-Monitor during a sand storm, rainfall or humidity of more than 95%.
• Only carry out maintenance work on the Sunny String-Monitor if the environment is dry and sand-free.
• Always lock the Sunny String-Monitor.
• Always store the Sunny String-Monitor in an upright position with the connection area facing downwards.
Damage to electronic components due to electrostatic discharge
Electrostatic discharge can damage or destroy electronic components.
• When working on the Sunny String-Monitor and handling components, observe all ESD safety regulations.
• Wear suitable personal protective equipment for all work on the product.
• Discharge electrostatic charge by touching uncoated, grounded enclosure parts (e.g. at the grounding conductor
connection on the doors). Only then is it safe to touch electronic components.
Installation Manual SSMxx-21-IA-BS-JP-en-20 9
3 Scope of Delivery SMA Solar Technology AG
3 Scope of Delivery
Check the scope of delivery for completeness and any externally visible damage. Contact your distributor if the scope of
delivery is incomplete or damaged.
Sunny String-Monitor for Wall Mounting
Figure2: Components included in the scope of delivery for wall mounting
Position Quantity Designation
A 1 Sunny String-Monitor
B 1 Switch cabinet key
C2 Wall mounting rail
D 8 Screw for the wall mounting rail
E 1 Installation manual, circuit diagram
Accessories
Fuses and cylindrical bridges are available as accessories.
10 SSMxx-21-IA-BS-JP-en-20 Installation Manual
SMA Solar Technology AG 4 Product Description
4 Product Description
4.1 Sunny String-Monitor
The Sunny String-Monitor is a PV array junction box to which several strings can be connected in parallel. The
Sunny String-Monitor monitors the input currents of the strings and detects failures, thus helping to minimize power and
yield losses.
The string currents are monitored by the measurement PCB String-Monitor Unit (SMU) located in the
Sunny String-Monitor.
The string fuses in the Sunny String-Monitor protect the PV modules of the strings from reverse currents.
Block Circuit Diagram of the Sunny String-Monitor SSM8-21-BS/SSM16-21-BS
Figure3: Block circuit diagram of the Sunny String-Monitor SSM8-21-BS/SSM16-21-BS
Installation Manual SSMxx-21-IA-BS-JP-en-20 11
4 Product Description SMA Solar Technology AG
Block Circuit Diagram of the Sunny String-Monitor SSM8-21-BS-JP/SSM16-21-BS-JP
Figure4: Block circuit diagram of the Sunny String-Monitor SSM8-21-BS-JP/SSM16-21-BS-JP
4.2 String-Current Monitoring
The string currents are monitored via the measurement PCB String-Monitor Unit. The String-Monitor Unit measures the
string currents and continuously calculates the mean values of the string currents. The string currents are compared with
the mean values. If a string current exceeds or falls short of the mean value by the set tolerance value, the warning 380
SMU is displayed.
With central inverters, you can use the user interface to set the parameters for the string-current monitoring and read off
the mean values (see operating manual of the respective central inverter).
The total failure of a string can be detected via the parameters set. Marginally increased string currents are reliably
detected over several query intervals and distinguished from typical current fluctuations of the PV array.
The sections below describe:
• the conditions under which the string current is monitored
• the intervals at which data is transmitted
• the key parameters for the sensitivity of the string-current monitoring.
Requirements for Activating the String-Current Monitoring
☐The DC power PDC of the PV array exceeds 5% of the nominal AC power P
P
> 0.05 * P
DC
☐ The mean value of the string currents of the individual groups l
l
M String
AC nom
≥ 0.5 A
is equal to or greater than 0.5 A.
M String
of the Sunny Central.
AC nom
Error Sum
The error sum is a measure of the sensitivity of string-current monitoring. The error sum can be parameterized via the
tripping time and the tolerance and can be calculated using the following formula:
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SMA Solar Technology AG 4 Product Description
The individual error sums of the measuring channels are reset at midnight.
Query Intervals
The Sunny String-Monitor continuously measures the string currents and performs cyclic storage of the measured values.
The data logger reads out these values every five minutes.
Tripping Time
The tripping time is the time span between the occurrence of an error and the error message. The tripping time is set to
180 minutes by default. You can set the parameter for the tripping time to between 2 minutes and 1,440 minutes.
Tolerance
The tolerance indicates how much the string current is allowed to deviate from the mean value. If the string current is
outside the tolerance limits, the data logger detects the deviation and stores it. The tolerance can be set between 10%
and 100%.
Grouping the Strings
To simplify monitoring, you can assign the strings to the eight measuring channels. Should individual strings be shaded,
aligned differently or fitted with different PV modules, it is also possible to group the individual measuring channels. This
makes it possible to compare measuring channels with the same properties.
Comparison
Every five minutes, the data logger compares the string current with the mean value for the group. If the string current
exceeds the tolerance limit, the data logger records the deviation. If at the next query, there is still a deviation between
the string current and the mean value, the deviations are added together. If the sum of the deviations exceeds the error
sum, the data logger issues the warning 380 SMU. When the error is acknowledged, the error sum is reset and the
warning disappears from the display.
It is possible to see which Sunny String-Monitor and which measuring channels deviate from the mean value of the group
via the Sunny Central Control or via the SC-COM.
Example:
It is assumed that at time t
range is from 4.5 A to 5.5 A. The tripping time is set to 10 minutes. The query interval is five minutes. The error sum can
therefore be calculated as follows:
the mean value of a group is 5 A. The set tolerance is 10%. This means that the tolerance
0
All string currents are compared with this mean value at the five-minute query interval. If all the string currents are within
the set tolerance of 10%, no addition is carried out.
However, if one string has a string current of 6 A, the difference between the actual string current of 6 A and the tolerance
limit of 5.5 A is added. The difference is 0.5 A which is a deviation of 10% from the mean value. This difference of 10%
is now added to the total until the error sum of 20% is reached.
The error sum is reached when the error remains the same for two query intervals. The data logger issues the warning
380 SMU.
Installation Manual SSMxx-21-IA-BS-JP-en-20 13
4 Product Description SMA Solar Technology AG
If a string fails, the current difference in the above example is 4.5 A which equates to a deviation of 90% from the mean
value. Assuming that the settings in the above example remain unaltered, i.e. tolerance at 10% and tripping time at
10 minutes, the error sum of 20% will already be reached after the first query interval of 5 minutes. The data logger
now issues an SMU warning.
4.3 DC Load-Break Switch
The Sunny String-Monitor can be disconnected on the inverter side by means of a DC load-break switch. Use of the DC
load-break switch is only permissible if LV/HRC fuses with gPV characteristic are installed upstream in the inverter or the
main DC distribution box.
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SMA Solar Technology AG 4 Product Description
4.4 String Fuses
The string fuses protect the PV modules of a PV system from reverse currents. Only install string fuses supplied or approved
by SMA Solar Technology AG as accessories for Sunny String-Monitors.
Figure5: Principle of reverse current
A reverse current can occur when different open-circuit voltages are applied to PV modules connected in parallel. In this
event, the reverse current can be much higher than the short-circuit current of the PV modules. The higher the reverse
current, the more the PV modules of the faulty string will heat up. Strong heat build-up can destroy the modules of the
faulty string.
Reverse current can have the following causes:
• short circuit in one or more modules
• short circuit in one or more cells of a module
• double ground fault in a module
• double ground fault in the cabling
The string fuses trip when the string current is too high and protect the PV modules of the faulty string. The
Sunny String-Monitor informs the inverter of the string failure.
In the case of grounded PV arrays, the positive or the negative terminal can be grounded in the inverter. To do this,
cylindrical bridges are fitted in the Sunny String-Monitor instead of string fuses. Cylindrical bridges are available as
accessories.
4.5 Overvoltage Protection
Depending on the device type, the Sunny String-Monitor is equipped with one or two surge arresters for overvoltage
protection.
In order to guarantee the overvoltage protection function, the surge arrester must be connected to the external grounding.
Components to be protected SSMxx-21-BS SSMxx-21-BS-JP
DC main cable of the Sunny String-Monitor ✓ ✓
RS485 interface and RS485 communication
bus
Installation Manual SSMxx-21-IA-BS-JP-en-20 15
✖✓
4 Product Description SMA Solar Technology AG
Components to be protected SSMxx-21-BS SSMxx-21-BS-JP
Voltage supply to the Sunny String-Monitor ✖ ✓
The integrated surge arrester for the DC main cable can be monitored via the Sunny String-Monitor.
4.6 LEDs on the String-Monitor Unit
The LEDs are installed on the String-Monitor Unit. You can determine the status of the communication, voltage supply or
surge arresters via the LEDs.
Figure6: LEDs on the String-Monitor Unit
Designation Name of LED Status Explanation
A DIN1 glowing green The surge arrester is active.
off The surge arrester has tripped.
B RS485 off No data is being exchanged via the
RS485 interface.
glowing yellow Data is being transmitted via the RS485
interface.
C Error off The String-Monitor Unit is functioning
correctly.
glowing red The String-Monitor Unit is defective.
4.7 Type Label
The type label clearly identifies the Sunny String-Monitor. There are two type labels attached to the Sunny String-Monitor.
The type labels are located inside the right-hand door and on the right-hand outside panel of the Sunny String-Monitor.
You will find the following information on the type label:
• Device type and option code
• Serial number
•Production version
• Device-specific characteristics
You will require the information on the type label to use the product safely and when seeking customer support from the
SMA Service Line. The type label must remain permanently attached to the product.
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SMA Solar Technology AG 4 Product Description
Symbols on the Type Label
Symbol Explanation
Danger to life due to high voltages
The product operates at high voltages. All work on the product must be carried out by qualified
persons only.
Risk of burns due to hot surfaces
The product can get hot during operation. Avoid contact during operation. Allow the product to
cool down sufficiently before carrying out any work. Wear personal protective equipment such as
safety gloves.
Observe the documentation
Observe all documentation supplied with the product.
CE marking
The product complies with the requirements of the applicable EU directives.
WEEE designation
Do not dispose of the product together with the household waste but in accordance with the locally
applicable disposal regulations for electronic waste.
Degree of protection
The product is protected against interior dust deposits and splashing water from all angles.
Installation Manual SSMxx-21-IA-BS-JP-en-20 17
5 Mounting SMA Solar Technology AG
:$5 1,1*
&$87,21
5 Mounting
5.1 Wall Mounting
5.1.1 Selecting the Mounting Location
Fire hazard due to wrong choice of mounting location
Under fault conditions electric arcs may occur in the Sunny String-Monitor. Electric arcs can cause fires if the
Sunny String-Monitor is mounted on flammable materials.
• Do not mount the Sunny String-Monitor on flammable construction materials.
• Do not mount the Sunny String-Monitor near highly flammable materials.
• Do not mount the Sunny String-Monitor in potentially explosive atmospheres.
Requirements for the mounting location:
☐ The mounting location must not be in a living or office area.
☐ The mounting location must not block any escape routes.
☐ The mounting location must be freely and safely accessible at all times without the necessity for any auxiliary
equipment (such as scaffolding or lifting platforms). Non-fulfillment of these criteria may restrict servicing.
☐ The mounting location must be suitable for the weight and dimensions of the Sunny String-Monitor (see Section12
"Technical Data", page51).
☐ The mounting location must not be exposed to direct solar irradiation.
Requirements for mounting
• Mount the Sunny String-Monitor so that the connection area is facing downwards.
• Do not mount the Sunny String-Monitor in a horizontal or inclined position.
• An external cable support rail must be provided.
Example: Mounting the Sunny String-Monitor
If the PV array is mounted on a free-standing structure, the
Sunny String-Monitor can be fixed to this structure in a shaded
position. Make sure that the Sunny String-Monitor enclosure is not
mounted in the path of rainwater flowing off the module surface.
5.1.2 Mounting the Sunny String-Monitor
Danger of crushing if the Sunny String-Monitor is dropped
• When mounting the Sunny String-Monitor, take the weight of up to 70 kg into account.
• Two people are needed to mount the Sunny String-Monitor.
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