EE314|Electrical Systems Design-Building Services

EE314|Electrical Systems DesignELECTRICAL SAFETY: Voltage Surge Protection

Course Coordinator & Lecturer: Mr. Hamendra ReddyContentsOvercurrent protectionEarth leakage protectionOvercurrent vs Overvoltage protection Standards requirementsCircuits 2014 H.Reddy, The University of the South PacificEE 3142So far in overcurrent protectionOvercurrent protectionReduce chances of fire: Causes i2Rt heat in conductors that could lead to fire if not managed well.Protection against electrical shock (ventricular fibrillation): Circuit breaker/fuses work best for severe overload (worst case being short circuit condition) when fault currents reach over 5x rated value. Breaker time is stipulated by all international standards (AS 3000/BS 7671) as 0.4 seconds for final sub-circuits where portable hand held apparatus would be plugged in. and 5 seconds for other circuits.Circuit breaker is only protects human life in the circumstances when human body bridges active an neutral. HOWEVER, protection depends on the circuit breaker type or setting at the source end of the circuit.Hence it can be safely concluded that C/B an/or fuses (the device that is equipped to detect overcurrent mainly suffices fire protection) 2014 H.Reddy, The University of the South PacificEE 3143Human Protection and EarthingEarthing circuitA redundant conducted reticulated in the low voltage AC wiring that it connected to all exposed and accessible conducting parts of appliances and fixtures to allow low impedance path if active to earth breakdown occurs. This will allow the circuit breaker to detect the fault easily.Earthing also allows any unbalanced currents (in 3-phase) and leakage currents to exit.Leakage currents can occur in heaters between heating elements and the appliance body since they are mainly made of metals. Standards require a minimum resistance of 10 kiloOhms.Human protection against electrical shockA residual current device (RCD) is used with a general setting of any earth leakage more then 10mA should isolate the circuit within 0.4seconds. It detects the vector difference between the active and neutral currents. So anyone touching just the active conductor will have currents flowing to ground therefore there will be a difference between active and neutral currents.

2014 H.Reddy, The University of the South PacificEE 3144Voltage Surge Protection and IEEE & ANSI C62.41.2What causes voltage surges?Large starting currents in adjacent circuits.Transient surges.LIGHTNING!How does it affect circuits?Higher voltages means providing larger potential for the charge to flow effectively pushing the components beyond limits before they breakdown.IEEE & ANSI C62.41.2recommended surge protection levels for indoor and outdoor electronic equipment connected to the mains power lines. for outdoor applications, requires the recommended surge protection level of 6 kV/3 kA for low exposure conditions and, 10 kV/10 kA for high exposure conditions. 2014 H.Reddy, The University of the South PacificEE 3145Voltage Surge Protection and IEEE & ANSI C62.41.2 2014 H.Reddy, The University of the South PacificEE 3146Source: Philips Application Notes: Protecting LED systems in accordance with IEEE & ANSI C62.41.2; Transient Surge Requirements; 2011SPD connection scheme

Voltage Surge Protection and IEEE & ANSI C62.41.2 2014 H.Reddy, The University of the South PacificEE 3147Source: Philips Application Notes: Protecting LED systems in accordance with IEEE & ANSI C62.41.2; Transient Surge Requirements; 2011SPD connection scheme

Voltage Surge Protection and IEEE & ANSI C62.41.2Category C SPDStandard testsOptional testExposure1.2/50 s Voltage generator

Minimium open-circuit voltage evaluationto be applied to SPD8/20 s Current generator

Current to be driventhrough the SPD100 kHz Ring Wave forfront-of-wave responseMinimium open-circuit voltage evaluationLow6kV3kA6kVHigh10kV10kA6kA 2014 H.Reddy, The University of the South PacificEE 3148 The scope of these tests is limited to SPDs, in contrast with all the other recommended tests that may be applied to equipment other than SPDs. Values shown for the current are applicable for each phase of the SPD. In contrast with a test applied to equipment for the purpose of assessing its response to the surge environment, a test applied to characterize the performance of an SPD requires that the specified current be driven through the SPD. For the low exposure, this can be accomplished with a typical Combination Wave generator. For the high exposure, twoseparate generators, in two successive tests, must be used to apply the specified values. For low exposure tests, if a Combination Wave generator is used instead of two separate generators, the generator charging voltage has to be adjusted to obtain the stated current amplitude.Voltage Surge Protection and IEEE & ANSI C62.41.2 2014 H.Reddy, The University of the South PacificEE 3149Source: Philips Application Notes: Protecting LED systems in accordance with IEEE & ANSI C62.41.2; Transient Surge Requirements; 2011Combination wave open circuit voltage

Voltage Surge Protection and IEEE & ANSI C62.41.2 2014 H.Reddy, The University of the South PacificEE 31410Source: Philips Application Notes: Protecting LED systems in accordance with IEEE & ANSI C62.41.2; Transient Surge Requirements; 2011SPD categories staircase

Voltage Surge Protection and IEEE & ANSI C62.41.2 2014 H.Reddy, The University of the South PacificEE 31411Voltage Surge Protection Types ANSI/UL 1449-2006.Type 1- A permanently connected SPD intended for installation between the secondary of the service transformer and the line side of the service disconnect overcurrent device, as well as the load side, including watt-hour meter socket enclosures and intended to be installed without an external overcurrent protective device. Also previously known as surge arrestors with rating of 10kA ~ 20kA for discharge currentType 2- A permanently connected SPD intended for installation on the load side of the service disconnect overcurrent device, including SPDs located at the branch panel.