Earth Fault Breaker
Extracted by Chew Bee Teng
PROTECTION AGAINST EARTH FAULTS
With Earth Leakage Circuit Breaker (ELCB) or Earth Leakage Switch
These units are also called Residual Current Circuit Breaker (RCCB) or Residual Current Device (RCD).
ELCB’s/RCCB’s and Earth Leakage Switches/RCD’s are devices capable of sensing earth leakage current and interrupting the circuit automatically when these currents exceed a predetermined value. An earth leakage current is the current flowing to earth from live parts of an installation.
CBI Earth Leakage Protection Devices are the core balance type which monitors the difference in the current flowing in the live and neutral conductors. Under healthy conditions the vector sum of the currents in the live and neutral conductor will equal zero and no operation is necessary. If an earth fault occurs the live and neutral currents will not balance and the difference will be detected by the Earth Leakage Circuit Breaker or Earth Leakage Switch. This imbalance is used to open the circuit and thereby stopping the current flow. This is also true for three or four wire circuits, whether or not the load is balanced or unbalanced, the vector sum equals zero.
EARTH LEAKAGE TRIPPING CURRENT (SENSITIVITY)
This is measured in milliamps (mA) and is referred to as the degree of protection in an accidental shock hazard situation.
CBI follow the IEC Standard 1008/1009 of 30 mA sensitivity for domestic and personal protection with the tolerance of 30 mA plus zero and minus 50%, that is, a range from 15 mA to 30 mA. CBI earth leakage units are manufactured to operate in the tolerance band of 19 to 26 mA.
For personal protection 30 mA offers a high degree of protection and will operate by cutting off the earth fault current well within the time specified in the IEC Publication 1008/1009.
Lower sensitivities above 30 mA are sometimes used for individual circuits where there is less chance of direct contact such as in hot water tanks in a roof or under floor heating. These earth leakage units from 100 to 375 mA provide reasonable protection from the risk of electrical fires, but it should be noted that under certain circumstances a current of less than 500 mA flowing in a high resistance path is sufficient to bring metallic parts to incandescence and start a fire.
TEST BUTTON
All earth leakage units are provided with a test button. When pressed, the test button causes an imbalance to simulate an earth fault operation. The test button should be pressed often to prove the unit is in working order. If the unit does not trip instantly, expert advice should be sought to check the electrical installation.
WHY ELECTRONIC AND NOT ELECTROMECHANICAL ELCB’S?
South Africa's 40 years of experience in the manufacture and application of sensitive earth leakage protection devices, together with the more recent global experiences covering millions of installed units over several decades have resulted in a better understanding of not only the advantages, but also of the limitations of ELCB’s.
In Europe, where electromechanical ELCB's are used almost exclusively, the question of reliability of installed ELCB’s has become a subject of major concern and attention. The popular hype regarding perceived reliability of electronic components was not sufficient to prevent CBI, some five years ago, from changing their entire ELCB range from electromechanical to electronic technology ELCB’s. The improvements in reliability that resulted from this decision are complemented by their freedom from safety performance limitations often found in lower specification electromechanical earth leakage circuit breakers.
FUNCTIONAL EARTH CONNECTION
The statistical probability of accidents resulting from broken neutral conductors is relatively low, since several fault conditions would be required to occur simultaneously for a hazardous situation to arise. In recognition, however, of even the remote possibility of hazardous situations arising, this potential shortcoming in ELCB’s has been entirely overcome by the introduction of a FUNCTIONAL EARTHING connection into modern electronically operated ELCB’s.
The functional earth provides an alternative path for ensuring the continuity of supply energy to the ELCB even in the event of a total break in the neutral supply conductor. The low energy requirements of modern ELCB’s ensure safe and reliable operation of the ELCB even in extreme situations where the earth return path bond resistance is orders of magnitude higher than that normally permitted by mandatory or utility regulations.
Under normal operating conditions, the functional earth (FE) circuit is quiescent and does not influence the performance of the ELCB, whether the FE is connected to earth or not.
The connected FE circuit becomes operative immediately a total break or high impedance in the neutral conductor is detected, ensuring full protection even under abnormal conditions.
APPLICATION
GRZ100 is a full-scheme high-speed numerical distance relay applied to transmission lines of a solidly earthed network.
The relay can be integrated with a local PC or a remote PC through a communication port.
GRZ100 provides the following protection schemes.
As a backup protection for high-resistance earth faults, GRZ100 furnishes the following four functions.
A local PC can be connected via the RS232C port on the front panel of the relay. A remote PC can also be connected through the RS485 port on the rear panel of the relay.
GRZ100 has five models which differ according to incorporation of auto-re-close function or a fault detector.
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Model 100 |
－Minimum configuration model －No auto-re-close －No fault detector |
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Model 200 |
－With auto-re-close for single breaker scheme －No fault detector |
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Model 300 |
－With auto-re-close for one and a half breaker scheme －No fault detector |
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Model 400 |
－With auto-re-close for single breaker scheme －With fault detector |
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Model 500 |
－With auto-re-close for one and a half breaker scheme －With fault detector |
GRZ 100
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