for grid energy storage systems (ess) - bender2 grounded ess ungrounded ess multi-string systems...

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BrochureNAE1111850 / 05.2016

Ground fault protectionFor grid energy storage systems (ESS)

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Grounded ESS

Ungrounded ESS

Multi-string systems

Monitor multiple strings from a single device with the RCMS series

Single-string systems

True RMS, AC/DC ground fault measurements with the RCMA423 series

Single- and multi-string systems

Detect and locate ground faults on large-scale ungrounded ESS with the iso1865P and EDS440

ENHANCED SAFETY SOLUTIONSFor energy storage systems, from the leader in electrical safety.

© 2016 NEC Energy Solutions, Inc. - Used with Permission

As power generation evolves around the world to meet demand, more smart grids require the storage of excess generated electri-city to maximize peak efficiency. With every year, battery storage systems become more and more ubiquitous.

Smart electical safety equipment is a must to help today's smart grids operate. Proper electrical safety doesn't just protect person-nel - it helps protect equipment from electrical and fire damage, helping to extend the life expectancy of equipment. With over 70 years of electrical safety experience, Bender is a global leader in providing safety equipment to help smart grids maximize uptime and efficiency.

The Bender advantage

�� Works with grid connected ESS regardless of power generation type - solar, wind, coal, nuclear, and more

�� Works with virtually all battery types (lead-acid, lithium-ion, exotic types, etc.)

�� Monitor both grounded and ungrounded systems

�� Locate both AC and DC faults automatically on multi-string and multi-inverter systems

�� Communicate information to a centralized location using modern industrial communication protocols

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Grounded ESS: single-string systemsAC/DC ground fault monitoring with the RCMA423 series

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Battery Battery Battery

BidirectionalInverter

RCMA423

ESS Grid


RCMA423 series AC/DC ground fault monitor

The RCMA423 monitors for ground faults in grounded AC/DC systems. Features include true RMS readings, real-time values displayed onboard the device, and two separately adjustable alarms with two SPDT contact outputs. A wide range of current transformer sizes allows for easy installation.

Features:�� True RMS readings (AC + DC)

�� Digital display with real-time readout

�� Adjustable trip level, from 30 mA up to 3 A

�� Wide range of current transformer sizes

�� Two separate SPDT contact outputs

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Bender's RCMS460 and RCMS490 monitor for ground faults in grounded and high-resistance grounded AC/DC systems, as well as systems with variable frequency drives. Up to twelve separate strings / inverters can be monitored in parallel, with individually set alarm levels. The device's LCD display shows the status of each channel in real-time.

Features:

�� Multi-channel ground fault monitoring for up to 12 separate AC/DC branches

�� Individually set alarm levels for each branch - as low as 6 mA, and as high as 20 A

�� Display shows each branch's measured ground fault level in real-time

�� Harmonics analysis

�� Option for individual output relays for each channel (available in RCMS490 models)

�� Compatible with Bender's remote communication system

Grounded ESS: multi-string systemsMonitor multiple strings and inverters from a single AC/DC capable device

The multi-channel advantageMonitor up to twelve branches for AC and DC ground faults from a single device

�� Monitor up to twelve branches from a single device

�� Modular design allows for individualization - each channel has its own trip level, current transformer size, and more

�� Simple bar graph indication shows the alarm status of each channel

�� RCMS490 devices feature individual contact outputs for each branch - individually notifiy or interrupt

�� Connect to Bender's remote communication system - remotely view alarm status, measured values, and more

RCMS series multi-channel ground fault monitor

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Online, automatic ground fault locationLocate faults in battery strings automatically while the system remains online with the EDS440

�� Automatic detection and location of ground faults down to the load level with EDS440 ground fault location modules

�� Greatly reduce time required for ground fault hunting

�� Supports branch sizes from small to large with varying cur-rent transformer sizes

�� Modular system allows for easy retrofitting / upgrading, such as adding future strings / inverters

�� Additional portable fault location system (EDS3090 series) allows for ground fault location with a handheld device - perfect for ground fault hunting in virtually any system or during scheduled maintenance

Ungrounded ESS: single- and multi-string systemsDetect and locate faults with Bender's advanced insulation monitoring

iso1685P ground fault detector for ungrounded solar arrays

EDS440 series ground fault location module

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iso1865P

ESS Grid

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EDS440

The iso1685P provides maximum system monitoring for large-scale battery deployments on ungrounded systems. The iso1685P monitors an entire system's insulation resistance from a single point. Measurements maintain accuracy even on systems with high leakage capacitances.

Combining the iso1685P with the EDS440 creates an automa-tic fault location system. Ground faults are located on strings automatically. Up to 12 strings can be monitored from a single EDS440. Both devices are compatible with Bender's communi-cation system, remotely notifying staff of located faults.

iso1685P features:

�� Designed for large-scale deployments: Works on systems with up to 2000 цF leakage capacitance

�� Adjustable insulation resistance alarm of 200 Ω to 100 kΩ

�� Automatic system data logging, stored on microSD card

�� Works with EDS440 to create fault location system


EDS440 features:

�� Combine with iso1685P to locate faults automatically on up to 12 strings from each EDS440 - add on more devices to increase monitoring points

�� Indication of faulty branch onboard the device

�� Varying size current transformers- individually specify sizes per string / monitoring channel


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Technical and application informationBattery-based grid energy storage systems

Battery-based storage systems come in many varieties, including lead-acid, lithium-ion, and other exotic types. For ground fault protection, the type of battery system is of negligible importance. Wiring and grounding scheme is the primary factor determining the proper ground fault protection.

System components

The typical energy storage system (ESS) is comprised of three key components:

�� Battery: Medium for storing electrical energy

�� Bidirectional inverter: Responsible for AC/DC conversion to and from the grid

�� Transformer: Isolation or tie-in for voltage adaption to the grid

Typical grounding methods

Electrical systems are typically either solidly grounded or ungroun-ded. Grounded systems have a wye or star configured transformer connecting to the grid. The star point / neutral is tied to ground. This configuration is typical in North America for the vast majority of applications. Failures may generate large currents to ground, and typically lead to interruption and downtime. Ground faults are detected relatively quickly, as they are monitored by fast-acting current detecting equipment, such as current ground fault relays and ground fault circuit interrupters (GFCI). Faults are measured in milliamperes or amperes. To avoid stray and circulating currents, only one ground bond should be present in a single, isolated system.

Ungrounded power systems are used in applications where uptime is critical and hazardous currents are unacceptable. The first fault in an ungrounded system does not cause high leakage currents to flow to ground. Instead, it converts the ungrounded system into a grounded one. Using insulation monitoring equipment, ground faults can be detected and corrected in a first fault condition while the system remains online. Since a first fault condition does not generate significant leakage currents, insulation monitoring equip-ment measures for these faults in Ohms.

ESS systems can be run either grounded or ungrounded, and are up to specifiers at the time of design. Grounding takes place at the transformer. This is in contrast to grid-tied solar arrays, a similar application, where grounding typically takes place at the inverter.

Battery

Storage batteries in this application are typically not earth groun-ded, as this takes place elsewhere in the system.

Bidirectional inverter

The inverter in ESS systems is also left ungrounded. This is in contrast to other grid-tied energy systems, where grounding may take place at the inverter. A "light" grounding may be present at the inverter, due to RC filtering circuitry for EMI noise reduction.

Transformer

The transformer is either grounded or ungrounded depending on specification. Wye / star configured transformers are typi-cally grounded, and delta configured transformers are typically ungrounded. Grounding typically takes place at the transformer.

Grounded ESS - single string, single inverter configuration

Figure 1: Typical configuration for single-string, direct grid-tied ESS

Figure 1 shows a typical configuration for connecting a string of batteries to the grid. Each fault to ground will cause a moderate to high magnitude of current to flow. A fast-acting, current-sensing type ground fault relay is required. Because ground faults in this application can be both AC and DC, the relay must be able to detect both types of current (Europe has a specific designation for this type of device, known as "Type B"). Ideally, the device reads true RMS leakage values, and is placed as close to the grid tie point in the system as possible. The Bender RCMA423 detects both AC and DC ground faults, as low as 30 mA and as high as 3 A.

Grounded ESS - multiple strings with fault location

Figure 2: Typical configuration for single-inverter, multiple-string ESS with fault location (RCMS) and communication

Figure 2 shows a system with multiple battery strings tied to a single inverter. With the number of batteries involved, faults will still be detected quickly. However, locating which of the many hundreds of cells has caused the problem can be difficult. A multi-channel device, such as the Bender RCMS series, can monitor multiple strings from a single device for both AC and DC ground faults. The faulty string can be automatically detected and indica-ted. The information can be remotely communicated connecting to standard and industrrial Ethernet networks.

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RCMA423

ESS Grid


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RCMS460 / 490

ESS Grid

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COM465IP

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An active IMD, such as the isoPV, measures the system's insulation resistance to ground continuously by superimposing a small, line-to-ground measurement signal on the system. The device connects directly to the system, as opposed to using current transformers. The isoPV's measurement signal is specially designed to overcome prevailing system conditions which typically cause measurement issues, such as inverter filtering circuitry and other forms of possible system noise.

Ungrounded ESS - multiple strings with fault location

Figure 5: Typical configuration for ungrounded ESS with multiple strings, insula-tion monitoring device (iso1865P) and fault location (EDS440)

Fault detection and location is still possible when using large-scale ESS with multiple battery strings. The iso1685P is specially desi-gned to maintain accurate measurement techniques with large systems that may have high leakage capacitances to ground. When combined with the EDS440 ground fault location module, faults can be localized while the system remains in operation.

The EDS440 utilizes a special tracer signal which travels naturally through a present ground fault. Using special current sensing equipment placed at each string, the EDS440 will locate the fault down to the string level. An additional sensor may be placed in bet-ween the ground fault detector and inverter, to notify technicians if the inverter itself is the source of a ground fault. Fault location times vary, depending on a number of factors, such as size of the system and magnitude of leakage capacitance.

This system is also communication capable, connecting to modern networks to notify staff of located ground faults.

Grounded ESS - multiple strings and inverters

Figure 3: Typical configuration for ESS with multiple strings and inverters

Figure 3 shows a configuration with the difference that smaller, individual inverters are used for each battery string. From a ground fault protection perspective, the application is fundamentally similar to configurations using a single inverter. Similar protection methods are utilized.

Ungrounded ESS

Figure 4: Typical configuration for an ungrounded ESS string with an insulation monitoring device (isoPV)

The previous application examples have shown typical configura-tions for grounded ESS. Figure 4 shows a delta-delta transformer configuration with no bond to ground. In this system, a first fault condition will not generate sufficient leakage current to ground for a typical current-sensing device.

In order to detect a first-fault condition before a second fault con-dition creates hazardous leakage current, an insulation monitoring device (IMD) is used. The IMD measures the system's resistance to ground. This value will decrease proportionally to the strength of the ground fault present in the system. Not only does this method provide accurate measurements of first-fault conditions, it also allows for trending system insulation over time.

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RCMS460 / 490

ESS Grid

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COM465IP

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isoPV

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iso1865P

ESS Grid

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COM465IP

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Technical and application informationBattery-based grid energy storage systems

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USA, Mexico, and Central AmericaExton, PA • 800-356-4266 / [email protected] • www.bender.org

Canada • Mississauga, ON • 800-243-2438 / [email protected] • www.bender-ca.com

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