basics of low voltage switchgear - sitrain lms

Basics of Low Voltage SwitchgearA quickSTEP Online Course

www.usa.siemens.com/step© Siemens industry, Inc.

© Siemens Industry, Inc. 2017

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Siemens is a trademark of Siemens AG. Product names mentioned may be trademarks or registered trademarks of their respective companies.

ANSI is a registered trademark of American National Standards Institute

National Electrical Code® and NEC® and NFPA 70® are registered trademarks of the National Fire Protection Association.

NEMA® is a registered trademark and service mark of the National Electrical Manufacturers Association.

UL® is a registered trademark of UL, LLC.

Other trademarks are the property of their respective owners.

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Course Topics

Welcome to Basics of Low Voltage Switchgear. This course covers the following topics:Chapter 1 - Introduction

• Overview• WL LV Power Circuit Breakers

Chapter 2 – WL LV Switchgear• WL LV Switchgear Design• Arc Resistant LV Switchgear• Sm@rtGear LV SwitchgearFinal Exam

If you do not have an understanding of basic electrical concepts, you should complete Basics of Electricity before attempting this course.

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Course Objectives

Upon completion of this course you will be able to…• State the differences in operating voltage between low voltage and medium voltage switchgear• List the maximum voltage rating and maximum bus current ratings for WL low voltage switchgear• Describe the most important design characteristics of WL low voltage power circuit breakers• List the most significant specifications that affect the design of low voltage switchgear• Identify the range of continuous current ratings, interrupting ratings, and short-time withstand ratings

available for WL low voltage power circuit breakers• Identify operational features of WL low voltage power circuit breakers• Describe the key differences among the various electronic trip units available for WL circuit breakers• List the communication options available for WL circuit breakers• List the enclosure types available for standard WL low voltage switchgear• List the types of sections and section widths commonly for WL low voltage switchgear.• Identify the ANSI/IEEE arc resistant testing standard that applies to both low voltage and medium

voltage switchgear• Describe the difference between accessibility levels 1 and 2 for arc resistant switchgear• Describe the key similarities and differences between WL low voltage switchgear and the arc

resistant version• List important features of Sm@rtgearTM LV switchgear.

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Power Distribution

Power from a power generating plant is distributed to customers through transmission lines and substations. The most efficient way to do this is to increase the voltage while at the same time reducing the current. Electric utilities, which must provide power to customers of various types, use transmission systems that operate in the high voltage or extra high voltage range.

Once the electrical energy gets near the end user, the utility steps down the voltage to the level needed by the user. The amount by which the voltage is stepped down at the user end depends on the needs of the facility. Many large commercial or industrial facilities have service entrance equipment that operates in the medium voltage range. Other facilities have low voltage equipment at the service entrance.

Medium voltage (MV) systems generally operate between 1000 and 38,000 volts (1 to 38 kV), although some MV systems can operate above 38 kV. The switchgear covered in this course is referred to as low voltage (LV) equipment. For the purposes of this discussion of power distribution equipment, LV systems operate at 1000 VAC (nominal) or below. Keep in mind that to account for power system differences the maximum voltage of equipment is usually higher than the nominal system voltage. Page 1-6


Medium Voltage Switchgear

A large industrial facility receives electrical power from the utility company at high transmission voltage levels. The voltage is stepped down to a medium voltage or low voltage level at the substation for distribution throughout the facility. Large industrial facilities can be spread out over several acres and may incorporate many large buildings. Multiple MV switchgear units, sometimes called MV metal-clad switchgear, could be used if the power demand is large enough.

Switchgear is a compartmentalized system of coordinated devices used for power distribution, control, and circuit protection. Switchgear performs the same function as switchboards, but different standards dictate the design of switchgear. In addition, because medium voltage (MV) switchgear must handle higher levels of electrical energy and must be capable of interrupting higher fault currents, it is larger and more heavily constructed.

Siemens manufactures multiple types of MV switchgear to meet varied customer requirements with voltage ratings up to 42 kV.

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WL Low Voltage Metal-Enclosed Switchgear

A Siemens WL low voltage (LV) metal-enclosed switchgear assembly consists of one or more metal-enclosed vertical sections. WL LV switchgear is designed around the innovative features of Siemens WL LV power circuit breakers. Each vertical section consists of up to four individually-enclosed breaker or auxiliary compartments sized to provide uniform section height.

Included in each assembly are components such as circuit breakers, instrumentation and control equipment, transformers, relays, three-phase bus work, and all internal wiring, connectors, and other supporting equipment.

WL switchgear has horizontal and vertical bus rated for 6000 amps maximum. It is rated for use on 50 or 60 Hz, three-phase, three-wire or three-phase, four-wire systems with a maximum voltage of 635 VAC.

This course covers Siemens WL LV metal-enclosed switchgear and the WL low voltage power circuit breakers that this equipment incorporates. An overview of the following variations of WL LV switchgear is also included: four-pole WL LV switchgear, front-connected WL LV switchgear, marine WL LV switchgear, arc resistant LV switchgear, and Sm@rtGear WL LV switchgear.

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Large Facility Power Distribution Example

In large commercial, industrial, or institutional facilities, the supplied voltage must be reduced multiple times to accommodate the needs of various types of electrical equipment. While some machines require voltages above 480 volts, most factories and many large commercial and institutional faculties use AC motors, drives, motor control centers, and other devices that operate on three-phase, 480 volts and other equipment that requires even lower single-phase or three-phase voltages.

In the accompanying example, power is stepped down at the utility company’s substation to 38,000 volts (38 kV) and applied to the incoming section of the facility’s 38 kV medium voltage metal-clad switchgear.

One distribution branch is stepped down to 4.16 kV and another to 13.8 kV and further distributed through MV metal clad switchgear units. A 13.8 kV branch is applied to a secondary unit substation and further reduced to 480 volts. Further down this path, a single-phase transformer reduces the voltage to 120 V.

In this example, the LV switchgear is incorporated into a secondary unit substation. Keep in mind that LV switchgear sections may not set up in this configuration. Page 1-9


Secondary Unit Substations

Some customers require an integrated assembly, called a secondary unit substation, to provide electrical service to a facility. A secondary unit substation consists of a primary switch and one or more transformers mechanically and electrically connected to switchboard or switchgear sections. All elements of the substation are engineered to the specific needs of the application.

The incoming service to the primary switch is typically 2.4 to 13.8 kV. The primary switch is used to connect and disconnect the secondary unit substation from the incoming service. The transformer section can be liquid filled, ventilated dry type, or cast coil type and is used to step down the voltage to 600 V or below. The outgoing sections can be switchboard or LV switchgear sections.

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WL Low Voltage Power Circuit Breakers

Siemens WL circuit breakers are designed to address the increasingly demanding requirements of today’s electrical power distribution systems and incorporates the following characteristics.

• High reliability• Compact size• Ease of use• Modularity of design• Flexibility of system communications• Safety-oriented features

Siemens WL family of circuit breakers includes both insulated case circuit breakers that conform to the UL 489 specification and low voltage power circuit breakers that conform to the UL 1066 and corresponding ANSI and NEMA specifications. The WL circuit breakers used in WL LV switchgear are LV power circuit breakers.

One important characteristic of an LV power circuit breaker is its ability to withstand a designated level of fault current without damage for a short time. This is important because an LV power circuit breaker is often required to delay tripping for a short time when a fault current is sensed so that a downstream breaker closer to the fault has time to trip, thereby avoiding a larger system outage.

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Low Voltage Switchgear Standards

The terms switchboard and switchgear are often confused because these terms are similar in spelling and both types of equipment are used in power distribution systems. However, low voltage switchgear conforms to ANSI, IEEE, and UL standards that differ from NEMA and UL switchboard standards.

The accompanying chart shows the most significant ANSI, IEEE, and UL standards that apply to LV switchgear assemblies and devices.

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Low Voltage Switchgear Applications

WL LV switchgear is designed for use in a wide variety of applications. The accompanying chart shows examples of typical applications for LV switchgear.

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Low Voltage Switchgear Versus Switchboards

LV switchgear and switchboards are similar in appearance and perform similar functions, but there are some important differences. In general, low voltage switchgear is typically more rugged than comparable switchboards. This difference translates into a higher manufacturing cost and selling price for low voltage switchgear.

Another important difference relates to the different design standards for switchboards and LV switchgear. The U. S. standards for LV switchgear were provide earlier in this course. In comparison, consider that switchboards are designed to NEMA PB-2 and UL 891 standards. In addition, shown in the accompany chart, switchboards are capable of incorporating a broader range of overcurrent protection devices. This means that more device standards apply to switchboards.

In summary, There are applications that can be handled effectively with either switchboards or LV switchgear; however, there continues to be a need for both types of products. Switchboards offer flexibility and a lower initial cost, and LV switchgear offers increased ruggedness and reliability that for many companies translates into a lower total cost of ownership.

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Chapter 1 – Introduction

This chapter covers the following topics:

• Overview

• WL LV Power Circuit Breakers

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WL LV Three-Pole Power Circuit Breaker Ratings

WL low voltage power circuit breakers, also referred to as WL UL 1066 circuit breakers, are used in WL low voltage switchgear as drawout-mounted breakers. They have a rated maximum operating voltage of 635 VAC and are available in two frame sizes with frame ratings from 800 to 6000 A and continuous current ratings from 200 to 6000 A. Additional details for three-pole WL power circuit breakers are provided in the chart shown below. Note that frame size I is not shown here because it only applies to WL circuit breakers that conform to the UL 489 specification. Ratings for four-pole WL power circuit breakers are provided in the chart on the following page.

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WL LV Four-Pole Power Circuit Breaker Ratings

Four-pole breakers provide the neutral isolation capability that is advantageous for low voltage switchgear applications where multiple, separately-derived power sources are individually grounded. Ratings for four-pole WL power circuit breakers are provided in the chart shown below. Note that frame size I is not shown here because it only applies to WL circuit breakers that conform to the UL 489 specification.

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WL Circuit Breaker Operational Features

WL circuit breakers can be fused or unfused and optionally delivered with any of these operating mechanisms:

• Manual operating mechanism with mechanical closing (standard)

• Manual operating mechanism with mechanical and electrically-interlocked closing

• Motorized operating mechanism with mechanical and electrically-interlocked closing.

As shown in the accompanying graphic, WL circuit breakers have a number of standard and optional features that enhance the safety and usability of the breaker, reduce errors, and minimize training time.

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Ready-to-close Indicator

One of the standard safety features of WL low voltage power circuit breakers is the ready-to-close indicator that provides an at-a-glance visual indication that the all eight of the necessary conditions have been met and the breaker is in the ready-to-close state.

The WL circuit breaker is ready to close if the following conditions are met;

1. The breaker is in the open position2. The stored-energy springs are charged3. The under-voltage release (UVR) is

energized4. The shunt trip is not energized5. The closing coil is not energized6. No interlocks are activated7. The mechanical closing lockout is reset8. The racking handle is stowed away

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Modularity of Design

WL circuit breakers have a flexible modular design that includes common plug-in accessories, field upgradeable trip units, and field-changeable contacts and arc chutes.

This design minimizes inventory, allows for last-minute changes, and is cost-effective to support.

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Field Installable Accessories

WL circuit breakers offer a variety accessories and trip units that are easily mounted at the front of the breaker and each of these devices fits all frames. Examples of some of the more common accessories are shown in the accompanying graphic.

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Electronic Trip Units – Part 1

Three electronic trip units (ETUs) are available for use with WL circuit breakers. The protective functions and additional capabilities available for these trip units are shown in the accompanying diagram. Some of the optional functions are briefly described below and on the next page

The switch-selectable I2t or I4t characteristic curve function allows the breaker’s long-time characteristics to be set to either an I2t curve or an I4t curve to make it easier to achieve optimal coordination.

Switchable parameter sets simplify adapting the system to rapid changes, such as when power is switched between utility power and a generator. Switching between parameter sets can be done quickly and, if desired, remotely.

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Electronic Trip Units – Part 2

Dynamic Arc-Flash Sentry (DAS) employs the unique dual protection settings of the ETU776 trip unit coupled with the ability to toggle to a lower arc flash parameter set. A normal parameter set can be optimized for selective trip coordination with the alternate parameter set optimized for lower arc flash energy levels initiated when someone approaches the arc flash protection boundary.

Extended Instantaneous Protection (EIP) is designed to provide any WL low voltage power circuit breaker with the capability to be applied at the short-time withstand rating of the breaker with no instantaneous override. This feature gives downstream breakers the maximum possible time to clear a fault and reduces the likelihood of a system-wide outage.

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Electronic Trip Unit Modularity – Part 1

The modularity of WL circuit breakers extends to the ETUs. For example, any ETU model can be installed in any WL circuit breaker. In addition, as described below, selected ETU models can be easily adapted to changing conditions in the field by the addition or replacement of the following ETU modules:

• Display• Ground fault protection• Rating plug• Metering function/Metering function plus• Communication.

The alphanumeric LCD display is an option for ETU745 (shown in the accompanying graphic) and ETU748. ETU776 comes equipped with a graphical LCD display.

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Electronic Trip Unit Modularity – Part 2

Ground fault trip and alarm and ground-fault-only modules are available for ETU745, ETU748, and ETU776.

The rating plug is a replaceable module used to set the continuous current rating for the circuit breaker. Rating plugs are available for frame size II from 200 to 3200 amps and for frame size III from 800 to 6000 amps.

The integrated metering function can be installed on ETU745, ETU748, and ETU776 to measure currents, voltages, power, energy, power factor, and frequency. All metered quantities are real-time values with min/max recording. The metering module also provides additional alarm setpoint and protective relay functions. The metering function plus module has additional recording capacity and supports harmonic analysis.

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Communications Options – Part 1

CubicleBUS forms the backbone of the WL circuit breaker communication system. CubicleBUS is an internal system bus that connects all intelligent components in the WL circuit breaker and simplifies the connection to external components.

CubicleBUS is incorporated into all WL circuit breakers with ETU745, ETU748, and ETU776 trip units. The modular design of this system simplifies retrofitting of communications functions. All modules shown attached to CubicleBUS in the accompanying graphic directly access useful circuit breaker data.

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Communications Options – Part 2

With the addition of a COM15 PROFIBUS module for PROFIBUS DP communications or COM16 MODBUS module ( not shown) for MODBUS RTU communications, WL circuit breakers with ETU745, ETU748, and ETU776 trip units can have ETU parameters changed, and the breaker can be opened and closed remotely. In addition, data can be shared with other systems. For trip units with the metering function or metering function plus option, the breaker can take on an even wider role in a power management system.

The Breaker Data Adapter (BDA) incorporates configuration software and embedded web pages. This enables online configuration and diagnostics and allows configuration data developed offline to be downloaded to the trip unit.

The BDA Plus has all the functionality of the BDA and can also connect to an Ethernet network.

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CubicleBUS I/O Modules

A variety of CubicleBUS input/output (I/O) modules are available to expand the capabilities of the WL circuit breaker. The following paragraphs summarize the capabilities of this modules.

The digital output module with rotary switch (not shown) allows up to six binary signals to be connected to external signaling devices or used to control other equipment. Digital and relay output versions of this module are available.

The configurable digital output module allows up to six binary signals to be triggered by protective or setpoint events. Optionally, three of these outputs can be assigned in a logical-OR arrangement connected to up to six events. Both digital and relay output versions of this module are available.

The analog output module can be used to output a variety of measured values (amps, volts, power, power factor, etc.) to analog display devices on the cubicle door. Up to two modules of this type can be connected to the WL breaker.

The digital input module can connect to a maximum of six digital (24 VDC) inputs. This enables the status of a switch or the cubicle door to be communicated to the circuit breaker.

Zone selective interlocking (ZSI) is a method that allows two or more circuit breakers to communicate so that a short circuit or ground fault is cleared by the breaker closest to the fault in the minimum time. The ZSI module is used to interconnect WL circuit breakers in this arrangement. Page 1-29


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Chapter 2 – WL LV Switchgear


• WL LV Switchgear Design

• Arc Resistant LV Switchgear

• Sm@rtGear LV Switchgear

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Enclosures

The following types of enclosures are available for WL low voltage metal-enclosed switchgear:• NEMA 1 (shown in the accompanying graphic)• NEMA 3R outdoor (non-walk-in)• NEMA 3R outdoor (walk-in)

For NEMA 1 enclosures, rear covers with captive hardware are standard. Rear doors with quarter-turn latches and captive screws and rear doors with three-point latches are optional. In addition to the standard ventilation design, a tamper-resistant ventilation design is available as an option.

NEMA 3R enclosures are painted, weather-resistant steel housings. Both enclosures sit on a six-inch high, formed steel base which provides rigid support and a tight bottom seal. A heavy-duty protective undercoating is applied to the under side of the enclosure. Shielded ventilation housings permit proper airflow. Walk-in enclosures have a 42-inch lighted and unobstructed service isle.

The integrally mounted breaker hoist, standard on walk-in outdoor and optional on indoor switchgear enclosures, travels along rails on top of the switchgear to assist in breaker handling.

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Section Types

WL low voltage switchgear can be configured in many ways by combining different section types. Up to five vertical sections plus a transition section can be shipped together as a unit. If requested at order entry, the switchgear can be shipped so that it can be tilted onto its back to transport it during installation.

The major assembly sections include: • Transition Section - used as transition to a

liquid filled transformer, to an outdoor dry-type transformers, or other equipment such as MCCs or switchboards.

• Auxiliary Section - used as incoming bus duct or cable entrance when a main breaker is not used. Also utilized when utility metering or full height control section is required.

• Main Section - used to contain a main breaker and may house metering and feeder breakers.

• Feeder Section - used to contain feeder breakers and other equipment such as instrumentation.

• Tie Section - used to contain a tie breaker and other equipment such as feeder breakers.

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Main Sections

The accompanying graphic shows the possible configurations for WL LV switchgear main sections, which are sections that include a main breaker, but not a tie breaker.

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Main and Tie Sections

The accompanying graphic shows the possible configurations for WL LV switchgear main and tie sections, which are sections that include a main breaker and a tie breaker. A tie breaker is a circuit breaker used in systems with two power sources. The tie breaker allows the user to select which source provides power to the load.

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Tie Sections

The accompanying graphic shows the possible configurations for WL LV switchgear tie sections, which are sections that include a tie breaker without a main breaker. A tie breaker is a circuit breaker used in systems with two power sources. The tie breaker allows the user to select which source provides power to the load.

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Feeder Sections

The accompanying graphic shows the possible configurations for WL LV switchgear feeder sections, which are sections that include feeder breakers and do not include main or tie breakers.

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Front Accessible Features

The WL LV switchgear design incorporates exceptional front access to key features. For example, all breaker settings and displays are clearly visible with the breaker door closed. The breaker can also be racked into its connect, test, or disconnect positions with the breaker door closed.

Control and communication wiring is routed through vertical and horizontal wireways in the front of each breaker compartment and separated from the power cables which are terminated in the rear. Opening the breaker door provides access to the vertical wireway.

Standard control and communication wiring is number 14 AWG extra-flexible, stranded copper type SIS.

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Bus Design – Part 1

The standard main bus is silver-plated copper. Tin-plated copper bus is optionally available. Vertical and horizontal bus bars utilize a channel shape design to maximize short circuit withstand capability and minimize heat rise. All bus joints include grade 5 bolts and conical spring washers. Provisions for future extension of the main bus include plated joints and high tensile strength steel hardware.

The main three-phase horizontal buses are arranged vertically one phase above the other with edge-to-edge alignment to provide high, short circuit strength. Insulated main bus with isolated vertical bus is optional.

Vertical bus ratings available are 1600, 2000, 3200, 4000, 5000, and 6000 amps continuous current. Horizontal bus ratings available are 1600, 2000, 3200, 4000, 5000, and 6000 amps continuous current.

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Bus Design – Part 2

A neutral bus is furnished when specified, and can be rated 1600, 2000, 3200, 4000, 5000, or 6000 amps continuous current.

A 1/4” x 3” standard copper ground bus extends through all sections. Cable lugs are mounted to the ground bus in each section. Standard short-circuit withstand (4 cycle) and short-time withstand (60 cycle) bus bracing is 100,000 amperes. Higher short-circuit withstand bus bracings (150 kA and 200 kA) are available.

Load side runbacks for feeder circuits are copper construction, are insulated with sleeve tubing in the main bus area, and are supported by high-strength bus bracing.

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Compartments

Each complete vertical section contains the following three compartments:• Front compartment containing breakers

and/or auxiliary equipment• Bus compartment containing the

horizontal and vertical buses• Rear cable compartment containing the

load-side runbacks connecting the load side of the breaker to the load cable terminals.

Within the front compartment, each breaker is barriered and compartmented from all other breakers. This design also isolates the breakers in the front compartment from the bus compartment.

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Optional Barriers and Lugs

Optional barriers can be supplied to isolate the bus compartment from the rear cable compartment. Other optional barriers include:

• Full depth section barriers to isolate one section from the adjacent section(s).

• Barriers to isolate the incoming line side connections to the main breaker(s) from the load-side bus and connections in the switchgear section.

(Note: line/load barriers are provided as a standard feature for service equipmentmain breakers.)

Cable compartment mechanical lugs are standard. Compression lugs are available as an option. If requested and supplied, lugs can be pointed directly to the rear or rotated up or down at 45 degree angles.

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Siemens Advantages

In summary, WL low voltage metal enclosed switchgear offers a number of significant advantages.

The small foot print for switchgear sections minimizes the amount of space required, saving on construction costs for new facilities and simplifying installation for existing facilities.

It incorporates advanced WL circuit breaker features such as Extended Instantaneous Protection, which reduces the impact of system faults, and Dynamic Arc Flash Sentry, which increases worker safety.

It offers many features, such as the elimination of front ventilation and heat sinks and a unique and rugged bus design, that enhance system reliability and reduce maintenance costs.

Its flexible design incorporates many field-installable accessories and front-accessible control and communications connections, thereby reducing the cost of adapting the system to changing facility requirements.

And finally, its extensive communication capabilities provide the ability to interconnect WL switchgear with other equipment to enhance system-wide control, reliability, and energy management. Page 2-13


Four-pole WL LV Switchgear

Four-pole breakers provide the neutral isolation capability that is advantageous for low voltage switchgear applications where multiple, separately-derived power sources are individually grounded.

In a typical 3-phase, 4-wire main-main or main-tie-main LV switchgear application, the neutral is solidly connected throughout the equipment and is grounded (bonded) at each incoming source. This provides multiple paths for ground fault and normal neutral current to flow. If a three-pole breaker is used in conjunction with traditional residual or zero sequence ground fault, nuisance ground fault tripping and/or failure to trip on ground fault can occur.

With a four-pole main breaker, the neutral is disconnected (isolated) when the breaker is open, and, provided that only one main breaker is closed at a time, the problems associated with multiple neutral grounding points and multiple paths for ground fault and normal neutral current are eliminated.

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Four-pole WL LV Switchgear Sections

The accompanying graphic shows the possible configurations for four-pole WL LV switchgear sections.

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Front-connected WL LV Switchgear

With traditional rear-connected LV switchgear, each vertical section contains the following three compartments.• Front compartment containing breakers and/or auxiliary

components.• Middle compartment containing vertical and horizontal bus• Rear compartment containing breaker connections(line and/or

Typically the breaker connections are cables ,but could be busway.

With front-connected LV switchgear, the rear breaker connection compartment is relocated to a separate vertical section beside the vertical section containing the breakers. All incoming and outgoing breaker connections are accessible from the front.

Front-connected WL LV switchgear is typically wider than a comparable rear-connected LV switchgear lineup, but it isn’t as deep and doesn’t require rear working space. While the front -connected LV switchgear footprint may be larger than a comparable rear-connected switchgear lineup, the total required electrical room space (including working space) is typically smaller.

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Marine LV Switchgear

Siemens offers LV switchgear for marine and offshore applications. Siemens WL Low Voltage Switchgear can be manufactured to meet ABS, USCG, DNV and Lloyd’s of London standards. Additionally, all Siemens Type WL LV switchgear is built to the applicable UL, ANSI, and IEEE standards.

Equipment Ratings• 635V AC maximum• 3-phase 3-wire, 3-phase 4-wire• 50/60 Hz• 6000 amp maximum horizontal bus• 6000 amp maximum vertical bus• Silver-plated copper bus standard, tin-plated

copper optional• Standard bus bracing 100kA –optional up to

200kA

Seismic QualificationSeismic qualification to all major seismic construction standards (IBC, UBC, CBC, SBC, BOCA and IEEE 693) is available.

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• Arc Resistant LV Switchgear

• Sm@rtGear LV Switchgear

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Arc Fault and Arc Flash

There are two broad categories of electrical faults, bolted faults and arc faults. Bolted faults occur in conductors that are solidly connected when no arcing occurs. Standard design low voltage metal-enclosed switchgear withstands the mechanical forces that occur on load terminals as a result of a bolted fault (within equipment specifications) until a circuit breaker has time to interrupt the fault current.

Arc faults occur when electricity flows through air. Arc faults can be caused by a variety of conditions such as overvoltage, corrosion, excess humidity, aging or overstress of insulation, improper installation and maintenance practices, the intrusion of small animals, etc.

For conductors operating at the voltage levels found in a typical residence, arc faults are a problem because of their potential to cause a fire. Hence, the increased requirement for arc fault circuit interrupters in residential environments.

At higher voltage and current levels, such as those found in commercial, institutional, industrial, and utility applications, arc faults pose an even greater safety hazard. At these higher energy levels, an arc fault can result in an arc flash, where heat energy is suddenly and often explosively produced. An arc flash can cause temperatures and explosive forces sufficient to vaporize equipment. Because of the hazards posed by arc flashes, numerous safety standards have been put in place to enhance workplace safety. Page 2-20


Switchgear Testing Standard

Because the danger from an arc flash increases with the energy level, arc flash safety has long been a concern for equipment operating at medium voltages and higher. However, the potential for an arc flash is present with low voltage switchgear as well.

As a result of the increased awareness of the need for arc flash protection in low voltage switchgear, IEEE standard C37.20.7 (IEEE Guide for Testing Medium-Voltage Metal-Enclosed Switchgear for Internal Arcing Faults ) was revised to include low voltage metal-enclosed switchgear that is intended to be designated arc resistant. The revised standard is IEEE standard C37.20.7-2007 (IEEE Guide For Testing Metal-Enclosed Switchgear Rated Up To 38 kV For Internal Arcing Faults).

The revised standard does not require all metal-enclosed switchgear to be designated arc resistant, nor does it define the design changes needed for metal-enclosed switchgear to be considered arc resistant. However, because of the safety issues involved, it does set rigorous testing requirements that a switchgear design must comply with to be designated arc resistant.

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What Does Arc Resistant Mean?

Because the causes of internal arcing and the potential for an arc flash cannot be may be present and undetected, and it is not always possible to de-energize power distribution equipment when someone is nearby, companies are required to comply with a number of standards intended to improve workforce safety. Even the best safety practices, however, cannot guarantee worker safety.

One additional step that companies can consider when replacing existing low voltage switchgear or designing new or expanded facilities, is to use arc resistant low voltage switchgear, but what does arc resistant mean in this context?

For one thing, it means that the switchgear has successfully completed testing in accordance with the IEEE C37.20.7-2007. This means that the equipment has been constructed to provide an additional degree of protection in the event of an arc flash.

This specification identifies two zones of accessibility in relation to the equipment that identify the area for which additional protection is provided. Equipment tested to provide type 1 accessibility provides additional protection only from the front. Equipment tested to provide type 2 accessibility provides additional protection from the front, back, and sides. Each of these accessibility types requires that all equipment covers and doors are installed and closed. These accessibility levels are often shown with suffix letters. Suffix A applies if no other suffix letter is applicable. Suffix B indicates that the arc-resistant functionality extends to designated low voltage compartments.

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WL Arc Resistant Low Voltage Switchgear

Ratings• ANSI/IEEE Type 2B accessibility• Maximum internal arcing short-circuit current: 100 kA @ 508 V and

85 kA @ 635 V• WL power circuit breaker frames range from 800 A to 6000 A • 3 and 4 pole WL power circuit breakers• Maximum arcing duration: 500 msec• Vertical bus continuous current ratings to 6000 A• Horizontal bus continuous current ratings to 6000 A• Maximum voltage: 635 V• 3 Phase 3 Wire, 3 Phase 4 Wire• 50/60 Hz

Industry Standards• UL-1558• ANSI/IEEE C37.20.1• ANSI C37.51• ANSI/IEEE C37.20.7

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Standard Features

Siemens arc resistant low voltage switchgear provides an added degree of protection over standard metal-enclosed switchgear. In addition to bolted faults, Siemens WL arc resistant low voltage switchgear is designed and performance tested to ANSI/IEEE C37.20.7 to provide protection from the hazards of internal arcing faults.

Standard Features• ANSI/IEEE Type 2B Arc Resistant to protect personnel at the front, back and sides of the equipment.• UL listed, performance tested and classified as arc resistant in accordance with ANSI/IEEE C37.20.7.• Reinforced enclosure to withstand pressure from internal arcing faults.• Internal venting system with pressure dams and pressure vents to channel the flow of arc fault gases and vent these

gases out the top of the gear and away from personnel.• Reinforced and gasketed front doors with additional hinges and latching means.• One piece circuit breaker compartment doors with insert panels for control devices such as fuses, indicating lights,

and circuit breaker control switches when required.• Reinforced bolted rear covers.• Insulated/Isolated bus bar system.• Integrally-designed circuit breaker door sealing frame that allows the user to rack a circuit breaker to connect, test or

disconnect position without having to install additional hardware (bellows, shrouds, etc) and still maintain arc resistant rating of the apparatus.

• Shutters in circuit breaker compartments.• Riser base with integrated arc plenum.• Four high power circuit breaker stacking capability. No additional stacking/configuration restrictions.• All section configurations available. Available in solidly grounded or resistance grounded configurations.• Non-fused, non current-limiting circuit breakers allow full power coordination.

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Recommended Optional Features

The following optional features of WL arc resistant LV switchgear provide additional protection and are recommended where appropriate.

Overhead plenum with exhaust duct. The system is designed to transfer the byproducts of the arcing event (smoke, particulate matter, heat, etc.) away from the immediate vicinity of the low voltage switchgear when an internal arcing fault occurs. Typically, the exhaust duct will vent the byproducts to a location usually outside of the room in which the low voltage switchgear is located. The overhead plenum is attached to the roof of the low voltage switchgear, and can be exhausted in any direction ((left, right, forward, backward) away from the switchgear assembly or unit substation.

Dynamic Arc Flash Sentry (DAS). DAS employs the unique dual parameter setting capability of the ETU776 trip unit, coupled with the ability to easily toggle to a lower arc flash parameter set. A normal operation parameter set can be optimized for selective trip coordination, while the second set is optimized for lower arc flash energy levels. The dynamic action comes from the ability to switch from the normal operation set to the arc flash limiting set based on the presence of personnel as they approach the flash protection boundary.

Zone Selective Interlocking (ZSI). If WL circuit breakers are arranged in several levels and minimum delays are desired, it is advisable to use the ZSI module. The circuit breakers are interconnected by these modules. In the event of a short-circuit, all circuit breakers communicate to determine and isolate the exact short-circuit location. Thus, only the closest upstream circuit breaker will be opened. The ZSI module provides the complete range of selectivity with the short delay time of tzsi = 50 ms. By shortening the delay time, the ZSI module significantly reduces arc duration, stress and damage in the event of a short-circuit in the switchgear.

High resistance grounding. Reduces available fault current during ground faults, thereby reducing arc energy.

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How-to Video Library

This extensive library of short videos was created by our instructional experts to meet the real-world needs of industry, with all levels of experience in mind. By providingon-demand, how-to instruction in easy-to-understand bites, the How-to Video Library helps maintain the critical industrial and manufacturing knowledge and skills developed during instructor-led training courses. Videos are typically three-minutes long and conveniently available via any computer or mobile device with Internet access.

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• Arc Resistant WL LV Switchgear

• Sm@rtGear™ LV Switchgear

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Sm@rtGear™ Low Voltage Switchgear

Traditional hard-wired remote control panels provide additional safety, but Siemens Sm@rtGear™ low voltage switchgear (LVS) can provide the same breaker remote control plus remote monitoring and configuration of all embedded intelligent devices.

Siemens Sm@rtGear™ low voltage switchgear (LVS) is pre-configured and pre-programmed low voltage metal-enclosed switchgear that provides out-of-the-box remote monitoring, configuration, and control of embedded intelligent devices.

The Sm@rtGear™ LVS communication backbone is installed and tested at the Siemens factory, and the user only has to connect the three communication cables that connect the low-voltage switchgear to the remotely-mounted touch screen human machine interface (HMI).

The remote HMI allows the user to access the intelligent devices embedded in the switchgear. Using the HMI, the user can monitor, configure, and control the intelligent devices. TheSm@rtGear™ LVS CPU acts as the local master and can also be a remote slave tied into an upstream supervisory system.

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Standard Features

Sm@rtGear™ LVS has the following standard features:

• Industrial computer with pre-programmed software to remotely monitor, configure, and control embedded intelligent devices and structural monitoring devices.

• 22-inch touch screen human machine interface (HMI) is pre-configured and programmed with application-specific graphics.

• Communication backbone links embedded intelligent devices, CPU, and HMI.

• ETU776 trip units in all breakers support Dynamic Arc Flash Sentry (DAS) that enables arc flash incident energy reduction.

• Electrically-operated breakers with spring charge motor, shunt trip, and remote closing coil.

• Metering and protective relaying functionality in all breakers.

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Remote HMI

The remote HMI communicates with the entire system architecture to monitor, configure, and control the Smart LVS from a safe distance outside of the arc flash boundary. A partial list of the preconfigured and built-in features available with the Smart LVS includes:

• Remote configuration, monitoring and control• Arc flash hazard calculation• Self-diagnostic data• Preventative/predictive maintenance data• Environmental data• Product documentation• Maintenance/status reports that summarize data for all

installed devices.

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Optional Features

Sm@rtGear™ LVS optional features include:

• Hot-swappable, redundant PLC• Environmental monitoring (ambient temperature, humidity,

smoke, and water)• Bus bar temperature monitoring• Power cable temperature monitoring• Autothrowover - When the primary power source does not

meet specifications, the system automatically switches to an alternate source.

• Zone differential relaying• Load shedding• Open breaker door monitoring and alarm• Control power monitoring• Breaker trip coil monitoring• Strip heater monitoring• Remote breaker racking device• Enhanced historical event logging• High resistance grounding

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Simulators

Engineered to provide a real-world experience, Siemens simulators are fully functional, ready-to-use systemsavailable in a variety of configurations.

System-level design makes the simulators an invaluable tool for program testing and debugging, reinforcing learning, shop floor troubleshooting, and more. With portable construction and hard-shell cases, they can be easily transported. Custom-built systems are also available.


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SITRAIN® Training for Industry

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SITRAIN World

From the basics to advanced specialist skills, Siemens SITRAIN courses deliver extensive expertise directly from the manufacturer and encompass the entire spectrum of Siemens Industry products and systems.

Worldwide, SITRAIN courses are available in over 200 locations in over 60 countries.

For additional information including a SITRAIN world map and SITRAIN contacts worldwide: http://sitrain.automation.siemens.com/sitrainworld/Default.aspx

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Course Completion

This course covered the following topics:Chapter 1 - Introduction

• Overview• WL Power Circuit Breakers

Chapter 2 – WL LV Switchgear• WL LV Switchgear Design• Arc Resistant LV Switchgear• Sm@rtGear LV Switchgear

This course has covered the topics shown on the left. Thank you for your efforts. You can complete this course by taking the final exam and scoring at least 70%.

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