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Janet Roadway Product Manager, Power Breakers Curva Tempo-Corrente FFF 1E4s 1E3s 100s 10s 1s 0.1s 1E-2s 0.1kA 1kA 10kA Discrimination of protection devices on installations Topics of Discussion Explaining the terminology Degrees of discrimination Different techniques to achieve discrimination Backup protection Protection devices Any Questions? Protection - Basics Lets go back to basics……… •Question: Why do we use protection devices???? •Common Ans: To prevent Faults Wrong! Protection whether by fuse, circuit breaker or relay cannot prevent faults from happening. Only good design, high quality components, careful installation, preventative maintenance along with good working practices can prevent major faults However, protection devices can limit the damage and inconvenience caused if faults occur. Protection - Overload What do we mean by a fault? Overload Operating condition in an electrically undamaged circuit which causes an current to flow in excess of the full load current Example: Starting condition during DOL start If this type of fault continues indefinitely because of an anomolous operating condition., damage begins to occur creating………. Protection – Short Circuit What do we mean by a fault? Short Circuit Operating condition in an electrically damaged circuit where there is an accidental or intentional connection by a relatively low resistance between two points of a circuit which are normally at different voltages This type of fault can generate high current flows, arcing and fire if not cleared quickly Discrimination Coordinate devices to: Guarantee safety for people and installations Identify and exclude only the zone affected by a problem Limiting the effects of a malfunction Reducing the stress on components in the affected zone Ensuring service continuity with good quality supply voltage Achieving a valid compromise between reliability, simplicity and cost effectiveness Explaining the terminology Discrimination or Selectivity To make it possible to isolate a part of an installation involved in a fault condition from the overall system such that only the device located immediately on the supply side of the fault intervenes Discrimination Needs Fast Fault Detection Fast Fault Elimination Let-Through High Energy Reduction Fault Current Withstanding WAIT! CONTINUITY OF SERVICE GO! FAULT FAULT DAMAGE Explaining the terminology X A XB Fault occurs here XC Degrees of discrimination Total Discrimination This means that the isolation described occurs for all fault levels possible at each point of the circuit Degrees of discrimination t B A Prospective Fault Current Icc I Degrees of discrimination Partial Discrimination This means that above certain current levels there is simultaneous operation of more than one protection device Degrees of discrimination t B A Prospective Fault Current Icc I Discrimination Traditional solutions Current Time discrimination Energy Zone discrimination discrimination (logical) discrimination Discrimination Current discrimination Discrimination among devices with different trip threshold setting in order to avoid overlapping areas. Setting different device trip thresholds for different hierarchical levels. Discrimination Current discrimination An example: Discrimination Current discrimination Applications: final distribution network with low rated current and low short-circuit current ACB chains Fault area: short circuit and overload Discrimination limit current: low Discrimination levels: low Devices: ACBs, MCCBs and devices with time/current curves (contactors with thermal relays, fuses …) Feasibility & discrimination study: easy Customer cost: low Discrimination Time discrimination Discrimination among devices with different trip time settings in order to avoid overlapping areas Setting different device trip delays for different hierarchical levels Discrimination Electronic release Time discrimination An example: L (Long delay) S (Short delay) I (IST) E4S 4000 PR111-LSI R4000 Setting: 0.9 Curve: B Setting: 8 Curve: D Off E3N 2500 PR111-LSI R2500 Setting: 1 Curve: A Setting: 10 Curve: C Off S7H 1600 PR211-LSI R1600 Setting: 1 Curve: A Setting: 10 Discrimination Time discrimination Applications: low complexity plant Fault area: short circuit and overload Discrimination limit current: low, depending on the Icw of the upstream device Discrimination levels: low, depending on the network Devices: ACBs, MCCBs and devices with adjustable time curves Feasibility & discrimination study: easy Customer cost: medium Types of Discrimination Energy Discrimination Many Low Voltage protection devices such as Circuit breakers and Fuses have the ability to limit the peak of the current let through them to a value lower than the prospective short circuit peak. Any protective device which clears short circuits in less than 1/2 cycle of the sinusoidal wave (i.e 10mS for 50Hz) will current limit to a certain degree Energy based discrimination is the only way to determine true discrimination between current-limiting devices Discrimination Energy discrimination Discrimination among devices with different mechanical and electrical behaviour depending on energy level It is necessary to verify that the let-through energy of the circuitbreaker upstream is lower than the energy value needed to complete the opening of the CB downstream Discrimination Energy discrimination An example: Energy discrimination up to 24 kA Time-currents Curve Discrimination Energy discrimination Applications: medium complexity networks Fault area: Short circuit only Discrimination limit current: medium/high Discrimination levels: medium, CBs’ size dependent Devices: ACBs, MCCBs, MCBs & Fuses Feasibility & discrimination study: medium complexity Customer cost: medium Discrimination Zone discrimination Discrimination among devices in order to isolate the fault zone keeping unchanged feeding conditions of maximum number of devices Zone discrimination is implemented by means of an electrical interlock between devices Zone 3 Zone 2 Zone 1 Discrimination Zone discrimination Applications: high complexity plant Fault area: short circuit, overload, ground fault Discrimination limit current: medium, depending on Icw Discrimination levels: high Devices: ACBs, MCCBs with dialogue and control features Feasibility & discrimination study: complex Customer cost: high Explaining the terminology Cascading or Backup protection Uses supply circuit breakers or fuses with current limitation effects to protect downstream devices from damage The amount of energy let through (i2t) by the supply device needs to be lower than that which can be withstood without damage by the device on the load side By using this effect it is possible to install devices downstream that have short circuit breaking capacities lower than the prospective short circuit current Back-up protection/Cascading Back-up protection or Cascading is recognised and permitted by the 16th Edition of the IEE Wiring Regulations 434-03-01 and is covered by IEC 364-4-437 standard Why Use Back-up Protection? Substantial savings can be made on downstream switchgear and enclosures by using lower short circuit ratings Substantial reductions in switchgear volumes can also result What about Discrimination? Backup protection should not be confused with discrimination. Backup protection does not infer discrimination can be achieved but in practice, discrimination is normally achieved up to the maximum breaking capacity of the downstream device BACKUP Discrimination WAIT! CONTINUITY OF SERVICE GO! FAULT FAULT DAMAGE Practical Example Problem: Installation requires the use of Busbar rather than cable to distribute electrical power. Fault level calculations reveal 25kA prospective fault level at the point of installation of standard MCB distribution board Practical Example Solution - Using a standard Isolator as the distribution board incoming device - all the MCBs would need to be 25kA or above Using an MCCB as the incoming device such as an ABB Tmax T3N250TMD100, 6kA S200 MCBs could be safely used A word of caution …... Back-up protection can only be checked by laboratory tests and so only device combinations specified by the manufacturer can be guaranteed to provide coordination of this type. Types of protection available Fuses Miniature Circuit Breakers Moulded Case Circuit breakers Air Circuit breakers Typical fuse Ultra Reliable Standard Time (s) High Characteristic current limitation effects High threshold on low overloads ( clears overloads at approx 1.45x rated FLC) Current (A) Fuseless technology Two main types:- Thermomagnetic protectionMCB and lower rated MCCB plus older type protection relays Electronic protection – Microprocessor based relays fed from CTs either external to switches or integral within a circuit breaker Thermomagnetic Offer thermal longtime overcurrent protection using Bimetal technology ( operates at 1.3x FLC) Time (s) Thermal curve Uses the magnetic effect of short circuit currents to offer shorttime short circuit protection Magnetic curve Current (A) Electronic Relays Overcurrent functions such as:Long Time (s) time overcurrent Short time instantaneous protection Short time time delayed protection Ground fault or Earth fault protection Current (A) Electronic Relays Overcurrent functions such as:Long Time (s) time overcurrent Short time instantaneous protection Short time time delayed protection Ground fault or Earth fault protection Current (A) Protection releases: general features Complete set of standard protection functions MORE Rc D U RV OT UV OV RP Complete set of advanced protection functions MORE A V Hz Complete set of measurements functions W VA VAR E THD MORE Data logger: a professional built-in fault recorder. 500 Voltage L1-L2 400 Neutral Current phase 1 300 Current phase 2 200 Current phase 3 100 -100 time 0 -200 -300 -400 -500 Data logger: a professional built-in fault recorder. Standard in PR122 and PR123 Recording of 8 measurements (currents and voltages); Configurable trigger (i.e. During a fault); Sampling frequency up to 4.800kHz; Sampling time up to 27s; Output data through SD-Pocket or TestBus2. Exclusive from ABB SACE. BACK Conclusion So what is the secret to achieving a successful discrimination study The secret is to be aware of the capability of the technology you are using and to design your installation within the limits of the protection you have chosen Protection releases: news on standard protection functions Double S* Used to obtain discrimination in “critical” conditions MORE Double G* Two different protection curves, one with the signal coming from internal CTs and the other from an external toroid MORE Dual Setting* Two different set of protection parameters in order to protect in the best way, two different network configurations (e.g. normal supply and emergency supply) MORE BACK * = These features are available on PR123/P Protection releases: news on standard protection functions Double S “low” setting on S protection function due to the settings on MV circuit-breaker The circuit-breaker on LV side of the LV-LV trafo needs “high” settings due to the inrush current Protection releases: news on standard protection functions Without double S Protection releases: news on standard protection functions BACK With double S Protection releases: news on standard protection functions Double G It’s possible to protect the network, with the same protection release, against earth fault both upstream and downstream the circuit-breaker Restricted Earth Fault: the fault is upstream the LV circuitbreaker MV LV Restricted Earth Fault Protection releases: news on standard protection functions Double G It’s possible to protect the network, with the same protection release, against earth fault both upstream and downstream the circuit-breaker Restricted Earth Fault: the fault is upstream the LV circuitbreaker Unrestricted Earth Fault: the fault is downstream the LV circuitbreaker MV LV Unrestricted Earth Fault Protection releases: news on standard protection functions Double G The combination of both Unrestricted and Restricted Earth Fault protection is named “Source Ground Return”. The new PR123/P is able to detect and to discriminate both earth faults If the fault is downstream the LV circuit-breaker the PR123/P will trip Emax circuit-breaker L1 Trafo secondary windings Emax internal CTs L2 L3 External toroid N PE Protection releases: news on standard protection functions Double G The combination of both Unrestricted and Restricted Earth Fault protection is named “Source Ground Return”. The new PR123/P is able to detect and to discriminate both earth faults If the fault is downstream the LV circuit-breaker the PR123/P will trip Emax circuit-breaker If the fault is upstream the LV circuit-breaker the PR123/P will trip the MV circuit-breaker L1 Trafo secondary windings Emax internal CTs L2 L3 BACK External toroid N PE Protection releases: news on standard protection functions Dual setting It allows to program two different protection parameter sets in order to adapt them to the different network configurations The most representative example is a network with supply by the utility and by emergency generator With dual setting the discrimination between CBs is guaranteed in both network conditions Protection releases: news on standard protection functions Dual setting “Normal” network condition CB “A” >>> closed CB “B” >>> open Discrimination is guaranteed between A and C Protection releases: news on standard protection functions Dual setting “Emergency” network condition CB “A” >>> open CB “B” >>> closed Discrimination is not guaranteed between B and C, due to the “low” settings (protection of the generator) of C protection functions Protection releases: news on standard protection functions Dual setting “Emergency” network condition CB “A” >>> open CB “B” >>> closed Discrimination is guaranteed between B and C thanks to the second set of protection parameters BACK Protection releases: advanced protection functions RC Residual current D Protection against directional short-circuit with adjustable time-delay U Protection against phase unbalance OT Protection against overtemperature (check) UV Protection against undervoltage OV Protection against overvoltage RV Protection against residual voltage RP Protection against reverse active power M Thermal memory for functions L and S UF Underfrequency OF Overfrequency BACK Protection releases: measurements functions Current (phases, neutral, earth fault). Accuracy: 1,5% Voltage (phase-phase, phase-neutral, residual). Accuracy: 1% Power (active, reactive, apparent) Accuracy: 2,5% Power factor Accuracy: 2,5% Frequency and peak factor Accuracy: 0,1Hz Energy (active, reactive, apparent, meter) Accuracy: 2,5% Harmonics calculation (display of waveforms and RMS spectrum up to 40th @50Hz) BACK Protection releases: measurements functions Current (phases, neutral, earth fault). Accuracy: 1,5% Voltage (phase-phase, phase-neutral, residual). Accuracy: 1% Power (active, reactive, apparent) Accuracy: 2,5% Power factor Accuracy: 2,5% Frequency and peak factor Accuracy: 0,1Hz Energy (active, reactive, apparent, meter) Accuracy: 2,5% Harmonics calculation (display of waveforms and RMS spectrum up to 40th @50Hz) BACK