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Ground-Fault Relay Advancement and

the EL731 Earth Leakage Relay

Presented by

Adam Detillieux and

Jeff Glenney, P.Eng.

WMEA San Antonio 2012

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First a Few Safety Tips

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Be EXTRA Careful when you are working and

Fatigued. Recognize the Signs!

I asked a customer his opinion on some of the signs:

What do you think Monte?

Slumped shoulders

Shut eyes

Nodding Forehead

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Age isn’t always the culprit

Wearing Appropriate PPE

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For Safety use the RM Buddy System

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Littelfuse Business Units

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Electrical Business Unit

Littelfuse offers over 50,000 SKU’s covering every

circuit protection need for multiple markets:

• Automotive

• Construction

• Electronics

• Energy/Utilities

• Engine/Generator Control

• Industrial / MRO

• Marine

• Mining

• Telecom

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Ground-Fault Products

Ungrounded DC

Systems SE-601

Solidly or Resistance

Grounded Systems

(PGR-4300, SE-701, SE-704, etc)

Ungrounded Systems

(PGR-3100 & PGR-3200)

Grounded DC System or

Resistance Grounded Systems EL731

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Ground-Fault in a Single-Phase

System

IFault 120 V

15 A

BLACK

WHITE

GREEN

RECEPTACLE

TOASTER

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Historical GF protection.

Iron Core CT’s and Spinning Discs

Older electromechanical relays as shown

required drive to spin the discs to reach the

targets and cause the relay to operate. Modern

circuits don’t require the same energy.

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Courtesy of Jack Woodham – Jedson Engineering

Power System Grounding Course

System Failures – Short Circuits (Faults)

Industrial Power Systems

1. LINE TO GROUND

2. PHASE - PHASE

3. THREE PHASE

FAILURE MODE

PERCENTAGE

OF FAILURES

MOST THREE PHASE FAULTS ARE MAN-MADE:

I.E. ACCIDENTS CAUSED BY IMPROPER OPERATING

PROCEDURE.

98 %

<1.5 %

<.5 %

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Challenges in Mining Applications

Using Ground Fault CT’s on the high resistance

grounded systems where there is much less

current available

Detection levels need to be able to detect faults

even on extremely low levels. (0.5 A grounding

resistors are common in many mining

applications)

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THE BEST WAY TO DETECT AN AC GROUND-FAULT:

• CURRENT SENSING

– Usually with a zero-sequence core-balance

current transformer (CT or ZSCT)

– Permits selective coordination and

ease of finding a fault

Sensing Ground-Faults

in a Grounded Electrical System

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Locating Phase Conductors in a

Zero-Sequence-CT Window

Symmetrically locate the phase conductors in the CT window

The gap between the conductors and the CT should be at least

12.7 mm (0.5 in)

It is preferable to have a gap of 25.4 mm (1 in) or more

GAP A

B C

SPACER

C C

A

A

B

B

FLUX

CONDITIONER

C

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Keep the conductors at a 90 degree angle

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Introducing the EL731

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EL731 Main Features

AC/DC ground fault protection and metering for solidly

grounded or resistance-grounded systems

Temperature monitoring and metering

Wide frequency response (0- 15 kHz)

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EL731 Faceplate

Trip: LED Indication

Alarm: LED Indication

CT: CT Verification LED

32 Character OLED Screen

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TYPICAL APPLICATIONS

EL731 can monitor for ground-faults on AC or DC systems

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Variable Frequency Drives

VFD/ASD’s are used extensively in

heavy industry

Benefits of VFD’s

1. Speed Control

2. Reduced power consumption

Disadvantages of VFD’s

1. Harmonics

2. Ground fault’s are also variable frequency

These drives require additional protection

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Misconceptions about VFD ground faults

VFD’s DO NOT isolate the load

– a ground-fault at the load is seen at the line side

Often, built in ground-fault protection is not

designed for HRG

– Designed for solidly grounded system

– Trip level is not adjustable (usually 50% of IL )

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SE-70x series with VFD

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Earth was obviously involved

But the ground fault was not detected!

What Happened Here?

The System:

• Low-voltage

• Variable-speed drive

• 5-A neutral-grounding resistor (NGR) Some type of fault occurred with

The Result:

• Melted copper and steel

• Luckily, no fire

Is Inability to Detect a GF in an ASD System a Problem?

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What Happened Here?

The System:

• Low-voltage

• Variable-speed drive

• 5-A neutral-earthing resistor (NER)

Could the damage be the direct result of the earth fault?

No.

P = I2R and IGF ≤ 5 A. Furthermore, for 5 A to flow, the fault

impedance R must = 0 Ω (so P=0). As fault impedance rises,

current decreases and power dissipation at the fault is small.

0

200

400

600

0

10

20

30

40

50

60

70

80

90

10

0

11

0

12

0

13

0

14

0

15

0

16

0

17

0

18

0

19

0

20

0

Watt

s

Fault Impedance (Ohms)

Fault Power Dissipation 600-Vll, 5-A NGR

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What Happened Here? A Theory

A phase-to-winding connection became

disconnected in the terminal box, but electrical

continuity was maintained by (hi-impedance)

contact with the grounded terminal-box cover.

VFD

Motor 51G > 5 A

Iθ = Imotor + 5 A, max

IGF = 5 A max

This fault wouldn’t cause an overcurrent trip

And the ground fault was not detected

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SYSTEM CAPACITANCE

All electrical systems have phase-to-earth capacitance

• distributed throughout the system

• modeled here as “lumped” values

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CHARGING CURRENT

Definition of charging current:

The current that flows when one phase of an

unearthed system is shorted to earth

Note: A core-balance CT at “1” will measure charging current

A core-balance CT at “2” will measure zero

2 1

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CHARGING CURRENT & SYMPATHETIC TRIPPING

A core-balance CT on an unfaulted feeder will detect its feeder’s

charging current when an earth fault occurs on another feeder.

• To avoid sympathetic tripping, protection must be set above the charging current level

• Protection level may be set below charging current if sympathetic tripping is acceptable

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CAPACITANCE UNBALANCE

Balanced Phase-to-Earth Capacitance: Xa=Xb=Xc

• Phase capacitive currents are equal

• Core-balance CT reads zero.

Unbalanced Phase-to-Earth Capacitance: XaXbXc

• Phase capacitive currents are not equal

• Core-balance CT reads a finite value

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SE-70x Frequency Response

Frequency (Hz)

Filte

r O

utp

ut

SE-70X Frequency ResponseVariable Frequency Peak Detection

10 20 30 40 50 6070 100 200 300 400500 700 10000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

Peak-Detection Filter

(labeled as Variable Frequency)

400 Hz 1000 Hz

Conventional ground fault

relays have a limited

frequency response.

VFD’s and DC systems need

accurate DC-60Hz

measurement.

VFD’s often have significant

high frequency harmonic

components that should be

monitored.

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Broad Spectrum Ground Fault Monitoring

Use either CT1, CT2, or both CT1: 0-90 Hz CT2

20-15000 Hz

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EFCT- Earth Fault Current Transformer

EL731 requires EFCT series current transformer

Continuously monitors CT health

CT1 & CT2 have independent trip settings

CT1: 0-90 Hz

• 30-5000 mA trip level

• 0-2 s trip time

CT2: 20-15000 Hz

• 30-5000 mA trip level

• 0-2 s trip time

• Low-pass filter 20-90 Hz

• High-pass filter 190-15000 Hz

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THIRD HARMONICS: A Special Case

In 3-phase systems third harmonics are in-phase

• their values add; they do not cancel

+ +

=

Can cause nuisance earth-fault tripping Example: Fundamental & 3rd harmonic

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Multiple primary turns supported (up to 6)

1. Wrap the primary n times around the CT

2. Program n using EL731 controls

3. View ground fault current without conversion

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Temperature Monitoring

VFD’s can cause excessive motor heat due to:

– Harmonics

– Slower internal fan speed at lower frequencies

EL731 is the only ground-fault relay on the

market with temperature protection.

Trip or alarm on over-temp

View real time temperatures

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DC Ground Fault Monitoring

Feature: Ability to detect DC faults with a CT

Unit will trip if fault is downstream of CT

Can use multiple EL731’s on

various legs of system

Alternate technology (SE-601)

allowed 1 per system.

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Outputs

3 Programmable Form C Contacts – Trip or Alarm (other functions!!)

– Fail-safe/ non-fail-safe

– Trip memory (fail-safe system)

4-20 mA analog out

Remote reset

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Communications Capable

Communications available in a variety of protocols

– DeviceNet -Ethernet

– Profibus -Modbus

Flash upgradeable via optional communication adapter

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Use Web Browser to View/Change Parameters

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Password Protected option

1st of our ground-fault relays with this feature.

Important if you know of any customers that

were removing knobs to make it more difficult to

change settings on SE-704’s or SE-701’s

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Mounting Options

Metering on the door

Panel-mount adapter not required for door

mounting.

Optionally available surface-mount adapter

(AC700-SMK)

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Rigorous Testing

100% of the relays are tested on computerized test jigs. Shown here mounted on racks for burn-in testing. The relays are powered up and kept in the burn-in room at 60 degrees C for 3 days.

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PWB – Conformal Coating… MIL 1-46058 qualified UL QMJU2 recognized

Adds resistance to moisture, corrosion and mold, lessens the impact of mechanical stress, vibrations and its improves its ability to cope in extreme temperatures.

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EL731 Overview

•Designed for: •AC Systems

•Variable-Speed Drives

•Grounded DC Systems

•Main features •Full spectrum ground-fault monitor

•Temperature monitoring

•Metering

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Conclusions

There are a wide variety of Ground-Fault Relays

available

There are some ideally suited for the hi-tech

demanding requirements of mining customers

Next WMEA will discuss our 480V and 600V

GFCI’s

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Thank you

Questions?