overview protection relays

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OverviewProtection Relays

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The Power In

Ground Fault Detection, Location, and Protection ProductsA comprehensive line of ground fault protection products, utilizing the latest in technology, and covering a multitude of applications and sy-stems. BENDER‘s ground fault relays safeguard equipment, personnel, and processes while reducing your costs and system downtime.

Global Experts in Electrical SafetyFor over 70 years, BENDER has been a global leader in ground fault protection. With over 50 agencies and partners across the globe, BENDER has a local office to help you from the design phase through the support phase. Our years of technical experience and broad portfolio of products utilizing the latest in protection technology will help you create the best solution to meet your needs. Top-notch service and support ensure that your electrical network remains in peak condition. From industrial plants to mines to hospitals, customers trust BENDER to protect their electrical systems.

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www.bender.orgYour online electrical safety resource

n Complete listings of products with comparisons, documentation, datasheets, and technical information

n Your electrical safety questions answered in our extensive knowledgebase with application notes

n Ground Fault Relay and GFCI Selection Tools

n Current Transformer Sizing Application

n Complete Isolated Power Solution Builder

n Local representative information

Electrical Safety

Voltage and Current RelaysA multitude of protection relays for monitoring system performance and safety outside of ground fault protection. Voltage relays, current relays, frequency relays, and more provide predictive maintenance and troubleshooting for your electrical system.

Hospital Isolated Power SystemsHospital grade isolated power panels and monitors to ensure your critical areas remain fault-free. Our panels are built to your specifi-cations and include the state-of-the-art LIM2000plus Line Isolation Monitor.

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Ground Fault Detection / LocationUngrounded AC/DC Systems

Reduce system downtime and provide predictivemaintenance capability by locating ground faults quickly

Reduce maintenance costs by detecting groundfaults before a hazardous situation occurs

BENDER Ground Fault Detectors for Ungrounded SystemsUngrounded systems offer an invaluable advantage - a first ground fault does not generate sufficient leakage current to create a hazardous situation. Early detection allows for critical systems to remain online while problems are located and resol-ved. BENDER Ground Fault Detectors and Location Systems detect ground faults quickly and easily across all types of applications, including DC systems as well as systems containing variable frequency drives (VFDs).

Online Ground Fault Location - the BENDER DifferenceWhen others say ground fault location in an ungrounded system is not possible, BENDER says it is. The EDS series of ground fault location products offers fast and easy-to-use location of faults with both portable and installed options. BENDER‘s advanced EDS system can locate ground faults down to the load level to find the faulty device, all while the system remains online.

The BENDER AdvantageBENDER‘s complete line of ground fault products for ungrounded systems offers impressive advantages to keep your system online and running healthy:

n Exceeds requirements for NEC 250.21(B) and CEC 10-106(2) for ground detectors on ungrounded systems

n Works in AC, DC, and AC/DC applications up to 7.2 kV

n Works with Variable Frequency Drives (VFDs)

n Detects symmetrical faults

n AMP measuring principle allows for accurate insulation measurements across all types of systems

n Simple and fast ground fault location in ungrounded AC and DC systems with both portable and fixed equipment

n Reduce cost, reduce downtime, and protect vital equip ment and processes with accurate early warning ground fault detection and location

Complete Ground Fault Location System

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IR425-D4 - Ground Fault Detector - Low Voltage AC/DC Ungrounded SystemsThe IR425-D4 Ground Fault Detector monitors ungrounded AC/DC circuits up to 300 V for early indication of ground faults. A digi-tal display gives real-time readings of the system‘s insulation resistance to ground to provide predictive maintenance capability and troubleshooting for ground faults. Its compact size allows for easy installation and retrofitting.

IRDH275 and IRDH375 - Ground Fault Detectors - Ungrounded AC/DC SystemsThe IRDH series of ground detectors provides state-of-the-art protection for your ungrounded system. The AMP Plus measuring principle ensures that an accurate measurement is taken through all forms of power conversion, such as DC rectifiers and drives. A digital display gives a real-time reading of the system‘s resistance. Optional RS-485 communication is available.

EDS3090 - Portable Ground Fault Location System - Ungrounded AC/DC SystemsThe EDS3090 provides a portable location system to quickly find ground faults in any size system. The system can be used in conjunction with BENDER‘s installed ground fault detectors or on its own as a completely portable location system. The simple clamp-on meter provides quick location of faulty loads. Installed location devices additionally provide RS-485 communication.

Ground Fault ProductsUngrounded AC/DC Systems

Features

n For AC and DC systems up to 300 V

n Digital display with real-time readout

n Adjustable setpoint from 1 to 200 kΩ

n Two separately adjustable alarms with

N.E. / N.D. SPDT contacts for each

Features

n For AC and DC systems up to 793 VAC, 650 VDC (voltage couplers extends range up to 7.2 kV AC. 1.6 kV DC)


n Adjustable setpoint from 1 kΩ to 10 MΩ

n Two separately adjustable alarms with

Features

n For AC and DC systems

n Installed and portable versions

n Quickly identify and locate ground faults

n RS-485 communication with installed

location devices for remote indication

More information: bender.org/ir.aspx

More information: bender.org/irdh.aspx

More information: bender.org/eds.aspx

Applications

n Single-phase AC and DC systems

n Industrial control circuits

n Remote operated vehicles

n Low-voltage motors and drives

n General low-voltage applications

Applications

n Single- and three-phase AC and DC

n 480 V / 600 V industrial systems

n Variable frequency drives

n Solar fields

n Offshore platforms

n Backup battery systems

Applications


n Large motor control centers

n Ships

n Power stations

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Ground Fault MonitoringGrounded AC/DC Systems

Protect equipment from damage and fire andreduce your bottom line

Protect personnel from shock hazards and injury

BENDER Ground Fault Monitors for Grounded SystemsBENDER ground fault relays provide critical protection for personnel and equipment in environments where safety is a must. The RCM series provides advanced warning of ground faults without the problems associated with nuisance tripping on grounded and high-resistance grounded systems. Accu-rate tripping across steplessly adjustable setpoints means BENDER‘s RCM series can easily be tailored to your particular application. Output contacts can be used for indication, inter-ruption, or both.

AC/DC True RMS Detection - the BENDER DifferenceThe RCM series provides relays that not only protect AC, but pure DC power as well. Pure DC measurements are still taken via a special current transformer. Digital versions feature true RMS reading of the leakage current. The multi-channel relays even feature harmonics analysis of the leakage current down to the 40th harmonic. This device also features RS-485 commu-nication capabilities for remote analysis.

The BENDER AdvantageBENDER‘s complete line of ground fault products for groun-ded and high-resistance grounded systems offers impressive advantages to keep your system online and running healthy:

n Works on AC, DC, and AC/DC systems

n Utilization of a single current transformer means voltage and load current do not impact measurements

n Works on systems with Variable Frequency Drives (VFDs)

n Digital series provides true RMS readings and frequency ranges up to 2000 Hz

n RS-485 communication capability for remote monitoring and integration into signaling systems

n Reduce cost, reduce downtime, and protect personnel and and equipment with BENDER ground fault protection AC/DC Multi-Channel Ground Fault Monitoring System

Grounded SystemCurrent transformersfor AC/DC loads (0 2000 Hz)

Current transformersfor AC loads (42 2000 Hz)

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RCM470LY - Ground Fault Monitor - Grounded and High-Resistance Grounded AC SystemsThe RCM470LY family of ground fault monitors detects ground faults in grounded and high-resistance grounded AC systems, both single-phase and three-phase. A wide, steplessly adjustable trip range allows for flexibility in application and installation. A DPDT alarm contact can be utilized for both remote indication as well as power interruption.

RCMA420 - Ground Fault Monitor - Grounded and High-Resistance Grounded AC/DC SystemsThe RCMA420 monitors for ground faults in grounded and high-resistance grounded AC and DC systems. Features include a true RMS reading, real-time values displayed on its LCD screen, and two separately adjustable alarms with an SPDT contact for each. This device is perfect for grounded and high-resistance grounded systems running variable frequency drives (VFDs).

RCMS460 / RCMS490 - Multi-Channel Ground Fault Monitors - Grounded and High-Resistance Grounded AC/DC SystemsThe RCMS family detects ground faults in grounded and high-resistance grounded AC and DC systems. Up to 12 separate channels may be connected to one device. Features include a detailed LCD display of each individual channel‘s value, harmonics analysis, and contact outputs for each individual channel on the RCMS490 model. RS-485 communication is also available.

Ground Fault ProductsGrounded AC/DC Systems

Features

n LED bar graph indicating ground fault

n Adjustable trip level from 10 mA to 10 A (optional 6 to 600 mA trip range available)

n Failsafe or non-failsafe mode selectable

n N.E. / N.D. DPDT contact output

Features

n True RMS readings


n Adjustable setpoint from 30 to 500 mA

n Two separately adjustable alarms

n Works with DC power and drives

Features

n For AC and DC systems

n Digital display indicates real-time values for each individual channel

n Quickly identify and locate ground faults

n RS-485 communication, DPDT contact outputs; 490 model features individual outputs

More information: bender.org/rcm.aspx

More information: bender.org/rcma.aspx

More information: bender.org/rcms.aspx

Applications

n Single- and three-phase AC

n General industrial use - panel boards, motors, generators, and more

n Heat tracing systems

Applications



n Variable frequency drives (VFDs)

n DC battery systems

Applications



n Large motor control centers

n Heat tracing systems

n DC battery systems

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Ground Fault Circuit InterruptersGrounded AC/DC Systems

Lifeguard Series Ground Fault Circuit InterruptersThe BENDER Lifeguard series of Ground Fault Circuit Interrup-ters gives your system the added safety of both ground fault detection and interruption. The Lifeguard series is customiz-able to fit the needs of your system, from load amperage (up to 100 A standard, higher versions available upon request), voltage (including 480 V and 600 V systems), trip level, and more.

The BENDER AdvantageBENDER‘s complete line of ground fault circuit interrupters offers impressive advantages to keep your system online and running healthy:


n Customizable to many different types of systems, including 480V and 600V three-phase systems

n Many setpoint options available: 6 mA, 20 mA, or steplessly adjustable options

n 6 mA and 20 mA options operate on an inverse time curve per UL943

n Connection monitoring and grounded neutral protection

n Customizable enclosure options available, including NEMA 4X fiberglass and stainless steel options

Protection Against Nuisance TrippingThe Lifeguard GFCI contains a special ground fault monitor that protects against nuisance tripping while still maintaining the level of protection you require.

Features of the 6 mA and 20 mA versions include:


n Inverse time curve for tripping per UL943

n Advanced filtering circuitry

n Connection monitoring

n Grounded neutral protection

Features of the adjustable versions include:

n Works on AC (AC/DC version available)

n Adjustable trip level

n Adjustable time delay

n Connection Monitoring

Inverse time tripping curve built into BENDER‘s6 mA and 20 mA versions

Applications

n Motors and Drives

n Pumps

n Generators

n Spas and pools

n Construction

Build your GFCI online: Visit bender.org/selector/gfci.

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VME420 and VMD420 - Voltage and Frequency RelaysThe VME420 (single-phase AC and DC up to 300 V) and VMD420 (three-phase AC up to 500 V) relays are powerful, all-in-one devices monitoring overvoltage, undervoltage, overfrequency, and underfrequency. Precise, explicit values may be entered in for alarms and real-time values may be viewed via the onboard LCD display.

CME420 - Current RelayThe CME420 monitors for overcurrent and/or undercurrent in AC systems. The digital display gives real-time readouts of the current being measured. The CME420 may be directly connected to a system up to 16 A. The device may also be connected to x/5 current transformers. Entering the current transformer ratio into the device will negate the need for any type of calculations.

Voltage and Current RelaysAC and DC Systems

Features

n True RMS readings


n Precise voltage and frequency alarms may be entered

n Two separately adjustable alarms

n Works with DC power and drives

Features

n True RMS readings


n Precise alarm values may be entered

n Two SPDT contacts

n May be directly connected (up to 16 A) or connected via an x/5 current trans- forner

More information: bender.org/voltage-relays.aspx

More information: bender.org/current-relays.aspx

Applications


n General industrial use

n Battery monitoring and charging stations

n Dump load controller

n Generators

Applications

n AC systems

n General industrial use

n Generators

n Pumps

n General load monitoring

BENDER Voltage and Current Relays for AC/DC SystemsBENDER‘s portfolio is not just limited to ground fault protec-tion - it also includes powerful safety relays for monitoring many different aspects of an electrical system. The VME420, VMD420, and CME420 monitor for many different alarms, including voltage, current, phase loss, phase sequence, and more. True RMS readings are shown via digital displays in real-time. Two highly configurable SPDT contacts on each device may be set to trigger on whichever type of alarm your application demands. Optional versions also include standard analog out-puts (0 - 10 V, 0 - 20 mA, 4 - 20 mA) for remote signaling.Current relays may be connected either directly to the system or through current transformers. If a current transformer is used, the ratio may be entered into the CME420. Once this is entered, you may set alarms and view readings as if the device were directly connected - no calculations necessary.

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Communication

Integrate BENDER Devices Into Your Safety NetworkMany BENDER ground fault detection devices can be linked together across a communication network for remote moni-toring. Utilizing a special protocol across RS-485, these devices can give control stations detailed information as to the condition of the system. Gateway devices utilizing standard protocols such as Ethernet, MODBUS and PROFIBUS ensure your BENDER system is easily integrated into an exisiting com-munication system. Special remote indicators placed in critical areas and connected to the network can also display device information. Many devices also support settings changes via remote communication.

The BENDER Advantage

n Fast, detailed information and parameterization from a central point

n Easily integratable into an exisiting communication system

n Gateway device to standard protocols such as Ethernet, MODBUS, and PROFIBUS

n Option to view status of all devices via a web browser

n E-mail and SMS alerts when an alarm becomes active

n Optional Remote indicator station provides information on all connected devices

n Reduce costs and downtime

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Accessories

Current Transformers

Name Features and Description For Use With

W Series Current transformers for use in single-phase and three-phase AC systems RCM series, RCMS series, EDS series

WAB SeriesCurrent transformers for use in single-phase and three-phase AC and DCsystems

RCMA420, RCMS series

WF SeriesFlexible, rope-style current transformers for use in single- and three-phase AC sy-stems

RCMS series

More information: bender.org/ct.aspx

Remote Indication

Name Features and Description For Use With

9604 and 7204 SeriesAnalog external meters indicating percen-tage towards alarm for RCM devices or in-sulation reading for IR devices

RCM470LY, RCM420-DM Series,IR470LY, IRDH Series

MK2430 Digital remote indicator for multiple de-vices connected via RS-485

IRDH B Versions, EDS Series,RCMS Series

More information: bender.org/remotes.aspx

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Information and ApplicationsUngrounded Systems

Ungrounded Systems

Floating systems are derived from a power source where there is vir-tually no connection to ground. 480VAC delta configured transformers are a typical supply for a floating system. Some deltas in the mining industry can be found in hoists. 480VAC deltas are also in wide spread use to supply 1000Amp - 2000Amp main feeder circuits in general industrial applications. Floating systems are often used in areas where a sudden shut down must not occur. Examples are intensive care units (ICUs) in hospitals, signal circuits, and emergency backup systems.

The magnitude of ground fault current in an ungrounded system on a first ground fault is very small. It depends on the system voltage, the resistance of the ground fault causing part and the system capacitances.

Example: If a grounded object with low resistance touches a live con-ductor, the resulting current flow will be negligible. The ground fault loop will be incomplete because the return path to the source is mis-sing. Grounding may only occur through system leakage capacitance to ground. The Possible resulting current is also known as charging current.

On a single ground fault, ungrounded systems will not produce the amount of fault current needed to trip a common GFR. The IMD is the device of choice for the protection of floating systems.

T2

T3

T1

GND

Leak

age

capa

cita

nce

L1

L2

L3

L1

L2

L3

Gro

und

Fau

lti.e

. D

ead

shor

t

circuit breaker motor, 3 phsupply side, 480 VAC

The ungrounded system with one ground fault path.

The Active IMD on AC SystemsAn active IMD is the ground detector of choice for ungrounded systems. The active IMD can detect ground faults regardless of quantity and severity, as well as the ability to have early warnings and trending.

The active IMD is considered to be an online megger. It connects via pilot wires between the system and ground. A constant measuring signal is sent from the IMD into the power wires. It will spread out evenly into the secondary side of the transformer and the attached loads. If this signal finds a breakthrough path to ground, it will take this path of least resistance and return to the monitor. The IMD‘s internal circuitry will process the signal and trip a set of indicators when the resistance of the fault reaches a certain trip level. By the nature of the ungrounded system, leakage current may or may not be present at this time, however the ground fault will still be seen through the insulation resistance. Because of this, IMDs measure in Ohms (resistance) and not in Amps (current). A ground fault will be indicated as insulation breakdown.

A good insulation value for a typical system would be a value of multiple kΩ to MΩ. A low insulation value for a typical system would be low kΩ to less than one kΩ. However, the value of a system‘s overall resistance may vary depending on the number of loads, type of insulation used, age of the installation, environmen-tal conditions, etc.

T2

T3

T1

GND

L1

L2

L3

L1

L2

L3

GF

(i.e

.D

ead

shor

t)

BenderIMD relay (1)

V 1G=4

80 V

V 2G=4

80 V

V 3G=0

V

AMP measuring mode

circuit breakersupply side, 480 VAC motor, 3 ph

Ungrounded three-phase AC system with BENDER IMD

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Information and ApplicationsUngrounded Systems

The Active IMD on DC Systems

The active IMD is the preferred choice for ungrounded DC systems as well. As in floating AC systems, a DC IMD will be connected via pilot wires between the system and ground. A constant measurement signal will be sent from the IMD into the power wires. From there, it spreads out evenly into the secondary side of the supply (e.g. a battery) and the attached loads. Again, the signal will take the path of least resistance and return to the monitor if it finds a breakthrough to ground.

For DC systems, as well as AC systems that have varying volta-ges or power conversion equipment including variable fre-quency drives, a special measurement signal is applied. BENDER‘s AMP Plus measurement principle, found in devi-ces such as the IRDH275, have the ability to be used univer-sally in AC, DC, and AC/DC systems, as well as overcoming adverse system conditions, such as high leakage capacitance.

Supp

ly s

ide:

Batt

ery

syst

em12

5/25

0 V

DC

Schematic 21: 125 / 250 V DC system with Bender IMD technology

L1

L2

circuit breaker

+

-+

- V 1N=1

25 V

V 2N=1

25 V

L1

N

L2

V 12=2

50 V

V 2G=1

25 V

V 1G=1

25 V

125 V load 250 V load

BenderIMD relay (1)

GF

= r

esis

tanc

e br

eakd

own

to 1

000

Ohm

s on

tw

o le

gsi.e

. ca

ble

unde

rwat

er(B

alan

ced

faul

t si

tuat

ion)

AMP measuring mode

Ungrounded 125/240 VDC system with BENDER IMD

Ground Fault Location in an Ungrounded System

Locating ground faults in an ungrounded system is simple with the right technology. The techniques are different than loca-ting ground faults in a grounded system. In a grounded system, locating faults is done via a multi-channel Ground Fault Relay utilizing current transformers to pick up on leakage current for each individual circuit/load. However, due to the nature of the ungrounded system where a first ground fault will not create leakage current, a different technique must be employed.

Ground fault location in an ungrounded system can be done via a fixed installation, portable devices, or a combination of both.

A controlling device with a pulse generator is present upstream in the system. This device sends a low level artificial signal into the faulted system. The signal will be impressed between the power wires and ground. Naturally, it will follow the ground fault path into ground and return to the pulse generator. This signal can be traced with special fixed current transformers or a special portable current probe. This method works while the system is still online, and ground faults can be located down to the load causing the problem while all systems remain in operation.

Ground Fault Location - Fixed Installation

The fixed installation is useful where 24/7 monitoring is required, as well as giving portable location a head start as to which cir-cuit is causing the problem. The system consists of the following:

- IRDH575 Ground Fault Detector and Controller

- EDS460 or EDS490 Ground Fault Location Devices

- W series current transformers

The Bender EDS ground fault location - detection system is an excellent tool for the maintenance personnel in a large facility with extensive wiring. Faults will be located automatically during normal business operation. No shutdown is required. No hand-held tracing and/or accessing panels is required. The beauty of this system lies in its non invasive operation. The ungrounded system is only safe for its user as long as the occurring faults are immediately traced down and eliminated. If that is not the case, then the second ground will follow sooner or later and short circuit the system.

Ground Fault Location - Portable

The EDS3090 portable ground fault location series can be used as a completely standalone location system or used in tandem with installed units. Pulse generation is done either by an installed IRDH575 or a portable pulse generator that can be connected up to the main system. The pulse is traced via a hand-held clamp. The general pro-cess for this system is by starting at the point of pulse generation, and tracing the pulse down to the load causing the ground fault with the clamp. Ground faults can be located quickly and easily while the system remains online and operational. Using the EDS460 and EDS490 installed ground fault locators in tandem with the portable EDS3090 system gives technicians a head start as to where to begin clamping.

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Information and ApplicationsGrounded Systems

Grounded Systems

Grounded systems are derived from a power source where the neutral is solidly tied to ground via a ground neutral bonding jumper (NG). Often encountered is the typical three phase 208/120V Y or 480/277V Y configuration. Another possibility is a single phase transformer where the neutral is tied into ground or sometimes, in very rare occasions, corner-grounded delta configurations are employed. The general public is very familiar with solidly grounded systems due to the fact that nearly every residence in the U.S. is derived from a 240/120V trans-former with center tap. The center tap is bonded solidly to ground.

As always, there are advantages and disadvantages to the grounded power system. One disadvantage is the high amount of possible fault current in a ground fault situation. Fire damage or personnel injury can occur. Nevertheless, a tripped overcurrent breaker or a GFCI will enable the electrician to quickly identify a faulty branch. Action will often be taken after a fault has occurred. Preventative main-tenance is not necessarily associated with the grounded system.

Neutral Ground (NG)Jumper

T2

T3

T1

GND

L1

L2

L3

L1

L2

L3

V

V12=480 V V13=480 V

V23=480 V

V3G=277 VV

VNG=0 V

circuit breakersupply side, 480 / 277 VAC motor, 3 ph

The grounded system.

The magnitude of a ground fault current in a solidly grounded system can be very high. Its magnitude depends on the system voltage and the resistance of the ground fault causing part itself. The ground fault current can easily reach a value which is multiple times higher than the nominal load current. A simplified calculation will explain how the high amounts of current are generated:

IF = Fault Current

V3G = Voltage between faulted phase and ground

RGF = Resistance value at shorted point

RGR = Resistance of ground path

RNG = Resistance of neutral ground bonding jumper

A theoretical fault current will be devastating if a dead short occurs. Nevertheless, a ground fault relay or overcurrent protec-tive devices should trip immediately and interrupt power from the load. How many Amps would flow if a human would touch the same circuit? Answer: Replace the dead short value of 0.1 Ohm with a more realistic figure for a human body part. Lets assume that a person is resting on the frame of a motor. For example, assume 1000 Ω of resistance from phase L3 and a human body.The current is a multiple of 15 mA, which is considered to be the let-go value for humans. 50 mA is considered to be lethal.


L1

L2

L3

L1

L2

L3

Motor, 3 ph

T2

T3

T1

GND

Fault 1(break)

Fault 2 (GF)i.e. dead shortResistance = 0.1 Ohm

VV3G=277 V

Fault current path via ground(resistance assumed 0.2 Ohm)N

G p

ath

(res

ista

nce

assu

med

0.1

Oh

m)

circuit breakersupply side, 480 / 277 VAC

The grounded system with a single ground faultand broken ground.

Ground Fault Relays on Grounded Systems

Most technicians are very familiar with a current transformer based ground fault current relay. Even non-technical personnel encoun-ter them on a daily basis in public restrooms protecting a wall outlet in a wet area. The operating theory behind the relay is as follows. A current transformer (CT) or “donut” is placed around the power wires leading to the protected load. It is important that hot and neutral wires are fed through the CT. This goes for both, single phase and three phase systems. One might come across a three- phase system without a neutral, feeding a pump or an industrial motor. In this case the three phases only will be fed through the CT.

For three-phase systems, if a neutral is carried out to the load, it should be fed through the CT. The ground fault relay will still func-tion properly when monitoring a load not using the neutral.

�� 0.1 Ω � 0.� Ω � 0.1 Ω � ��.� �

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Information and ApplicationsGrounded Systems

The current transformer will always read zero current in a healthy system even under a full load condition. In accordance with Kirch-hoffs laws, incoming and outgoing currents will cancel each other out. Assume a 10A load connected to a 480/277VAC system. 10A will be fed from the source into the load, therefore 10A will have to return from the load back to the source. The CT will measure both simultaneously since it is placed around all conductors.

The schematic below is a typical application of current transformer based ground fault detection. In a healthy system, the current across all three phases will equal zero.

A ground fault (as an example, 1 A) will divert some of the current from the arrangement and bypass the CT via the ground wire, a frame or the building ground and return back to the source.

The new equation for the CT is now: 10A - 5A - 4A = 1A where 10 A goes into the load, 9 A returns to the source via the phase L2 and L3, and 1 A returns to the source via the ground wire. The CT will step the current (1A) down and forward it to the Ground Fault Relay (GFR). The GFR will then alarm when its set point has been increased. The GF relay in combination with a zero sequence CT will work in resistance grounded systems as well. It will run into its limitations in circuits where waveform modifying equipment, such as Variable Frequency Drives (VFDs), or rectifier components are installed.

Grounded DC Systems

Bender RCMA devices monitor DC and mixed AC/DC systems. The unique measuring principle can be used for protection if the DC system is grounded as shown below. In this case the negative pole of the DC power supply or the battery is tied into a chassis or the building ground. The active CT would be placed around both, the negative and positive conductor leading to the load. A DC leakage current will bypass the CT through ground.

Variable Frequency Drives

60 cycle GFRs have limitations when the circuitry involves VFDs (Variable Frequency Drives). A variable frequency drive converts the incoming AC internally into DC, which will then be modulated again into a variable cycle AC leading to the load. Internal VFD - DC grounds can not be detected with conventional GFR technology. The common “passive” CT needs alternating currents to detect a ground fault, therefore DC currents will go unnoticed. Some drives may be equipped with their own internal scheme to detect ground faults which will eventually trip in the high Ampere range. Early war-ning or personnel protection cannot be guaranteed in this case.


T2

T3

T1

GND

L1

L2

L3

L1

L2

L3

I1=10 A Fault 1(isolation)

I1=5 A

I1=4 A

I1=1 A

BenderGF relaywith summationtransformer


transformer,passive motor, 3 ph

The grounded system with single ground faultwith ground fault relay.

L+

L-

I(L+)=10 A

BENDER RCMA relaywith active transformer

+

- I(L-)=9 A

Fault(isolation)

IF=1 A

V

V (L-G

)=0 V

V

V (L+G

)=24

V

GN

D

T2

T1

A1

A2

F1

F2

circuit breakersupply side, 24 VDC

transformer,active

motor, DC

Grounded 24 VDC system with single fault andRCMA technology


T2

T3

T1

GN

D

L1

L2

L3

L1

L2

L3diode SCR

Rectifier InverterEMI filter DC link

PossibleAC fault60 Hz

CapacitiveleakagethroughEMI �lters

InternalDC fault

AC faultVariablecycleAC faults


BENDER RCMA relaywith active transformer

variable frequency drive motor, 3 ph

The grounded system with drive and RCMA technology

Other issues include: EMI filters sometimes incorporated into drives can provide a leakage path to ground and add to the overall system leakage; multiple KHz carrier frequencies used can cross the gap bet-ween insulation and ground; and harmonic content. The solution: Pro-tect by means of an active current transformer with built-in filtering technology. RCMA devices employ a double-coil system which enables them to accurately measure AC, DC, and mixed AC/DC currents from 0 to 2000 Hz.

Solutions For Your Electrical Safety NeedsWith our complete portfolio of relay protection products

For over 70 years, BENDER has been a leader in meeting elecrtical safety needs with our large portfolio of ground fault protection products. BENDER products enhance the safety of electrical systems and help to save money, reduce down-time, and give the peace of mind that your system is protected by the latest in electrical safety technology.

n Ground Fault Monitors and GFCIs for grounded and high-resistance grounded systems

n Ground Fault Detectors for ungrounded systems

n Voltage, Current, and Frequency Relays

n Remote Communication Solutions

General Purpose Protection RelaysGround Fault Protection for Ungrounded Systems

Ground Fault Protection for Grounded Systems

n A-ISOMETER® Ground Detector Series

n EDS Ground Fault Location Systems

n RCM Series Ground Fault Monitors for Single-Phase and Three-Phase AC Systems

n RCMA Series Ground Fault Monitors for Single-Phase AC, Three-Phase AC, and DC Systems

n RCMS Series Multi-Channel Ground Fault Monitors for Single-Phase AC, Three-Phase AC, and DC Systems

n Lifeguard Series Ground Fault Circuit Interrupters for Single-Phase AC, Three-Phase AC, and DC Systems

n Undervoltage and Overvoltage Relays for AC and DC Systems

n Overfrequency and Underfrequency Relays

n Overcurrent and Undercurrent Relays for AC and DC Systems

Communication Solutions

n Standard Protocol Converters for Ethernet, MODBUS, and PROFIBUS

n Customizable Visualization Capabilities

n Simple System Integration

Visit www.bender.org for information, tools, and more:n Complete listings of products, documentation, datasheets, and technical information

n Knowledgebase of technical information answering your ground fault questions

n Product selection tools, including ground fault relays, currrent transformers, and more

n Local representative information

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Canada5 Edvac Dr, Unit 14 • Brampton, ON L6S 5P3Toll-Free: 800-243-2438 • Fax: 905-799-3051

North American Headquarters700 Fox Chase • Coatesville, PA 19320Toll-Free: 800-356-4266 • Fax: 610-383-7100

USA, West Coast Office4555 West Chermak St • Burbank, CA 91505Toll-Free: 800-236-3378 • Fax: 818-565-3552

www.bender.org • E-mail: [email protected]

overview protection relays

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