abb_rcd_protection_press_geig_02122010.pdf

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ABB GroupDecember 16, 2010 | Slide 1

Ian Richardson, Product Manager, December 2010

Goldfields Electrical Industry GroupRCDs and the Wiring Rules


Examining RCDs and the Wiring Rules

AS/NZS3000:2007

RCD Arrangements as per AS/NZS3000:2007

Current danger curves

RCD Operation

Load types and the effect on RCD selection

RCD Classification

Nuisance Tripping

Some Applications


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AS/NZS3000:2007

Prepared by Joint Technical Committee EL-001

Joint Australian and New Zealand standard

Published on 12 November 2007

All new installations are currently bound by the newstandard



Some notes in AS/NZS3000:2007 with respect to RCDs

Clause 2.6 Additional protection by residual current devices

Selection Clause 2.6.2.1

Types of RCDs Clause 2.6.2.2

Arrangement Clause 2.6.2.4



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RCD Arrangement requirements of AS/NZS3000:2007

Clause 2.6.2.4 Additional protection by residual current devices

Not more than three final sub circuits protected by any one RCD

If there is more than one RCD and more than one lighting circuit, thelighting circuits must be distributed between the RCDs

In domestic installations having more than one final sub-circuit, aminimum of two RCDs shall be installed.


Additional requirements of EnergySafety, Department of Commerce WA

Since August 2009, people selling their home and all landlords must ensure

two RCDs are installed to protect power and lighting circuitsHome sellers are required to install prior to sale and landlords before a new

tenant moves in

Landlords must install in any case prior to 9 August 2011


Effects on the body Current danger curvesIEC 60479-1


Increasingrisk ofventricular

fibrilation

AC-1 Perception

possible but usuallyno startled reaction

AC-2 Involuntary

muscular

contraction-noharmful effects

AC-3 Strong

muscularcontractions,

reversibledisturbance toheart function

AC-4 Possible

cardiac arrest,breathing arrest,

ventricular fibrilation

30


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2. Tripping relay

6. Primary

conductor

8. Secondary circuit

Transformer-tripping device circuit without residual current

A0

2

8

6

Residual Current Devices (RCDs) RCDs: the electromagnetic relay as actuator



2. Tripping relay6. Primary

conductor

8. Secondary circuit

Transformer-tripping device circuit withresidual current

A0

2

8

6

Tripping of switchingmechanism

Residual Current Devices (RCDs)

RCDs: the electromagnetic relay as actuator



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According to the load type,the waveforms of the earth faultcurrents can be different in terms of shape and frequency and canbe classified in four types:

Linear loads (resistance, impedance, capacitor) generate, in the case ofan earth fault, a sinusoidal alternating current, suddenly applied or slowlyrising, maintaining the frequency of the voltage supply.

Refer clause 2.6.2.2 Note 2 (a)

Line current Earth Fault current


Protected by a Type AC RCD


Non linear loads (diode, transistor, etc) generate, in the case of an earthfault, an alternating and/or pulsating current with a DC component,suddenly applied or slowly rising

Refer clause 2.6.2.2 Note 2 (b)



Protected by a Type A RCD


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Presence of a device that contains a rectifier section (like a half waverectifier, three-phase simple or double half-wave rectifier, single-phasedouble half-wave rectifier) can generate a smooth DC current.

Refer clause 2.6.2.2 Note 2 (c)

PE

Three-phase star

N

L1L2L3 I

IB IB

t

I

t

I

t

IB

tPEN

L1

L2L3

I

IB

Six-pulse bridge



Protected by a Type B RCD


Some situations may require a time delay on the residual currentprotection specifically designed to attain a predetermined operating timedelay, corresponding to a given value of residual current.

Refer clause 2.6.2.2 Note 2 (d)

Often used upstream in conjunction with other rapid residual currentoperated circuit breakers to guarantee selectivity and limit the poweroutage to the portion of the system affected by the fault.


Protected by a Type S RCD


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AS/NZS3000:2007 Wiring Rules clause 2.6.2.1RCDs shall be so selected, and the electrical circuits so sub-divided,that any leakage current that may be expected to occur during normaloperation of the connected load or loads will be unlikely to causeunnecessary tripping of the device

Notes:

RCDs may operate at any value of residual current in excess of 50% ofthe rated residual current.

To avoid unwanted tripping because of leakage currents and transientdisturbances.it is recommended that the loading of a circuit does not

exceed one third of the rated residual current.

Nuisance tripping


Why splitting circuits is a general recommendation?

The increased in use of electronic devices that contain EMC filters in an installation provide an accumulationof earth leakage currents.

Typical values of earth leakage current of electronic devices are shown in the table below.

To

1,5 mA

1 mA

0,75 mA

1 mA

2 mA

Earth leakage current

around 1 mAFilters

0,5 mAPhotocopiers

0,5 mAFax machines

0,5 mASmall portable appliances

0,5 mAPrinters

1 mAComputers

From

Appliances

Nuisance tripping

For example: A typical office final sub-circuit may trip with as few as eightcomputers on a 30mA RCD protected circuit.


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An Alternate Solution

Consider three different samples of RCDs*:

Instantaneous RCD 30mA

Selective RCD 300mA

Hi Immunity Type RCD 30mA

The different behaviour has been illustrated in the nextslides.

* these values result from tests on single devices therefore valuesare representative only of this phenomenon.


The instantaneous 30 mA intervenes around 22mA with a tripping time 35mswhich decreases with the increase of the I nup to 10mA.

Instantaneous tripping characteristic

Instantaneous 30 mA



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The selective 300mA intervenes at around 200mA with a tripping time of180ms, which reduces with the increase of the Inremaining however higher

than that of the 30mA instantaneous.

Selective 300mA

Selectivetripping characteristic

Instantaneous 30 mA



Selective 300mA

Instantaneous 30 mA

High immunity30mA

The 30mA high immunity intervenes at around 25mA with a tripping time of 100..120ms whichdecreases with the increase of the I

nup to 20 ms remaining always however in the same trippingzone of a 30mA instantaneous.

High immunity RCD tripping characteristic



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Application notes: when does a high immunity RCD solve specificsituations

1. Presence of an overvoltage due to lightning

2. Simultaneous switching of fluorescent lamps withelectronic ballasts

3. Simultaneous connection of computer or electronicdevices

4. Devices with capacitors which connect phases to the

earth installed in a long length circuit

5. Installation of Soft starter/Variable Speed Drive motor controllers


abb_rcd_protection_press_geig_02122010.pdf

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