In an electrical circuit, the electric current normally enters the phase and leaves the neutral. If there is no leakage in a properly functioning electrical circuit, the input current and the output current are equal to each other. However, if there is a leakage in the circuit, in this case, part of the electric current entering from the phase is over neutral and some part is over the leakage. As a result, the balance between phase and neutral is disturbed by the leakage current. The residual current protection relay is a device that recognizes this imbalance and opens the circuit. In this way, unwanted situations resulting from leakage are prevented.
There may be many causes of electrical leakage. Cables over which electrical current passes may be crushed or frayed, insulating parts in electrical equipment may be worn and worn out, electrical equipment may be faulty insulation. In these cases, the conductors remain exposed and leakage current is generated if people contact these conductors directly or with another conductive object. This leakage current flows to the soil.
Leakage currents on damaged cables or device connections can sometimes cause an arc and may cause a fire. The arc generated by a leakage current of 300 mA creates a high temperature for the ignition of objects. If a device with a leakage current is touched by hand, the electric current flows through the human body and can cause serious injury and death. The human body is a conductor and the leakage current passing through the body flows into the ground and completes the circuit.
Importance of Measurement of Fault Current Protection Schemes
The Regulation on Grounding in Electrical Installations, issued in 2001, defines the fault current as the current passing through an insulation failure. The fault current can be a short-circuit current or a ground contact current. The earth fault current is the current flowing to the ground of the electric current if the line has only one earth contact point. According to the regulation, an earth fault current must be interrupted in less than half a second.
Grounding systems are installed against the potentials that may arise in case of the highest fault currents threatening human health and safety. There are three important points in such a system: the value of the fault current, the duration of the fault condition, and the characteristics of the soil.
In the measurement of fault currents protection devices, it is determined whether the specified values are met by using the appropriate dimensioning devices. The measurement mainly consists of the following quantities: insulation resistance, earth resistance, loop resistance, partial discharge voltage, touch voltage and leakage current.
In this regulation, the leakage current is defined as the current flowing from an error-free current circuit to earth or to a foreign conductive object.
In the Annex of the Regulation on Health and Safety Conditions in the Use of Work Equipment, related to maintenance, repair and periodic inspections (Annex-III), measurement of fault current protection devices (leakage current relay test operations) is included in the subject of installations.
Legal regulations to be considered include:
- Regulation on Grounding in Electrical Installations
- Regulation on Electrical High Current Plants
- Electrical Internal Facilities Regulation
- TS EN 60079-14 Electrical devices - Used in explosive atmospheres - Part 14: Design, selection and installation of electrical installations
- TS EN 60079-17 Explosive gas atmospheres - Part 17: Inspection and maintenance of electrical installations
- TS EN 61008-1 Residual current circuit breakers - Without integral overcurrent protection - Used in domestic and similar places (RCCB) - Part 1: General rules
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